Section 9: Maintenance and Protection
9.1 Quality Assurance
The success of a tile and stone installation in a mass transit installation depends entirely on a thorough quality assurance program which is implemented at all levels of the project. Unfortunately, comprehensive quality assurance programs remain the most overlooked and ignored process in the design and construction of both the facility and the tile/stone installation.
There is an important distinction between the terms “quality assurance” and “quality control”. The distinction is that quality assurance is preventative in nature and encompasses all of the procedures necessary to ensure a quality job. Quality control is typically corrective in nature, implemented during or after a procedure, and is only one component of a more comprehensive and planned quality assurance program.
A quality assurance program should include quality checks during the design, specification and bidding phases as well as during and after construction. One factor of tile/stone used in mass transit facilities is that the quality of the installation is only as good as each component, and its installation within the system. Therefore, choosing the proper products and installing them correctly is critical to the long-term performance of the installation.
A comprehensive quality program for the design and construction of tile/stone installations in mass transit applications should involve, but not be limited to the following:
Owner
Define Scope of Work
Organizational Requirements
Quality Objectives
Design Professional
Tile/Stone Installation System Product Component Design, Specification, Installation, and Inspection Procedure Training
Pre-Installation Conference on Materials and Methods
Identification of Construction Progress and Post Installation Inspection, Testing and Evaluation Requirements; Identify Resolution Methods for Non-Compliant Donditions
Develop and Specify Post Installation Preventative Maintenance Programs
Construction Professional
Substrate Preparation
Control of Materials (Evaluation of Contract Document Performance Requirements, Material Suppliers, Delivery, Handling, and Records)
Product Use Monitoring and Documentation (Pot Life, Curing, Protection and Batch Mixing)
Setting or Fixing All Tile/Stone – Adhesion Monitoring (Spreading, Thickness, Open Time, Tackiness, Beat-In, and Coverage)
9.2 Preventative and Corrective Maintenance
A systematic maintenance plan is a critical required final step, which is often overlooked. Industrial installations are demanding environments that are often exposed to harsh chemical cleaners, sanitizers, heavy foot traffic, vehicular traffic, extreme temperature variances, deicing salt applications, and much more. Without regular maintenance, any normal deterioration or degradation of a standard grout would be accelerated. The end result would be a loss of performance and shortening of the expected service life.
Facility maintenance is categorized according to how and when maintenance actions are taken. Preventative maintenance is planned and pro-active actions, which maintains specified performance and prevents potential defects or failures, are taken. Preventative maintenance includes anticipated routine actions and repairs, such as application of protective sealers or deteriorated sealant replacement, as well as unexpected repairs such as replacement of cracked tile or fixing water leaks that may manifest into structural problems later.
The benefits of preventative maintenance are well documented; prevention has been proven to increase expected service life, and cost a fraction of more extensive remedial action typically required once a problem occurs.
Corrective maintenance is remedial action, which repairs a defect after occurrence. Corrective maintenance is necessary to prevent further deterioration or total failure of a tile installation. Corrective action typically involves evaluation with either a non-destructive or destructive test procedure.
For exterior installations in freeze/thaw climates, the use of excessive deicing salts may have a negative impact on not only the structural steel reinforcing of concrete or mortar beds, but also on the integrity of the portland cement in these components. The use of a deicing compound that will not deteriorate or otherwise harm portland cement products is recommended.
9.3 Protection and Sealing – Water Repellant Sealers and Coatings
The purpose and performance of these materials is widely misunderstood by design and construction professionals. Generally, clear water repellant coatings can aid in retarding surface water absorption of porous materials, and reduce adhesion of staining materials. However, these sealing materials often give a false sense of security which is often due to a lack of understanding of the suitability, compatibility and performance in regards to conditions or to tile/stone type. Water repellents can reduce water leakage and deterioration in normally porous tile, stone and grouting materials, but they are not a cure to abnormal leakage caused by fundamental defects in detailing and construction.
There are several general principles for use and application of sealers. Water repellent sealers are not waterproof, and generally cannot bridge gaps or hairline cracks in grout joints or building material, so these materials are useless when used over cracks or very porous surfaces. Sealers suitable for use over slab-on-grade concrete must be vapor permeable and allow the floor to “breathe” or allow vapor to pass through the system. Sealers can also create functional or aesthetic defects that are intended to be prevented or corrected by their application.
As sealers age, wear out or weather, several other problems can occur. Effectiveness is typically reduced over time, so periodic reapplication (depending on the manufacturers formulation and recommendations) is necessary; typical effective service life ranges from 1 – 5 years. Sealers may also allow variable wetting of a portland cement grout or tile from poor application or weathering; this can produce a blotchy appearance. In some cases, the sealer can be reapplied; in others, it may be necessary to allow it to completely weather off, or be removed chemically to restore a uniform appearance. Check with the sealer manufacturer for complete information on the use and suitability of their products.
Compatibility of sealers is also important, not only with the materials to be sealed but also with adjacent and underlying components of the system. The appearance of certain tile/stone or grout can be affected by sealers. Poor application or poor quality products can darken or change the appearance of the tile/stone or grout. Application (or overspray) of sealers onto non-porous tile, such as porcelain, will result in visible residue or a dripping, wet appearance from sealers that do not absorb (e.g. urethanes or acrylics). Sealant joints, waterproofing membranes and metal are some of the system components, which might be affected by solvents in some formulations.
9.4 Non Destructive Testing
Non-destructive testing (NDT) is the examination of an object or material with technology that does not affect its future usefulness. NDT is not only useful in that it can be used without destroying or damaging a facade cladding system, but certain techniques can provide accurate evaluation of this type of complex multilayered construction. Because NDT techniques allow inspection without interfering with construction progress and final usefulness, they provide balance between quality assurance and cost effectiveness. NDT incorporates many different technologies and equipment, and can be used to detect internal and external defects, determine material properties and composition, as well as measure geometric characteristics. NDT can be used in any phase of the construction of tile/stone cladding, including materials assessment, pre-construction test area assessment, quality control during progress of installation, and post-installation maintenance. Non-destructive testing of direct adhered cladding currently encompasses the following techniques:
Types of Non-destructive Testing
Visual and Optical Testing (VT)
Computer Modeling (Finite Element Analysis [FEA])
Acoustic Impact Testing
Thermographic Scanning
Ultrasonic Testing (Pulse Velocity and Echo [UT])
Radiography (RT)
Moisture and Soluble Salt Content Testing
Visual Testing (VT)
As with any type of tile or stone installation, a systematic post-installation maintenance plan should be developed (and ideally implemented) by the design architect or engineer. Whether defects develop from exposure to normal service conditions, or exist from defective installation, they typically are hidden from view and do not manifest as problems until an advanced stage of deterioration or failure. Therefore, it is essential to develop, as a minimum, a systematic plan of visual inspections during pre-construction material and sample evaluation and during construction. Upon completion of the construction, the inspections should continue on a 2–3 year basis. Visual comparisons with reference samples, and observation for obvious signs of distress, (e.g. cracked tile or jointing material, signs of water leakage, etc…), should be accompanied by minimal acoustic impact (tap) testing or thermographic scanning. This will provide a quick, cost-effective qualitative record of installation conditions and serve as the basis for further testing if deemed necessary. In addition to inspecting the condition of the finish material, other critical components of the installation system, such as movement joints, should be inspected and assessed.
