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Flooring and Carpeting/installing padding and carpet over tar residual concrete flooor


We have a Church space that is 2400 sq ft,water damaged the wood floor on concrete slab. When it was removed we found tar paper and mastic underneath.That has been scraped off with tar residue still on the concrete. What do we need to put on the concrete before we put padding and carpet down?

Hi Alan,

If the floor has been scraped rather smooth you can install the padding over the tar residue. Padding will hide a multitude of sins and will not be affected by small deviations, such as 1/8"-3/16"

If the residue is so terribly tacky that you can not walk on it or shoes stick and pull off your feet I suggest this method.

Purchase a 25 lb. bag of Mapei Plani Patch at the local Lowes  
or Henry's 25 lb bag of floor patch at the Home Depot.

Sprinkle the dry powder patching compound over the heavy areas and broom around until the tar is rendered non tacky , scrap again and continually refresh the 4" scraper blades until you are satisfied. This is time consuming so don't be afraid to take short cuts...just knock down the highest ridges / spots and when you can walk over it without losing a shoe you are ready to sweep up or vacuum and install the padding.

Mechanically, Home Depot rents a floor polishing machine and a disc that will take down tile cement it spins and builds heat the tar might become quite sticky again, so that defeats the whole operation.

If you are adept with a trowel you can skim the whole floor with the product by mixing with water in a 5 gallon bucket...much like the videos on You Tube depict. About 10-12 bags will do you. With a thin coat to just cover the tar.

I suspect from the picture that was in fact a moisture barrier??? I would leave as much as possible and just neutralize the tackiness as I suspect you are already attempting to do with the white powder.


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20+ years flooring installation ...carpet,wood,tile and vinyl. Residential and commercial. I do not sell the products , just install what ever the shop / customer has purchased. I actually love seeing the finished project completed and it gives me great satisfaction to help others acheive that goal. If I don't know the answer I will say so, and then I will recommend another expert for you. I may even research the subject and answer to the best of my ability ...including links to my sources. I wish you all success Chris


20 years as an independant contractor

H.S. diploma A.S. agriculture Mt San Antonio JR. College

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