Re: Bathroom floor layers
To add ---- personally I like to use 5/8 plywood rough side up.
Lay the plywood first and then drill the holes for plumbing after --- saves the trouble of measuring and drilling when laying the plywood.
Then apply an uncoupling / waterproofing material such as Ditra
This will help prevent tiles or grout cracking from any bounce in the floor as well waterproofing under the tiles.
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