Introduction

Technology is changing everything, even backer boards. Manufacturers are offering a wide variety of products, from the traditional fiberglass-covered cement boards to products that incorporate innovative, recycled materials and green building concepts.

Choosing the right backer board for the right job is critical. Backer boards are available in ¼”, ½” and 5/8” thickness and come in many different dimensions. Because not all surfaces are perfectly flat, these products can provide a more stable surface for the application of tile and stone products. Whether one is installing backer board for floors, walls or counter tops, the craftsman has many product application decisions to consider. There are a number of different products available for application in wet or dry areas in relation to a water-resistant or waterproof backer board.

The introduction of light-weight backer boards with a foam core that is covered in fiberglass mesh and cement coating have created new options since the original solid cement core products. Light-weight backer boards are less cumbersome and have greatly reduced weight loads for easy handling in the field. Backer boards have an advantage in that they have low mass, are quick to install and relatively inexpensive, while providing a good base for stone and tile areas that transition with existing floor and wall covers.

Industry Trade Association and Recommendations

The format for this report is based on the categories within the 2005 TCA handbook and the1999 American National Standards Institute, a publication for the compilation of voluntary standards for the installation of ceramic tile.

The Tile Council of North America (TCA) handbook/conference acknowledged other backer units that are on the market for use as a backing and underlayment with ceramic tile. However, the conferees felt there was insufficient experience and test data available to consider specific comment as to their use. In these cases, follow the manufacturer’s recommendations.

Products and Trade Applications

ANSI A108.11- A118.9-1999 Interior installation of cementitious backer units and American national standards for test methods and specifications for cementitious backer units.

ANSI A108.11 / ANSI A-4.8 These voluntary standards define the interior installation, test methods and physical properties of cementitious backer units (CBU’s) as a substrate for the installation of ceramic tile. They are intended to serve as a guide to the general public, manufacturer’s, architects, installing mechanics, testing laboratories, and other businesses and professionals in producing, specifying, installing and testing cementitious backer units.

ANSI A118.9 / L-2.1 Cementitious backer unit (CBU) - A nailable/screwable backer board or underlayment panel which is composed of stable Portland cement, aggregates, and reinforcements that have a significant ability to remain unaffected by prolonged exposure to moisture.

Cementitious Backer Unit (CBU)

1. TCA Reference
   A backing and underlayment designed for use on floors, walls, and ceilings in wet and dry areas, this board is applied directly to wood or metal wall studs or over wood subfloors. Ceramic tiles can be bonded to it with dry-set, latex/polymer modified Portland cement mortar, or epoxy by following the manufacturer’s instructions. Complete interior installation and material specifications are contained in ANSI A108.11 and A118.9 or ASTM C1325.
   
   
2. General Product Description
   The name cement is derived from the Latin word caementum meaning rough stone. Cement manufacturing involves a mix of raw materials, typically about 85% limestone or similar rocks like marble or marl, with the rest mainly clay or shale. This mixture is heated until it nearly melts and is then ground into a powder. When cement is mixed with water, it creates a paste. When the paste is mixed with aggregates, the paste binds them all together because a chemical reaction occurs, called hydration. The crystals radiate outward from the cement grains and mesh with other adjacent crystals or adhere to the aggregates, creating the finished product.
   
   
3. TCA detailed drawings for this product can be referenced as follows, B412-05,
   B415-05, C315-05, C513-05, F144-05, RH135-05, RW800-05, SR614-05, TR420-05, and W244-05.

Coated Glass Mat Water-Resistant Gypsum Backer Board:

1. TCA Reference
   A backer board conforming to ASTM C1178. Designed for use on floors, walls and ceilings in wet or dry areas, this board is applied directly to wood or metal wall studs or over wood subfloors. Ceramic tile can be bonded to it with dry-set, latex/polymer modified Portland cement mortar, organic adhesive, or epoxy.
   
   
2. General Product Description
   The mineral name gypsum is derived from the Greek word gypsos, which means plaster. Originally it referred to the type of gypsum which was heated to a high temperature to drive off water, the water in its crystal structure; this is called calcined gypsum. Gypsum belongs to a group of minerals called sulfates, and is the most common of the approximately 150 sulfate minerals. Sulfates are compounds of one or more metals with oxygen and sulfur. The oxygen and sulfur join together to form the sulfate ion, gypsum. Only a 2 rating on the Moh’s hardness scale, gypsum is a very soft mineral.
   
   
3. TCA detailed drawings for this product can be referenced as follows: B419-05, B420-05, C311-05, C315-05, C513-05, F146-05, RH135-05, and W245-05.

