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01-23-2014, 09:56 AM
I know I already have a project thread on here, but this is for a new project my parents will be (mostly) doing.

The master bedroom's small bathroom is 50 years old and the original shower is starting to literally come apart. They're going to demo it to the studs, have a new plywood subfloor installed, and any repairs made, and then they're going to do the rest of the work themselves. For the shower base they're going to use a cast iron Kohler base, so no worries about having it constructed wrong. Then it'll be Wonderboard all around with RedGard.

Regarding the demo, it was built using mud on lathe. Are there any tricks or warnings to tearing it out? Would it be worthwhile renting a rotary hammer?

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Houston Remodeler
01-23-2014, 10:16 AM
Normally we use a right angle grinder to cut the walls into chunks we can carry. Dusty but effective.

01-23-2014, 10:58 AM
I just ripped out our MB mesh/mud walls. The angle grinder is aggressive and quick, but as Paul says the dust is an issue if you cannot contain it well.

A slightly less dusty method I settled on was using a good-quality wood blade in a sawzall (recipro saw). I cut out about 1.5 sqft chunks. Choose a low tooth number blade, like 6 or 8 tooth/inch which will dig through the mud and diamond lath pretty well. Still dusty, but you don't have the great speed of the grinder blowing dust into your chili on the stove either :tup2: Take care that you know where your plumbing, electric, hvac, etc are, since the 6" sawzall blades will do more damage inside a wall than will a grinder. You can easily end up carving into the MB tv cables on the other side of the wall if you're not careful. And if you're really worried about the dust, you can have someone stand next to you with a spritz bottle of water and gently mist the cut as you go.

Have fun!

01-23-2014, 11:11 AM
I favor the little hand-held wet saw for the initial part of that sort of demo, Zoltan. Depth of cut is not always fully adequate, but you still get the bulk of the cutting done without dust. There's a water mess to deal with, but if the tub or shower pan are still intact that's not difficult to deal with at all.

Not sure if this one is still available, but there are lots of other brands of the same concept. Mine cost fifty bucks as I recall.


02-24-2014, 07:25 AM
Well, the bathroom is stripped to the studs. There is rot on a couple of studs, and part of the floor under the shower was rotten through. The old lead pan liner had been laid directly on the subfloor with no preslope and weep holes, if any, were completely filled with mortar. Considering the shower was 50 years old, I'm surprised there weren't serious problems with mold.

My next question regards the subfloor. The only dimensional lumber subfloor needs to come out and I want to install plywood. On my bathroom the door was oriented such that I was able to carry in the whole sheet and lay the subfloor with no joints (small bathroom). Unfortunately, my parent's bathroom has the door right in the middle, so I don't see any way to get the plywood in there in one piece. It looks like I'll need to lay it as two 4'x4' sections.

So my request is, would someone please educate me on the correct way to lay a tongue and groove plywood subfloor? I can lay it out so the plywood seam sits on top of the joist, but I'm a little worried about the plywood only being supported by 3/4". Additionally, would I put fasteners through the t&g joint to secure it to the joist? Obviously, I need some education here.

02-24-2014, 08:16 AM
Zoltan, on remodel projects in small rooms like that a T&G panel frequently becomes more of a liability than a benefit.

If you're having a fitting problem, I would recommend using square-edge plywood and making your own edge blocking from pieces of the same material and installing them as the panels, or sections of panels, are installed.

A five-inch wide strip of 3/4" plywood can be glued and screwed to the edge of an installed panel such that half of it extends beyond the panel edge to catch the edge of the next panel. That will actually provide better edge bracing than the T&G edge and will make life a lot easier for the installer in a restricted work area.

Keep your blocks a quarter-inch or so short of the between-joist space so they cannot touch the joist at either end.

Regardless how you must size your plywood panels to get them in the space, they must still be oriented with the face grain perpendicular to the joists.

My opinion; worth price charged.

02-24-2014, 08:51 AM
Roger. Would that be preferable to gluing and screwing a 2x4 to each side of a joist and having the panels meet on top of the joist?

Using the 3/4" plywood for blocking as you described, would it end up looking like the picture below (excuse my MS Paint skills)? If so, would the panels of plywood which are joined by the blocking be butted together or would you keep an 1/8" gap between them?

02-24-2014, 09:08 AM

The joints I'm talking about blocking are those that are perpendicular to, and between, the joists.

The joint you show in your drawing (which is quite sufficient) should fall on top of the joists. If you're concerned with fastening on the joist top, you can add 2x nailers to the side of the joist to help with that.

