The largest group of floor finishes belongs to the surface finish category. A surface finish is one that forms a durable and protective coating over the wood. Here, the durability of the finish varies based on the product being used, its application thickness and the duration and condition of the curing process. Historically, these finishes were natural varnishes and shellac. As modern chemistry advanced, so did the floor finish industry. Natural resins were replaced with alkyd resins, and those have been upgraded to mostly polyurethane resins. The modern field-applied urethanes are then broken down into various types based on chemical composition or how they cure. The top 4 are:
1) Oil-modified urethane is a solvent-based product and is very common and relatively easy to apply. It dries or cures through the evaporation of the solvent and its reaction with oxygen in the air. The durability is considered very good and it is available in various sheens, from high gloss to matte. Being oil-based, its color tends to shift toward amber hues with age. Dry times can run up to 8 hours and change with humidity levels.
2) Water-based urethanes, as their name implies, are water-based and cure and harden through the evaporation of the water component. These water-based finishes typically have a subtler odor than their oil-based counterparts and tend to dry a bit quicker. These finishes also do not yellow with age like the oil-based finishes. Some people find this appealing; others find them “milky.” These are often marketed as being greener than oil-based products and many times command higher prices.
3) Moisture-cured urethane is a bit more durable than both the oil-modified and water-based products. Moisture-cured urethanes are more difficult to apply and are oil-based, with satin or gloss sheens available. They are also formulated in non-yellowing and ambering types. Moisture-cured urethane has a stronger odor than the more common oil-modified products and is most often applied by professional flooring contractors.
4) Swedish finish or catalyzed urethanes are another of the oil-based products that are applied by pros. They are one of the most durable field-applied finishes, but they emit high volumes of VOCs during the drying and curing process. These finishes are comprised of a base and hardener and have quick dry times. Even though these have some of the most VOCs of any flooring product, they are usually installed by professionals with the proper training and equipment to render them safe.