View Full Version : cbu subfloor under shower base?

04-14-2007, 06:11 PM
Iím redoing a small bathroom that has not seen any TLC in 45 years. I now ready to install a new Swanstone neo-angle shower base; just not sure what the best way to do this is.

The subfloor is 3/4" t&g board. Itís in good condition, just not perfectly level.

Option 1: I put 15lb felt and metal lath on the subfloor and install the base in mud.

Option 2: I put cement backer board on the entire bath room floor, add two coats of Redgard and install the shower base directly onto the cbu - nested in mud for stability. That seems to be easier and faster but is cbu OK under the shower base?

Which way would be best? I would like that bathroom to last for the rest of my life, so ďoverkillĒ is just fine :)



04-14-2007, 08:19 PM
i wouldn't do option #2, but i would first get Swanstone to say what they require in terms of strength under the neo-angle base, like for example L = 1/360 deflection in floor, or how much?


04-15-2007, 02:56 PM
Deck mud should be probably thicker than you want. How out of level is it? A medium bed thinset can be installed up to about 1/2" or maybe more depending on the brand - no lath required.

04-17-2007, 12:02 PM
well, I went with 15lb felt, metal lath and a bag of mason mix. nearly forgot to cut a hole for the drain in the lath ;-)

shower base is level and rock-solid.


04-17-2007, 01:13 PM
that should work! The main goal is to prevent the fiberglass or whatever system from flexing when walking around in the shower. Fully supporting it both makes it feel much more substantial and prolongs its life by preventing stress cracks. A secondary, but necessary function is it gives you the opportunity to level the shower floor, which is very important for proper draining and trying to make the walls look good.