Computer Modeling (Finite Element Analysis)
Finite element analysis has been in use for several years as a design and diagnostic method to assist in determining the structural behavior of complex systems like direct adhered exterior cladding or mass transit tunnels. However, only recently has powerful computing technology become more widely available, allowing engineers to consider this design and testing technique as being cost effective.
Acoustic Impact (Tap) Testing
The Acoustic Impact Testing method is a simple and traditional test, born of common sense and necessity, which involves the tapping of finish materials with a hammer or other solid implement (e.g. golf ball). The frequency and damping characteristics of the resulting sound caused by impact can indicate defects such as delamination or missing areas of adhesive. The Acoustic Impact Test is purely qualitative; a solid, sharp, high frequency sound most likely indicates good adhesion, and a dull, reverberant, low frequency sound most likely indicates no contact or hollow areas caused by poor coverage of adhesive mortar. Tap testing only suggests that defects may exist, warranting further investigation using quantitative test methods such as ultrasonic pulse velocity testing. However, a general guideline is that if tapping of a tile/stone installation reveals more than 25% of an individual tile’s area sounds hollow, the tile should be replaced, even though it may have functional adhesion. For installations on walls, tap testing is only useful for adhesive systems that require full coverage support and adhesion of the adhesive mortar. This testing system would not be applicable to systems employing spot bonding with epoxy (e.g. LATAPOXY® 310 Stone Adhesive) or silicone adhesives.
Advantages of Acoustic Impact (Tap) Testing
The primary advantage is that tapping is a cost-efficient test; no sophisticated equipment is necessary (a hammer or golf ball is recommended but any hard object will suffice), and the test is easily conducted during the progress of installation or at any point afterwards.
Limitations of Acoustic Impact (Tap) Testing
While tap testing of a large installation system is labor intensive, the primary limitation is the qualitative nature of the test results. Interpretation of soundings is very subjective, and requires experience to discern different sounds which can be influenced by factors such as mass or density of the cladding material, or the location of the defect within the composite installation system. Even with an experienced technician, isolated hollow soundings are not necessarily an indication of a condition that would adversely affect performance. Tap testing is recommended only as a general assessment technique to identify suspect defective areas for further testing using other more accurate and quantitative destructive or non-destructive test methods, such as tensile adhesion pull testing or ultrasonic testing.
Thermographic Scanning
Thermographic scanning, also known as infrared scanning, infrared photography or IR, has been used as a diagnostic technique for many years in other fields such as medicine and the aerospace industry. This technique is used primarily for identifying remote or inaccessible areas of heat loss or gain. Thermographic scanning has been applied in the construction industry for determining heat loss and gain from buildings, detection of water leakage, and more recently, for detection of structural defects in composite systems, such as delamination of tile and stone installations. The basic concept behind thermographic scanning is that all objects emit electromagnetic radiation in the infrared spectrum (invisible to humans). This invisible infrared radiation can be received and converted into electrical signals which are then deciphered as visual images (colors of line contours) which depict the temperature distributions on the surface of an object.
Advantages of Thermographic Scanning
The use of thermographic scanning as a quality assurance and post-installation diagnostic technique for identifying potential defects in mass transit tile systems is highly recommended. This is because the technique is safe, non-destructive, and does not require direct access to the finish material (which is important in testing on floors or walls where repairs may require blocking off large sections of high traffic areas). This makes it a very cost effective and time saving diagnostic method. Thermographic scanning is valuable not only for post installation defect diagnosis, but also as a quality assurance and preventative maintenance tool. Thermographic scanning can identify minor defects hidden from view that, in their present state, do not currently affect safety. These areas can be identified and documented for periodic monitoring and maintenance to prevent further deterioration. The use and results of thermographic scanning can be much more effective and concise if this technique is used to establish a reference thermographic image before construction begins. Sample panels can be constructed both according to specifications and with various defects, and then scanned to establish a reference thermal “pattern” that can be used as a quality assurance technique during and after construction.
Limitations of Thermographic Scanning
This technique has some significant limitations. Thermographic scanning cannot be used to pinpoint exact cause or locations of defects, and cannot quantify the nature of a defect. This method can only be used as a qualitative tool to provide a general assessment of the quality of the adhesion/cohesion of the outer finish layer. The reason is that thermographic scanning can only detect heat flow near the surface of the finish material, and therefore cannot easily detect defects in the underlying substrate. Therefore, thermographic scanning should only be used as an efficient, cost-effective method to identify and isolate potential defects from large areas for further, more conclusive testing using more quantitative methods. Conducting the test and subsequent interpretation of the images of heat flow is affected by many factors and must be made by qualified individuals trained to recognize false influences on thermal infrared images. Thermal images can be affected by factors such as viewing angle and distance of the test from the tile/stone installation as well as by extraneous factors that can affect measurement of heat flow, such as direct solar radiation, escape of internal heat (or cold), climate, air flow, and finish tile or stone texture.
Application of Thermographic Scanning to Exterior Façade or Wall Applications
Thermographic scanning can be used on mass transit facilities where the exterior tile or stone facade is exposed to daily cycles of heating and cooling from solar radiation, as well as changes in ambient air temperature. As the facade is warmed in the day, or cooled at night, heat loss or gain will be uniform through a continuous and homogeneous material such as tile or stone. Thermographic scanning detects potential defects by measuring the conduction of heat through the cladding and underlying wall assembly. Potential defects are identified as those areas where there is internal discontinuity, such as voids, cracks or separation (delamination) of materials. The areas of discontinuity will insulate and impede the conduction of heat across the air space. As a result, the thermal transmittance will be distorted at areas of defects and the temperature will differ from surrounding areas. During the day, this means that defective areas will stay cooler because the cladding (or underlying layers of the wall system) is insulated and does not allow heat to be conducted and absorbed by the underlying wall. Conversely, the loss of heat at night is impeded, and the defective areas will remain warmer than surrounding areas.
Test Procedures and Equipment for Thermography
The following basic equipment is necessary to conduct thermographic scanning:
Thermographic (Infrared) Scanning Equipment
Infrared (IR) Detector
Processor Unit With Monitor and Recording System
Interchangeable Lenses
Tripod or Fixed Mounting (With Swivel Head)
The actual test procedures will vary accordingly with different types of equipment. Generally, the viewing angle should not be greater than 30 degrees from perpendicular to the surface of the cladding. Follow the IR detector’s written instructions and contact IR detector manufacturer to answer any questions.
Ultrasonic Pulse Velocity
Ultrasonic Pulse Velocity is commonly used in building construction to identify and quantify structural defects. The basic concept of ultrasonic pulse velocity is that ultrasonic sound waves travel through solid materials at a known velocity (dependent on material density and elastic properties), and changes in velocity and direction can be measured at the interface between different materials. Ultrasonic pulse velocity is typically employed to determine the quality and uniformity of solid materials, such as underlying concrete floors or mortar beds in the case of mass transit facilities. Ultrasonic pulse velocity is used primarily for detection of delamination (loss of bond) or air voids (areas of missing adhesive). This test method can also be used for determining the uniformity of the underlying leveling mortars and concrete structure, as well as for locating cracks hidden from view. The test equipment, which is compact and easy to use, consists of an electronic display/pulse unit, and two transducers. The transducers can be placed for direct transmission through a wall assembly, or placed on the finish material surface for indirect or surface transmission (Figure 9-1).
