Section 4: Comparison of Alternate Mass Transit Flooring and Wall Cladding Systems

This section will provide general information on alternate systems (e.g. epoxy coatings, terrazzo, stamped concrete, polished concrete, metal wall panel cladding and more) which can be used in mass transit applications. It is important to note that mass transit tile/stone flooring systems are much more forgiving and require less overall maintenance than these alternate systems. The Tile Council of North America has conducted an extensive life cycle cost analysis comparing ceramic tile to other finish flooring types. See Section 5 for advantages in using ceramic tile/stone finishes in mass transit applications.

4.1 Seamless Epoxy Flooring Systems

Generally speaking, epoxy floors can be defined as “a floor which is finished with an epoxy coating that is used as the wearing surface”. In actuality and for many reasons, the term epoxy floors can be difficult to define. One of the main reasons why this is true is the fact that there are differences in how the epoxy coating manufacturers define the term “epoxy floor”.

Seamless epoxy floors are used in many applications. It is important to note that these epoxy floor coverings are much different than epoxy painted surfaces. For example, warehouses, labs, automobile shops and dealerships, loading docks, and many more applications use epoxy coatings.

One manufacturer can define an epoxy floor by saying, “Multiple layers of epoxy placed on a floor surface, regardless of the kind of epoxy resins applied, provided that the total thickness of all layers is a minimum of 2 mm”. Another manufacturer may call out for a specific epoxy material in a specific number of layers to a specific thickness. There are also industrial epoxy coatings which carry their own definition.

For the purposes of this Technical Design Manual we will use the following epoxy coating definition; “Any epoxy coated floor that consists of three (3) layers of 100% solids epoxy resins that have a total minimum thickness of 2mm and is used as the finished, wearing surface”.

General Information on Epoxy Coatings

Epoxy Coatings

Each epoxy coating material has its own unique characteristics that help to define exactly how these materials can and should be used. A poor choice of epoxy coating, based on the needs of the application, can result in rapid degradation of the epoxy. For example, some epoxy coating formulations have increased chemical resistance, better temperature resistance, the ability to be applied underwater, resistance to yellowing and UV damage, and slip resistance to name a few. An important note, however, is the fact that there can be a vast difference in performance properties with industrial level epoxy coatings vs. ‘watered down’ epoxies that are less expensive and perform at decreased levels. Epoxy coatings can be expensive, but there are ways to “water down” the epoxies with solvents and/or non-solvent thinners. These diluted epoxy coating materials do not perform as well as the more expensive industrial epoxy coating materials which are installed as recommended by the manufacturer.

Life Expectancy

The life expectancy of epoxy floors is one of the shortest in the industrial flooring industry, and one of the most expensive floor coverings based on life cycle cost per square foot per year. When compared to a quarry tile installation (commonly used in mass transit and commercial applications), the Life Cycle Cost per ft2 (m2) per year of a poured epoxy coating is approximately 5 times more expensive and the installed cost is 25% higher than tile.

The expected life of the epoxy flooring system is around ten years, but there are many variables that determine how long the epoxy coating is going to perform. Assuming that the correct epoxy coating material was chosen and was properly installed the installation may survive for ten years. However, the life span can be reduced for applications that are subject to harsh chemicals and aggressive cleaning regimens. One cleaning regimen, steam cleaning, must be considered when choosing and installing epoxy coating materials. Some epoxy coating materials may start to soften and lose adhesion when exposed to temperatures of 140°F (60°C) and higher. There are special formulations of epoxy coating materials that can withstand elevated temperatures, but the cost associated with these types of epoxies can be very high, especially when compared to other floor coverings, such as tile. In addition, epoxy floors can exhibit wear in traffic areas and are susceptible to bacterial attack in some harsh environments.

Epoxy Coating/Flooring Facts

Epoxy coatings must be applied to concrete which has undergone proper surface preparation. The concrete can have no surface contamination or any type of additive applied before, during or after the concrete pour which can inhibit the bond of the epoxy coating material. Since epoxy coatings are typically vapor impermeable, they may be sensitive to moisture and high moisture vapor emission rates (MVER). Concrete must be allowed to cure for a minimum amount of time, have moisture content at or below certain levels, and have a continuing MVER level that does not exceed certain levels. The manufacturer of the epoxy coating material would be able to provide the information stating the required cure time of the concrete and the prescribed MVER levels. Tile, on the other hand, can be installed directly to new concrete as soon as the installers can walk on the concrete by using LATICRETE® 254 Platinum or LATICRETE 211 Powder gauged with LATICRETE 4237 Latex Additive.

