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I'm remodeling my Bathroom and I had to lay down new 2 x 6" T&G boards. I plan to lay tile so I bought Hardiebacker (cement backer board). I was planning on laying down the backer board, lay thinset over T & G boards then backer board, but after reading a lot of sites I'm not sure if this is the best way to go. My tile area will be about a 4' x 5' foot section on the floor. I'm also reluctant to put down 1/2" plywood then backer board then tile because it will create a big lip between the bathroom and hall way.

  • What is the height difference from the hallway to the bathroom floor. Will you be laying the t&g over existing plywood? Or are you starting at the floor joist? – cano Jul 1 '17 at 21:16
  • Wow, 2x6 decking? That seems like a lot. I think you could use 1x6 if they're spanning 16" or 24"...but, no, you do not need plywood too, but yes, you should use cement backer board, unless it's a shower, then I wouldn't use thinset. – Lee Sam Jul 2 '17 at 3:53
  • @LeeSam, 2X6 decking is used a lot out here in the pacific NW, the joists are 4' centers, and are huge. The OP will need to confirm joist spacing since the 2X6s will flex individually over the 4' span. The T&G is not that tight. – Jack Jul 2 '17 at 16:58
  • My hallway floor is 1/8th inch higher than my bathroom floor. Right now the bathroom floor is T & G over support beams. This is a 45yr old house and thats how the built the floors with over a craw space. So the floor is not level. This part of the bathroom is not the bath/shower I am putting in.Just the area in front of the toilet and sink. – Dave G Jul 2 '17 at 23:10
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If those T&G boards are your subfloor, you'll be fine putting the cementboard panels right over them. Just screw them down to the wood subflooring with plenty of screws; don't use thinset for that. DO use thinset to cover the cementboard seams and screw holes, then tile right over it.

  • I am using the 1/2 inch hardie backer because my flooring where my new tub is , is about 1/4 inch higher so it does even out the floor. I also figured the 1/2 inch will give me more firmness and not have to worry as much that the T&G boards aren't even all the way across. And the area which will have traffic is just 3' x 4'. But I was going to use the thinnest to help make up for the low lying sub floor boards because there are areas that are about 1/8 " lower. Do you think this will be a problem? Not using thinnest and just screwing down the backer board. – Dave G Jul 3 '17 at 0:28
  • Using thinset to fill a 1/8 depression sounds fine for peace of mind. – iLikeDirt Jul 4 '17 at 9:38
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Cement board is brittle and is not suitable for unsupported use as a floor. When it is supported by plywood or such it is much more resilient provided they are sufficiently bonded (screws work fine as iLikeDirt mentioned, but some like to supplement that with construction adhesive for a quieter floor. On the other hand, there are alternatives to cement board. One system is thinset over lath which you can easily do at 3/16" or if you are careful at 1/8". However this is a much more expensive system, more brittle (add underfloor bracing) and more difficult to do. It also needs lots of staples.

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