What are solids?
In water-based hardwood floor coatings, solids are whatever is left on the floor after the coating cures. Solids are usually expressed as a percentage of weight. A coating with 50% solids will be half gone after it dries.
To put it simply, the higher the solids, the more coating you will have left on the floor after it dries. Keeping this in mind, let's examine two misconceptions or myths about solids.
MYTH #1 - The more solids, the better.
Solids can be anything that does not evaporate during the curing process. As you know, the word "anything" can apply to all sorts of stuff. You have to look at what makes up the solids and what each of them does. Merely comparing finishes by percentage of solids is not an adequate test of their capabilities and performances.
Finish solids are often a blend of several ingredients, each having a specific purpose. Many of these have nothing to do with how long a finish will last. These various ingredients help the finish resist scuffs, reduce bubbling, improve adhesion, alter clarity, regulate sheen, and last, but not least determine overall durability.
The point is, ingredients used to adjust sheen or to control bubbles may add to the solids, but they do nothing for durability.
MYTH #2 - Pure urethane solids are best.
Like the first myth, this one concerning urethane solids is also incorrectly based on the concept "If a little of something is good, then a lot must be better." Many people (and some manufactures) think omitting acrylic will improve a water-based coating. We've found the opposite to be true, and we're not alone. For flooring applications, urethane resins work best when blended with acrylics.
Water-borne architectural wood finishes often use urethane and acrylic physical blend. By blending, the formulator can obtain, "the best of both worlds" and meet the specific requirements of the application. Urethanes impart impact resistance and toughness to the finish, while acrylics promote adhesion and gloss. Acrylics also contribute strongly to proper rheology (the application and drying characteristics of liquid coatings such as flow and leveling).
A key to the performance of these finishes is the balance of urethane and acrylic latex concentration.