Applying thinset on backerboard in wet areas.


Brining shower pan liner six inches up the wall.
The NTCA is a non-profit trade association dedicated to the proper installation of ceramic tile and its allied products. One area where our staff spends an inordinate amount of time is in taking telephone calls related to problem tile installations. We keep track of the amount and nature of the calls. The data compiled provides valuable insight into issues affecting our trade on the jobsite.

Wall tile installations are the source of many of our calls. The following are five of the most common problems or questions our staff encounters on a daily basis. Hopefully, some of the answers will shed some light to the reader to prevent the same mistakes from re-occurring again and again.

5. My bathroom project involves three different walls. I know the contractor purchased the material at the same time, yet the tile looks to be a different shade on one of the walls. Did the contractor install two different dye lots?

Perhaps. However, another consideration that is often overlooked is how the light fixtures are placed in the room. In addition, many rooms with large windows allow outside natural light in, casting shadows on the tiled surface. An excellent suggestion to prevent this situation is to have the permanent lights in the room installed before the tile. Lighting should be moved at least 24 inches from the wall, and preferably to the center of the room.

There have been instances in which walls have been torn out and re-installed, only to find that the problem was in the lighting. This situation occurs both residentially and commercially, and can be extremely costly if you are unaware of it. Dal-Tile Company has produced an excellent brochure on the critical effects of lighting on tile that explains this complex issue in more detail.

4. We have rust colored stains coming through our grout. Do we have a problem with our water, or what else can be causing this?

Most likely the rust is coming through the grout joint as a result improper fasteners being used to adhere the backerboard to the studs. These fasteners most often do not resist corrosion, especially when subject to an inordinate amount of moisture. It is very important that you specifically follow the manufacturer's recommendations on what types of fasteners to use when applying their backerboard for a wall tile installation. There are many different manufacturers of backerboard that are suitable for tile and stone in wet areas. Be sure to specifically use the fastener they will warrantee.

3. There is a long, continuous crack running through several tiles in my shower. Can you tell me what may be the cause of this?

This is something we encounter often. If you were to tear out the tiles that were cracked, you are most likely going to find a seam there where two sheets of backerboard meet. It is highly likely that these seams were not taped, or were applied incorrectly.

Testing shower pan for leaks prior to installing tile in shower floor.

Using an alkali resistant fiberglass tape, properly tape all seams of the backerboard. Prior to applying the tape, pack the seams with a dry-set or latex-Portland cement mortar, or the specific setting material recommended by the backerboard manufacturer. Using a flat trowel, strike the setting material over the top of the tape, leaving a smooth surface. Note: The use of drywall tape or drywall compound is strictly prohibited for taping backerboard seams.

One other possible cause would be that the fastener spacing and patterns are not being followed according to the backerboard manufacturer requirements.

2. Do I have to waterproof the entire tub enclosure or shower? What is considered to be a wet area?

According to the Tile Council of America Handbook for the installation of ceramic tile, a wet area is defined as tile surfaces that are either soaked, saturated, or regularly and frequently subjected to moisture or liquids (usually water), such as gang showers, tub enclosures, showers, laundries, saunas, steam rooms, swimming pools, hot tubs, and exterior areas.

Areas subjected to continuous moisture, such as a steam room or sauna, would require a waterproof membrane to be applied throughout the entire area. In a tub enclosure or shower, the crucial parts to be waterproofed include the shower floor and the bottom area of the wall. The membrane should run up the wall at least three inches above a shower curb or six inches in a shower where no curb is installed. Note: To ensure proper installation of a membrane in a shower floor, it is recommended to pour water on the membrane prior to installation to make sure it does not leak.

The tub enclosure does not specify that a waterproof membrane needs to be installed. However, it is vital to properly seal the joint where the backerboard meets the tub with a flexible sealant. NTCA also recommends the use of dry-set or latex Portland cement mortar at least in the bottom area of the installation where moisture build-up is a concern. Some backerboards will wick moisture when used in wet areas and will remain wet. Organic adhesives (mastics) are not recommended in areas continually exposed to moisture. Failure to do this can cause the tile or the grout to yellow and discolor.

1.The local building code says that I can use water-resistant greenboard in a tub enclosure or shower. Is this something you recommend?

We are amazed at the amount of installations still occurring on greenboard in wet areas. It is true that many local building codes still have not changed this specification. However, the industry for a long time has cautioned against this practice.

There are many practical uses for greenboard; wet areas is just not one of them. That is why backerboards have been invented to prevent deterioration of the substrate. The fact of the matter is that there are numerous options to properly install tile in these applications. Some manufacturers now make excellent waterproof membrane systems to be applied over the greenboard if it is already installed. Either way, you must consult with the manufacturer on proper installation and applications of backerboards.

In today's society, the issue of mold has caused concern to builders and subcontractors all over the country. The tile installer runs great risk when using products such as greenboard in a wet area. Don't make this mistake, no matter what the code says. You would be amazed at how many home builders still call our office wanting to know why a tile contractor insists on a backerboard other than greenboard in a tub enclosure or shower. Don't be bullied into making this mistake. Once you accept the method, you buy the problem.