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Old 07-03-2010, 09:43 AM   #1
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Tile over Redgard

I am installing tile in my entire house. In 3 rooms, there was old wood with 1950's black mastic (likely asbestos) Rather than scrape the mastic, we covered it with a layer of Redgard, and will install the tile on top.
Will this work? Any thing else we should do?
Also, the rest of the rooms are just bare concrete with a lot of cracks. (we live in California) Should we extend the Redgard over everything? Or just put the tile directly over the concrete in the areas that don't have the black mastic?
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Old 07-03-2010, 09:54 AM   #2
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Hi Ron, welcome. I assume the whole floor is concrete. I have used a lot of Redgard on slabs and have had very good luck with it. You have to get it thick enough though. I have found that while spreading, if I can see thru the Redgard, it is too thin. I go back over it and get it a little thicker.

I have never put it over the black mastic so I can't say. I usually get all that up that I can. If the Redgard seems to have stuck well, I'd go for it. I would probably try to peel up a spot just to see how well it bonded.

If the floor has cracks going every which way, cover the whole thing with Redgard. It's cheap insurance.

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Old 07-03-2010, 09:56 AM   #3
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Welcome to the JB Forums. I don't think putting RedGard on the cutback was the correct solution. I wonder if the RedGard will bond with the cutback. If the RedGard releases from the cutback after you have set the tile then you can imagine that the tile is going to suffer.

Do the cracks in the slab have any differences in height or are they on the same plane? If they are on the same plane I would recommend a membrane of some type. Perhaps Fracture Free (available at HD by special order) made by the same people who make RedGard. It's less expensive than RedGard. There are many to choose from.

If that doesn't work, I'll always think it should have.
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Old 07-03-2010, 10:16 AM   #4
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More info

Thank you for the feedback.
Davy, yes the whole floor is concrete. It seems to have bonded. I tried to peel and it's stuck pretty good.
Brian, my thought had been that the Redgard would be the membrane. And yes, everything is mostly on the same plane. There are two slabs, laid at different times, that are uneven. I was going to use deck mud on the small one to raise it so it's the same level, then Redgard over that.
The cost of the Redgard isn't an issue. I just want to do all I can to prevent cracking for years to come. So if there's a better way, better I find out now!
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