Dog accidents have damaged my wood floors. What can I do?
Q: My dogs have heavily damaged the hardwood flooring in my 1956 house. Is there a way to refinish the floor so it’s impervious to dog urine? My handyman has suggested vinyl flooring, but I appreciate the hardwood and am reluctant to just cover it over.
A: It’s possible to wipe up pet accidents on hardwood floors without leaving smells or stains, but the finish needs to be intact and you need to clean up the mess promptly. If cat or dog claws scratch through the finish, or if the spills are left on for long enough to sink into the wood, it becomes much more difficult. Urine gets into the wood, stains develop, and odors linger. Often, the only remedy then is to replace damaged boards, sand off the finish and scratches in remaining boards, and apply a new finish.
In a house built in 1956, wood flooring is almost certainly the traditional, solid-wood type. Individual boards are probably ¾-inch thick and milled so that a “tongue” on one edge fits into a groove on the next board. Installers would have nailed the boards in place at an angle through the tongue edges, creating an interlocking system without visible nails except perhaps near the edges of the room. The system allows individual boards to expand and contract as relative humidity changes, leaving gaps that change in size but aren’t especially noticeable because the floor boards are narrow so each gap stays small. But this type of flooring can’t be sanded down and refinished forever. At some point, the heads of the nails will begin to show. The wear layer over the nail heads starts out about ¼-inch thick. But if the floor has been sanded down and refinished a few times, which is likely in a house almost 70 years old, the wear layer now could be just paper-thin.
If you have floor registers, it might be possible to remove the grates and gauge how much wear layer is left. Getting estimates from professional floor finishers would be another way to assess whether it’s even possible to refinish your floor.
The most scratch-resistant finishes for wood floors contain very finely ground aluminum oxide, the same grit material found in most sandpaper. These finishes need to be baked on, so they are available only in pre-finished flooring. If you decided to replace your existing floors, you would get the best scratch resistance by buying pre-finished wood, probably with a wear layer of natural wood above a base made of other material with interlocking edges.
For floors that will be finished after they are sanded or floors that are being refinished, the website of the National Wood Flooring Association, a trade group, lists six options: water-based finishes, oil-based finishes, moisture-cured finishes, conversion varnishes, UV-cured finishes and floor waxes.
Brett Miller, the organization’s vice president of technical standards, training and certification, said in a phone call that oil-based finishes are less permeable than water-based finishes, so oil-based finishes give you more time to clean up a puddle before liquid gets into the wood. He thinks that’s because oil-based finishes have a higher solids content and tend to be applied in multiple coats, so they build up into a thicker layer on the floor.
But for resisting urine damage, a finish’s chemical resistance also matters, Miller said. For that, he recommends two-component water-based finishes, which need a separate hardener mixed in just before application, similar to epoxies. Bona Traffic HD is one of the best-known of these products, but similar ones are available from most floor finish manufacturers. These finishes are sold to professionals, rather than consumers. The official safety sheet for Bona’s hardener advises against consumer use. The reason? “Safe use cannot be demonstrated.” The hardener contains isocyanates, which can cause severe allergic reactions if safety precautions aren’t followed. But as the hardener reacts with the finish, the risk diminishes. Bona says this finish dries in two or three hours, is 80% cured after 24 hours and is fully cured in three days.
If you do hire a pro to refinish your floors, Miller recommends asking for multiple coats applied at the manufacturer’s recommended coverage rate. The more finish builds up, the more time it will take for spills to get through. But the weak point in the finish will still be the edges of each of the boards. The inevitable seams in a wood floor mean that it can never be fully waterproof.
What about covering the damaged floor with something that is waterproof, such as sheet vinyl? It comes in wide widths, so for many rooms you might need only a single, seamless piece.
It’s a bad idea, Miller said. “We have files and files of photos” of problems with trying to fix wood floors that way, only to find that the floor became moldy and rotten, he said. The vinyl is waterproof, and while that does stop spills from getting into the wood from above, it also keeps moisture that gets into the wood from underneath from evaporating. That can happen not just from leaks but also from condensation, which can form when a cold surface hits a warm surface. Flooring over a ventilated crawl space in a warm, humid climate can become wet enough to rot if it butts up to an air-conditioned space, where moisture in the air turns to liquid.