TECHNICAL ADVICE FOR SEALING CONCRETE FLOORS

Source:www.stonediamondtool.com Date:2022/2/9 Read:160

Decorative concrete expert, and vice president of sales and marketing with ChemSystems Inc, Chris Sullivan, provides in-depth answers to common problems associated with sealing concrete floors.

Cause of dull spots in sealed floor

Question: Four years ago I covered my basement floor with a patterned overlay (I am in the decorative concrete business). I applied a two-part polyurethane sealer to it. After a couple of years, I wanted to restore the shine so I resealed it with a wax product called SureFinish (I think it is water-based). Over the course of a few months, the floor looked more and more dull in spots, especially where walked on with wet shoes. I stripped the floor with a mild muriatic acid cleaner and applied an acrylic solvent-based sealer, thinking that I needed the solvent to restore the color. The floor looked great at first, but after about a month it began to dull again in spots. When I wash the floor it looks great, but the dull spots show up when it dries, and over time I'm getting more and more spots. Do you know why this is happening? Is it perhaps because the original sealer was a polyurethane that the others sealers are not bonding to, and with washing and water exposure, they are coming off? How do I now reseal over the original sealer?

Answer: I think you are on the right track in terms of the other sealers not bonding to the original polyurethane sealer. Now you have multiple layers of different sealers, all of which seem to be wearing. Applying a water-based wax and then a solvent on top was also not a good idea.

What is probably happening is diffusion. Where a sealer coat starts to come off, light no longer travels through it but instead diffuses, resulting in dull or white and hazy spots. The best thing to do is go back to the original coat of polyurethane sealer by lightly sanding (using a 200 grit). Then apply very light coats (800 to 1,000 square feet per gallon) of the wax. Test this remedy in a small area first to make sure it is working.

Removing bubbles and roller marks in a sealer

Question: I recently applied a two-component, high-solids aliphatic polyurethane sealer to a stained floor in a spa. First, I applied the primer coat with a roller and then applied the polyurethane, which has a longer pot life, with an airless sprayer. While applying the primer on the first half of the floor, I could see roller marks and bubbles and the primer started to string up on me. I mixed a new batch and proceeded to finish rolling the rest of the floor but at a much faster pace, and I seemed to have no problem. But now roller marks are visible throughout the entire floor, not to mention the bubbles.

To remove the bubbles, I was told by the sealer manufacturer to go over the floor with a floor buffer or 150-grit sandpaper and then seal again. But will buffing be aggressive enough to take out the marks? Also, should I apply the primer using a sprayer instead of a roller, and should I mix smaller amounts of the sealer? I think I may have rolled on the primer too fast producing the roller marks. What do you recommend to fix the issue?

Answer: Sanding will take surface bubbles out, but buffing with a floor machine will not be aggressive enough. If the bubbles go deeper than the surface, you may need to strip and start over. My suggestion is to try sanding out the marks and then reapply your topcoat. If this does not work, strip down to a point were no roller marks or bubbles appear and start over. Do a test area before doing the entire floor.

I am not a fan of rolling in general, especially heavier bodied materials like epoxies or polyurethanes. All rollers produce lines, with more material coming off the ends of the roller as it moves across the surface. Depending on the material used, application temperature and pot life, the roller lines may or may not even out. The speed of rolling, the amount of material on the roller and the weight pushing down on the roller also play a role in leaving roller marks. Picture a car tire that has mud on it. If you drive slowly, the mud comes off the tire evenly. If you speed up, the mud flies all over and leaves more prominent marks on the outside edges of the tire. Heavy-bodied materials are always best applied in small batches and with a push-pull applicator such as a lamb's wool or micro-fiber pad or a T-bar.