My opinion; worth price charged.

02-24-2014, 09:31 AM
Ah. That makes more sense, thank you. With the size and shape of the bathroom I won't have any plywood joints perpendicular to the joists. I'll just have one joint parallel with the joists. Should that joint be tongue and groove?

Also, do I need to install blocking around the perimeter of the room?

02-24-2014, 09:40 AM
Also, do I need to install blocking around the perimeter of the room?
As CX would say, I can't see it from here! But, it's safe to say that perpendicular to your joists, you'll want blocking or a proper T&G joint anywhere where you have an edge.

03-04-2014, 08:17 AM
Aaaaaaaaand done! The 3/4" subfloor is installed. I've cut the 1/2" plywood underlayment and it's currently sitting on the bathroom floor waiting to be screwed down.

What is the edge and field spacing for the underlayment screws? From wait I've read it's between 4" to 6". Personally, I'd like to go with the 6" spacing just because we'll be putting down CBU and driving an additional 200 screws into the floor shortly.

03-04-2014, 09:07 AM
Here's a good resource ( our (Liberry) for your fastener schedule.

03-07-2014, 09:06 AM
Quick update:
The new subfloor is done. It warms me inside knowing it's been built to standard and best practices.

Aside from a couple of small projects, now we just have to wait for the shower pan to arrive. My parents are using a Kohler cast iron shower base. Given all the horror stories I've read on here about shower pans being installed incorrectly, I figured this is about as fool proof as possible. Cost-wise it's about the same as well.

03-07-2014, 11:30 AM
The shower base we're using requires us to build a toe kick under the front rim of the shower base. I'd like to use either concrete or clay bricks to build it instead of wood. Would tile have any issues adhering to concrete or clay bricks using modified thinset?

Richard Tunison
03-07-2014, 11:56 AM
I personally would use wood over your wood sub floor and face it with a piece of backer board.

03-25-2014, 07:47 AM
I'm thinking of using Durock Next Gen for my parents' shower surround since it seems significantly stiffer than Wonderboard. We're planning on using RedGard to waterproof it. Any issues using RedGard over Durock?

Another question. The subfloor is 3/4" ply, the underlayment is 1/2" ply, and we'll be using 1/4" CBU for the floor (with thinset underneath). The CBU screws come in 1 1/4", 1 5/8", and 2 1/4" lengths. What length should I be using? I think ideally I'd only want to screw into the underlayment to avoid screw jacking, but even the 1 1/4" screws are long enough that they're penetrate the subfloor slightly.

03-25-2014, 09:18 AM
1. No.

2. The 1 1/4" screws will be fine.

My opinion; worth price charged.

05-13-2014, 06:59 AM
1/4" Wonderboard has been laid on the floor.

The shower walls need to be furred out 3/4" so the cement board will properly overlap the tile flange (it's a cast iron base with a thick flange). Since my parents want to maybe eventually add some grab bars in the shower, instead of just ripping 3/4" plywood strips they're installing a whole sheet of 3/4" ply on the two walls of the shower without plumbing. That way they can mount the bars wherever they want and will have wood to screw into.

I know plywood is supposed to run perpendicular to floor joists, but in this application is it ok to just run it parallel with the wall studs?

06-11-2014, 08:32 AM
The RedGard just finished being applied.

My question is, how are we supposed to seal around the plumbing penetrations? Just caulk? Or is there something better?

06-11-2014, 10:47 AM
Give more hints, Zoltan.

What sort of plumbing penetrations into what?

06-11-2014, 10:52 AM
Sorry. There are five places were plumbing will penetrate the wall: main valve, diverter valve, shower head, toe tester, and hand shower.

I'm not worried about the shower head since it's above the level of the water. However, in those other four locations you have plumbing that's creating a hole in the waterproof layer. How do I keep water from getting through there?

06-11-2014, 10:56 AM
Generally by sealing the associated escutcheon plates or trim pieces to the tile wall, but if you wanna caulk around the pipes you can do that after the permanent pipes are installed to replace the rough-in nipples, if any.

My opinion; worth price charged.

06-11-2014, 11:08 AM
How wide of gap could I safely bridge with caulk?

06-11-2014, 11:19 AM
Whatever it says on the caulking tube.

06-11-2014, 11:22 AM
We'll be using Latasil and it says it the max joint width is 1" (which is impressive to me) but I'm assuming it needs some sort of backer for that. Could I use spray foam as a backer for it? The Latasil data sheet says to use a polyurethane or polyethelene backer rod, and the spray foam is polyurethane based, so I think it would work.