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Unread 01-25-2009, 05:34 PM   #1
jaysonhaines
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Tile over black mastic

Is there any way to tile over old black mastic? I have a small area I would like to tile, but removing the old mastic will take days. The mastic is over concrete slab. Are the any alternatives? Thanks.
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Unread 01-25-2009, 05:51 PM   #2
java
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jayson - That black glue is also called cutback and it's nasty stuff.

Some on here are gona say you can use a good modified thinset and set right over it.

Others (me included) are gona say it's gotta be removed.

I use a product called Jasco (get at HD). It's a chemical stripper and you have to be careful using it.

I'm cooking some good venison and will be back in a little bit to explain the process if you don't get the answer first.
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Unread 01-25-2009, 05:51 PM   #3
Brian in San Diego
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Jason,

Welcome to the forum! I am the bearer of bad news...the mastic or cutback as it is called has to come up. the problem is getting a good bond. Usually cutback is removed by using a 4" razor scraper. If it's a small area then be thankful. I had a heck of a time on my floor and it was around 90 square feet. Can't imagine if I was up againts a couple hundred feet or more...I would rent a scarifier if that happened.

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Unread 01-25-2009, 06:16 PM   #4
jaysonhaines
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thanks for the replies. My problem is that the mastic or cutback is so thick, the chemical stripper I tried to use couldn't eat through it. It was citrustripper. Will the jasco work better than that?

Would it be possible to somehow apply a layer of schluter kerdi? Maybe some adhesive that will bond the kerdi to the cutback and then I could thin set?
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Unread 01-25-2009, 06:22 PM   #5
cx
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Welcome, Jayson.

I strongly recommend against the use of chemical strippers for that kind project. While it might remove most of your cutback, it's also likely to very effectively soak into your concrete surface and render it very much sealed.

While there are a lot of thinset manufacturers that advertise one or more of their products as suitable for use over cutback, I'm not sure they'd be as excited about use over an effectively chemically sealed concrete.

I'd at least wanna talk to the maker of whichever thinset you plan to use before I took a chance on that.

My opinion; worth price charged.
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Unread 01-25-2009, 06:36 PM   #6
Jaz
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Brian,

Isn't that a picture of parquet? If so, what does it have in common with cutback?

It isn't recommended to use solvents unless they're the type that lift the mastic out of the slab. Most solvents soften and dilute, causing the mastic to go deeper as CX already mentioned.

You need to scrape the cutback down to the concrete. Stop when you see gray, then use a thinset that is compatible with it. There are many, but not all modified thinsets qualify.

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Unread 01-25-2009, 07:46 PM   #7
Brian in San Diego
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Jaz,

It was indeed parquet and it was glued down with an adhesive that maybe by definition wasn't cutback (it wasn't black) but it still left a residue all over the floor that IMO had to get scraped up prior to setting tile.

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Unread 01-25-2009, 08:08 PM   #8
ceramictec
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yeah, wood floor adhesive, clear, cutback or any type of glue needs to come up clean as you can.
some of the SLC's say you can go right over them with the primer.
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Unread 01-25-2009, 08:15 PM   #9
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I'm not sure why so many are against chemically stripping the floor.

I have done it many times and it leaves a clean floor. I know it's not chemically sealed concrete when I'm done because I can perform a water test and see the water being absorbed quickly.

I will tell you what is a chemically sealed floor and that is a floor covered in cutback. I have done more than a few tile floors that were being replaced because of a faulty install and the fault was setting over cutback. Easy tear outs let me tell ya.

I don't understand the backwards thinking on this. Some say don't chemically strip the floor because you might rinse the cutback in deeper. Why is it better to lay on a thick layer of the stuff then a little that may or may not be rinsed in? Plus, if it was a good idea to set over cutback, why don't we use it as substrate intentionally? Sure would be a good crack isolation membrane on problem slabs.
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Unread 01-25-2009, 08:34 PM   #10
ceramictec
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cutback has oil in it, once broke up by the chemical stripper you now
have a floor with saturated oil all over it as a bond breaker.

XI.A.3. Cutback Asphalt or Cutback Asphalt Cement: Any asphalt which has been liquified by blending with a VOC, such as a petroleum solvent diluent or, in the case of some slow cure asphalts (Road Oils), which has been produced directly from the distillation of petroleum.

Emulsified Asphalt or any other coating or sealant, including but not limited to those produced from petroleum or coal, which contain more than five percent of oil distillate as determined by ASTM Method D-244 is included in this definition.
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Unread 01-25-2009, 09:54 PM   #11
George K
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I successfully removed 1300 sq. ft. of cutback from my basement floor using Bean-e-doo from Franmar chemicals. [ www.franmar.com ]. It is a soybean based product with a very good looking MSDS. I followed up with the recommended detergent that removed any residue. I then scarified the floor. I used an unmodified thin set to put down Ditra. My tile job is tight to the floor. Do a search of my posting on cutback for a detailed story of my cutback adventure. It was hard work.

Good luck,
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Unread 01-25-2009, 10:23 PM   #12
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