Tile Over Concrete Floor

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Old 08-21-09, 03:54 PM
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Tile Over Concrete Floor

House is a split level. Family room is in the lowest level and damp. I pulled up the carpet and there is vinyl tile glued to the concrete floor. I put some plastic over a bare patch of concrete for a couple days and no moisture collected.
I'm having someone tile the place and told him I wanted Ditra put down first before the tile.
He called to tell me that the Ditra was a 'water-proofer' and that he thought I needed a 'vapor barrier'. He said he would most likely use a Laticrete product to form the vapor barrier since I said I wanted to try and reduce the dampness

Would a vapor barrier do any good if my little 'plastic test' didn't show any moisture ?
Should I go with the Laticrete or the Ditra ?
He also gave me the indication that he wasn't going to attempt to remove the glue from the concrete once the tiles were removed, is this OK ?

Thanks !
 
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Old 08-21-09, 04:47 PM
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The vinyl tile almost acts as a vapor barrier in and out of itself. I would rip it up, including the glue. You will want him to get all the glue up until it's basically a stain in the concrete.

Ditra is a waterproofer and vapor barrier if installed per Schluters instructions.

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Old 08-23-09, 09:22 AM
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Thanks for the info
One more question:
If the vinyl 'almost acts as a vapor barrier' do you think I'd notice any difference in the general dampness of the room once the tile job was finished using the Ditra ?
 
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Old 08-24-09, 02:36 PM
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Lew

What's your concern with "dampness"? Is there some problem you are not telling us about? If you have water problems, you'd best resolve them before you install ditra, tile or anything else.
 
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Old 08-24-09, 03:42 PM
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Nope, no secrets here. Just wonderin'
 
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Old 08-24-09, 04:18 PM
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Sorry I didn't respond earlier, Lew.

How much "dampness" we talking about here? Do you find condensation on your current floor? Tile thinset is a little forgiving when it comes to moisture, but anything in excess can be detrimental.
 
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Old 08-24-09, 05:19 PM
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No, just stuff like mildew on the wallpaper and moulding. I did put some plastic over a spot where a tile came up and didn't have any visible moisture appear after 3 days.
 
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Old 08-24-09, 05:53 PM
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Sounds like your floor is alright then for tile, just some moisture seeping in from the walls.
 
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Old 08-25-09, 07:57 AM
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No, just stuff like mildew on the wallpaper and moulding.
This is caused by excess humidity in the air, common in lower levels of a home. Running a dehumidifier will solve this problem.

As to the floor, remove the vinyl tile and the adhesive down to a stain. The adhesive needs to be removed mechanically, as chemical strippers can be bond breakers for thinset. Make sure that the thinset you use says that it can be used over cutback adhesive. Not all can.

You don't need a vapor barrier or waterproofing over the slab. If you have water issues, ditra won't help. Ditra is an isolation membrane and a waterproofing membrane, but it's designed to keep water from penetrating the substrate from the top, not from underneath. If you have hydrostatic pressure from underneath, ditra will fail.

Ditra is good insurance as to horizontal movement of the slab and isolating that movement from the tile, but it's not absolutely necessary. For the record, ceramic and stone tile has been set directly to concrete slabs for many many years, and is still done today with great success. I'm not trying to talk you out of ditra, as I think its a great product. Just saying that it may not be necessary in your case, and it is an added expense.

After you remove the vinyl tile, what does the slab look like? Are there cracks in the slab or is it rock solid and intact? If there are cracks, describe them, are they hairline cracks, something bigger, is one side of the crack higher than the other?
 
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