Advantages of Ultrasonic Pulse Velocity
The Ultrasonic Pulse Velocity method is recommended when accurate, quantitative information on voids, cracking, and delamination of finishes is required. The ultrasonic pulse is introduced locally at the cladding surface, and the sound waves are reflected back at any air voids such as cracks, missing areas of adhesive, or separation (delamination) of the cladding or other components of the wall system. This method can identify exact location, orientation, size and shape of air void defects, and can be used in conjunction with diagnostic tools such as thermographic scanning to locally verify areas with suspected defects.
Limitations of Ultrasonic Testing
The primary limitation is that ultrasonic testing requires direct access and full scale contact to the cladding surface, which makes testing of large areas cost prohibitive. As with thermographic scanning, there are external factors, such as the skill of the test interpreter or surface texture of the finish material, which could falsely influence echoes and be interpreted as improper thickness of adhesive. It is very important to consider that while the presence of voids can be accurately identified, the voids may not necessarily indicate present or potential failure of a tile or stone system. Therefore, the type, size and location of voids must be very carefully analyzed and interpreted to be an effective diagnostic tool.
Future Ultrasonic Test Methods
There are new ultrasonic test methods in development which use lasers to provide remote sensing capabilities of up to 100 meters, but these methods may currently be cost prohibitive for large areas. Current applications are being used for testing of polymer composites in the aerospace industry and in high temperature precision metal part fabrication. With the combination of remote sensing capabilities and accurate quantitative results, laser-ultrasonic testing may prove to be the diagnostic tool that will allow wide acceptance of tile and stone installation systems in the future.
Radiography (RT)
Radiography uses much the same technology as medical x-rays. Penetrating gamma or x-radiation can be directed through a construction component and onto a film located on the opposite side. The resulting shadowgraph shows the internal integrity of construction as indicated by density changes. Radiography in construction is expensive, requires direct access to both sides of an assembly, and requires clearing areas to prevent unwanted radiation exposure. Radiography is used primarily for further evaluation of potential structural defects identified by other less accurate techniques.
Moisture Content Testing
The effects of moisture sensitivity of installation system components, substrates, cladding materials and adhesives have been discussed in detail in this manual. Testing and measurement of the moisture content of materials is a valuable quality control and defect diagnosis technique. There are several test methods and types of equipment used in determining proper moisture content of material and installation assemblies. Test results not only provide valuable information to determine suitability of substrates to receive moisture sensitive claddings, adhesives and waterproofing membranes, but also to diagnose water infiltration or condensation that may have deteriorating effects on any component of a wall or floor assembly. There are basically two methods of testing for moisture content:
Conductivity Test
Hygrometer Test
Conductivity testing provides the average percentage of moisture content in a material. The moisture content is the weight of water expressed as a percentage of the dry weight of the material. In hard materials such as concrete or mortar, pins are driven into the material, or holes are drilled and filled with a special conductive gel. An electric moisture meter automatically senses and calculates moisture content. There are different thresholds of acceptable moisture content for different materials. Moisture content is calculated as follows:
A heavy material such as concrete, will have a much lower percentage moisture content than a lighter material (e.g. wood) that has the same amount of water within it. This is because, as you can see from the formula, the divisor (dry weight) is a larger number for a heavier material. So a moisture content of 10% for wood is relatively dry, while in concrete 10% is considered damp. An additional problem with percentage moisture content is that the moisture content of building materials can vary through the cross section, meaning that materials can be both wet and dry at the same time (depending upon where the reading is taken. The general rule for percentage moisture content is that readings less than 10% in cementitious materials are safe for application of water sensitive claddings, membranes or adhesives.
Salt Contamination Testing
The presence of soluble salts on a substrate can be evaluated using either chemical testing or proprietary electronic test equipment. The primary reason for detecting the presence of salts is the potential danger of bond failure resulting from continued depletion of calcium that may occur from the formation of efflorescence, and the subsequent strength loss of cementitious materials. The crystallization of soluble salts, especially those that form in the adhesive/cladding interface, can exert more pressure than the volumetric expansion forces caused by ice formation. This mechanism may result in spalling of the cladding material, degradation of the setting bed or bond failure of the adhesive. Salt contamination can also accelerate the setting of cement mortars. Flash setting may result in reduction or failure of adhesive bond strength.
9.5 Destructive Testing
Tensile Pull Strength Testing
Tensile pull strength testing, also known as pull-off or uniaxial tensile adhesion testing, measures the amount of force required to be applied perpendicular to the cladding plane until failure. Failure may occur at an adhesive interface, or cohesively within a material such as the substrate or the tile/stone; in other words, the adhesive interface is stronger than the material being adhered. Tensile stress in a direct adhered finish is typically considered non-consequential, or, a force rarely if ever applied to a tile installation system. Shear stress parallel to the cladding plane is by far of greater concern. However, buckling or warpage outside of the tile plane caused by thermal or moisture movement can cause tensile failure, and is therefore, a valid qualitative measure of in-service performance. Tensile pull strength testing is a destructive method and can be conducted with a variety of equipment each using slightly different methods.
There are several standards that address tensile pull test methodology;
International Standard ISO 13007-2 Provides Test Procedures Specific to Ceramic Tile Installations
European Standards EN 12004 Provides Test Procedures Specific to Ceramic Tile Installations
British Standards BS 5980 Provides Test Procedures Specific to Ceramic Tile
ASTM D 4541 “Standard Test Method For Pull-Off Strength of Coatings Using Portable Adhesion Testers”
American Concrete Institute ACI 503–30 “Field Test For Surface Soundness and Adhesion”
These test methods provide additional information on this type of testing. The most common tensile pull strength test method involves securing a 2" (50 mm) diameter metal disc to the surface to be tested with a two component epoxy resin adhesive. This method will provide pure surface strength of the cladding material. The epoxy typically has significantly greater adhesive strength than the materials being tested. If an adhesive interface below the surface requires testing, it is necessary to isolate the cladding by core drilling or sawing through the finish material. The disc is then attached to a self-contained hydraulic pull tester and a force is applied to the surface until failure (separation) is induced
Results are measured and expressed in N/mm2 or Megapascals (MPa). There are several difficulties in interpreting results from tensile pull testing. First and foremost, the results are best used as a qualitative rather than quantitative assessment of the bond between two materials. Since the effective area of adhesive contact is uncertain, the force required to separate the surfaces may give no clue as to the strength of the adhesive bond at the points where contact does occur. There must be adequate sampling in order to qualify the results. Also, results are reported as force per unit area, and should be interpreted as average stress rather than uniform stress across the contact area. Stress distribution is rarely uniform across an adhesive assembly. Results are also greatly influenced by other factors such as core size or alignment of the test equipment to the surface. Test results are also difficult to interpret because there are no uniform standards for tensile adhesive strength of finish material or of the cohesive strength of plasters or mortars.
