ASK THE EXPERTS Many people reading the Ask the Experts on page 22 in our June issue (and the TileLetter Weekly Tuesday Tech Tip on July 3rd) were puzzled by an answer that appeared to a question about T&G boards. The problem was the answer addressed issues with porcelain planks and expansion joints, and it left a lot of people scratching their heads. We admit it, we had a bit of an email mix up and so the answer to a different question that origi- nally appeared in the same thread was posted. This is the T&G board question paired with the correct answer: QUESTION I’ve got a new question for you all. What about homes with sub- floors consisting of T&G boards, not plywood? They run diagonally. In this one specific case, there is actually 3/4” solid wood installed over the top of it. My thought is that it would require double 3/4” plywood, and I can’t find a single method in the book that identifies such a subfloor. ANSWER We get this question quite often. The movement between the planks can be too much for a tile installa- tion. Most manufacturers require 3/4” OSB or plywood to install concrete board and uncoupling membranes for ceramic and porce- lain tile installations. Installations involving stone require additional layers of plywood. You really have two options here: you can remove the existing layer of plank subfloor and replace with plywood, or add additional layers of plywood to the existing plank. Check with your manufacturer, but most will warranty the installa- tion by adding an additional layer of 1/2” plywood before installing their product. Fasten down any loose planks, and sand or chis- el down any high planks before installing your plywood. Use the correct amount and type of mortar between the plywood and concrete board or uncoupling membrane. With concrete board installation use the right type and number of fasteners, stagger sheets from each other running them perpendicu- Sponsored by Ask the Experts Q&As are culled from member inqui- ries to NTCA’s Technical Support staff. To become a member and make use of personal, targeted answers from Technical Support staff to your installation ques- tions, contact Jim Olson at 20 TileLetter | August 2018