Tom Smeal

02:49AM | 03/18/04
Member Since: 02/02/04
13 lifetime posts
I just installed 1/2" wonderboard over our 5'X 5' bathroom floor (excluding bath/shower). Is it advisable to install 15lb roofing paper on top of the wonderboard before installing the new 12"X12" ceramic floor tiles?

I plan to seal the grout of course, but I just want the extra protection while I have the opportunity.

Thanks for any advice.



05:34PM | 03/18/04
Member Since: 03/15/04
28 lifetime posts
Don't think I've ever heard that suggestion, and don't know why you would think you need it. The backerboard is resistant to moisture. It will not deteriorate even when submerged. You're also going to have a layer of thinset that is basically a solid bed of cement over it, and then tile. If you're really concerned that moisture could soak into the plywood thru all that, and for your peace of mind, I would suggest you use a product like RedGuard. It's available at H.*me D.ep*t and is a roll-on waterproofing and anti-fracture membrane for ceramic tile.

Tom Smeal

03:42AM | 03/19/04
Member Since: 02/02/04
13 lifetime posts
The roofing felt idea came from a tile book I bought. It was suggested, along with the Red Guard option you mentioned.

Thanks for the advice.



08:31AM | 07/06/07
Member Since: 07/05/07
1 lifetime posts
i've heard that i should not use both roofing felt behind my backerboard and Red Guard on top. Something about mold development. Could you weigh in on this? I am working on a the walls surrounding an existing tub. Thought this would be the best way to ensure a waterproof wall.


07:39PM | 07/06/07
Member Since: 07/03/05
283 lifetime posts
By doing what you talked about you are encapsulating the cement board with no ability for it to breathe and exhaust any moisture buildup that might occur. There is still air between the cement board and the roffing paper. Condensation could occur when one side of the board gets warm while the other side stays cold. Cement boards do not promote the growth of mold as they are not a food source like a gypsum board would be. But other contaminents on the board or in contact with it could create an issue.

If you are doing a steam shower the paint on waterproofing should cover the cement board as you dont want steam vapors to collect behind the board. A regular tub/shower is usuually waterproffed from behind the board. Actually waterproofing is a misnomer because once a nail punctures the roofing paper or plastic sheet it is no longer waterproof. At that point we consider them to be moisture retardent.


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