Michael Purser

Finishes for wood floors fall into two categories: coatings and penetrating products. They have two jobs to do, protect the wood and provide an attractive surface. In that context, coatings have been the overwhelming favorite. The biggest rap against them, though, is how they wear over time and how difficult it is to repair them when damaged or worn.

The appeal of penetrating products is they don’t form a film that can be abraded and damaged; theoretically, they are absorbed into the wood without leaving one on the surface. They may not show wear or damage as much, but their Achilles heel is the inability to provide minimal protection from casual contact with just about any liquid. For that reason, they are often used under coatings as a sealer or stain.

What would be ideal, of course, would be a domestic stand-alone penetrating finish. Hardening oils appear to have filled that void. But do they work? To answer that, let’s start by comparing hardening oils to the solvent-based penetrating products that have been available in North America for decades. Open any can of a U.S.-made penetrating product and look inside. The product might be clear or could have color added to create a stain, but two-thirds to three-quarters of the contents of the can are solvents. The remainder is what I call “the good stuff” (TGS)—the resins, dyes, pigments, driers, and drying oils that give the product its working characteristics. The solvents are smelly hydrocarbons that can stink up a jobsite. They dilute the good stuff (TGS) and keep it in suspension so you can get it out of the can, spread it on the wood floor, let it penetrate, and then remove the excess to avoid any type of film formation. After proper application, the wood is supposed to be sealed and protected.

With a can of hardening oil, you may also be looking at a clear or an opaque product that may have color added to qualify it as a stain. The big difference is the lack of solvents. This is possible because the vegetable-base oils (linseed and soy being the most common) are highly refined and purified. Several manufacturers claim they use no solvents at all. If a solvent is used, it’s down around the 2% range, which, in my book, still qualifies as no solvents. So, everything you are seeing in that can of hardening oil is TGS. You can take the contents out of the can, spread it on the floor, let it penetrate into the wood, and buff off any residue. You end up with no film formation. You don’t have noxious, smelly, and flammable hydrocarbons saturating the air and posing a threat to a worker’s health and the natural environment. As good as that is, do not lose sight of the fact that when the solvent-based products are absorbed into the wood, most of what is absorbed is solvent and not TGS. On the other hand, the hardening oil that’s absorbed is nothing but TGS.

I’ve worked with tons of U.S.-made penetrating finishes over the years. But after applying them, I’ve always covered them with multiple layers of a film-forming coating, usually some type of urethane, because you cannot rely on a solvent-based penetrating stain or finish to protect wood from casual contact with most liquids. Like most wood flooring contractors, I know that conventional penetrating products wish they could seal and protect, but the reality is, they won’t without help.

In contrast, the hardening oils I’ve used have done an outstanding job of providing the needed protection without a topcoat of finish. When the oils saturate the wood, they work at a molecular level and attach to the walls of the wood cells. Since a solvent does not dilute the oils, you’re getting the full benefits of TGS. Once in the walls of the wood cells, the oils start to harden, bonding all that TGS that has been absorbed.

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