Fiber-Cement Underlayments

1. TCA Reference
   A dispersed fiber-reinforced cement backer and underlayment designed for use on floors, walls and ceilings in wet or dry areas, this board is applied directly to wood or metal wall studs or over wood subfloors. Ceramic tile can be bonded to it with latex/polymer modified Portland cement mortar, organic adhesive, or epoxy by following the backer board manufacturer’s instructions. General interior installation and material specifications are contained in ANSI A108.11 and ASTM C 1288.
   
   
2. General Product Description
   Fiber-reinforced cement backer board is a product produced by composite materials consisting of Portland cement, fine aggregates, water, alkali-resistant glass fibers and additives which, when mixed in exact proportions, achieve construction–grade physical properties that allow it to be used for numerous applications, especially those where weight is a significant factor in design.
   
   
3. TCA detailed drawings for this product can be referenced as follows: B412-05, B415-05, C513-05, F144-05, RH135-05, RW800-05, TR420-05, W223-05, and W244-05.

Fiber-Reinforced Water-Resistant Gypsum Backer Board/Underlayment:

1. TCA Reference
   A backer board/underlayment conforming to ASTM. Designed for use on floors, walls, and ceilings in dry or limited water exposure areas, this board is applied directly to wood or metal wall studs or over wood subfloors. Ceramic tile can be bonded to it with latex/polymer modified Portland cement mortar, organic adhesive or epoxy by following the backer board manufacturer’s instructions.
   
   
2. General Product Description
   Because gypsum was discussed in the preceding category and that reference can be used for the core of this product, this paragraph will be dedicated to the minerals of glass and fiberglass properties. Once again we find that fiber additives incorporated into these backer board products originate from natural minerals.
   
   a. Soda Ash is anhydrous sodium carbonate. It is made by the processing of the minerals Trona and Nahcolite with sodium carbonate-rich waters, called brines.
   
   b. Feldspar is the mineral distinguished by the presence of aluminum and the silica ion in their chemistry. This group includes aluminum silicates of soda, potassium and lime.
   
   Industrial sand, gravel, soda ash and feldspar are mixed together, incorporated in the proper manufacturing process and create glass fibers. Most, if not all backer boards use a glass mat or fiber mesh.
   
3. TCA detailed drawings for this product can be referenced as follows: B430-
   05, C315-05, C513-05, F170-05, RH135-05, RW800-05, W223-05, W247-05.

Cementitious Coated Foam Boards

1. TCA Reference
   A waterproof backer board constructed from extruded polystyrene and coated
   with a cementitious coating, designed as a substrate for ceramic tile and stone in
   wet and dry areas. Designed for use on floors, walls and ceilings in dry or wet
   areas, this board is applied directly to wood or metal wall studs or over wood
   subfloors. Ceramic tile can be bonded to it with dry-set, latex/polymer modified
   Portland cement mortar, or epoxy by following the manufacturer’s instructions.
   Material specifications are contained in ASTM C578, Minimum TypeV1 and
   ASTM D4068-01 (Annex2).
   
   
2. General Product Description
   Extruded polystyrene is closed-cell foam. The production of extruded foam starts with solid resin pellets. The pellets are fed into an extruder where they are melted and mixed with other materials. Then, a blowing agent is injected to make the mixture foamable. Under controlled heat and pressure conditions, the foamable mixture is forced through a die, at which time a shaping occurs and a finished foam product is produced. Foam densities can vary depending on the amount of pressure provided during the manufacturing process. The continuous extrusion process produces a uniform, closed-cell structure that makes extruded polystyrene highly resistant to moisture intrusion and yields reliable compressive strength durability. Polystyrene is a thermoplastic material which means it is recyclable.
   
   
3. TCA detailed drawings for this product can be referenced as follows, B425-05, B426-05, C315-05, F175-05, and W246-05.
   

Conclusion

The building products incorporated in this report originate from earth minerals and have low impact on our ecological environment or are sustained within the recycled manufacturing process. New technologies and by-product applications are producing many new materials that qualify for green building concepts. The new technologies are greatly improving the backer board industry. The choice of products and their specific applications will require the responsibility of the craftsman to maintain current product knowledge and up to-date application techniques. It has become very obvious in today’s world that every product application is unique and must be researched from all governing code authorities and manufacturers’ suggested installation procedure.

Reference Materials:

ANSI, For the installation of Ceramic Tile 1999
TCA, Handbook for Ceramic Tile 2005
PCA, Portland Cement Association
Mineral Information Institute
Extruded Polystyrene Foam Association

The preceding article was researched and written by Richard Jacobs, CTC, a graduate of the CTIOA Inc.
Ceramic Tile Consultant Course. The report was reviewed and approved by the CTIOA Inc. Technical Committee.