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The answer is that yes, there is a tool that the consumer can use for gauging relative coverage between competitive products. It is quite simple but you will first need to know certain specific information about the particular stains that you want to compare. That specific information is a physical measurement called volume solids. The volume solids percentages of any particular coating automatically contain in that information its theoretical coverage. But before I proceed I must digress to clarify the difference between volume solids of a coating and weight solids of a coating.
VOLUME SOLIDS
The Volume Solids of a coating represents the amount of dried material that
remains after the liquid portion of that coating has evaporated. It is a percentage
that is determined by first measuring an established volume of the liquid
material, evaporating off the entire liquid portion and then measuring the
volume of the remaining dried solid portion. The difference in volume of the
coating in its liquid form minus the remaining volume in its dried state is
called volume solids. It is the volume solids that directly determine the
coverage and amount of material deposited on a particular surface.
WEIGHT SOLIDS
The Weight Solids are different because weight solids represent the actual
weight of the dried material after the liquid portion of that coating has
evaporated. The weight solids are the percentage determined by first weighing
an established amount of stain in its liquid form, evaporating off the entire
liquid portion and then weighing the dried solid portion. The difference in
weight of the coating in its liquid form minus the remaining weight in its
dried state is the called the weight solids. Weight solids are, as a rule,
higher in percentage than volume solids and are never used to determine the
coverage. (It is not unusual for companies, when listing solids in their particular
coating, to only list weight solids. That is because weight solids are the
higher number and the higher number is obviously more impressive to the consumer
than the lower volume solids number.)
I hope that I was clear with these concepts and that you now know the difference between the two solid’s measurements of a coating. As stated earlier the volume solids are directly related to theoretical coverage of a coating. This coverage is determined by a standard formula that bases coverage of a paint material at 1 millage thickness over a non-porous surface. The mathematical formula is 16.03 X each 1% volume solids = the square foot coverage of one gallon of a given coating over a non-porous surface.
TYING
UP LOOSE ENDS
A Non-Porous Surface?
The question now becomes: “Why measure coverage over a non-porous surface”?
Why not use real world calculations? After all, wood stains are applied over
wood and wood is a porous surface… That is quite true. Wood is porous
and because it is porous is the reason that a wood surface cannot be used
to accurately and with fairness determine the coverage of different types
of wood stains. When applying a wood stain over a porous surface, the ability
to measure its coverage becomes much more difficult because of the absorption
rate of the liquid into the porous surface. In addition to the physical characteristics
of the wood stains themselves, absorption rates will vary because of the differences
in wood species, the dryness of the wood, the wood’s natural porosity,
the surface variations caused by the processing of the wood, etc. Because
of all of these variables, determining stain coverage is at best an educated
guess. However, by introducing a non-porous surface into the equation, it
takes the guesswork out of coverage comparisons because there are no longer
the surface variations to distort the data.