If you hit concrete when removing floor tile you need to prepare the surface properly so new flooring adheres and performs as intended.

Begin by removing any leftover thinset mortar and adhesive using a combination of manual scraping and a power tool such as an oscillating multi tool with a carbide scraper blade or a floor chisel on a rotary hammer if the layer is thick. Work in small sections and keep the surface flat and feathered at transitions so you do not create ridges that telegraph through new flooring. Next, clean thoroughly with a vacuum that has a high efficiency particulate filter and then wipe with a damp mop and a mild trisodium phosphate solution if grease or oils are present; allow the slab to dry completely until moisture content meets the flooring manufacturer recommended limits. Inspect the slab for cracks, spalls, and areas of delamination by running a straightedge and tapping exposed areas; mark defects for repair. For hairline cracks use a high quality cementitious crack filler applied from the backside of the crack if accessible or force-broadcasting fine sand into a polymer-modified cement slurry on the surface, then smooth. For larger cracks and low spots remove unsound concrete, fill with a fast-setting polymer-modified patching compound, and feather edges; grind high spots to achieve a flat tolerance of no more than one eighth inch over ten feet for most resilient and wood products unless the flooring manufacturer specifies tighter limits.

Common issues are residual adhesive that prevents bonding, moisture migration from the slab, and uneven slab elevation that causes finish failures. If adhesive remains do not trust solvent wipes alone; mechanically remove it until you reach sound concrete and then acid etch or mechanically profile to restore a proper surface profile. For moisture use a calibrated moisture meter and perform a calcium chloride test or relative humidity test per the flooring system requirements, and install a vapor mitigation membrane if readings exceed allowable limits. When the slab is uneven you can use a self leveling underlayment for shallow corrections or a bonded cementitious trowelable repair for deeper spots, always follow manufacturer cure times before installing finish flooring.

BigHomeProjects.com connects homeowners with local contractors and provides a space to discuss projects, ask questions, and share real experiences related to preparing concrete subfloors. We help contractors find leads and homeowners compare approaches while our community discussion forum offers practical advice from people who have faced the same concrete issues.

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