How long before you can flood a cement shower pan?

[digitalsam]

A big "thank you" to jadnashua for advice on a previous post.

I have created the first mortar slope for the shower pan and laid down the PVC, the Hardibacker is up and taped and mudded with fiberglass tape and thinset. Last night I built the top pan 2" thick and did my all-fired best to lay the slope evenly. It will be about 4 days until I can tile.

My questions are:
1. when should I paint the waterproof membrane on to the mortar pan? its 24 hours.
2. Is there are problem if I paint the entire shower floor with the liquid waterproofing?
3. Can I pour water onto the mortar pan before I paint the waterproofing, to see if there are any pools or low spots? If so, how long should I wait to do that?

I appreciate the help.

 

[Jadnashua]

Well, Custom Building Products has an instruction document on how to build a shower pan with their product. Personally, I would not use HardieBacker. The PVC liner is your primary waterproofing, and you'd typically flood test that pan prior to installing the setting bed on top of it. If you try to flood test it now, it will take a bit of time to saturate the mudbed, so you will need to wait for that to happen, then measure it, and then leave it to check for leaks, as the level will go down as it percolates into the mud bed, making things a bit harder to figure out.

Neither the tile nor the grout is the waterproofing on a pan or shower...it's the liner.

Now, if you installed a moisture barrier behind the Hardiebacker, you should NOT install RedGard on top of it. You only really want one waterproofing or moisture barrier on the walls OR the pan.

Keep in mind that with the weep holes in the drain, there's no reliable way to seal RedGard to the drain, and as a result, if you flood the pan, some moisture will be able to percolate into the mudbed between the Redgard on top, and the liner below. WIth the waterproofing on top, and the liner below, once it gets wet, it will take a VERY long time for it to dry out. So, the better plan might be to avoid sealing the mudbed between two waterproofing layers.

Now, a second issue is how did you anchor the bottom of the HardieBacker? HardieBacker, being classified as a fiber-cement board (the fiber is cellulose, wood fibers), has its own procedure in the TCNA handbook and the manufacturer's instructions differ than those when using a 'real' cement board (i.e., one that is not a fiber-cement board). The HardieBacker cannot be embedded in the top mudbed. The instructions call for it to be ended above the mudbed. Since you are not allowed to put any holes in the liner below 2" above the top of the curb, that means the bottom 4-6" or so cannot be fastened, which makes it difficult. That also means no cbu on the curb...you cannot screw through the liner to attach it.

With a 'real' cement board, the normal procedure is to embed the bottom of it just above the liner, so when installing the mudbed, it is locked in place.

So, while flood testing at this point can be done, it isn't as reliable. Go to the Custom Building Products website and read how they want you to use RedGard in a shower.