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Old 11-14-2010, 06:55 AM   #1
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Need help from tile experts please!!


I'm reposting b/c no one had answers before, but I'm desperate! My husband and I are putting down new tile in the kitchen. We busted up the old tile to discover that they put the tile down on 3/4 in plywood over the subfloor (so, it's subfloor, then plywood, then tile). What to do? Do we clean up the plywood and tile over it again? Do we tear up the ply and use backerboard (we bought 1/4 in backer thinking we would need it). How exactly do you tear up the ply if they used screws and glue to put it down on the subfloor? Do we just put the backerboard over the ply and "deal with" how much it will raise the kitchen floor over the surrounding hard wood and carpet?? The old tile was already above the other floor by about 1/4in if we add on top of the plywood, it will be about 3/4 inch above the other floor. Help please, we put tile in the mud room fine, but we used backer board. I REALLY don't want to screw this up, please help!

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Old 11-14-2010, 08:29 AM   #2
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I am not a flooring expert and maybe one will come along here soon. You will need to clean the 3/4 plywood and install the 1/4 inch backer. The way I installed mine was put the backer down in a bed of thinset and tape the joints.

Some folks don't put the thinset bed under the backer but the thinset is not for adhesion but to fill any voids and inconsistencies under the backer. Apply the thinset for each sheet of backer at a time, you don't want to put the thinset down and let it dry, so do one sheet at a time.

Do not take the plywood up as you need that stiffness as the subfloor by itself isn't stiff enough.

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Old 11-14-2010, 10:01 AM   #3
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And remember, the CBU adds no structural strength.
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Old 11-14-2010, 10:15 AM   #4
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Schluter's "DITRA" membrane...look it up. This is exactly what it's for.
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Old 11-14-2010, 11:08 AM   #5
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Thanks guys--I guess I'm completely confused. Everything I read says that backerboard is supposed to go directly onto the subfloor, then tile. If we leave the 3/4 in plywood over the subfloor (it's 3/8in sub) AND add backer board on top of that, then we will be about an inch above the adjoining floors. So, you aren't supposed to put backerboard over subfloor??
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Old 11-14-2010, 11:18 AM   #6
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CBU (cement backer unit) is possible for floors but it such old technology precisely because of the height issues it gives. You're not alone.

Schluter's Ditra is available at HD and is only 1/4" high. You thinset that onto the plywood - providing the plywood is thick enough to prevent cracking in the future.
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Old 11-14-2010, 04:07 PM   #7
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if the plywood is fastened down well it's just adding to your subfloor. if you wanted to remove it you would skilsaw a grid and use a crowbar to pop up the pieces. as others have said, if it's solid and not a height issue, just go over it
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Old 11-19-2010, 07:20 PM   #8
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Hi,

For what it's worth, I have had unreliable results with Ditra matting and myself and most other tilers I know in the U.K. don't use it. I would recommend keeping your plywood (if you can clean it up well enough) and then using a flexible adhesive and grout. A good flexible adhesive is BAL Rapidset Flex, but there are others about depending on where you live. I have slate flags on plywood over floorboards and it works fine. Just remember p.p.p.p.p.p and get the ply as clean as possible. Also make sure you prime it first.

Just my humble opinion, but it may be some help.

Martin
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Old 11-19-2010, 08:27 PM   #9
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Martin,

What problem are you having when installing Ditra? It is not possible that Ditra is the cause of the difficulty, but maybe we can help. You guys use different products and perhaps methods there, I suspect you're using mastic instead of thin set mortar. And, priming plywood would be wrong to do with the products we use here.

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Old 11-20-2010, 04:37 AM   #10
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Hi, Jaz.

I wonder if it's because of different construction methods. Do you use floating floors with polystyrene backing? We have found that we have had problems with tiles lifting / cracking on floating. With our type of floating floor you can't screw it down as recommended as it prevents it doing what it was designed to do. Also there is an element of vertical movement or bounce in the floor.

Would be very interested in hearing your opinions.

Martin

Last edited by diydisasterdude; 11-20-2010 at 04:38 AM. Reason: spelling
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Old 11-20-2010, 04:51 AM   #11
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I agree, if the plywood is solid and in good shape then just go over it if height is not an issue. It might become an issue if a dishwasher is involved, I'm not sure if the plywood is under the cabinets or not.

However I used 1/2" DensShield tile backer, made by Georgia-Pacific. It is sold at Lowes. However be sure to use a 1/4" notched trowel and place thinset UNDER the tile backer before screwing it down. Use a mesh tape and seal all the joints. Then use your thinset again on top the tile backer and lay your tiles.

I bought the materials, and paid a hack to lay the tile in my upstairs bathroom. I wondered why he had all these bags of thinset left over? I later found out he didn't do the layer of thinset under the tile backer. Two years later my grout is all cracked and is loose. Ugh, another project!
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Old 11-20-2010, 07:38 AM   #12
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Quote:
Originally Posted by diydisasterdude View Post
Hi, Jaz.

I wonder if it's because of different construction methods. Do you use floating floors with polystyrene backing? We have found that we have had problems with tiles lifting / cracking on floating. With our type of floating floor you can't screw it down as recommended as it prevents it doing what it was designed to do. Also there is an element of vertical movement or bounce in the floor.

Would be very interested in hearing your opinions.

Martin
Martin:

Yes we have floating floors, and some with polystyrene - but the ideas of tiling over them doesn't make much sense using thinset, nor even using what you call a flexible adhesive. No wonder you have problems with DITRA...and even without this anti-fracture membrane, it seems you would have cracking problems - that I doubt any membrane would solve.

What does "p.p.p.p.p.p" represent? Also would you please shed some light on the "priming of plywood" question. Prime it with what? why? against what?
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Old 11-20-2010, 02:33 PM   #13
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Quote:
Originally Posted by ccarlisle View Post
Martin:

What does "p.p.p.p.p.p" represent? Also would you please shed some light on the "priming of plywood" question. Prime it with what? why? against what?
Sure. We generally used BAL SBR for priming. It's recommended to apply SBR to the underside and edges of the ply but not to the surface that you're tiling onto. You apply it to these surfaces to reduce atmospheric moisture variations distorting the ply. Bal's adhesives don't require the tiling surface of the ply to be primed.

As far as p.p.p.p.p.p is concerned: Proper preparation prevents p*ss poor performance!
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Old 11-20-2010, 03:31 PM   #14
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i have done tile for numerous years. i worked for a man who did it for 40 years. he was old school but thorough. take the plywood up. if you are worried about strength of the sub floor put a layer of 7/16" plywood down. (you will be at your original plywood hieght with 1/4" backer and thinset) but that is not necessary if you dont want to. spread a layer of thinset (i like to use mastic) and put your backerboard down screwing it down with 1 5/8" screws every 6" in each direction (which i would rather use durock or anytype of cement board it bonds better). make sure you use a thinset with a little flex in it. have fun and tile away!!!


Last edited by wellcraft; 11-20-2010 at 03:33 PM.
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