For substrates scheduled to receive a waterproofing membrane, maximum amount of moisture in the concrete/mortar bed substrate should not exceed 5 lbs/1,000 ft2/24 hours (283 µg/s•m2) per ASTM F1869 or 75% relative humidity as measured with moisture probes. Consult with finish materials manufacturer to determine the maximum allowable moisture content for substrates under their finished material.

Many renovation projects or new ownership in buildings desire to install new tile over existing epoxy coatings. There are two options for installing tile over an epoxy floor coating:

The first option would be to remove the epoxy coating by shot-blasting, bead-blasting or mechanical scarification. Once all the epoxy is removed, installation of the tile can commence directly over the concrete.

The second option would be to install the tile with LATAPOXY® 300 Adhesive. The only type of product that will bond to an epoxy coated floor is an epoxy adhesive. The existing epoxy floor must be well bonded with no loose peeling epoxy or chips in the epoxy coating. The coating needs to be very clean and free from all dust, oils, waxes, or any other possible bond breakers. If there are loose peeling spots or chips in the coating, it is a good indication that the coating may need to be completely removed prior to installing tile.

4.2 Polished Concrete Floors

Polished concrete is just as the name implies; concrete which is mechanically grinded, chemically hardened (densified), sealed, and then polished. This process produces a dense concrete which inhibits water, oil and other contaminants from penetrating the surface.

Polished Concrete Limitations

Polished concrete is not recommended for some heavy use mass transit applications. As in the case of any concrete material, the floor may not hold up to acid based chemicals and aggressive cleaning regimens to which many demanding mass transit applications are subjected. Steam cleaning alone can cause the floor to dull, and wet polished concrete surfaces can be slippery. One of the most difficult and challenging aspects of any mass transit floor is the time required vs. time allotted to perform repairs. A quarry tile / porcelain paver floor grouted with LATICRETE SpectraLOCK 2000 IG requires less maintenance and stands up to chemical exposure to a higher degree than polished concrete.

The process used to create a polished concrete floor eliminates the ability to directly bond tile to the concrete surface. The extremely hard, dense polished concrete surface, as well as all sealers, would have to be removed by shot-blasting, bead-blasting or mechanical scarification. This procedure would open the pores of the concrete and allow the LATICRETE thin-set product of choice to achieve maximum bond.

4.3 Terrazzo Floors (Cement Based and Resin Based)

Terrazzo flooring is a composite material poured in place or pre-cast which is used for wall and floor finishes. Terrazzo can consist of marble, quartz, granite, glass and other types of aggregate chips mixed with a binder that is portland cement based, resin based or a hybrid of both types along with colored pigments. Poured in place terrazzo is cured and then ground and polished to the desired surface finish.

Various types of terrazzo are available which include:

Venetian – utilizes a large size chip.

Standard – the most common type of terrazzo which generally utilizes a small size chip.

Palladianna – utilizes thin random fractured slabs of marble.

Structural – cement based terrazzo topping placed over a minimum of 4" (100 mm) thick concrete slab.

Rustic – textured terrazzo finish in which the chips are exposed.

Resinous – generally an epoxy or polyester based binder mixed with small chips. Terrazzo can be applied as thin a 1/4" (6 mm).

Terrazzo floors can range in thickness from 2-1/2" (62 mm) for sand cushion terrazzo floors to as thin as 1/4" (6 mm) for resin based terrazzo pours. Epoxy resin, polyester resin and polyacrylate terrazzo types have certain chemical resistant properties.

Pre-cast terrazzo tiles can be installed using traditional tile setting methods as outlined by the TCNA and are then either grouted as traditional tile pavers or ground and polished in place. Pre-cast terrazzo is also used for stair treads / risers, window stools, base and thresholds (www.ntma.com).

One of the most desired features of terrazzo flooring is lack of “clicking noise” from luggage and carts rolling across the flooring finish. Terrazzo also has a very good life cycle cost that is similar to ceramic tile finishes. For more information on cement-based terrazzo please visit www.laticrete.com, or, for general information on all types of terrazzo please visit www.mtma.com.

