dry film thickness why is it important

By Ron Bryze at WoodFinishingTech.com

DRY FILM THICKNESSWHY IS IT IMPORTANT

There are usually two numbers on manufacturersProduct Information Sheet that most often re-ferred to. They are the % Solids by Weight, andthe % SOLIDS by VOLUME. The % Solids byWeight is a number that really is only used whenmixing the formula; however it is usually higherthan the Solids by Volume number so a lot ofsales types will quote it to make their productmore impressive…

The number that really has any meaning to you,the finisher, is the % SOLIDS by VOLUME. Thisis the number that can tell us how much finish isleft on the wood after the solvent evaporates.This is called the Dry Film Thickness. It is recom-mended that when you add up the thicknesses ofall of the coats of finish on a piece that youachieve a total Dry Mil Thickness of 3-4 Mils. It isrecommended that you do not exceed 5 Dry Mils.You will notice that when you calculate the DryMils for Pigmented Systems that the System To-tal is often greater than 5 Mils. This is because ofthe primers in these systems. They need to besanded back rather aggressively, so the totalsystem thickness will be less than 5 Dry Mils.

Greater than 5 Dry Mills and a finish can becomebrittle, wrinkle, spider web and cause all kinds ofother problems.

It is usually recommended that when applyingyour finish, you apply 4-5 Mils of Wet finish ontothe wood. You should use your wet mil gauge tocheck on how much you are putting down. Basedon a 5 Mil wet coat of finish there are a number ofcharts that I have included to help you calculateyour Dry Film Thickness and number of coatsneeded.