Q: We refinished our ipe patio furniture with Penofin penetrating oil finish. Unfortunately, several large spots of the finish fell onto our slate patio. We noticed the spots immediately and tried to power wash them away to no avail. We looked online for advice but found nothing definitive. What should we do to remove the spots?

Fairfax, Va.

A: Performance Coatings in Ukiah, Calif. (penofin.com; 800-736-6346), which owns the Penofin brand, makes a variety of wood stains, including a solvent-based penetrating oil finish labeled as Penofin Stain & Sealer. This is a traditional oil finish, and you can’t clean it with water, even if you add soap and the force of a pressure washer. (Soapy water does work, though, on some newer finishes that use modified oils along with waterborne technology. Penofin’s TMF Hardwood and TSF Hardwood are in this category.)

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Assuming you used Penofin Stain & Sealer, the instructions say to clean up with mineral spirits, also known as paint thinner. That usually works, as long as the cleanup is done within 24 hours, according to the company’s customer service department.

After 24 hours, though, the finish generally has cured and is impervious to mineral spirits. At that point, the manufacturer recommends switching to Penofin Pro-Tech Wood Cleaner ($33.98 a quart on Amazon). The main ingredient is sodium percarbonate, a combination of sodium carbonate — also known as washing soda (a laundry aid) — and hydrogen peroxide. Sodium percarbonate is an oxidizer that releases hydrogen peroxide and soda ash as it breaks down. You need to protect your skin and eyes when you use it, but it’s biodegradable, and the runoff shouldn’t hurt plants or contaminate soil.

A customer service representative for Performance Coatings said to add one cup of the cleaner, a powder, to one gallon of warm water in a garden pump sprayer. Mix well. Spray the spots and let the solution sit for 15 minutes. Check often and re-spray, if necessary, so the surface stays wet. After the time has elapsed, scrub the spots with a bristle brush, then rinse well.

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Many retailers that carry Penofin stains also carry the cleaner. But if you can’t find the product locally and don’t want to wait for an online order to arrive, the customer service representative said, you could instead use an oxygenated laundry powder, such as OxiClean Versatile Stain Remover. Use the same concentration and procedure as if you were using the Penofin cleaner.

If an oxygenated cleaner doesn’t work, you might need to resort to a stain remover made for professionals in the stone industry. The Nova Stone Center (thestonecenter.com), which has multiple locations including in Manassas and Ashburn, Va., carries a variety of specialty cleaners made by SRW Products. The one you would want is SRW’s TR Tar, Gum & Rubber Remover ($37.90 for a 29-ounce can on Amazon). Labeled as a way to spot-treat stains that won’t come off any other way, this product is powered partly by a citrus-based solvent, limonene. Though that might sound benign, the product comes with a list of hazard warnings. You wouldn’t want to scrub your whole patio with it, because it’s flammable, the vapors are harmful to breathe, and splashes can kill plants or dissolve plastics. If you just spot-treat and rinse with plenty of water, however, your exposure should be minimal and nearby plants should be fine, said Joel Baker, product manager for SRW Products. “You’re just not using any volume that would cause a problem.”

Instructions say to pour a small amount onto a stained area, let it soak for five to 10 minutes, scrub lightly with a stiff-bristle brush, and rinse with water. Rinsing with a pressure washer would be helpful, Baker said.

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The remover should completely dissolve the oil component of the stains, Baker said. If spots remain, pigment from the oil finish may have become embedded in the stone, Baker said. With luck, they would become less noticeable over time.

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