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Question:

Need Help On setting cement backer board?

I have a small bathroom approximately 4'x8' and I laid down and screwed in cement backer board. However, in my attention to detail I neglected to put down thin-set mortar underneath prior to screwing and taping down the board. I tried to pull the cement board up but I cant get under the tape that I mortared down to get to the screws. Am I in trouble here or can I go ahead and skip that and continue to tile? Please help...

Answer:

Make sure your screws hit framing members and not just plywood. Use an exterior grade deck screw, penetrate the framing member a minimum of 3/4 @ 5 o/c.
May 11, 2017
OK... You didn't specify whether you're doing a floor tile job or a wall tile job. If doing a floor tile job, here is the procedure: You can (but don't have to) apply thin set directly to the plywood and then lay and screw down the cement backer board onto the wet thinset. If your floors are pretty firm already, you don't even need to put the thin set on the plywood. Just screw the cement backer board onto the plywood. The thinset makers tell you to put thinset between the plywood and the backer board just to sell more product. It's an unnecessary step if your floors are already pretty stiff. Make sure you screw the backer board down and hit the floor joists underneath with the screws. Screws only going into the plywood is not sufficient. All screws must enter the joists, so get those marked before you start. Use thinset with a notched trowel on top of the backer board to lay the tile into.
May 11, 2017
I have used a modified thinset to ..... set the cement boards and it didn't stop a crack from forming at a beam. SO I guess what I'm saying is. move on using a GOOD modified thin set mortar. you will be fine. But stuff happens. you are skipping the safety...... but I would live dangerously.
May 11, 2017
I have not seen thinset used under the cement board unless the surface had high/low spots. As long as the area is flat, continue on.
May 11, 2017
skip it continue on
May 11, 2017

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