4.4 Sand Set and Bitumen Set Pavers Versus Mortar Set Pavers

Brick, concrete, permeable, interlocking and stone pavers are a very popular paving option for exterior plazas, walkways, driveways and other mass transit applications. These pavers are very durable, offer many patterns and design options, are able to withstand vehicular traffic while maintaining their integrity in demanding exterior freeze / thaw climates. For the purposes of this comparison, the most common type; brick paving will be featured. Brick pavers should be specified to perform in the intended application according to the following industry standards:

Pedestrian paving brick – meeting ASTM C 902 “Standard Specification for Pedestrian and Light Traffic Paving Brick” (pedestrian – minimum. 2-3/8" [60 mm] thickness)

Light traffic paving brick – meeting ASTM C902 “Standard Specification for Pedestrian and Light Traffic Paving Brick” (pedestrian and residential vehicular – minimum. 2-3/8" [60 mm] thickness)

Heavy Vehicular paving brick – meeting ASTM C1272 “Standard Specification for Heavy Vehicular Paving Brick” (heavy vehicular traffic – minimum 3-1/8" [80 mm] thickness)

Weather classifications:

Class SX – exposed to water and freezing

Class MX – exposed to water but not freezing

Class NX – interior only

Traffic classifications:

Type I – sidewalks, driveways in public areas

Type II – residential sidewalks and driveways

Type III – floors and patios

For more information on brick pavers, consult the Brick Industry Association, Reston, VA; www.gobrick.com.

There are three basic types of setting options for these types of pavers in mass transit applications:

Sand Set – Type F

Bitumen Set – Type R

Fixed Mortar Set – Type R

There are advantages and disadvantages to the three methods. An architect or specifier will have to make an informed decision concerning the area of use and the amount of long-term maintenance that will be required for each of the systems. The following is a comparative analysis of the three methods:

Sand Set Pavers

Sand set pavers have the lowest initial cost of the three options. The setting system can be altered depending on the level of traffic that will be exposed to the installation system. The installation starts with the grading and compaction of the soil under the pavers. A geo-textile drainage layer can be placed over the soil to help facilitate drainage. Next, a layer of gravel / trap rock (3/4" [19 mm]) is placed and compacted well over the soil (up to 95% of standard Proctor density as specified in ASTM D-698 “Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3 [600 kN-m/m3])” or to ASTM D 1557 “Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft3 [2,700 kN-m/m3])” for areas subjected to vehicular traffic). The gravel / trap rock layer is then “rough screeded” to get the level of this layer close to the design level. This layer can be adjusted depending on how robust the setting system is intended to be. For example, heavy vehicular traffic will require 12–16" (300 mm–400 mm) of the gravel / trap rock base. Pedestrian traffic areas generally require 4–6" (100–150 mm) of the gravel / trap rock base. This base layer serves as the support for the sand set paving system. In addition, the gravel base facilitates water runoff and drainage. Next, the sand layer is used to bed the pavers. The sand layer (meeting ASTM C33 “Standard Specification for Concrete Aggregate” or CSA A23.1 “Concrete Materials & Methods of Concrete Construction Methods of Test for Concrete” (coarse, clean masonry sand) can range in thickness from 1–2" (25–50 mm) thickness. The sand layer is placed compacted and screeded to the desired height. The pavers are then dropped into the sand layer. The pavers are tamped / compacted into place and finished to the desired height with a vibrating plate compactor capable of exerting 3,000 – 5,000 psi (21 – 34.5 MPa) of centrifugal compactions force operating at 75–90 hertz. A plastic or rubber mat should be used on the compactor to avoid paver damage. Generally, at least two passes are made to seat the pavers.

Traditional masonry sand is swept into the paver joints to fill the joints. This process also helps to secure the pavers into place. The pavers are then compacted again until the joints are full. Polymeric sand can also be used for this process and is generally worth the cost upgrade. The polymeric sand will harden and set firm to a degree once it is exposed to moisture. The polymeric sand stands up better to point loads within the joints are resists “wash-out” when compared to traditional sand swept joints. Possibly the most critical issue with sand set pavers is the edge restraints. Edge restraints can range from typical paver edging strips and spikes to poured concrete curbs and sidewalks. Most sand set paver issues arise from the fact that the edge restraints are not designed to withstand the “pushing” and “movement” that traffic will place on the system. The edges can push out which in turn causes the paving system to sink and start to experience issues with maintaining its designed level. It is to be expected that sand set pavers will require periodic ongoing maintenance to fix areas that have moved, dipped to vehicular patterns. Ongoing long-term maintenance costs should be factored into the life cycle analysis of sand set paving systems.

