cement board under bathtub

[Graven Water]

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'd like to replace the plywood with something that doesn't grow mold. Would 1/4" cement tile backer board do? The bathtub weighs about 350 pounds and half that weight 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? thanks Laura

[ransley]

How did you figure that there is mold under the tub, which most people never see!!! No Mold grows because of moisture, is it on an outside wall, is it a contractor telling you, it could be condensation causing it and your contractor is a crook and its normal for your design which is defective in itself. You are jumping to conclusions.