European and ISO Norms require minimum tensile pull strength of 0.5 MPa (72.5 psi) to meet the lower classification (C1) and minimum tensile pull strength of 1 MPa (145 psi) to meet the higher classification (C2) for direct adhered cladding. Demanding applications (e.g. mass transit facilities) typically require the higher classification to be reached.
Some standards require as high as 1.5 MPa (218 psi), or as low as .35 MPa (50 psi). For example, transit authorities that have oversight and jurisdiction over their projects will put into place a quality control program which obliges the installation contractor to conduct a specified amount of tensile pull tests which achieve a prescribed minimum threshold.
An important note; tensile pull strength results are not to be confused or compared with shear bond strength commonly provided by tile installation material manufacturers as a measure of adhesive mortar performance with certain tile/substrate combinations. While there is no direct correlation between the two tests, studies have indicated that tensile pull strength is approximately 57% of the direct shear bond strength. One of the benefits of a tensile pull test is that it provides not only a measurement of adhesion strength between materials, but also confirms the quality of the tensile or cohesive strength of the adhered materials (cohesive qualities of adhered materials may be weaker than the adhesive bond between them).
The Portland Cement Association has also determined that the tensile strength of concrete is approximately 8 to 12% of its compressive strength. A tensile pull test conducted over 2,000 psi (14 MPa) compressive strength adhesive mortar should yield results of 160 – 240 psi (1.1 – 1.65 MPa); however, this is only an approximate measure of a cement mortar’s cohesive strength. An example is where a pull test induces failure within the cement plaster/render layer. This is very common when high strength cladding and adhesive mortars are employed, only to be sacrificed by a poor quality plaster/render mix and installation. Similarly, a fragile cladding material such as a “young” slate stone will typically fail cohesively along the parallel cleavage plane of the stone during a tensile pull test.
In-situ Shear Bond Strength Testing
The different types of movement presented in Section 2 can cause differential movement parallel to the tile plane. Shear bond strength testing is a common method used to determine the amount of force required to be applied parallel to the plane of the tile surface to induce failure at the adhesive interface. This test is more meaningful than an adhesion or tensile pull strength test because tile/stone installations are exposed primarily to shear stresses. However, tensile testing is also important to gauge resistance to out of plane buckling. Unfortunately, shear bond strength testing is cost effective only as a laboratory test using core samples from mock-ups or the actual construction, and not as an “in-situ” or in service test. While equipment for conducting in-situ shear bond tests exists (hydraulic flat jacks) difficulty remains in configuring equipment to induce stress parallel to the cladding plane. Technology is currently being developed that will create reliable and effective in-situ shear bond testing that will deliver linear and consistent results. In-situ shear bond testing will provide design professionals with information that will help them to more reliably specify tile/stone installations where it may have been questioned in the past.
Core Drilling
This test method involves the use of specially designed electric or hydraulically operated drills with carbide or diamond tipped core drill bits that can extract a core up to 6" (150 mm) in diameter to various depths. Equipment to drill cores up to 24" (600 mm) in diameter are available, but the size and logistics of operating this equipment may be cost prohibitive and does not add any value over smaller diameter cores. The purpose of core drilling may be to visually examine the cross section of an installation assembly for any obvious material or construction defects, to subject the sample to laboratory testing of compressive or tensile strength, or to chemical analysis. Selection of equipment specifically designed for this purpose will prevent percussive damage to adjacent areas and minimize damage from binding. In order to minimize difficult to repair destruction to in-service installations caused by this technique, it is recommended that this test method be employed primarily in evaluating specifically installed test panels in advance of full scale construction.
9.6 Types, Causes and Remediation of Defects
Defects in a tile or stone installation system can generally be classified according to type and location. The type of defect can be either aesthetic or functional. Aesthetic defects affect the appearance of an installation, but do not typically affect the safety. Some aesthetic defects, such as efflorescence, can ultimately lead to functional defects if the fundamental cause is not identified and remedied. Functional defects, such as bond failure, affect appearance and human safety, as well as the integrity and safety of other components of the installation system. Common aesthetic and functional defects are listed below:
Common Types of Defects
Aesthetic Defects
Staining
Efflorescence
Functional Defects
Cracking
Delamination and Bond Failure
Movement and Grout Joint Failure
The location of the defect is also critical in evaluation and recommendation of corrective action. A direct adhered installation system consists of three distinct layers:
Locations of Defects
Tile/Stone Layer
Adhesive layer
Substrate or Back-Up Wall Layer
Most common defects can occur at the interface between each layer, or within any of the three layers. Evaluation of these areas hidden from direct view and contact is often one of the most difficult aspects of quality assurance for any tile/stone installation system. Careful analysis of defects is very important, for in many cases, the symptoms manifest in locations other than the point of origin. Cracking and efflorescence are perfect examples, as they typically manifest on the surface of the cladding, yet may originate from poor moisture mitigation detailing and construction.
Staining and Weathering
Staining and weathering are primarily aesthetic defects, although prolonged exposure to weather and certain types of staining, such as that caused by atmospheric pollution or efflorescence, can lead to functional defects and subsequent deterioration or failure of the cladding materials.
Causes of Staining and Weathering
Water Exposure and Infiltration
Solar Exposure
Corrosion of Metal Components
Biological Growth
Atmospheric Pollution
Efflorescence (Soluble Salt Migration)
Fluid Migration (Adhesives, Sealants)
Corrosion of Metal Components
Concrete reinforcing (rebar) or steel wire mesh is often incorporated into concrete, cement leveling mortars/plasters/renders to help reinforce the component, or to isolate poor surface conditions or incompatible substrate materials. Smooth concrete surfaces, friable surfaces (e.g. cellular CMU (AAC), deteriorated or contaminated surfaces, or substrates which may undergo significant differential movement are examples where wire mesh in mortars should be employed. It is important to note that a corrosion-resistant metal or galvanized coating should be used for both the mesh as well as the fasteners (if required). Corrosion of the fastener is a common mode of failure in wire mesh applications, and can result in staining. Rust staining can also be a symptom of the early stages of failure of structural attachment or the entire tile/stone system.
Efflorescence
Efflorescence is in effect a type of staining. Efflorescence staining is a white crystalline deposit that forms on or near the surface of concrete, masonry, and cement based materials. It is the most common post-installation defect in ceramic tile, stone, and brick systems. Efflorescence can range from a cosmetic annoyance that is easily removed, to a serious problem that could cause adhesive bond failure or require extensive corrective construction and aggressive removal procedures. Efflorescence starts as a salt (present in all portland cement products) which is dissolved by water; the salt solution is then transported by gravity or by capillary action to a surface exposed to carbon dioxide in the air, where the water evaporates and leaves behind the crystalline salt deposit. Efflorescence can also occur beneath the surface or within ceramic tile, stone, or brick units. Occasionally, staining on tile/stone installations, especially on direct adhered facades is misdiagnosed as efflorescence. Vanadium and molybdenum compounds in ceramic tile and manganese compounds in brick can be dissolved by acid cleaning, leaving behind an insoluble deposit. Efflorescence occurs from the occurrence of the three simultaneous conditions listed below. While theoretically efflorescence will occur if one condition does not exist, it is impracticable to completely eliminate the confluence of these conditions in any tile/stone installation. However, the conditions that cause efflorescence can be controlled and the symptoms minimized, to the point where deposits are not visible, or are easily removed and non-recurring.
