Q&A / 

Ceramic Tile Backer Boards


Water is a very unusual compound. Several days ago, I spoke to a large group of gardeners. I indicated that water is necessary for the survival of their plants, so in that sense it is their friend. However, water used in abundant amounts too close to their houses can be their worst enemy.

The same is true for those of us who are not avid gardeners. Water is needed in our everyday lives. However, it can cause massive damage to our houses if not respected and controlled. Thus, those areas of our homes where water use is concentrated must be somewhat waterproof.

Bathrooms & Water

The average bathroom in a residential house has the highest concentration of water usage. It stands to reason that this area of the house needs the most protection from both water in the liquid form and water in the vapor state.

Shower and bathtub areas are of the highest concern, as it is here that water can most easily escape from the tub or shower area. Showering activity is really the biggest problem, especially if the shower area is constructed of ceramic tile. Think of it, we direct a concentrated stream of water against a wall surface that isn't integrally connected to the actual plumbing fixture (the tub).

The plumbing fixtures in a bathroom are always waterproof. They don't easily or readily deteriorate when exposed to water. Take toilets for example. Water sits in these fixtures from the day they are installed until the day they are removed without harm. Tubs are not harmed by water.

However, wall surfaces abutting plumbing fixtures can be seriously damaged by water which originates from the plumbing fixtures.

Waterproof Walls

Many people like the beauty and design possibilities which are possible when using ceramic tile. Ceramic tile is unaffected by water. In fact, standard ceramic tile is no different than the toilets we just spoke of above. Ceramic tiles and toilets are manufactured using refined clays which are glazed and hardened by a firing process in a high temperature kiln. The glaze turns into a thin coating of glass over the clay, making the tile impervious to water.

During the past several hundred years, homeowners and builders found out that concrete was not harmed by continuous exposure to water. It didn't take too long for them to figure out that you could apply a thin layer of concrete to a wall surface. Ceramic tile could be easily applied to this concrete surface by using a cement paste. In fact, if the ceramic tile was set into the fresh concrete surface within a day, the two became one in most instances. Prolonged exposure to water would not separate the two materials.

Modern Alternatives

The old method of attaching ceramic tile is still available. However it is very labor intensive. This added labor boosts the overall installation price beyond the capabilities of the average homeowner. Manufacturers of wall system products quickly responded to fill this gap.

Today there are three wall system products that you can use as a substrate for ceramic tile installations. All three are faster to install than the old fashioned concrete. However, there is a wide difference in overall performance of the three products. Fortunately, it is still possible to achieve the results of the old tile setters with several of the products.

Moisture Resistant Gypsum

Some gypsum wall product manufacturers make a gypsum board which is used by many builders and remodelers. It is marketed as moisture resistant drywall. The problem is that many people confuse "moisture resistant" with "waterproof." They are not the same. Not by a long shot.

Moisture resistant simply means that for some period of time the gypsum will resist the effects of moisture. After that period of time, deterioration will begin. My experience with these moisture resistant gypsum products is that they begin to fail within three to five years. Failure can occur at an earlier date if exposure to water is severe.

The process of deterioration begins with the paper which encases the treated gypsum core. The paper, even though it has been chemically treated to resist moisture, actually begins to dissolve or degrade when exposed to constant moisture. This deterioration exposes the chemically treated gypsum core to moisture. Eventually the gypsum core softens and your ceramic tile begins to fall from the wall.

The Next Step Up

Manufacturers were quick to realize that the moisture resistant gypsum couldn't do the job. So several of them developed products which exhibited higher performance characteristics. In fact, one product was based solely on the already known concrete system which had worked for years.

One day, somebody just thought "Why reinvent the wheel?" Why not manufacture concrete in manageable, easy to use sheets which can be nailed to walls? BINGO! Cementitious board was invented. This product has been around for approximately 15 years and has worked extremely well. It offers long-term durability with somewhat easy installation. What's more, with modern thinset cement adhesives, you can actually install ceramic tile on these boards that will not fall off when exposed to water!

Cementitious boards, however, are somewhat tough to install. You cannot nail close to the edge of a board without it fracturing. Also, cutting the board and producing a smooth edge is nearly impossible. Cutting holes is done either with a hole saw which produces dust, or by using a chisel, which makes a jagged cut. These disadvantages are minor, however, when you consider the fact that the products will not be affected by water.

The third alternative with respect to ceramic tile backer boards is a material which takes the qualities of moisture resistant drywall and cementitious board and blends them together. It is important to realize that this backer board is marketed as a water resistant material, not waterproof. It has a gypsum core made with a proprietary silicone treated chemical process. This board also substitutes fiberglass matting for the chemically treated paper found in the previously mentioned gypsum backer boards. The final component to this backerboard is a heat-cured, co-polymer water and vapor-retardant coating on the finished side of the board.

This new product is backed by a 20 year limited warranty. It can be easily cut with a standard razor knife and it installs just like standard gypsum products.

Water Vapor, Hmmmmmm

The fact that only one of the products has the ability to inhibit water vapor is quite interesting.The cementitious boards cannot make these claims. Water vapor can and does penetrate these products. Water vapor can also penetrate the moisture resistant gypsum.

Water vapor can be a significant problem if a shower or tub wall is also on an exterior wall, especially in colder climates. During cold weather, if a vapor barrier is not present on the warm side of a wall system, water vapor can pass through insulation and subsequently condense on the cold side of the wall. This condensation leads to serious water damage in short order.

The Bottom Line

If you want your ceramic tile job to last and you want peace of mind, what should you install? If you want ease of installation, choose the silicone treated gypsum product. If you want to be assured of long term durability, select a cementitious board installed with a plastic vapor barrier. Remember, the cement system has already proven that it can withstand the test of time. This we know for sure.

The key to success in using either material lies in proper installation. The materials must not be allowed to come into contact with water. This is especially true of moisture resistant gypsum board and the cementitious boards. Both of these materials can soak up water like a sponge. This water will destroy the gypsum in short order as we have discussed. It will not harm the cementitious board, however, it could begin to rot out the wood framing members to which the board is attached.

Just remember, do everything possible to keep water in its place, that is, in the plumbing fixtures!

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