Replies

1. GBA Editor
   Martin Holladay | Nov 14, 2012 06:17am | #1

   Brian,
   My guess is that the foam will be too squishy to work as a substrate for tile.

   My advice: (a) use XPS, not polyiso, (b) include a subfloor of plywood or cement backerboard above the XPS, and (c) choose a more flexible type of flooring -- not tile.

2. 
   [email protected] | Nov 14, 2012 07:53am | #2

   Thanks Martin. I was thinking that cover board was inherently not squishy. To confirm we're talking about the same thing, I'm attaching the following link. There is at least one other manufacturer with a similar cover board, but this will give you the idea: http://www.firestonebpco.com/roofing/insulation/coverboards/isogardhd/

3. GBA Editor
   Martin Holladay | Nov 14, 2012 08:36am | #3

   Brian,
   Just because an insulation board is stiff and rigid enough for roofing applications, doesn't mean that it's stiff and rigid enough to use under ceramic tile.

4. 
   [email protected] | Nov 14, 2012 08:41am | #4

   Fair enough. Thanks.

5. Expert Member
   Dana Dorsett | Nov 14, 2012 12:34pm | #5

   There's also the issue that in an over-slab application it's likely to take on groundwater over time, reducing it's effective R-value. Iso is oftenOK to use on basement walls, slabs, not so much (no matter how rigid the subflooring is for distributing the mechanical loads.)

6. 
   [email protected] | Nov 16, 2012 01:39am | #6

   Conceeded and appreciated. Thanks!