Advantages of Sand Set Pavers:

Economical

Low Initial Installation Cost

Designed to Accommodate Minor Movement Without Failure

Easily Repaired

User Friendly Installation Materials

No Off-Gassing of Installation Products

Easy Access to Repair Underground Utilities

Can be Designed as a Permeable Pavement

Disadvantages of Sand Set Pavers:

May Require a Thicker Base for Heavy Duty Applications

Edge Restraints Commonly Experience Problems with Movement and “Blow Out”

Pavers Show Traffic Patterns

Tree Roots Can Disturb Installation

Drifting of Pavers Will Occur

On-going Maintenance is Required

Can Present Point Loading Issues Within the Joints

Can Experience Erosion During Heavy Rain and Maintenance

Highest Life Cycle Cost

No Installation Warranties Apply

Weeds Will Grow in Between the Joints

Insects Will Build Nests and Disrupt the Appearance of the Paving System

Bitumen Set Pavers

The installation of bitumen set pavers is considered the middle ground as far as cost is concerned. A suitable concrete base or a 3–6" (75–150 mm) bituminous binder base placed over a compacted gravel base (8" [200 mm]) is required for this installation system. Once the concrete base is poured and properly cured, a layer of 3/4" (19 mm) asphaltic bitumen is placed over the slab followed by a 2% modified neoprene tack coat layer. This layer acts as an adhesive as the pavers are dropped into place. Once the pavers are set into place, the joints are filled in similar fashion to the sand set pavers with traditional masonry sand or polymeric sand. A bitumen layer is not considered a permanently fixed system in that the bitumen does allow some movement to take place. However, this method also requires good edge restraint to prevent paver separation and edge blow out. In addition, over time, vehicular traffic patterns can still reflect in the finish layer as the bitumen can experience long term fatigue.

Advantages of Bitumen Set Pavers:

Mid-grade Initial Installation Cost

Designed to Accommodate Minor Movement

Disadvantages of Bitumen Set Pavers:

Edge Restraints Commonly Experience Problems with “Blow Out”

Pavers Can Show Traffic Patterns

Drifting of Pavers Can Occur

Little Tolerance for Paver Thickness Variations

On-going Maintenance Is Required

Can Present Point Loading Issues Within the Joints

Sand Swept Joints Can Experience Erosion

Bitumen Can Emit A ‘Petroleum’ Odor

Bitumen is Not Considered to Be An Environmentally Friendly Product

Bitumen Can Off-Gas (Volatile Organic Compound)

Not Labor Friendly

No Installation Warranty

Weeds Will Grow in Between the Joints

Insects Disrupt the Appearance of the Paving System

Mortar Set Pavers

Of the three installation types, the mortar set system is considered to be the most permanent. The mortar set system, typically requires a concrete base and gravel drainage layer beneath the concrete slab. Once the concrete slab is in place and properly cured (e.g. 28 days at 70°F [21°C]), the mortar setting system can be placed. See section 7.3 Thick Bed Method (bonded) or Thin-Bed Method for the installation methodology and product selection for this application.

Mortar set pavers are now permanently fixed in place and require very little long term maintenance. Of the three paver setting methods, mortar set pavers has the lowest life cycle cost.

Advantages of Mortar Set Pavers:

Low or No Maintenance Required

Low Life Cycle Cost

Resistant to Point Loading

Resistant to Fatigue

Resistant to Edge Blow Out

User Friendly Installation Materials

Installation Materials Do Not Off Gas

Long Term Manufacturer Performance Warranties

No Weeds Will Grow in Between the Joints

No Insect Damage

Disadvantages of Mortar Set Pavers:

High Initial Installation Cost

Repairs Are Difficult and Expensive

4.5 Metal Wall Panels

Metal wall panels are typically used to clad and cover unsightly concrete pours and exposed utilities. In addition, metal panels are used as finish materials in metro and roadway tunnels. One of the advantages to the use of the metal panels is the speed of installation. There are certain drawbacks to the use of metal panels in many of these applications. The fabrication cost can be prohibitive. Replacement costs for damaged panels can be very high as the disassembly, fabrication and re-installation process can be very tedious. Corrosion is also a factor to consider when utilizing certain metal finishes. Ceramic tile finishes have many advantages over this cladding type.