Tile over "tacky" concrete?

Hi all,
We're just about to start a small tile job (<45 sq ft bathroom). Last night we tore up the ugly vinyl tile floor. It came up pretty easy with a heat gun. The concrete slab underneath is in great condtion, but is noticably "tacky" from the vinyl tile adhesive. We're not talking globs of adhesive or anything, in fact it isn't really visible at all, except for a little bit of gloss here an there and some other discoloration of the concrete. But nothing like big black or yellow/gold blobs of adhesive like I've seen elsewhere.
So my question -- will my thinset stick to this, or should I attempt some sort of chemical strip? We used some household cleaner (409) and a wire brush, then mopped with a strong floor-cleaner solution, and that helped a little, but it's still quite tacky when you feel it or walk on it.
I'm guessing the original floor is circa mid-80's if that matters.
Thanks much for your help -- I'd apprecate any replies as we hope to do some work on it yet tonight.
-Tim
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Tim Fischer spake thus:

To get rid of the residual sticky stuff, I'd use some low-impact petroleum solvent: either paint thinner (*not* remover) or charcoal lighter (naphtha). These are relatively benign, will probably dissolve some, but not all, of the sticky stuff, and can be removed with any kind of soap or detergent. (You can use low-odor paint thinner if you're concerned about the smell.)
After that, if any stickiness remains, try using denatured alcohol (shellac thinner) the same way. I've found that it sometimes takes a combined attack of naphtha and alcohol to get rid of certain sticky substances. As above, wash the alcohol afterwards, though most of it will just disappear through evaporation.
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David Nebenzahl writes:

Charcoal starter is kerosene.
Naphtha is much lighter. Coleman fuel. Definitely not for charcoal.
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Richard J Kinch spake thus:

Nope, you're wrong: I also stock kerosene (have 2 portable heaters that use it), and that's a completely different "product". Easily recognizable by smell alone.
Both charcoal starter and lighter fluid (e.g., Ronsonol) are naphtha, which is a lighter fraction than kerosene (paraffin for our UK friends).
You're thinking of "white gas" for Coleman fuel. I'd definitely stay away from that stuff!
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David Nebenzahl spake thus:

Amending my post: boy, this is one confusing area, especially if you try to get information on the web. A lot of this information seems to be plain wrong.
So apparently, ordinary charcoal lighter *is* a mixture of naphtha and kerosene. However, the charcoal lighter I use (mainly to clean stuff) seems almost identical to pure naphtha, and evaporates at about the same rate. Kerosene evaporates much more slowly, and leaves an oily residue behind.
But it isn't the same thing as white gas, of that I'm sure, even though there are plenty of sites out there that say that white gas = naphtha. For one thing, white gas has a *much* more pungent odor than naphtha, and evaporates much more quickly. I did find one site that seems to have a good definition of white gas: http://www.everything2.com/index.pl?node_idw6626 . It is similar to gasoline.
Lighter fluid ("Ronsonol") *is* naphtha, so far as I've been able to determine.
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David Nebenzahl writes:

It's the "same thing" in any ordinary sense.
The odor isn't relevant. If a naphtha product sold as "white gas" has a strong odor, it's just a blended impurity that isn't worth removing in the fuel application. The naphtha from the paint store will be essentially the same stuff, but better purified of high-boiling impurities, because for painting and clean-up you want a solvent that doesn't leave a residue. This is the reason for the "VM&P" (varnish maker's and painter's) grade of naphtha.
The Walmart store brand camp fuel is the cheapest way to buy naphtha by the gallon. And always very pure of odors and residue in my experience with using it as a solvent.
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David Nebenzahl writes:

You're quite confused. Go to Walmart or paint store and read some labels. Or have a read in the Kirk-Othmer at the library.
White gas, white spirit, naphtha, Coleman fuel, Zippo fuel, Ronsonol, are all similar, very light petroleum distillate fractions.
Charcoal starter is a heavier weight, roughly kerosene. Using naphtha for such a purpose would be stupidly hazardous. Especially for those who have a habit of squirting it on a slow fire.
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Tim Fischer writes:

Methylene chloride stripper. Nasty but effective.
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Tim Fischer wrote:

Why do you care whether the thinset will stick? Am I missing something?
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Uhm, because if it doesn't stick (to the concrete) my tile will pop off? <grin>
Maybe you thought I meant I didn't want it to stick to the residue.
Anyway, I tried using thinner and a wire brush, then mopping with floor cleaner and water, and it seems to have gotten much better (not perfect, but much, much better. I then saw the other reply that said not to use solvents-- oops...
Well, we'll hope it all works out. I'll hopefuly be tiling tomorrow...
Thanks all, -Tim
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Tim Fischer wrote:

I remember speaking to the tiling 'Gurus' at Home Depot once and they advised me against trying to remove the adhesive with a solvent, rationalizing that residue would soak into the concrete and may cause problems with the thinset in times of high humidity.
Having said that, let me point out that I am no tiling expert and not trying to argue with our resident experts here.
Lewis.
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If the adhesive becomes an issue, a possible option is to put 1/4" cement board over it? Gives you a fresh start. Not sure if this raises hell with your fixtures and floor transitions.
But by now you are probably into trying all kinds of solvents and are high as a kite! :-)
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mineral spirits or your chemical/cleaner of choice and an old towel cut into smaller pieces to remove the tack
mop up with very hot water, plenty of times to remove all residue of any chemical and/or cleaner
sand with coarse sandpaper wrapped around a piece of wood for a backing to get down to concrete
if you don't want to get down to concrete, an old tile pro said you can trowel on armstrong s-184 skim and patch coat right on top of the old sticky surface (black - oil base glue; or yellow - water base glue ) then lay your tile on it
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oddly enough after trying a few things i took mine off in a room with hot water and a good scraper....not too much trouble, i was surprised. My slab is pretty finished and slick though.
- shawn
Tim Fischer wrote:

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