Causes of Efflorescence
Presence of Soluble Salts
Presence of Water (For Extended Period)
Transporting Force (Gravity, Capillary Action, Hydrostatic Pressure, Evaporation)
Presence of Soluble Salts
There are numerous sources of soluble salts listed in Figure 9.10. There is always the potential for efflorescence when concrete and cement mortars, adhesives and grouts are exposed to the weather or to water. Other sources of soluble salts can be monitored, controlled or completely eliminated.
Efflorescence – Sources of Soluble Salts
Hydration of Cementitious Materials (Calcium Hydroxide)
Calcium Chloride Contamination (Deicing Salts, Sand)
Mixing Water (Water Softeners)
Cement Accelerator or Anti-Freeze Admixtures (Calcium Chloride)
Acid Etching and Cleaning Residue (Chlorides)
Lime in Mortars (Calcium Sulfate)
Cement Hydration – The most common source of soluble salts is from cementitious materials, such as concrete, cement plasters/renders, concrete masonry units, cement backer board, and cement based mortars, including latex cement adhesive mortars. One of the natural by-products from cement hydration (the chemical process of hardening) is calcium hydroxide, which is soluble in water. If cementitious materials are exposed to water for prolonged periods and evaporate slowly, the calcium hydroxide solution moves with the water to the surface of the installation, reacts with carbon dioxide in the air, and forms calcium carbonate (CaCO3), one of many forms of efflorescence. Once the calcium hydroxide is transformed to calcium carbonate, it is no longer soluble in water, making removal difficult.
Calcium Chloride Contamination – Common sources of soluble salts on exterior mass transit tile/stone installations are deicing salts. Mixing water can also be contaminated with high levels of soluble salts. Figure 9.11 shows the analysis of samples from 6 different city water supplies as compared to sea water. Typically, water with less than 2,000 ppm of total dissolved solids will not have any significant effect on the hydration of portland cement, although lower concentrations can still cause some efflorescence.
Acid etching (see "Removal of Efflorescence")
Lime in Mortars
Unhydrated lime used in leveling mortars/renders contains calcium sulfate, which is a soluble salt. Uncontrolled water penetration through unprotected openings, cracks or incorrectly constructed joints may allow sufficient saturation of lime mortars to dissolve these salts in large quantities. The benefit of the autogenous or “self-healing” qualities of lime mortars has long been the subject of debate in the masonry industry. The very chemical reaction which can seal hairline cracks in lime mortars can also cause efflorescence.
Presence of Water
While you cannot control naturally occurring soluble salts in cementitious materials, proper design, construction and maintenance of exterior installation systems can control and minimize the installation components from water penetration. Without sufficient quantities and periods of exposure to water, salts do not have adequate time to dissolve and precipitate to the surface of an installation, and efflorescence simply cannot occur. Rain and snow are the principal sources of water.
Several wall construction types are designed (barrier, cavity, and pressure equalized rain screen walls) to control or prevent water penetration. Each type of wall is designed to minimize efflorescence by either providing barriers against water penetration, minimizing water contact with potential contaminants, or controlling the flow of water that contacts contaminated materials.
Proper architectural detailing and materials are necessary to help prevent water infiltration. For example, waterproofing, proper pitch to drains, properly placed and installed drains, leaders, and other factors will contribute to quick and easy removal of water. The simple truth is; if there is less water, there is less chance of problems caused by water.
Sealers and Coatings
Water repellent coatings are commonly specified as a temporary and somewhat ineffective solution to fundamentally poor design and/or construction. In some cases, water repellents may actually contribute to, rather than prevent the formation of efflorescence. Water repellents cannot stop water from penetrating the hairline cracks in the surface of cladding, or from penetrating through improperly designed or constructed joints and openings. Water repellents do not prevent water infiltration caused by poor design or construction. As the infiltrated water travels to the surface by capillary action to evaporate, it is stopped by the repellent, where it then evaporates through the coating (most sealers have some vapor permeability) and leaves behind the soluble salts to crystallize just below the surface of the tile or stone. The collection of efflorescence under the water repellent coating may cause spalling of the finish material, or may result in gross accumulation of efflorescence.
Effects of Efflorescence
The initial occurrence of efflorescence is primarily considered an aesthetic defect. However, if the fundamental cause (typically water infiltration) is left uncorrected, continued efflorescence can become a functional defect and affect the integrity and safety of an installation system (e.g. direct adhered façade). The primary danger is potential bond failure resulting from continued depletion of calcium and subsequent loss of strength of cementitious adhesives and underlying cementitious components. The crystallization of soluble salts, especially those that form in the adhesive-cladding interface, or within the cladding material can exert more pressure than the volume expansion forces caused by ice formation.
This mechanism may also result in spalling or bond failure.
Fluid Migration
Fluid migration from sealant joint materials is a common source of staining in stone installations. This defect most often occurs with certain types of silicone sealants, but can also be caused by some types of soluble polymers found in mortar additives. This problem is more a function of a manufacturer’s formulation than polymer type. There is no correlation with a particular polymer type (i.e., silicone vs. polyurethane), because the problem is typically caused by plasticizer additives and not the polymers. Fluid streaking though, depends on both formulation and sealant polymer type. There are several new generation silicones on the market, (such as LATICRETE® Latasil™) which have specifically addressed and overcome the above aesthetic problems associated with sealants used as both movement joints and fillers between tile and stone.
Fluid migration may also be known as “latex migration” when referring to staining caused by water soluble latex additives. It is recommended to verify that a manufacturer’s polymer formulation for a liquid latex additive or a dry redispersible polymer powder is not water soluble. Similarly, all exterior installations of tile or stone which use latex cement adhesive mortars must be protected from significant rain exposure during the initial setting period (typically 12–24 hours). It is during this time when latex polymers may be subject to fluid migration or leaching.
Stain Removal Methods and Materials
Traditional stain cleaning methods for tile or stone installations include washing with water and detergents, and use of mild hydrochloric (muriatic) acid or fluoric acid solutions. Acid cleaning is less desirable today, not only due to environmental and safety concerns, but also due to the lack of skilled labor. As a result, there are several new, less invasive methods available on the market today for removal of efflorescence and staining. Less aggressive chemical cleaning compounds, such as mild ammonium bifluoride cleaning agents, with pH values of 4.5–4.7, are well suited to ceramic tile, stone and brick cladding and have been proven over the past 25 years. These cleaning agents are used in conjunction with high-pressure (1700 psi [120 kg/cm2]) hot water 180°F (80°C) to achieve maximum cleaning effect. The advantages of high-pressure hot water are the mechanical effect of the water pressure, minimal use of water, quick drying, and the high dissolving power of hot water 180°F (80°C) water, which has 16 times the dissolving power compared to 70°F (21°C) water. Another less aggressive cleaning method, known as “soft” cleaning, was invented over 40 years ago, but only recently has this method been more widely available and cost-effective. These types of systems use proprietary equipment that deliver a very fine, safe powder (limestone and aluminum silicate crystals) at low pressures (60 psi [4 kg/cm2]). The equipment also reduces the temperature of the compressed air at 200°F (93°C) to condense and separate out any water in the air; no water, chemicals or detergents are used. Proprietary equipment may also include enclosures which contain dust and flush residue. Soft cleaning systems are effective on a variety of soiling, stains, and efflorescence.
