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Acid bad advice for vinyl flooring

QuestionWe are do-it-yourself project people due to budget constraints. I have some questions about vinyl floor replacement in our 1980 home's basement bathroom, and I hope you can help.

We installed vinyl flooring in our basement bathroom and were instructed to glue it to the concrete floor. About a year after the warranty was up, the floor began to discolor. We were told by people at home improvement stores that to remove it meant we had to peel, scrape, and use acid to remove all remnants of the flooring. Yeah, that sounds like fun. (We did test the concrete floor for moisture with negative results.) Anyway, I would really like to avoid the scraping and acid part. My question is this: if we are able to separate the flooring from the glued paper (then not have to scrape off the glued paper and use acid), could we apply some kind of sealer over this glued paper and then install new vinyl flooring over this? The floor is also uneven, so we need to stick to vinyl sheet flooring. If using a sealer is okay, what kind do we use?

AnswerThanks for sending in your question. Over the years I have built new and remodeled a lot of basement bathrooms, and floor discoloration (especially around the toilet) was one thing I discovered when I later revisited these bathroom projects. I don't know exactly what causes it, but I suspect it comes directly from the mastic (glue/adhesive) and that it results from a chemical reaction between the mastic and the minerals present in concrete, some moisture or perhaps a combination of it all.

For that reason, I'm convinced that resilient flooring doesn't belong in a below-grade environment, especially in a bathroom. I also don't believe in shortcuts—ask my wife. If you believe that you still want vinyl as a floor covering after reading this, then yes, you'll need to apply some good old-fashioned elbow grease to scrape up the existing floor covering and its mastic so you can get a smooth substrate—providing that asbestos is not present. I know from experience that you will get a better finish job when all is said and done.

Asbestos was an ingredient in vinyl floor coverings, backings, and mastics installed in homes built prior to the 1970s. Because your home was built in 1980, it's possible that an older stock of floor covering was used. To make sure your floor covering does not contain asbestos, send a small sample (2-inches-by-2-inches) of the floor covering, including mastic, to an independent laboratory (found in the yellow pages under "Asbestos Consulting & Testing") for analysis. If the test comes back positive, don't proceed on your own but bring in a contractor who specializes in the safe removal of asbestos.

Once you know there's no asbestos present, it's safe to proceed on your own. The recommendation to use acid is bad advice. Instead, visit your local rental yard and rent a floor scraper and a heat gun. The heat gun will help soften the mastic so you can scrape it up with the floor scraper. This is not going to be as easy as one, two, three. You'll have to work in small areas at a time. Run the bathroom fan while you work and, if you have a window, open that as well for ventilation. When most of the mastic is removed, apply lacquer thinner, again working in small areas, and use a white rag to remove the remainder of the mastic.

Once you have a clean substrate, you can fix any irregularities or level it using a gray thinset by Custom Building Products (Versa-Bond). Remember that anything left on the surface of the concrete will telegraph through the finished vinyl flooring, so you need a smooth substrate for a smooth installation. To seal the substrate, I would use the smooth side of the trowel and spread down a very thin layer of the floor mastic to create a barrier. When the mastic has cured, you'll be ready to install vinyl floor covering. I suggest that you carefully read the warranty information on your new vinyl flooring to ensure that your installation meets the company's standards for warranty coverage.

Professionally speaking, I might risk the installation of quarry floor tile over the vinyl backing and old mastic, but I would definitely not install resilient floor covering. And I do know that—even with tile—putting any floor covering over existing material is risky. However, if you peel up the vinyl floor and remove any loose backing felt and then discover that the backing and mastic are securely bonded to the concrete floor, you could try installing quarry floor tile on top of it.

I would recommend that you first apply a thin layer of thinset using the smooth side of a trowel to seal the area. After the thinset has cured, reapply thinset to level and repair any trouble areas. You'd be surprised at the multitude of sins you can hide using the required notched trowel thickness of thinset and tile. There are no guarantees that the tile will achieve a permanent bond or that there will be no trouble with the installation down the road if you leave the old backing or mastic in place.

Good luck with your project!

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Copyright © 2004, 2006, & 2007 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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