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Old 10-02-2018, 01:00 AM   #1
mrgedman
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Brick walls, both interior and exterior shower

TLDR; Corner shower has 1 exterior brick wall and 1 interior brick wall. Skim of thinset, redguard and Studwall, shower valve, hardibacker and redguard, and respectively, with cloth waterproofing tape on the seam. Is this right? Would kerdi work much better here?

I am helping a friend with a bathroom remodel. I've done a few tile showers before, always with wood studs, where choice of waterproofing and backing has lots of options.

My friend wants subway tile throughout, hex on the floor, and subway wainscoting in the entire bath.

All the walls in the room im currently working on are exterior, brick walls- the bathroom is part of a lean-to addition, so all 4 walls are uninstalled, ~50 to 100 year old brick walls. They have about 1/8Ē to 1/4Ē of mortar, with about 1/8Ē to 1/4Ē of plaster over them. They are remarkably flat and strong (no cracks).

See attached floorplan- it is roughly to scale.

My friend wants a pre-form neo-angle shower pan. The south wall will be framed and I'm planning on using hardibacker and redguard. I think the masonry walls the arent being framed out only require stripping the paint, and skim coating to bring flat- (average dip/hump 1/8Ē to 1/4Ē over ~2ft, around 1/4Ē over 4', and not much more than that over 4.. ). They are already fairly flat, and the mortar/plaster is sound- I think from what I've read, I'll skim with polymer modified thinset and then redguard over that, using fabric (think I have lacticrete) on the seam. I dont think it will be easy/possible to attach metal lathe to the plaster/mortar/brick walls. I've tried tapconning 100+ year old brick before, and it does not end well.

As I understand it, the other brick walls can just be skimmed with thinset and then have subway on em.

I've done some searching on the forums, but this seems like a bit of a strange remodel, but I think it all makes sense. I recall reading somewhere that a vapor barrier/plastic sheeting on an exterior wall can often cause more problems than it solves... but this may not apply to an uninsulated masonry wall.

It seems a little tricky to waterproof the area where the pan liner flange and tile meet/overlap, but I recall a thread that goes over that I think...

Sorry for the essay, and thanks very much.
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Old 10-02-2018, 05:52 AM   #2
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I would figure out which system you want to use and stick with it. 1/4 inch in 4 ft isn't flat enough. I would want the walls flat and plumb, check them with a straight edge and level, then check the walls for square. I would Tap con lath to the bricks, if the bricks are too hard, drill into the mortar.
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Old 10-02-2018, 08:52 AM   #3
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thanks. I was hoping I could skip the tapcon and just skim the wall sans lathe...

as it turns out the walls are actually much more flat than I thought, but are pretty far from plumb/square.

it's a lotta floating for a wannabe mudman. I've done a mud pan once, but never walls.

I'll do some more homework.

thanks very much.
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Old 10-02-2018, 01:35 PM   #4
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This is sort of a questionable way to do it, but if you don't want to lath the walls, I don't see why you can't use a bonding agent for plaster for that little amount of skim. I'm not sure how a modified thinset would work with those bonding agents, there could be some sort of chemical incompatibility. Cheapest would be Quikrete Concrete bonding agent, but there's also Weld-Crete and others. Basically it's just paint on glue/sealer that makes it so whatever you put on doesn't get the moisture sucked up by the substrate.

I'm not 100% sure of how it would work with a Portland wall mud, and how thick you can or can't apply it, but you could easily use a base coat plaster like Structo-Lite and just replaster the walls true and plumb. From my own tests I do know Mapei Aquadefense adheres fine to Structolite, so you could have surface waterproofing that way. It is gypsum based, but the stuff does dry pretty hard, basically like concrete. To practice plastering I had a scrap sheet of Hardibacker that I used Structolite over, and it's been outdoors on my back porch with no mold or breakdown. Obviously Structolite is not TCNA approved and all that fun stuff, but I just wanted to throw it out there.

If you do a skim coat with a polymer thinset, after stripping paint off, you'd be best if you used a tile company's primer on the walls first, like Mapei Primer T or similar. The problem is the plaster is likely gypsum or lime, and both suck moisture out too fast, which could cause thinset adhesion issues without the primer. Then for waterproofing, once the walls are skimmed, just use Redgard/Aquadefense/Hydroban.
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Old 10-02-2018, 03:29 PM   #5
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Thanks Joe!

it seemed questionable, but I found a similar thread where a few people recommended it... until others came along and said "id just put the lathe up"

One of the reasons I wanted to try it my way is the waterproofing at the flange/wall intersection. I spent an hour or two today trying to find an example of a mud wall with a premade fiberglass pan, but couldn't find anything... I'll look some more.

Any ideas on the waterproofing premade pan/ mud wall intersection? I tried to talk my friend into a mud pan, but I she wanted the cheaper route.

I think I'm gonna just do lathe after all. the bricks actually take tapcons pretty well- it's almost too soft- some of the holes got too large while drilling.
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Old 10-02-2018, 06:24 PM   #6
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Ged, we've mudded many showers that had fiberglass bases. I usually use a product like Protecto Wrap at the bottom of the walls overlapping the lip on the base. PW is a peel and stick waterproofing. I then overlap the PW with my felt paper. Then the lath goes up.