Efflorescence Removal Methods and Materials
Prior to removal of efflorescence, it is highly recommended to analyze the cause of efflorescence and take corrective action to prevent reoccurrence. Analysis of the cause will also provide clues as to the type of efflorescence and recommended cleaning method without resorting to expensive chemical analysis.
Determining the age of the installation at the time efflorescence appeared would be an important first step. In buildings less than one year old, the source of the salt is usually from cementitious mortars and grouts, and the source of water is commonly residual construction moisture, rain/snow, or exposure to water in showers, tubs or steam rooms. The appearance of efflorescence in an older building indicates a new water leak or new source of salts, such as deicing salts or acid cleaner residue. Do not overlook condensation within a wall cavity or leaking pipes as a sudden source of water. Also, location of efflorescence can offer clues as to the entry source of water.
Chemical analysis of efflorescence can be conducted by a suitably equipped commercial testing laboratory using x-ray diffraction and petrographic analysis to accurately identify the types of minerals present. This procedure is recommended for buildings with an extensive problem, or where previous attempts to clean with minimally intrusive methods have failed. Removal methods can vary according to the type of efflorescence. Therefore, it is of critical importance to evaluate the cause and chemical composition of efflorescence prior to selecting a removal method. Salts which cause efflorescence are water soluble and may disappear with normal weathering or from dry brushing. Washing is only recommended in warm weather so that the wash water can evaporate quickly and not have the opportunity to put more salts into solution, thereby exacerbating the problem.
Efflorescence which cannot be removed with water and scrubbing will require chemical removal. Using muriatic acid is a conventional cleaning method for stubborn efflorescence, however, even with careful preparation, cladding and grout joints can get etched and damaged. There are less aggressive alternatives to muriatic acid, and several are described in the previous section on stain removal. Other methods use phosphoric acid or sulfamic acids which are less aggressive than muriatic acid. These acids, properly mixed with water (per acid manufacturer’s written instructions) should be strong enough to remove stubborn efflorescence without damage to the cladding or grout joint materials. Regardless of the cleaning method selected, the cleaning agent should not contribute additional soluble salts. For example, acid cleaning can deposit potassium chloride residue (a soluble salt) if not applied, neutralized and rinsed properly. Calcium carbonate efflorescence is a type of efflorescence where the calcium salts combine with carbon dioxide in the air and form a hard, crusty deposit which is insoluble in water. However, long term exposure to air and rain water will gradually transform this residue to calcium hydrogen carbonate, which is soluble in water. So long term weathering can help eliminate this type of efflorescence. Unfortunately, if the condition is not acceptable in the long term, and water or mild chemical cleaning proves ineffective, it may be necessary to wash the surface with a dilute solution (5–10%) of hydrochloric (muriatic) acid.
Aqueous solutions of acids are commercially available for ease of handling and prevention of dilution errors. For integrally pigmented grouts, a 2% maximum solution is recommended, otherwise, surface etching will reveal aggregate and wash away color at the surface. Acids should not be used on glazed tiles or polished stone, for the acid solution may etch and dull the glaze or polished surface, or react with compounds in the glaze and redeposit brown stains on the cladding which are insoluble and impossible to remove without ruining the tile. Before applying any acid solution, always test a small, inconspicuous area to determine any adverse effect. Just prior to application, saturate the surfaces with water to prevent acid residue from absorbing below the surface. While most acids quickly lose strength upon contact with a cementitious material, and should not dissolve cement below the surface, saturating the surface is more important to prevent absorption of soluble salt residue (potassium chloride) which then cannot be surface neutralized and rinsed with water. This condition in itself can be a source of soluble salts and allow recurrence of the efflorescence problem intended to be corrected by the acid cleaning. Application of acid solutions should be made to small areas less than 10 ft2 (1 m2) and left to dwell for no more than 5 minutes before abrading with a stiff, acid resistant brush and immediately rinsed with water. Acid solutions can also be neutralized with a 10% solution of ammonia or potassium hydroxide.
Functional Defects – Cracking
Cracking is a broad term applied to the distinct separation of a material through its cross section. Cracks may be structural and affect the safety of an installation, or may disfigure the appearance of the installation and allow wind, rain or dirt to penetrate. In a tile/stone installation assembly, cracking may occur in the tile/stone material, in the rigid joint filler material (grout), or in any one of the underlying installation system components hidden from view. In many cases, cracks develop in one component of the assembly, but are transmitted by composite action of the adhered assembly to other components.
Identifying Types and Causes of Cracking
While the mechanisms that cause cracking are quite complex, for purposes of this manual, types of cracking in tile/stone installation systems can be categorized according to the cause of cracking as follows:
Structural Cracks
Surface Cracks
Structural cracks are typically the result of fundamental defects in design or construction, or from corrosion of underlying structural concrete reinforcing bars or leveling mortar wire mesh reinforcement. Structural cracking is typically difficult and costly to remedy. These types of cracks are typically wide (over an 1/8" [3 mm]), are not localized at one particular tile or piece of cladding, and usually coincide with structural components or interfaces with adjacent or underlying materials/components of the installation assembly. In most cases, the cause of structural cracking can be identified by first analyzing the mechanisms of different types of structural movement (see Sections 2 and 3). Each type of structural movement manifests in typical locations. Types of structural movement are also associated with typical physical characteristics of cracking. For example, a diagonal crack originating at a corner of a window head and radiating or stepping through joints diagonally (re-entrant crack) would most likely be caused by lack of vertical movement joints to control shrinkage or creep, or by deflection or other structural inadequacy of the window lintel that supports the underlying wall at the window opening.
Physical Characteristics of Structural Cracks
Geometry – Vertical, Horizontal, Diagonal, Stepped Through Joints, Radiating
Orientation – Straight, Multi-Directional
Position – Origin, Termination
Size – Length, Width
The remedies for structural cracks should focus first on the identification and repair of the fundamental cause of the cracking, and then on the repair of the cracks. For example, removal and replacement of cracked tiles caused by lack of movement joints will not prevent recurrence of cracking if the cause is not corrected. In some cases, localized structural cracking can be repaired without major reconstruction if the cracking was caused by unusual or non-recurring movement. An example could be a seismic event that exceeded the design loads for the structure. The probability of recurrence is low, so repairs to cracking of underlying structural elements could be made with epoxy injection techniques, and the cladding could be locally replaced. Conversely, other situations that cause structural cracking, such as structural movement caused by poor soil composition and compaction, may not be remedied unless the cause of the problem is corrected. Repairs to the tile installation without addressing the cause of the problem can certainly lead to reoccurrence of the same problem.
Surface Cracking
Surface cracking is typically localized cracking that only occurs on the surface of the tile/stone, or in the filler joint (grout) material. These cracks are typically considered as non-structural in origin. Surface cracking can be caused by unintended impact with foreign objects (point loads), defective installation, or from normal weathering and deterioration (e.g. freeze-thaw cycling over a period of time). Surface cracking can also be a minor manifestation of structural movement, such as expansion or shrinkage.
