cement board or what under bathtub

Old 04-11-11, 02:28 PM
Thread Starter
Join Date: May 2010
Location: USA
Posts: 19
Upvotes: 0
Received 0 Upvotes on 0 Posts
cement board or what under bathtub

There's mold under my cast iron bathtub so I'm going to pull it out into the next room to redo the subfloor.
The bathtub is resting on 1/4" plywood over the subfloor. I don't want to use plywood because it grows mold.
So I'd like to replace the plywood with a 1/4" layer of something else.
Would 1/4" tile backing board do? Half the weight of the bathtub would be resting on the 5/16" thick edge of the cast iron apron. Would cement board under a lot of pressure crumble over time?
Or some other material? I'm trying to make my bathroom as waterproof as possible. Extending the waterproof layer whatever it is under the bathtub, and using some kind of tape going a couple inches up the walls seems like a good way to do this. Even if the caulk at the edge of the bathtub leaks, it still wouldn't cause mold.
Old 04-18-11, 04:20 PM
Temporarily Suspended
Join Date: Jul 2008
Location: NY
Posts: 10,265
Upvotes: 0
Received 0 Upvotes on 0 Posts
According to your thread on gardenweb, you have already decided. Other people recommend a sand mix.
Old 04-21-11, 07:54 PM
Join Date: Apr 2011
Location: USA
Posts: 14
Upvotes: 0
Received 0 Upvotes on 0 Posts
If you have mold you have moisture. Get rid of the moisture get rid of the mold.
Old 04-24-11, 07:38 AM
Join Date: Jan 2011
Location: USA
Posts: 4,459
Received 125 Upvotes on 110 Posts
There's only a few ways that floor molded up and none have to do with it being a plywood floor. There had to be a plumbing leak, the wall was leaking, there's no vaper barrier on the ground if there's a crawl space, or no one used silicone caulking where the tub meets the flooring material.
I'd use Advantec T & G subflooring with constrution adhesive on top of the floor joist.
Reset the tub then install new flooring materail.
A cast iron tub should not need morter under it, there self supporting.
No form of 1/4 plywood should be used if this is going to be a tile floor, it needs to be a min. of 3/8 thick.
If it's linolium flooring then do not use Louon plywood, use A/C sanded subfloor rated plywood.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: