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Old 05-20-2008, 09:04 AM   #1
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How To Remove Carpet Glue From Concrete Slab

I'm going to update the thread that I've got open for my current job, but I wanted to start this new one just to give it a title that's easily searchable.
I read about how hard it is to remove carpet glue from concrete and how many different methods folks have used. Several of those I tried myself and they didn't work very well.
In my opinion, the method I used today is the method that really works, is relatively low cost, very fast, and fairly easy too.
I rented a Home Depot drum sander today and asked for 24 grit belts. The HD guy have me 10 of them just to be on the safe side. I will return the unused ones. This worked exceptionally well. Attached are photos.
The first one shows the 200 sq ft room before I started. The second is the first "swath" I ran in about a minute. The next photo is the completed room. The last is a picture of the first belt. Note the glue that is stuck to the belt. If your room happens to have more glue on it, you might need more belts since it sticks to the belt and reduces the efficiency.
There are some spots that I'll maybe go back over that were dips or ridges that the flat belt could not easily get into. Other than the edges of the room where the machine could not get close enough, I suspect I could go with it as is without worry. In any case, I'll use the wire wheel with my drill to finish off. It works well for small areas.
This room took no more than an hour to do. The HD rep asked if I'd ever used one of these drum sanders. I told him no, but I'd read that they can be tough to handle. He reiterated that and said I'd really have to hold on to this thing. Turns out that even with 24 grit, it's not much harder to handle than a vacuum cleaner and in some ways easier. Must be that the slab is smoother than wood which is what this machine is advertised for.
I had to pass this along because I've seen so many people both on TYW but also just google'd that are so frustrated with the scraping and noxious chemicals, messy boiling water, razor scrapers, etc.
Trust me; this is it. My costs will be:
$31 - for the 4 hour rental
$3 - for the insurance
$14 - (two 24 grit belts)
and tax.
One last thing...when the tool rental guy asks if you want help putting it in the truck, tell him yes unless you're godzilla. The weight of this machine is deceptive because it rolls so easily.
I'm hoping that John Bridge will put this note in the Liberry because I think it truly deserves to be there.
I'm happy to pass this along to save others some aggrevation.
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Old 05-20-2008, 09:28 PM   #2
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Jeff, thanks for the tip.

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Old 05-21-2008, 03:20 AM   #3
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You're welcome Dave. I just had to pass this one along. I did the water test on an unsanded area where the machine could not reach and then a sanded area. The water beaded up on the unsanded as expected and spread out and soaked in on the sanded area, as hoped.
We'll see over time if other folks get the same results I did.
It took about three hours longer to get the stuff off the edges where
the machine could not reach. My 3x21 belt sander worked better than
the wire wheel. Goes through belts pretty quickly though. If I had it to do
over again, I'd order up some 24 grit belts for the belt sander to finish off
hard to reach areas. The home centers in my area don't carry 24 grit in stock
so I would have had to order them online somewhere.
-- Jeff
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Old 05-22-2008, 05:24 AM   #4
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Update - add'l info from Ardex (SLC) web site.

I've been researching SLC's to go on this concrete floor. Seems that Ardex is popular. I searched their site and found a concrete floor prep document that's worth noting below.
Basically they're saying that mechanical methods are best for removing contaminants and that sanding equipment is ineffective. I have to disagree with them based on the results from the particular equipment that I used. I think the problem for most DIY'ers is that we don't have the expensive equipment required to do this in the best possible way. Grinders, shot blasters, etc are probably pretty expensive.
I also wanted to point out that it may be important to test the glue residue or cutback to see if it has asbestos content before sanding. The sanding did kick up clouds of dust and I was wearing a mask. I did not test the glue though but I did test the glue under adjoining room's linoleum floor awhile back and it was negative.
I'm still struggling with whether to SLC or not. I think it needs to be, but it seems to require finess/experience that I don't have. I might just hire someone to do it and be done with it.

Below from Ardex web site -
The best way to remove any contamination in a concrete substrate is by an approved mechanical method. Mechanical cleaning removes the contaminant and the concrete to which it is adhered leaving only a clean, sound and solid surface behind. Ardex recommends that all concrete substrate preparation proceed using one or more of the following mechanical methods: shotblasting, scarifying, grinding, sandblasting, scabbling (bush hammering), chiseling, and in some cases, high-pressure water blasting.

Mechanical abrasion methods such as scarifying, scabbling and chiseling are aggressive methods recommended to remove unsound areas. Grinding can also be effective, but is slow for large areas. Sandblasting is an excellent method for cleaning weak surface areas, if environmental restrictions permit its use. High-pressure water blasting may also be effective for some weak surfaces; however, the concrete must be allowed to dry before proceeding with any patching or smoothing work.

One of the most cost-effective methods for removing a wide variety of contaminants from a large area of concrete is to use shotblasting. Using different sizes of steel “shot”, a shotblast machine can remove a variety of sealers, coatings, curing compounds and other contaminants quickly and effectively, leaving behind a surface ready to receive the specified ARDEX underlayment or topping.

The best way to remove most contaminants is by scarifying, shotblasting or similar mechanical method. Removal must be deep enough to eliminate all penetrated contaminants.

Methods to Avoid

Acid washing (or acid etching) is not recommended because it is difficult to control, to fully remove the residue, and to properly neutralize. Further, the acid can penetrate into the porous concrete and chemically react with the cement, thus affecting the long-term integrity of the concrete. Acid washing will not satisfactorily remove grease and oil.

The use of sanding equipment is not an effective method to remove curing and sealing compounds.

All types of solvents should be avoided. Their use will drive oil, grease and other contaminants further into the concrete, only to permit their release back to the surface at a later time. Physically removing oil-contaminated concrete is the only sure way to ensure a clean substrate.

Sweeping compounds can leave an oily or waxy film on the surface of the concrete. Their use can create a bond-breaking layer that will result in a flooring system failure. Using a clean dry broom, sweep and vacuum the surface prior to placing any underlayment or topping.

Also, never use adhesive removers or solvents to remove contaminants from porous concrete. These materials can carry contaminants into the pores of the concrete, which will later migrate back to the surface resulting in a floor covering bond failure.
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