This type of cracking can usually be repaired by simple replacement. In many cases, surface cracking, especially in filler (grout) joint material, poses no safety risk (this should be verified by testing), and the tile or stone may be left in place and behavior of the cracking monitored. While benign cracking may not be a safety risk, it does present other problems such as water infiltration. Water infiltration could lead to sub-surface efflorescence (cryptofflorescence) or spalling, which ultimately may pose a safety risk of bond failure. So neglect of benign surface cracking must be weighed against the risks under certain conditions.
Delamination and Bond Failure
Delamination and bond failure are, in effect, synonymous terms. Technically, there are subtle differences, but for the purposes of this manual, these terms both mean that either the tile/stone adhesive interface, or one of the underlying adhesive/substrate interfaces has physically separated. For vertical applications, this defect is the number one concern and fear of owners, architects, building officials, and construction contractors when considering tile or stone cladding. The result of delamination or bond failure on, for example, a wall is typically pieces or sections of cladding or other components of the wall which fall off and pose a serious risk to public safety. Delamination and bond failure can be categorized as either adhesive or cohesive.
Adhesive bond failure occurs at the interface of the adhesive to the tile/stone or the adhesive to the substrate. In fact, any tile or stone installation material that bonds to a surface (e.g. membranes, self-leveling underlayments, etc…) may lose interface to the substrate which is in effect an adhesive failure; adhesive bond failure does not necessarily have to involve an adhesive). Cohesive failure is a structural failure within a homogeneous material itself, such as a concrete wall surface or a cement render/plaster which separates internally. Bond failure is most commonly caused by defective design or installation, and is rarely caused by defective tile/stone or installation products. Prevention relies on implementation and enforcement of a comprehensive quality assurance program for both design and installation (see Section 9.1 – Quality Control and Assurance). A systematic preventive maintenance program provides an added factor of safety to check any oversights of the quality assurance program and prevent catastrophic bond failure.
Common Causes – Adhesive Bond Failure
Contaminated Tile/Stone Surfaces
Contaminated Substrate Surfaces
Partial Adhesive Coverage
Improper Setting (Bedding) Pressure
Improper Mixing/Application of Adhesive
Improper Specification of Adhesive
Differential Movement (Shear, Expansion, Shrinkage)
Proper methods and materials to prevent the above defects are described in Sections 2 and 3 – Structural Considerations, Section 2 and 3 – Substrate Preparation, Section 5 Types of Tile/Stone, and Sections 7 and 8 – Types of Mortars/Adhesives and Grouts and Methods of Installation. The following information provides a logical sequence of evaluating the cause of bond failure.
Delamination and Adhesive Bond Failure Evaluation by Location
Failure at the interface between tile/stone and adhesive – Adhesive failure can occur with tile/stone which have smooth backs and which offers little texture to assist in improving mechanical adhesion between the adhesive and tile. Glass tile, pressed porcelain (vitrified) ceramic tile and certain types of stone can fail in this way, especially if the tile/stone has very low or no absorption. High strength adhesives that rely primarily on pure adhesive strength rather than mechanical bond are recommended for extremely dense and impervious material. Adhesive failure is rare with the extruded ceramic tile, or quarry tile/pavers since these types of tile typically have grooves at the back which provide a larger surface area to improve mechanical adhesion with high performance mortars, traditional cement mortars or lower strength latex cement adhesive mortars. Failure at the tile/adhesive interface can also result from dust/contamination on the back surface of the tile/stone, improper adhesive coverage, or poor bedding of the tile into the adhesive. Industry standards for exterior and interior wet area tile/stone installation require 95% adhesive coverage as well as back-buttering (ANSI A108.5). However, these requirements are difficult to achieve on installations which do not employ proper equipment and quality assurance programs during the progress of installation.
Failure at the interface between adhesive and substrate – All too often the substrate is not properly prepared and does not induce good bond to be formed with the adhesive bedding mortar. This type of failure is more common on dense, smooth substrates with low or no water absorption. Very often dirt, grease, form release agents, curing compounds, or other surface contaminants are responsible for poor adhesion on concrete. In some instances, the substrate is treated to improve the bond between the substrate and the adhesive mortar. Skim/parge coats or slurry/slush coats (i.e. cement/sand slurries with or without latex additive), are sometimes applied to the substrate to improve adhesion of the setting mortar. Skim and slurry bond coats should be applied properly and should either employ a latex additive or be sufficiently cured to achieve adequate hardness and bond strength. Keep in mind that the substrate should be properly prepared to receive the skim coat or adhesion failure can occur as well.
Failure at the interface between cement leveling mortar bed / plaster and adhesive – In many projects where pitch to drain is required, the slab has been recessed, or, the floor or wall requires leveling or repair the substrate often receives a cement mortar bed / plaster before the adhesive mortar is applied. Failure at the mortar & plaster/adhesive mortar interface is not uncommon. There can be numerous reasons for failure; poor mortar bed/plaster material, poor preparation or poor installation methods. The mortar bed / plaster / render should be of good quality and it should be applied over either a wet latex cement slurry bond coat (for floors), over a hardened rough texture bond coat (for walls – spritz, dash or spatter dash coat), or over a hardened rough texture flat skim coat to provide a mechanical key for the adhesive mortar. Failure between the substrate and leveling bed is not considered a tile/stone failure, but it leads to failure of the tile/stone and should therefore be installed and prepared properly.
Vertical Applications
Thick layers of cement plaster/render to correct excessive plumb and level tolerance (i.e., bad workmanship) are not uncommon and are responsible for many failures. A single coat of cement plaster/render should be no thicker than 1/2" (13 mm). If a thick layer of leveling mortar is required to level off an uneven surface, the cement plaster/render should be applied in successive lifts (coats), each coat should be cured, scratched and prepared to receive the next coat.
A diamond metal lath (complying with ASTM C847 and ANSI A108.02 3.6) is often incorporated into cement leveling plasters/renders and attached to the structure or back-up wall construction, over a suitable cleavage membrane, to isolate poor surface conditions or incompatible substrate materials. Smooth concrete surfaces, friable surfaces such as cellular CMU (AAC), deteriorated or contaminated surfaces, or substrates which may undergo significant differential movement are examples where metal lath should be employed. It is important that a corrosion-resistant metal or galvanized coating is important for both the lath as well as the fasteners. Corrosion of the fastener is the most common mode of failure in wire lath applications, and can result in failure of any of the tile or installation components, or, the entire wall system.
Corrective Action for Delamination
In most cases, the only remedy to delamination is removal and re-installation of the defective cladding system or components of the cladding system. However, epoxy injection techniques can be employed under certain conditions. First, epoxy injection may be used if the delamination or void is thin and restricted enough so that adequate sealing of the delamination area is feasible in order to allow pressure build-up for proper delivery, distribution and performance of the epoxy. There also must be adequate access to the delamination to allow multiple “ports” or points of injection. Epoxy injection products are typically low viscosity materials used for structural repair of extremely fine hairline cracks. For larger volume repairs, special higher viscosity epoxy gel formulations may be necessary. Contact the manufacturer of the injected epoxy material for more information and for proper usage.
