Adhesive on concrete subfloors or walls presents a multifaceted dilemma. The adhesive is difficult to remove. If it is removed with an adhesive solvent, subsequently applied adhesive may not adhere effectively. And if the adhesive is older than 20 years, there is a chance it may contain asbestos fibers, which cause the serious diseases asbestosis and mesothelioma. The solution to the problem of adhesive on concrete depends upon the adhesive and the anticipated use of the concrete surface.
Black adhesives found under old asphalt flooring, sheet vinyl or vinyl composite tiles, may contain asbestos. Adhesive can be tested with an asbestos test kit purchased from a home improvement store. If the adhesive contains asbestos, the old flooring might also contain asbestos. Asbestos fibers in flooring and cutback adhesive are unlikely to become airborne, but to eliminate risk completely, both flooring and adhesive should be removed by a licensed asbestos abatement contractor. Other adhesives used on concrete are usually yellowish in color and may have an almost rock solid consistency. These adhesives pose no health risks, but chemicals that remove them do.
Strong solvent adhesive removers are most effective at dissolving stubborn solvent based adhesives like black cutback adhesive when a smooth, bare concrete finish is desired. Solvent adhesive removers contain volatile organic compounds, so they emit noxious fumes and are highly flammable. Always work with plenty of ventilation, and away from heat sources and open flame. Dispose of excess adhesive remover according to hazardous waste regulations in your community.
Citric acid, which has some properties of a weak solvent, is an alternative to potentially dangerous solvents. Adhesive removers with citric acid come in a liquid or paste which is useful for vertical surfaces. While they are relatively safe to use, citric acid removers do not remove all types of adhesive found on concrete. For best adhesive removal results, follow product instructions precisely, allowing the remover to soak into the adhesive thoroughly before scraping the adhesive from the concrete.
Adhesive removers often interfere with the performance of newly applied adhesive or painted concrete finishes. If new flooring requires application of adhesive or paint, old adhesive should be removed mechanically. A 4- or 8-inch razor scraper and a lot of elbow grease will remove most of the adhesive. Depending on the concrete surface, a grinder may be used to remove especially difficult adhesive lumps. To prevent remaining residue from interacting with the new adhesive, apply a sealer or mastic compatible with the new adhesive.
Removing adhesive on concrete is so labor intensive that some people choose to leave old flooring and adhesive in place, installing new flooring over it. Carpet can often be installed satisfactorily over old flooring, but flexible surfaces like old vinyl flooring may not be a sufficiently firm base for a new tile floor. If you are planning to install tile, removing the old flooring and adhesive from the concrete may be the less costly option in the long run.
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