Cement backer board

[PNelson]

I am confused. My brother in law and myself are installing a bathroom and shower for my mother in law. We have installed the backer board for the shower and I was concerned about what to do with the spaces between the boards. I have not heard nor seen what you could or should do to fix them Should I and if so what should I use? Thanks Phil

[tilejoe]

Hi Phil, welcome.

There is a fiberglass mesh tape you need to use on all the seams and corners of Cement board. It is alkali resistant tape, and the big box stores should have it. You tape the joints using thinset mortarand the fiberglass mesh.

Don't forget that you need to apply a waterproof liquid on top of the CBU. Redgaurd is available at home depot.

[DIYer-Ric]

Just to thow this out there for discussion, (I don't mean to hi-jack your thread).

Redguard is spendy stuff. Would it less expensive to use kerdi in it's stead?
Will kerdi work as a redguard alternative?

-Ric

[Edthedawg]

Phil,

yer scarin' us, man!

Assuming you're using Hardie backer? Have you read: http://www.jameshardie.com/homeowner...install-us.pdf yet?

As Joe notes, you need those gaps to be pretty small, gapped about 1/8" - 1/4" max. then bed alkali-resistant mesh tape into thinset on all the corners and seams to make a nice, monolithic structure, over which you would apply a waterproofing membrane (like RedGard).

unless you put poly sheeting or roofing felt behind the backer.

You didn't do that, did you?

And you weren't gonna tile w/ anything that comes pre-mixed in a bucket were you?

And those boards are set overlapping the pan tiling lip or mud-bed liner? What's the pan style you're using?

[tilejoe]

I think redgaurd in my area is about 40 or 50 bucks for a 1 gallon pail. That should do just fine for a shower, lest it's a huge one.

I like Kerdi, but if phil is all set up with a clamp drain and the pvc down, I would stay with the roll on waterproofer.

[DIYer-Ric]

Okay, so there's a point that confuses me.
Can't you just put kerdi on the walls, and then just tile your poured mud-pan without messing with the drain?

Everyone seems to talk like you HAVE to change the drain to use kerdi.
I was considering using kerdi on the walls as a redguard replacement (possibly), and then just tiling the floor.

Why is that a bad thing?

FWIW: I have a 3.5 gallon bucket of Redguard, so I'm prepared. I'm just curious about the drain issue.

[PNelson]

The backer board my brother in law picked up was not Hardie Board, I think it was made by GP. I used 1/4 " for the walls and my gaps are from 1/16 to no more than 1/8 wide. We did not install any sheeting behind the boards. (OOPS) This is our first made shower for any of us. As for the style you are talking about, I am not sure. It only measures 2' by 4'. We have backer board up on the walls to the height of 80" where we will stop the shower tiles. I have removed the bottom portion of the boards up the height of 2'. The lip of the shower is three 2 x4's screwed down horizonally. I have already put in the drain, and will install the pre slope this coming weekend. After that, maybe on Sunday, I will be able to install the liner and then put back on the backer boards. I did send my wife to the store and she came back with two buckets of premixed that I was going to take back. I am going to try and tile the shower in the next two weekends after I finish up tiling the bath floor. Any suggestions will be appreciated. Phil

[Edthedawg]

Phil,

You gotta know what you're working with. Because whatever you do has to be in conformance w/ that mfr's instructions.

But that's really neither here nor there...

Since you're doing a mud bed shower, I'll strongly encourage you to visit the Whirl-Famous Liberry up above, for its various awesome shower construction threads. You have myriad concerns, esp regarding stud notching, frame blocking, liner folds, curb-wrapping, weep-holes, avoiding/sealing fastener protrusions, and then the re-hanging and embedding of those bottom boards.

If you read thru there and still have questions, just ask 'em here of course

You will hear a lot of call for Kerdi from the situation you're in right now, and I can't say it's a bad idea. But also perfectly fine to continue w/ your PVC liner and whatever these CBU / backer boards may be, provided they're not greenboard / sheetrock. Install them per the mfr's instructions, tape/thinset it all together, run a liberal double-coating of RedGard over the whole thing, and you oughta be OK.

No pre-mixed anything in there - that's a very wise choice

[Brad Denny]

Phil,
I hate to say it, but you need to back up and punt. That 1/4" board ain't gonna do it for walls. Need to use 1/2".

[PNelson]

Thanks Ed. When you are working 150 miles from home each weekend it gets really tiring, so my knowledge of what I did gets stuck between my house and my monther in laws. Phil

[PNelson]

Brad, I said that I get it confused, I used 1/4 on the floor over the top of two sheets of 3/4 plywood. I used 1/2 on the walls for the very reason you mentioned. Phil

[Edthedawg]

Not to worry, Phil You have stumbled onto the Friendliest DIY Forum on the Internet We got ya covered - and we all been in the "wtf did i just do??" tired stages...

Keep digging on the details, tell us what you come up with, and we'll do whatever we can to help.