Sealing Hardiebacker and shower flange

[thedeanb]

I'm installing waterproof hardiebacker in a shower alcove. The shower pan has a flange that is 1/4" wide and 1 inch tall. If I installed the hardiebacker directly onto the flange, in some places the hardiebacker would be flush with the flange and in some cases it would be slightly proud of the flange. For various reasons, I cannot fur the walls to get the hardiebacker inside the flange. The question is, on these facts, the best way to seal the seam between the two:

1. leave 1/8 inch gap and caulk with silicone
2. leave 1/8 inch gap and mesh tape and thinset the gap and then redgard over the seam
3. kerdiband
4. use continuous window flashing all the way around that would extend from the inside of the flange and behind the hardieback about 4 inches up the studs/blocking
5. put silicone on the flange and then install the hardiebacker directly on top of the silicone (essentially no gap)
6. something else?

Again, I am limited so that I cannot use furring to bring the hardiebacker inside the flange. My current plan is to use silicone between the HB and the flange and then to use kerdiband over the seam (with kerdi fix on the flange and thinset on the HB) but maybe this is overkill or a bad idea.

[cx]

Welcome, Dean.

#3, with KerdiBand or a similar membrane, is a viable option.

#4 would also likely work just fine.

Both might create a bumb-out at the flange at those places where the wallboard is barely, or not quite, flush with the face of the flange. Using a 6mil polyethylene with your #4 proceedure would reduce that. I would want that to run a foot or so up the stud faces. The thinset mortar you use to set your tiles may be sufficient to fur them out over the tub's tiling flange and if your tiles were sufficiently large, that might work fine with the #4 procedure.

Using a true cement board (ASTM C1325) that is a full 1/2" thick (your Hardiebacker is not), might make either method work better.

My opinion; worth price charged.

[thedeanb]

Thanks, CX. This forum is outstanding.

I'm using 12x24 tile so that the thinset should be able to fur over any minor bump-out (i.e., I think I'll use a 1/2 inch notched trowel).

James Hardie recommends a 1/4" gap between the shower and the hardie board but that recommendation is based on a situation in which the board is installed inside the flange. Based on my install (using either kerdiband or 6mil poly), would you recommend that size gap or would you recommend a smaller gap or no gap?

If I use kerdiband (or similar membrane), would you recommend putting silicone in the joint between the hardiebacker and the shower flange first?

If I were to use the 6mil poly, do I attach it to the inside of the flange and, if so, what material should I use for attaching it?

Also, I haven't installed the hardiebacker yet so I could theoretically change my waterproofing system if a different system would work better in my situation.

Thanks again!

[cx]

1. With your parameters, a quarter-inch would be fine. No less than 1/8th-inch.

2. No. In that method I recommend trying to make a slight wedgie into that gap with your waterproofing membrane to better provide movement accommodation.

3. Not necessary. Let the moisture barrier membrane run long over the receptor edge and trim it after the tile has been installed. Also helps to protect the receptor from the mess from working on the walls.

My opinion; worth price charged.

[thedeanb]

Thanks, CX. Appreciate it.

[thedeanb]

So I spent an entire day shimming and planing studs to make my shower walls flat and plumb. This is a standard 32 x 60 inch alcove. I have the hardie backer up but realize I missed something since the long wall isn't plumb on the left side. The hardie board is installed horizontally on this wall and if I put my level vertically on the left side of the wall, I have a 1/8 inch gap at the bottom of the board on the left side (so more than 1/8 inch per 10 feet). I showed the guy who is going to do the tile and he wasn't worried about it. Said he'd allow for it when applying thinset. The tile is 12 x 24 so I am a little worried about it. I wanted to get another opinion. I think I can fix it by removing only 2 full boards. Does the hardiebacker degrade around the screw holes if I were to take the screws out and put them back in? Is there any reason I shouldn't just remove the hardie backer and fix this? Thanks.

P.S. started a new thread for the same project because this is a weird issue unrelated to my other issue.

