| 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 percent 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 three 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
- Taber abrasion tests are always accurate.
The only scientific data less reliable than a Taber
abrasion test result is what you get from your local weatherman. The American Society of
Testing and Materials (ASTM) state the accuracy of one Taber abrasion machine compared to
another may vary up to a range of 90 to 106 percent. This normal range means the tests can
be off by 100 percent and still be considered accurate. These results can occur even when
documented test procedures are used. That, in a nutshell, is why we don't value Taber
abrasion tests or comparisons very highly.
MYTH
#3 - 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.
Dr. Richard G. Coogan,
James J. Bilancieri, and Gail Pollano reported
benefits in blending acrylics and urethanes. They found, "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).
The authors of the study go further to stress the
importance of finding the proper ratio of resins. The report said, "A key to the
performance of these finishes is the balance of urethane and acrylic latex
concentration."
REFERENCES
Annual Book of ASTM Standards - Section 6: Paints,
related Coatings and Aromatics. Vol. 06.01 Paint - Tests for Formulated Products and
Applied Coatings, pp 670-671, ASTM Designation : D 4060-84, Standard Test Method for
Abrasion Resistance for Organic Coatings by the Taber Abraser.
Hawley's Condensed
Chemical Dictionary - 11th edition. Revised by N. Irving Sax, Richard J. Lewis,
Sr. Van Nostrand Rienhold. |
