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Old 09-18-2011, 02:31 PM   #1
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Tiling over VAT on concrete slab


Hi,

My basement (~250 sq. ft, raised ranch) recently flooded and I had to remove the carpeting. I discovered 9" x 9" VAT under the padding -- it's in pretty good shape, except for some cracked areas where the tacking strips were nailed down. Underneath the VAT is a thin black mastic directly applied to the concrete slab.

It is apparent that the slab is not entirely flat -- some areas have slight dips, and others slight hills (less than 1/8" over two feet). What I would like to do is put down ceramic tile, to ensure that any future moisture issues are not a problem for carpeting.

Before I ask my question, here are some stipulations:

1. I appreciate any and all help
2. I have scoured the internet looking for a solution, and have not found my exact scenario described.
3. I cannot afford to have the asbestos abated.
4. I know I cannot use SLC to level the floor, because it cannot be applied to VAT.
5. I know it is not recommended to lay CBU over a concrete slab -- the Tapcon screws will not countersink in the CBU, and you have to drill, etc...
6. I know that although the Ditra instructions claim it can be laid over vinyl, it is not recommended, and in any case, I don't think the floor is level enough for Ditra. Also I fear that the vinyl may start to come up, taking the Ditra with it.
7. The total height must remain less than 1 inch above the VAT.
8. There are a couple of areas around the bar which the previous owners tiled (some 12" X 12" 3/4" porcelain, some various sized 1/4" ceramic) -- they laid the tile directly over the VAT with some sort of adhesive, and it was holding fine -- no cracking, at least until I took a sledge to it

Given all that, my approach was going to be to use CBU anyway, pre-drill a hole for the screwhead, spread a modified thinset, and drill into the slab. I completely understand that this will invalidate the Hardiebacker warranty, and that pros would not do it this way.

What I would like to know is -- will this approach work (even though it is not ideal)?

If it is almost certain to fail, are there any suggestions on how I might proceed?

Thanks in advance!

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Old 09-18-2011, 05:45 PM   #2
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Tiling over VAT on concrete slab


You can remove the old tile safely all by your self---most states publish instructions.

What manufacturer forbids the use of self leveling compound over VAT?

If the wax is stripped before you use the SLC I think you will be fine---Check with Jiffset--When mixed with Linewebbers liquid latex that will stick to anything I've ever run across.

An unmodified thinset mixed with liquid latex is approved for use over VAT.

Where did your 'facts' come from exactly?-----Mike----

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Old 09-18-2011, 07:21 PM   #3
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Tiling over VAT on concrete slab


Thanks for the reply.

I think I could remove the VAT myself without much trouble, it is the mastic beneath that concerns me -- it appears to be somewhat crystallized.

Everything I've looked at, much of it on this site, has indicated that attempting to use SLC over VAT will pop, bulge or loosen the vinyl.

When you say "the wax is stripped", are you talking about a wax layer over the VAT? How would I strip that? Chemicals?

When you say "An unmodified thinset mixed with liquid latex is approved for use over VAT.", do you mean I could lay tile directly on the VAT? My concern is that the VAT will eventually begin to pop up, weakening anything I lay on top. That's why I planned to lay Hardiebacker over the VAT (with a thinset like you've described) but screwed down, so even if the VAT weakens, the substrate is firm.

My facts are based mostly on manufacturer's recommendations and information gleaned from this site. If I am misinterpreting something, please let me know.

Thanks.
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Old 09-19-2011, 07:09 AM   #4
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Tiling over VAT on concrete slab


Pop off the old tiles---use a razor scraper to remove as much of the old cutback as possible--

Hot water and a scraper sometimes works.

Then use an unmodified thinset mixed with liquid latex to install over the old cut back.

If the floor needs leveling use Jiffset and Linewebbers liquid before tiling.


Forget about adding a layer of cement board over the top of the concrete--that's not acceptable by any tile authority.
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Old 09-19-2011, 09:51 AM   #5
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Tiling over VAT on concrete slab


Thanks oh'mike.

The problem with the cutback is I believe it to be asbestos based as well, so I really don't want to scrape it.

I guess my question boils down to this: Do I have any options besides carpeting that allow me to leave the VAT in place?

Thanks
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Old 09-22-2011, 07:06 AM   #6
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Tiling over VAT on concrete slab


If the tile is bonded well to the floor you can tile over the top after stripping off the old wax.

Asbestos is only hazardous in a powder form when airborne---unless you are doing something to powder the tiles--the risk is minimal---your state publishes instructions for safe removal by the homeowner.

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