[Lazarus]

There are several Companies that offer wedges to space out the studs to get "True & Plumb" to attach the Hardi to. I can't mention them as that would be advertising, but YouTube might get you there....

[Davy]

Hi Dean. I'd take off the two sheets and fix it.

[cx]

Dean, we'd still like you to keep all the project questions on one thread so folks can see what you're working on and what's been previously asked and answered. A moderator can give the thread a more generic title any time you'd like to suggest one.

Can your tile contractor compensate for the out-of-flat condition? Maybe. Would it be better to make the wall as flat as the tile industry calls for for tiles that size? Yes, it would. Is it worth the effort in your case? I dunno.

If you remove and replace the wallboards, I'd recommend you fasten them again with your fasteners in new locations.

My opinion; worth price charged.

[thedeanb]

I've run into three issues on which seasoned advice would be great.

1. When installing waterproof hardiebacker, I put a screw too close to the corner and cracked it (pic attached but it is turned 90 degrees). I removed the screw and put a screw about 3 inches higher. This board has more than enough screws in it because the wall is 32" wide with 4 studs. The corner feels very solid and there is no movement when I press on it. This is the inside bottom corner of my shower. It's my current plan to install kerdi-band between the hardiebacker and shower flange (the rest of the joints will be finished with thinset, mesh tape and redgard). Should I replace this board or move on with my build since the kerdi band will fully cover this?

2. With respect to installing the kerdi-band, James Hardie says I must use a modified thinset but Schluter says use an unmodified thinset or use the Schluter All-Set modified thinset. I have a ton of Versabond LFT thinset so I'd rather not buy the Schluter modified thinset solely for the purpose of running 12 feet of kerdi band. I'm inclined to use Versabond and let it cure for 3-5 days before tiling but am looking for practical advice. You don't need to tell me it'll void the warranty. Unless there is a broad based failure of a product, no one is ever going to collect on a product warranty (in my view).

3. I have an outside corner where the Hardieback meets drywall. My current plan is to use a vinyl corner bead and use galvanized nails to install it (pre-drilling the cement board). I'd use joint compound on the drywall side and thinset on the cement board side. Any better way to do outside corners where drywall meets Hardiebacker? My plan is to run tile right up to the corner on the cement board side.

As always, thanks.

[cx]

1. I would have left the screw in place. In any case, install the Kerdi Band and never look back.

2. I would use VersaBond without a second thought. I've never used the LFT version. I suspect it will do as well, but I don't know it it uses a more coarse sand, which I would not want in that application.

3. Is the corner inside or outside the wet area?

My opinion; worth price charged.

[thedeanb]

Thanks, CX.

The outside corner is outside the wet area. The shower door will be about 3-4 inches inside this corner.

[cx]

If you're tiling all the way to the corner, I'd not use a corner bead at all. I'd use a metal reinforced drywall tape to create a sharp, straight corner and apply it with drywall compound in your application. No more compound than necessary to bed the paper edge on the tile side. No further finishing.

Yes, I know there is such a thing as ettringite, but I've never experienced it in small areas of drywall compound under thinset mortar in dry areas. See warranty information below.

You want to make sure that wall is very, very close to plumb as measured on the face not to be tiled or you'll have much difficulty making your tile installation fit pleasingly on the tiled side. And even if that's a traffic corner, the tile installation will provide plenty of protection without the use of a corner bead, which can interfere with the tile.

My opinion; worth price charged.

[thedeanb]

Thanks, CX. Good tip on the drywall side being very plumb. Thanks again.

[thedeanb]

As I am mesh taping and applying thinset to the hardiebacker joints, can I also use thinset in the joint in which the hardiebacker shower wall meets the drywall ceiling? I'm tiling to the ceiling so I was inclined to fill the small gap between the hardiebacker and the ceiling with thinset. That seems consistent with instructions from James Hardie for situations where hardiebacker meets flush drywall under tile but I can't find instructions exactly on point.

As always, much thanks.