Other Mechanisms of Adhesion Failure
Adhesion failure is usually a result of a combination or confluence of factors and is rarely caused by a single mechanism. Variations in moisture content, variations in temperature, creep of a structure, the use of unsuitable or poor quality installation materials, and poor workmanship may all be contributing factors to a failure. Identification of the origin or fundamental cause of failure is often difficult because the stresses may occur within any component of the system, but the loss of adhesion normally occurs at the weakest interface. For example, a ceramic tile on which the bonding surface has not been cleaned may result in reduced adhesion, but the lack of movement joints may be the actual mechanism that induces stress beyond the capability of the adhesive to bond to the contaminated tile back. It is typically indeterminate whether the dirty tile would have failed if movement joints were constructed properly, or, if the lack of movement joints would have caused the failure even if the tile were cleaned and installed properly. The following dimensional movements are usually involved and they can all act together or in opposition to cause the failure:
Moisture Expansion of Tiles
Reversible expansion and contraction due to wetting and drying of tiles are relatively small and can for all practical purposes be disregarded in this context, except perhaps where large areas are involved or where freeze/thaw conditions exist. The irreversible expansion of ceramic tiles and clay products, referred to as moisture expansion, can be relatively large. This rather slow process takes place over a long period of time and begins the moment the tile leaves the kiln. Tile with a low moisture expansion rate, not more than about 0.03%, should be used for any wet or exterior installations. There have been cases in which tile removed from installations where failure had occurred showed moisture expansion was as high as 7%. Semi-vitrified or fully vitrified tiles have a low moisture expansion and should not fail as a result of moisture expansion of the tile.
Thermal Expansion of Tiles
The thermal expansion of porcelain (vitrified) tiles is relatively small, but when large surfaces are exposed to large temperature differences, significant total and differential dimensional movement can occur, leading to stress. The thermal expansion of glass tiles can be higher than that of ceramic tile, stone or porcelain tile.
Shrinkage of Cement Mortars
Adhesive mortars and cement plasters/renders usually shrink more than the fully cured concrete substrate. To avoid or minimize stresses due to the shrinkage of mortars, it is necessary to use mortars which have low drying shrinkage. This can be achieved by using a proprietary, pre-mixed and bagged mortar powder, both for cement mortars/renders and adhesive mortars. If site mixed mortars are specified, use clean, well-graded sand and a good quality cement. Use a liquid to powder cement ratio which is appropriate for the type of application and environmental conditions. Fine sands which contain a high percentage of clay produce mortars with a high drying shrinkage. Mortars which are rich in cement or have too much gauging liquid added may also experience higher drying shrinkage. Mortars with high drying shrinkage also typically exhibit large dimensional changes during cycles of wetting and drying.
Differential Movements Between Structure and Tile/Stone
All structures creep from the weight (dead load) of the structure, and from imposed live loads, causing shortening or shrinkage of columns and walls, as well as deflection of beams and floors. These movements in the structure induce compressive stresses in adhesive mortars and cladding and are very often a contributing factor towards failure of tile/stone systems (especially vertical systems). Bulging or tenting of the tile/stone from the substrate is a common symptom of differential movement.
Efflorescence or Cryptoflorescence
The primary concern with excessive efflorescence (visible) or cryptoflorescence (hidden) is the potential for adhesive bond failure resulting from continued depletion of calcium and the subsequent loss of strength of the cementitious adhesive and any underlying cement based components. The crystallization of soluble salts, especially those that form at the adhesive/cladding interface, or within the tile/stone material (see sealers and coatings, this section) can exacerbate calcium depletion by exerting expansive stresses. The formation of salt crystals can exert more pressure on the installation than the volume expansion forces caused by ice formation (ice occupies 9% more volume than the volume of the original water). This mechanism may result in spalling of the tile/stone material or adhesive bond failure.
Expansion of Cementitious Materials Due to Sulfate Attack
Reaction between sulfates and aluminates in portland cement can occur in wet environments. This reaction is accompanied by large volume increases which can lead to the disruption of concrete, cement plaster, cement mortar and adhesive mortars and can cause failure at any cementitious interface within the installation system.
Sealant and Grout Joint Failure
Sealants are widely misused and are a common source and cause of defects in tile/stone installation systems, especially at movement or expansion joints. Sealants are a critical bridge at perimeter interfaces between cladding and other installation system components, and at cladding or movement joints, yet they are routinely designed, specified, and installed improperly. It is essential to understand that sealants cannot be relied upon to provide the only means of protection against water and air infiltration, especially in installations where the sealant joint may be the only line of defense. Even with proper back-up protection, compliance with installation guidelines is required to ensure proper elongation and compression without peeling or loss of adhesion (see Section 2 – Movement Joints). Failure of sealant joints, while posing no direct safety risk, will allow water, air, and dirt to infiltrate behind the cladding material. Water infiltration presents several problems, especially in exterior systems:
1. Potential freeze-thaw problems if voids are present
2. Reduction of adhesive strength from long term water saturation
3. Increased probability of efflorescence and staining
A preventative maintenance program should include periodic visual inspection of sealant joints for deterioration, loss of adhesion, peeling, or other defects described in Section 2. Failure (or impending failure) of sealant joints as indicated by extreme compression or elongation is a signal of excessive stress within the tile or stone system and the potential problem of cracking or adhesive bond failure. Joints between cladding that are filled with relatively rigid cementitious grout are often designed to provide stress relief of thermal and moisture movement. This condition is considered normal and does not have any significant effect on the performance of the tile system because the primary purpose of grout joints are to separate and fill the joints rather than to hold the cladding together. Hairline cracking is best minimized by the use of joint materials such as latex portland cement grouts which provide enough resiliency, relative to a more brittle material, to absorb much of the compressive stresses from expansion without crushing, and absorb tensile stresses at the cladding edges from contraction. In most countries, standards and regulations require a minimum grout joint width of 1/4" (6 mm) for joints between cladding to allow the pieces of cladding to move as single or isolated units, rather than monolithic units. Further, and more efficient, isolation of stresses is handled by separating sections of cladding with movement joints. This ensures that the grout or sealant joint will always fail first by relieving unusual compressive stress from expansion before it can overstress the cladding or adhesive interface. The dissipation of stress provides an additional safety factor against dangerous delamination or bond failure. Excessive cracking, deterioration, or fallout of grout material is commonly caused by a combination of several factors:
Excessive Movement
Partial Filling of Narrow or Deep Joints
Improper Installation Practices
Poor Quality Grout
Grout cracking from excessive movement is primarily a design consideration, and is prevented by following good architectural and structural design practices. Partial filling is prevented by proper joint width to depth ratio, and insuring proper tools and installation practices. Accepted installation practices, including protection against hot, dry conditions, and types of grout mix designs to prevent defects are described in Section 7.4. The TCNA provides a guideline for the proper design, placement and construction of movement joints in the TCA Handbook for Ceramic Tile Installation, EJ-171.
9.7 Alternative to Using Sealers
Use a low absorption tile/stone (e.g. porcelain tile, quarry tile, granite) and an epoxy grout (e.g. LATICRETE® SpectraLOCK® PRO Grout†, LATAPOXY® SP-100 or LATICRETE SpectraLOCKK® 2000 IG). These installation system materials never require sealing and can greatly lower the long-term, overall cost usually required to maintain the tile/stone installation.