Quick question regarding CBU in a shower - Ceramic Tile Advice Forums

Cyberwombat · 12-04-2004, 10:02 PM

Howdy, folks. My name is Dan, and I'm a self-confessed DIY'er. Gotta say, I've gotten a ton of good information here already, but still have a couple of quick questions.

Here's my scenario: I'm working on a shower rebuild and am at the point of installing the pan. I intend to use 1/2 Hardiback on the walls.

1) From photos I've seen (HD Tiling 1-2-3 book, and also a couple of links off of here) not everyone notches studs to recess the PVC membrane - most of the time, it seems they just install the CBU right over it. Won't that slope it a little at the bottom? Or is it not enough to worry about?

2) Where can I find the preformed corner patches? I bought the PVC shower pan membrane from HD but the help there looked at me stupidly when I asked about the patches. Is that even required/recommended with a PVC membrane?

TIA - Cyberwombat

Davy · 12-04-2004, 10:08 PM

Hi Dan, welcome.

Yes, if you don't notch the studs the CBU will bow out at the bottom. Notching them is the way to go.

Sometimes the corners are hard to find. Some Home Depots have them, you might check with a plumbing supply. The corners are important, don't give up.

Jason_Butler · 12-04-2004, 10:22 PM

Hi Dan,

You can also add 1/4" furring strips to the studs to make the CBU clear the liner buildup. Keep in mind this will leave the shower walls about 1/4" proud of the adjacent walls.

Corners....I think I got my from the Noble Company online. Never seen 'em @ HD or Lowes

Jason

Cyberwombat · 12-04-2004, 10:44 PM

Thanks to the both of you. The furring strips will probably work (I suppose the alternative is chiselling out some of the studs, which I'm not too keen on).

John Bridge · 12-05-2004, 11:49 AM

Howdy Dan,

I would do the chiseling. It's really in the corners that this needs to be done -- where the material is built up because of the folds.

You'll need to go to a real plumbing supply for the dam corners. Royal Plumbing at Long Point and Silber sells to the public. there is also a location somewhere near downtown.

Cyberwombat · 12-05-2004, 12:36 PM

Nuts...wished I'da seen that earlier, I just ripped a bunch of plywood strips.

Next question: how dry does the pre-slope need to be before I can lay down the shower pan? I finished it last night but it is still pretty damp. From what I read on here, mud takes a looong time to cure.

bbcamp · 12-05-2004, 01:00 PM

You can proceed when the mud is hard enough to walk on, which I calculate to be right about....now.

cx · 12-05-2004, 02:24 PM

Ol' Injineer Bob has hisownself a calculator for everything, eh?

Cyberwombat · 12-06-2004, 04:49 PM

Whaddaya know, Bob, you were spot on...

Next question: in MB's article he says that
The membrane material should lie flat against all surfaces. Wrinkles in the membrane will create air pockets behind the mortar, weakening and reducing the compressive strength of the mortar bed. On large pan systems, I often use a laminating adhesive (NobleBond 21) to bond the CPE to the subfloor and blocking, in an effort to eliminate potential air pockets beneath the membrane.

This doesn't make a lot of sense to me, as I would figure the mud on top of the membrane would pretty much flatten it out. Nothing else I've seen has mentioned doing this. Is he right? My pan material is fairly flat (no wrinkles but plenty enough raised spots).

cx · 12-06-2004, 04:55 PM

Michael does a number of things that no one else seems to do, Dan. That's one of them. He usta tell you to use roofing tar. Don't know zackly when he upgraded.

Another is to double the liner material at the drain; that one can actually cause problems and solves none, in my opinion.

Your membrane is fine. Dump some mud on it.

My opinion; worth price charged.

Rd Tile · 12-06-2004, 05:05 PM

Quote:

originally posted by Cyberwombat.The Romans did not create a great empire by having meetings...they did it by killing all who opposed them.

Sounds like alot of the morons we have in the world today.

I know, this belongs in the mud box.

Davy · 12-06-2004, 05:35 PM

Two things are normally the cause for wrinkles in the pan liner. One is if the drain flange is lower than the preslope, the preslope needs to be even with the flange, Two is if the preslope has too much fall or pitch. The pan will lay flat with 1/4 inch fall per ft.

Aces High · 12-06-2004, 05:43 PM

I just poured the mud into the middle around the drain and pushed it to the outsides as if I were pressing the air from under the liner...Don't know if it worked yet, but can't see why it wouldn't...

Rd Tile · 12-06-2004, 06:27 PM

I hope you meant placed the mud, you don't pour mud.

Cyberwombat · 12-07-2004, 02:10 PM

Great. I think I've bolloxed this all up.

First, it appears the pan leaks. I have no clue where, but the water level went down maybe an eighth of an inch in 6 hours. It is possible the plug wasn't set right, so I'm going to try the balloon plug and retest. However...if it still leaks, and there is no obvious place where, what next? Should I start by patching corners? Rip the whole thing out and try a new pan?

Second - and this may determine all - it appears I have some flat spots in the pre-slope as there is quite a bit of puddling. This may be due to the wavy pan membrane, but I'm not sure. I can post a pic if that would help.

Anyone have any suggestions?