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Lou_MA 04-19-2021 06:51 PM

Help with floating shower walls
3 Attachment(s)
I have an upcoming shower project where I’m going to try 2-coating the walls. Project is still a few weeks out but am trying to get all my ducks in a row (info wise).

Plan is to liquid Hydroban over mudded walls, and bonding flange drain and sheet membrane on floor.

Pics are attached, but I don’t know how to rotate them. Old pan and drain will be removed.

It seems like I don’t use a vapor barrier over studs in this case, so...

1. How do I prevent scratch coat from just falling through metal lath into stud bay? Staple up something like brown builders paper over studs, then lath?

2. Where the lath wraps around solid lumber, like the 3.5” face of shower jambs, do I still need to apply a layer of...something...between framing and lath?

3. How heavy / thick do I apply scratch coat? I’m assuming I just eyeball the thickness?

4. How much pressure do I apply the scratch with? Am I just concerned with getting it on the wire, or am I actually trying to press it through? Do I need to hit it from multiple directions, like if I’m grouting?

5. What’s the timing on when to scratch it? Do I want the scratching tool to leave smooth furrows like through fresh thinset? Or do I want the mud to be crumbling out?

6. Am I trying to scratch all the way back to the lath?

Just In Tile LLC 04-20-2021 04:24 AM

Atta Boy Lou,
Get that mud work going and you'll spoil yourself on a setting base.

1)I'd use roofing felt on the framing since it breathes if you're going to topical waterproof as well.

2)I would because.... that's how i was taught and like separating the mud from the wood. Just wrap your felt around.

3)The scratch is there to solidify the wire and make a stable base for your brown coat. You don't need much but want to cover the wire. If you have time, it's a good idea to have a level handy and add more mud where the wall is really out during the scratch. That way you won't need such a heavy float.
But again, it's a rough coat so you don't have to try and find every spot and plumb them out, just the major areas (if any)

4)In most the shower (where there is open stud bays) I lay the scratch on lightly, by "almost" letting it glide off my tipped trowel onto the wall. Reason being if you push too hard it just oozes out the back and wastes mud. Where you have solid backing push as hard as you want. You'll get a feel for it rather quickly when you see mud drop behind :)

5)Scratching goes pretty fast for me. 20-30 min maybe once the mud is made. I've done both; scratch each wall as I go, scratch it all at the end. Just make the mud like brick mud consistency and not too watery and your scratch will be fine to comb however best suits you. I'd probably scratch at the end because the shower looks smaller.

6)I'd say no, because you don't really need that much pressure, you just run your scratcher across the mud and its ok if you feel it skimming the wire/lath but I wouldn't say push it so you make SURE it's hitting the wire. I'd reference #3 again because sometimes you will add mud in different areas to make the float easier and you wouldn't want to add mud just to push it back to the wire again.

Just In Tile LLC 04-20-2021 04:41 AM

2 Attachment(s)
Probably bad to show you this because I don't make my scratches this nice but I knew I'd be posting them so I made them look "pretty".

Most times there's a little wire showing, lines from scratch aren't nearly as straight because again, it's just there to stiffen the wire. I don't waste too much time making them look pleasing to the eye because I spend that kinda time on my float the next day :)

Make sure your mixing valve is set a little farther out from stud bay BEFORE you scratch. In general 1-3/8" to plaster guard face from stud face. I find even after telling contractors/plumbers/homeowners-to-tell-plumbers, some will still go to habit and set them for a 1/2" wallboard. So just double check when you arrive on site.

edit:and IF you have those plastic pipe guards for your shower head stub out DO NOT mud them tight on float day...:)They wont thread out like a galvanized pipe does. Especially if they have grooves where your mud locks them into place....don't ask me how I know.

cx 04-20-2021 07:50 AM

1. You must put some roofing felt or polyethylene sheeting behind your metal lath in a shower wall, Lou, but it's not to keep the mud from going through, it's for water containment.

The mud will go through just enough to create a mechanical bond with the lath. The lath is trained from birth to be of exactly the proper size and shape to allow that to happen if your mud was mixed close to correctly and you don't try to force it all through the lath.

2. Yep. See #1.

3. No specification I'm aware of for the scratch coat. I think the correct amount is "some." :)

4. What Justin said.

5. See #4.

6. You're just trying to make a rough surface for your brown coat to bond to. No need to be forceful, just make it very rough.

Don't look at those photos Justin posted. A finished scratch coat never looks like that. Obviously photo-shopped. :D

My opinion; worth price charged.

John Bridge 04-20-2021 07:54 AM

Geez, Justin. That scratch looks like a finished shower. :D

Lou_MA 04-20-2021 09:44 AM

Justin now I’m going to think my scratch has to look like that.

CX - I’m going to Hydroban over the mud so water containment behind the lath isn’t necessarily needed or wanted, correct?

Roofing felt seems more breathable but wouldn’t poly would trap any moisture between it and Hydroban?

cx 04-20-2021 11:44 AM

Well, you can do that, I suppose, but that gets you the downsides of using a direct bonded waterproofing membrane on your shower walls and keeps you from having the advantage of more time to work your wall mud. I just don't think, as once I did, that there is any advantage at all to using a waterproofing membrane over mud walls. Mud over roofing felt is about as good as it gets from a building science and tile standpoint in my view.

