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. 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, improve slip resistance, and last but not least, determine overall durability.
Ingredients used to improve slip resistance or to control bubbles may add to the solids, but they do nothing for the durability. The chemistry used in Betco’s floor finish has improved to the point that solid content really does not matter. We use superior polymers, plasticizers, and waxes that combine to form incredibly durable finishes like Hard as Nails. So the next time that you decide to compare finishes make sure you are comparing apples to apples.

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http://blog.betco.com/2014/06/12/floor-finish-myth-a-higher-solids-finish-is-more-durable/#sthash.J7jHC28p.dpuf