TECH TIP TUESDAY: Q & A WITH NTCA TRAINING DIRECTOR MARK HEINLEIN
The concern that I have at this time is the installation of soft joints at the change of plane in the corners of the tub surround. The product is a 12″ x 24″ marble.
The tile pieces most definitely butt up against one another and it is my belief that the tile installer is going to place a bead of caulk up along the exposed surface of the two.
I am concerned this is not a soft joint to allow for movement of the tiles, but rather a bead of caulk to hide the connection (more aesthetic than functional). Would this be a concern for you? If so, what types of issues may I have in the future if there is no soft joint?
Thank you for contacting the National Tile Contractors Association!
The Tile Council of North America Handbook and ANSI Standards require functioning open movement joints at changes in plane. If those joints are tight butted there will be no room for them to properly function to absorb the natural flexing, movement, expansion and contraction that is inherent in all construction. Without being there in person I am not able to comment definitively however, the joints in your photos do appear to be either tight-butted or have too tight of a joint.
Movement joints at changes in plane are required and are functional and should be filled with a flexible sealant appropriate for the area it is being used. For a wet environment such as a shower, an ASTM C920 sealant such as a 100% silicone or urethane can be used. These sealants are manufactured to match as closely as possible the grout color.
Before applying the sealant in your marble installation, a test sample should be done along the edge of a scrap piece of marble. Some colors of sealants have colorants that may absorb into the soft stone and may cause staining that can be visible along the edge of the tile. This is a common pre-installation test that should be done with all marble installations. A phone call to the technical department of the sealant manufacturer may help determine which of their colors are best suited for soft stone.
The best way to find an NTCA Recognized Consultant in your area is to review our list at this link: http://www.tile-assn.com/?page=recconsultants. These are highly regarded consultants that may travel regionally or nationally. Feel free to let them know about the conversations we have been having.
I hope this helps.