But they ain't my mud walls, eh?

Lou_MA 04-20-2021 12:01 PM

Hmmm. I’m open to re-evaluating, I was thinking Hydroban over mud was best of both worlds.


...downsides of using a direct bonded waterproofing membrane on your shower walls...
What do you consider downsides?


...keeps you from having the advantage of more time to work your wall mud
I don’t quite follow. Mud would have to set for 3 days before liquid Hydroban. I don’t expect that to have an impact on the mud’s working time during scratch or final float.


I just don't think, as once I did, that there is any advantage at all to using a waterproofing membrane over mud walls.
What made you change your mind? I was thinking I’d get the flat / plumb / square of mud walls, plus shorter drying-out time in between shower uses from topical waterproofing.

cx 04-20-2021 12:49 PM

One of the downsides I'd not previously considered, and that we see here on the forums repeatedly, is any potential repair that involves removing a set tile. Just no way to accomplish that with a direct bonded waterproofing membrane.

The extra time I was referring to was time for the mud to set up sufficiently for screeding, which isn't so much an issue with a scratch-and-brown as it is for a one-coat mud job. I've done only a few scratch-and-brown mud jobs and always they were over roofing felt. Can't really say how it would work with nothing behind the lath.

Changed my mind about use of a direct bonded waterproofing membrane over mud shower walls primarily after some in-house testing of the water absorption of various CBUs as well as deck mud and some of the reported issues here on the forums from folks who used direct bonded waterproofing membranes. I'm not at all sure about the contention that the membrane shower walls dry out faster than mortar bed walls. The mortar is surprisingly dense and moisture resistant as compared to all the CBUs I tested. I doesn't really absorb much moisture at all and I'd expect it to dry quite readily. I know folks usually associate the drying problem with the deck mud shower floor in a traditional shower receptor and my experience with wall mud does not present the same sort of issue at all. That is all, of course:

My opinion; worth price charged.

Just In Tile LLC 04-20-2021 06:15 PM

My bad Lou, I knew those pictures would drive you to madness when you're scratching... maybe that was my plan all along. :D

I do appreciate those noticing though. John, Cx :wave:

I've direct waterproofed my mud before as well Lou, and CX brings up a very fine point of removing anything if need be. The only advantage I've seen to painting the walls is working time when you're actually tiling. Otherwise all the waiting can drag the job out for no reason.

I recently did a sheet membrane pan with liquid waterproofing for the walls over my mud...expensive shower, and when I went back a couple months later it didn't look any cleaner than any of my normal mud showers after use when people use all those body washes and shampoos.

I also, like CX, think a roofing felt mud shower is pretty much as good as it can get. You get to tile on it faster, and can still rub a stone over it and not worry about tearing or scratching any waterpoof layer as you tile.

Getting the shower to look it's best over time comes down to tile choice and like Mr. Bridge has mentioned, your dedication to drying out the shower after each use. -oh and a quality grout choice.

Davy 04-20-2021 06:32 PM

When I was a kid, I remember helping my dad scratch showers that had the lath nailed right to the studs. Of course all I did was chop the mud but I remember him saying that you have to lay the mud into the lath. If you force it into the lath, it goes right thru and it all falls inside the wall. The felt paper helps keep this from happening and adds the moisture barrier the others talked about.

Justin, that's just ridiculous, it's too purty to cover up. :D

Lou_MA 04-20-2021 06:44 PM

Thanks for all the great advice

Reason I’m leaning towards mud & Hydroban is in part just due to comfort level. I started on my own almost 10 years ago but can count on one hand the number of pvc liner and conventional clamping drain showers I’ve done...the bulk of my work has used surface applied membranes. And I like being able to prep and set almost all the walls without the worry of working over a partially or fully completed shower pan.

Tile replacement over surface applied membrane is a valid concern though. Although I’m slow as molasses so extra working time during setting is a definite advantage for me.

And yeah Justin - that IS ridiculous. You know I’m still gonna try and mimic it though

cx 04-20-2021 08:09 PM

Lou, I gotta say that being able to nearly complete a shower before even installing the drain is one of my favorite aspects of the direct bonded waterproofing membrane showers once I learned to do them.

But with traditional showers I just got used to cutting a piece of plywood the size of the floor and laying that on a folded drop cloth over the pan liner. Found that to work well enough even when I needed a ladder in there (much of the time). And I have seen at least a full handful of tile mechanics do absolutely nothing to protect the liner and build the shower walls with impunity. And never poked a hole in the liner that I was aware of. Weren't my showers, though.

Different strokes. Do what you're comfortable with so long as you build a good shower.

My opinion; worth price charged.

Davy 04-21-2021 07:34 PM

I'm usually tiling over a PVC liner. I leave the top grate part of the drain off and use :ducttape: to cover the lower section of the drain. Then I throw a scrap piece of carpet over the floor. Works for me.

CaliGrown 04-22-2021 03:44 AM

Dayumm, all the fun stuff happens when I’m away :D
Kick ass thread already, excited for your float Lou!!

Justin, classy stuff. That scratch Looks better than some of my tile jobs :)

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