gaps in top mud bed [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-02-2019, 08:35 AM
Hello everyone.
I am preparing to tile a shower -- my first shower, my third tile "experience."

I paid a regional tile installer to do the pan -- dry pack pre-slope, Oatey liner, and deck mud on top. The deck mud on top was super crumbly on one edge, so I called him and he came back and added another layer.

He attached the liner to the studs without notching them. I asked about how thick the folded liner was, and how that would impact the slope of the wall surface -- he told me to just screw the durock real tight to the walls down to about 5-6 inches above the floor and then not worry about remaining gentle slope. I have NOT done that yet. I found another problem with the floor, and wanted to sort that out before exploring putting notches in the studs.

I'm not to confident of his expertise at this point. And, I'm out of $$, so I need to sort this out myself if possible. So -- I have a couple of questions at this point.

The top mud bed has voids at the edges where it meets the liner. Not everywhere, but along the edge that was crumbly before he "repaired" it. How should I deal with these voids -- maybe 2-3 inches long, up to 3/4 to 1.5 inch wide, and appearing to go down pretty deep. Can I patch or fill them?
I haven't yet attached CBU in lower portion of shower. -- can I pull the line away from the walls & notch the studs at this late point?

I plan to use Redgard before the tile goes up.
Thanks so much for your advice and for this site.

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Fast eddie part deux
07-02-2019, 08:51 AM
Rather than notch the studs, why not add furring strips to build them out above. Run av2x4 through a table saw to make strips 1-1/2" wide (same as the studs) x maybe 3/8" thick ... or whatever you need. Avoids trying to work with the liner thats already in place.

07-02-2019, 08:57 AM
Welcome back, Julie. :)I'm not to confident of his expertise at this point.Nor would I be.

The material you have there does not appear to be deck mud, but something more like concrete. Not a concern for the pre-slope, but not at all what you want for the final mud bed.

I recommend you remove that material completely and re-do that top mud bed. That will also allow you to peel back the liner and notch your studs (surely he was not serious about not worrying about the wall slope at the bottom!) or fur them out as recommended above. I would prefer the notching if the furring will in any way affect your wall junctions outside the shower.

And be sure you do not fasten your wallboard below a line three inches above your shower curb. Unfortunately, you cannot embed the Hardiebacker in the top mud bed as you would do with a real CBU.

My opinion; worth price charged.

07-02-2019, 11:09 AM
Unfortunately, you cannot embed the Hardiebacker in the top mud bed as you would do with a real CBU.

The backer is Durock rather than Hardiebacker. Should it be embedded?

Is there a way to get the top bed out without destroying the liner? And, do you mean I remove down to the liner and start fresh?
Thanks tons,

07-02-2019, 11:22 AM
Not sure where I got the Hardiebacker idea, Julie. Sorry about that. Yes, you should extend your Durock down to about half an inch of the bottom of the liner and use the top mud bed to secure it against the blocking you should have behind the liner. That's very helpful as you cannot fasten your wallboard below the top of your pan liner, which must extend at least 3 inches above your curb top.

A few whacks with a medium pounder should show you how difficult or not it will be to remove that mud bed. You can usually do that without damage to the liner, but that presumes your mud bed is deck mud (aka dry-pack) and not what it appears to me you have.

Can't tell much about your liner installation from the photos you've posted, but given that fella's approach to shower receptor building you might wanna re-do the whole thing. You'll want at least to verify that you have the required minimum slope under the liner and that your liner is properly attached to the clamping drain, the weep holes are unobstructed and protected, and you have the proper corners at your curb ends.

My opinion; worth price charged.

07-02-2019, 11:59 AM
Thanks tons, CX. I'll give it try!

07-02-2019, 12:01 PM
I plan to use Redgard before the tile goes up.

Just to be certain, Julie. RedGard on Durock walls OK, but not on floor with liner underneath. Although if that's something closer to concrete on top of liner, it might not function in the same way that dry pack does, which is purposely porous.

07-02-2019, 01:27 PM
if that corner top smoothness is representative that guys is a slob. looks like cement. Not sure how he could have left such a gap like that?

07-02-2019, 02:36 PM
I've started chipping out the pan in one corner. I pulled back the liner and found that liner had been laid directly on the plywood subfloor! And, he charged me $600 for "install preslope shower pan, float out shower floor and have it ready to tile. It was $500 plus materials -- I had the liner on hand.

I'm in way over my head, but am feeling sure the whole drain installation is going to be wrong, as well.

Is there ANY circumstance in which it makes sense to lay the liner directly on the plywood subfloor?

Two big questions moving forward: I'm considering digging out the rest of the shower bed, having a good plumber remove the drain, and switching to a durock shower system. I can sell back the liquid waterproofing, and recoup $200, and be out around $50 for the switch, I think. Is this a good/easier solution?

And, can I reuse the durock already installed on some of the walls?

And, finally, this installer has a big business in a nearby city. I have the text stream with his itemized bill. I plan to get my money back since he didn't do what he agreed to do. Make sense?

Thank you all,

07-02-2019, 03:00 PM
Julie it always pains me to see another person on a tight budget get taken for a ride by a hack. I hope you do find a way to get your money back as he most definitely did not deliver the services you paid him for.

A pre-slope is never optional with a conventional shower pan liner build. It's also a plumbing code requirement in nearly all jurisdictions. But for some reason lots of plumbers and tile setters seem to be allergic to them, including a few fairly popular "professional" tile setting youtubers.

You can definitely switch to the Durock shower system if you wish. There are a few fans of their sheet membrane here on this board including the very well respect CX. If you are going to use their foam shower tray you may need to trim it to fit your space. The tray also depends on your subfloor being properly flat and level to insure proper drainage pitch all around. For that reason most of us prefer doing a mud bed. Also be aware that sheet membranes do have a learning curve. Plenty of DIY's have done fine with them on a first attempt but just take your time and watch some instructional videos.

The existing durock can most definitely be reused. You can fill any holes or imperfections with thinset.

07-02-2019, 03:29 PM
Just a note. That cement gets harder every day so decide soon ifs it's being removed.
Seems your not on her your head as much as your plumber.

Fast eddie part deux
07-02-2019, 03:48 PM
If you have peeled back part of the liner and you can see its directly on plywood, start taking lots of pictures. You shoupd definitely go back on him for what you paid, and you will need lots of backup. Think Judge Judy ... what would it take to convince her. Print out copies of all emails from him, especially ones where he says what he is going to do. Hacks like him are what gives decent contrsctors a bad name.

07-02-2019, 07:43 PM
If you paid via credit card, you should attempt a charge-back with your company. I did this once, and it saved my butt. You have valid documentation to submit for your complaint. This is a perfectly winnable case in small-claims court.

Dave Gobis
07-03-2019, 09:40 AM
If you decide to dig in for a fight, my mantra would be I just wanted a code compliant shower base. Get a copy of your local plumbing code and send it with your request.