You have to keep in mind that we do this for a living. The last thing we want is to have problems so we don't do anything that would be considered risky. If my customer wanted to do things a cheaper way than I would usually do it, I'd walk away from the job instead of taking the risk. If I was doing it for a friend, I'd tell them to wait till they save up more money then we can do it the right way. I doubt there will be very many threads on mudding shower walls over brick without using lath. I'm not saying your way won't work, it's just not something we would usually do.
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Old 10-03-2018, 12:37 PM   #7
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Davy,

Thanks for your feedback... The last time I started a thread here I did the same thing, asking for advice and tips about how to do it the wrong way. didn't realize how dumb it was then, and with my latest round of research didn't think I was quite as bad this time around

I think if it was just wainscoting, floating sans metal may not be so bad, but still not ideal.

I'm excited to try it out, and become an occasional mud man.
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Old 10-03-2018, 06:16 PM   #8
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Hey, nothing wrong with thinking outside the box. There's no dumb questions.
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Old 10-04-2018, 12:50 AM   #9
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Heh, I think there are some ignorant questions at least... but thatís not necessarily a bad thing.

I discovered earlier tonight the plumbers set the shower pan pretty far off my marks. Now the flange is pretty far from the brick wall in the corner, about an inch. My stud walls are nice and strong and flat... I had removed plaster/mortar from the wall so that the flange could be up against the wall to avoid this... seems like they pulled it out almost an I inch for some reason.

Iím worried if I put up the felt/tar paper that it will make a shelf as The flange is so far from the wall in the corner. Likely a mess 90 degree bend withan inch of mud on it...

It seems like I should fill at least this void, and perhaps a bit above it before I hang my paper and lathe.

1. Should I fill it? How far past the flange should I go vertically? Should I tapcon lathe in a small patch and practice muddling to bring it out, eventually putting another layer of wire on top of it?

2. Do I need to remove plaster/mortar down to the bricks? Remove the paint even? Itís in good shape unless hit deliberately with largish hammer. It seems like with felt and lathe,it really doesnít much matter what is behind the felt.

3. After adding more tap cons today, I lost a bit of confidence in their holding ability... some tend to not hold well at all.. Iím curious about using a slight smaller bit than recommended to help them hold. Is this correct?

Iím in a bit over my head with this, I didnít think the walls were so far out of square... itís really just a 6 inch band in the corner... yikes
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Old 10-04-2018, 05:55 AM   #10
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You could screw the lath right to the brick without the felt paper and then apply a surface membrane over the mud. Sometimes flat washers are needed with the screws.

If you need the mud to be extra thick, then apply a scratch coat for the first layer, let it set and then add the finish coat.

Sounds like you need a smaller bit.
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Old 10-04-2018, 10:58 AM   #11
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Davy-

I was under the impression that the lathe needed to be inside the flange. I suppose I could set it behind the flange, build it out and eventually put my sticks on the shower side of the flange, but it still seems like there would be a large void behind/beneath a portion of the fiberglass pan. Or were you suggesting I make a small patch to bring it out, and then follow with my metal inside?

I included a picture to be a bit more clear.

It seems like I could tapcon a 2x rip just in the corner, and that would bring the metal out nicely.

If the metal has to go behind the flange, Im not sure how I would wrap the lathe around the corner of the stall- I suppose I could cut a notch in it?

I assume the scratch coat is mortar mix/fat mud. 1/4 notch trowell or do i just want to fill the lathe? I need to read up on scratch coating.

Thanks very very much. I really don't want to mess this all up.
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Old 10-04-2018, 04:27 PM   #12
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If you want to get your walls flat and waterproofed, I'd stick some KerdiBoard panels up against the existing walls, tape the seams, and have a bit of insulation, a flat and plumb wall, and be done with it in probably a couple of hours then be tiling. Since you won't be flood testing a premade pan, you'd be tiling right after installing the panels. Flattening the walls then Redgard will require you to wait at least a day or so for stuff to dry out, then the time in between the Redgard coats...none of that is required if you go the KerdiBoard route.

Schluter has a couple of videos where they do that over a cinder block wall, but it should work the same over brick. You need a long level to press the panels in place after putting a bunch of globs of thinset (or you could use KerdiFix, but that costs a lot more) on the back side.
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Old 10-04-2018, 07:52 PM   #13
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I would have made the plumber reset the base where it needs to be. Because of their mistake, how much are you going to have to build out the wall to get it out over the lip? The face of the finish mud will need to get out past the lip. Then the Redgard or other membranes would go over the mud overlapping the lip.
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Old 10-04-2018, 09:03 PM   #14
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If you used Kerdiboard, and with the thinset bonding it to the wall wasn't thick enough, you could use a thicker version of it. It works easily if you put a rabbit joint on the bottom to come over the tiling flange if you either use KerdiFix there, or band it with KerdiBand.
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Old 10-05-2018, 11:35 AM   #15
mrgedman
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Davy,
as it turns out, I will have to build it out a lot less than I thought. prolly 3/4 to an inch max. may have to go just under 1/2" thick further down the wall, unless I build it out even further. that wall is the acute angle... see pics... it's not that bad, I'm just a baby


Jad,

yeah kerdi and gobs of silicone may have worked... but I'd rather do it the old fashioned way. I didn't bid the job right, it's for a friend, and if I make less money per hour, that's alright as I'm learning... and it's for a friend (i like the couple a lot, they're cool as can be)
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