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Discolored grout, installing of drywall, and pressure-treated lumber
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Ask the Experts Q&As are culled from member inquiries to NTCA’s Technical Support staff. To become a member and make use of personal, targeted answers from Technical Support staff to your installation questions, contact Jim Olson.
QUESTION My shower floor doesn’t look like it did originally. The grout has different shades and looks like it is growing mold on the surface. What is going on with it? ANSWER It’s hard to make a determination without seeing this in person, but I have seen shower floors that acted similar to this before. Sometimes the mold is superficial and resides only on the surface of the installation. Most shampoos and soaps contain organic matter, some more than others. When you have organic materials, temperatures, and moisture, you have a great environment for mold to grow. Proper and regular cleaning of showers removes those materials. When used and not cleaned regularly you can end up with a situation like this. Always use neutral PH cleaners approved for cleaning the stone or tile in your shower. And always test them in an inconspicuous area to make sure you will have no adverse reactions. Double check for mold or wet areas outside the shower as well to ensure there are no leaks. If water has escaped the shower assembly and has reached the wood substructure this can also provide the organic matter needed for mold to grow. If this is the case, you may need to dig into the installation to find the source of mold growth.
Protect Stone, Tile, Masonry and Grout from Stains
QUESTION I’m looking for the spot in the Handbook that states that you are not allowed to use pressure-treated lumber to build a bench or curbs.
ANSWER In the shower methods of the TCNA Handbook for Ceramic, Glass and Stone Tile Installation, the requirements for wood studs are that they must be dry and well braced. The general requirements for wall bracing are found in ANSI A108.11 in section 4.1 Wood Framing. This section states all framing lumber should have a moisture content not in excess of 19%. Most pressure-treated lumber has moisture content ranges of 30% to 70%. As pressure-treated wood starts to dry out, it has a tendency to twist and contort. The rigidity of the tile assembly cannot generally handle that type of movement, and failures can result from it.
QUESTION I want to install ceramic tile on a kitchen backsplash. There is currently drywall where I want to install the tile, between the countertop and cabinets. Can I install directly to the drywall or do I need to remove it and install a concrete board?
ANSWER When selecting installation methods and materials, how the area will be used in service must be considered. The TCNA Handbook for Ceramic, Glass and Stone Tile Installation has a section called Environmental Exposure Classification that deals with this issue. There are both Residential and Commercial ratings, which mainly deal with the amount of moisture an installation will receive. A kitchen backsplash like you described would most likely fall into Residential 1 classification (Residential dry). If the surface will not be exposed to moisture or liquids except for cleaning, there are recognized and acceptable methods for installation over gypsum board like methods W243 and W242, found in the Handbook. These methods describe the details for approved installations over gypsum board.