Unglued new floor tiles

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Old 07-09-15, 09:20 AM
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Unglued new floor tiles

My new tiles unglued themselves after installing them on plywood. Found out that I needed to paint a primer prior to installation in order to get them to grip. Now I got new tiles with old cement glue stuck on them. Can I use self leveling cement to reglue them without getting any extra height under them? Trying to find a way to salvage these tiles they are 24"x24" porcelain tiles. Lost a total of 23 huge tiles
 
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Old 07-09-15, 09:55 AM
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Sorry you're having this problem.

Sounds like you're using the wrong adhesive and method. Can you please tell us exactly what adhesive and trowel you're using? Tell us how many layer make up the subfloor/underlayment and what they are and their thickness. Start with that for now.

Jaz
 
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Old 07-09-15, 10:12 AM
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Jaz, in my opinion, understated the problem here. Please stop what you're doing and answer his questions as your next step - porcelain is not installed with glue nor directly on plywood.
 
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Old 07-09-15, 10:12 AM
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I added images below for a visual overview. You can see the plywood is around 1/2" thick and is residing on a sub-floor (in total the floor thickness is about 1 1/4" thick). Now that all the tiles have deglued I manged to apply a primer on the floor which I hope will help once I glue the tiles back. The issue I have now is that I am unsure if these unglued tiles can be reused or am I to buy new ones since the glue stuck on them can't be removed. The plywood had vinyl tiles prior which I removed and tried to remove as much of the black tar that was holding them. When I said glue I mean the tile mortar glue...

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Old 07-09-15, 10:14 AM
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What's the size, spacing and unsupported span of the floor joists?

You may be fine with all you have by adding 1/4" cement backer board on top of your plywood but need to fill in all the details first.
 
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Old 07-09-15, 10:46 AM
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The floor is 1 1/4" thick and is not flexible, not sure if that is the problem and that it requires an extra cement board (which will make the floor even higher then it's already is. I'll have to check the span between the joists underneath. The working floor area is 121" by 162".
 
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Old 07-09-15, 11:16 AM
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Ronen,

It is never a good idea to tile over plywood. It can work, but not the preferred method.

That mortar is good stuff and if everything is done right and the substrate is as specified, it'l work just fine.

That Primer was a bad idea. It's not made for under thinset and un necessary in the first place. I'm not sure if it adversely hurt anything though.

You said you removed vinyl tiles that were glued with black tar-type adhesive. What did you use to do that?

Jaz
 
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Old 07-09-15, 12:17 PM
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A heat gun and a plaster spatula
 
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Old 07-09-15, 12:51 PM
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Can you describe or post a pic of how it bonded to the plywood? Size of notches of trowel. Did you spread the thinset onto the floor with the flat side of the trowel before combing with the notched side?

Jaz
 
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Old 07-09-15, 01:31 PM
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The primer used is prep for self leveling compound and once used needs to be covered within a couple of hours of application. You can't let it sit over night or you have to re-apply. It is mainly for bond of the SLC to concrete and not plywood, so I suspect that it has not done any damage to this installation.

Addition of 1/4" cement backer board set in a troweled mortar bed should correct the problem. Don't forget to tape the seams. Make sure your thinset says that black cutback adhesive is a suitable substrate. Most of Mapei thinsets are. However, big blue has these unique bag labels that I am unfamiliar with as they differ in name than what the tile shops carry.
 
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Old 07-09-15, 02:30 PM
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Can I use 1/4" plywood and place a 1/4" cement board on it instead of the 1/2" plywood? So that I don't increase the height level...
 
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Old 07-09-15, 02:56 PM
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Can I use 1/4" plywood
Absolutely NOT! You mean you'd remove the " that's down already?

Jaz
 
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Old 07-09-15, 03:16 PM
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Nevermind too much of a hassle
 
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Old 07-09-15, 04:54 PM
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What's a hassle?

If you did remove the nasty contaminated underlayment you might be able to substitute ⅜" ply, then add Ditra which is ⅛" installed. Bang, back at " again. Much better job that way too.

Jaz
 
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