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Unread 07-16-2007, 09:14 PM   #1
bostonboston
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Does cement backerboard need to be damp to tile? Other questions also.

Hello,
I'm a long time reader of this site and now have a question. I did my preslope in the shower I am building last night and used to formulas found on the site(4 or 5-1) and had a question to my finished slope when I looked today. It is hard and solid but if I use a screwdriver or something to scratch the surface it seems a little soft and I can scratch a bit off like it is a bit too sandy or something in the mixture. It isn't super hard like normal concrete. Is this normal because of the mixture, or can anyone offer any suggestions? I want to put in the liner and finished slope tomorrow but don't want to screw it up.

Also, after I put the liner in, the back wall won't be notched because there was existing drywall there, so will it really cause a big problem when I put the durock up? Or is there another solution? The bit of liner thickness doesn't seem like it will cause too much of a problem. Please reply. Thanks
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Unread 07-16-2007, 09:19 PM   #2
jadnashua
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The mud mix isn't even close to the concrete you'd use for a sidewalk or driveway...it will be a little sandy and you can scratch it...sounds like yours is fine. The tripple liner thickness when you fold the corners adds up; the notches really help. I'll let someone else offer advice.
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Unread 07-17-2007, 09:48 AM   #3
bostonboston
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Great, sounds like mine is fine then.
Also, when I put the backer board on, how much space do I leave from the floor, and do I just fill it with the final slope above the liner?
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Unread 07-17-2007, 05:40 PM   #4
jadnashua
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The details are in the 'liberry', but if I remember, leave the bottom of the cbu about 1/2" above the bottom of the liner; no screws in this area, the final slope locks it in place.
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Unread 07-17-2007, 08:02 PM   #5
LivermoreMP
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Bostonboston:

Your preslope is going to be quite sandy and scratchable. Sounds like your mud is fine.

Regarding the folded area of the pan liner. From what I have read on this site, the folds will bulge or push out the cement board causing your tiling surface to become uneven. This in turn will either throw off your tiling pattern or start to push your tile away from the wall, which will lead to failure. So, if you have not notched your studs, then you will need to add firring strips. Get 1/4" plywood and cut strips as long and thick as your wall studs then tack them to the existing studs. This will give your backer enough room to adequately clear your folded pan. I've done both notching and firring and have found that the firring method is easier. This may be because I have a table saw and can easily cut ply. Somehow notching multiple studs necessary to support your roof and walls didn't seem to be a good idea to me. Probably OK, but I'm paranoid. I also globbed a bit of thinset to fill the void between the backer and my pan liner to prevent and bowing.

Good Luck.
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Unread 07-17-2007, 08:24 PM   #6
garypo
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Bostonboston,

If you are not removing the drywall and notching the studs just use a knife and score triangles in the corners where the liner will be folded and use a puddy knife to scrape out 1/4" of the drywall. You will be MUCH happier with the end product if you have a flat corner.

gary
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Unread 07-18-2007, 07:56 PM   #7
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Ok, figured out the corners, got it all flat now but I've got a new problem. The height of my walls are about 8' 4", so I put my sheets up, and have about 3 or so inches left on the bottom. At the time, I was thinking I'll just put a small strip in the bottom, but then about half way through putting the full sheets up I realized I won't be able to screw in the bottom sheets or else i'll go through the liner.

So my question is, can I just use mud and fill the 3 inches in? If so do I use "fat mud" like I'll be using on the curb? I don't want to take the sheets down unless absolutely necessary. Open to suggestions, please help.

Also, I got my drain in but I don't think it has weeping holes like the ones I've seen here. It is the 3 piece with base, middle piece and then screw in drain top. The only space I see where water would be able to go would be beside the screws there is a gap, is this correct?
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Unread 07-18-2007, 08:46 PM   #8
Brad Denny
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Hi again bb (from your other thread ), got that first name?? What kind of vapor barrier are you using? Some drains have grooves on the clamping part for weep holes. Make sure you put the grooves down if that's what you have. Check out this thread in the Liberry and let us know what things you've done that may not line up with posts there. http://www.johnbridge.com/vbulletin/...ead.php?t=5434
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Unread 07-18-2007, 09:11 PM   #9
bostonboston
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I did everything as it said to in the post except for the backer board being more than a 1/2 inch from the floor. For vapor barrier, I used poly on the walls. The floor was in the basement and just a slab so I used runny thinset then the preslope.

For the drain it only went together one way.
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Unread 07-18-2007, 09:47 PM   #10
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Back to your backerboard shortfall problem, I don't see fat mud being a fix for that. Without tying the lower portion of the walls into the floor, I think you've got tile and grout cracks waiting to happen. Can't use nails or screws as they would penetrate the liner. My opinion is, needs to be redone sorry to say.
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Unread 07-18-2007, 09:52 PM   #11
bostonboston
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Using the mud to extend it wouldn't tie it in? It seems like it wouldn't be able to move down or shift as the mud would lock it in. Unless someone else has another option and I need to redo it, do I just put a small strip at the top or do it another way?
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Unread 07-18-2007, 09:56 PM   #12
bostonboston
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Also, not sure if it matters, but the bottom of the sheets sit exactly on the top of the curb, would that help support it or tie it in?
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Unread 07-20-2007, 07:57 AM   #13
bostonboston
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Noone else with an opinion?
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Unread 07-20-2007, 08:27 AM   #14
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BB, from what I've read, Mike2 is correct (he is a professional afterall). The backer needs to go approximately 1/8" to 1/4" away from the elevation of your pan liner. Then you add your 1 1/2" to 2" layer of deck mud to "lock in" the bottom of your backer. Since you can't nail below the blocking for the liner, something needs to be used to secure the bottom of the backer. Otherwise you get flaring, which equals cracked grout, like Mike2 said.

I imagine your proposed alternative of mixing in deck mud up to the backer would create a seam. Your backer could bulge and flare causing the aforementioned problems.

It shouldn't take too long to unscrew the backerboard you've put up and move it into the correct position.

I would suggest getting John's book available through his website. I just got a copy in the mail and it looks like the DIY's Tiling bible. That or scan the Liberry.
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Unread 07-20-2007, 09:25 PM   #15
bostonboston
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Because the bottom of the backer board is only an inch or so past the top of the liner, I was able to screw pretty close to the bottom so it couldn't flare out.

I didn't understand what the difference was if the backer board was sitting on an inch or of the base or sitting on what would be 5 or so inches with the fat mud. If the only issue was to lock in the backerboard, I don't think that will be a problem since I could screw it in an inch or two from the bottom. Not saying anyones wrong, appreciate the info, just trying to understand it better. Thanks for all the help so far.
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