Instructions for use:
Press the gauge into the wet elastomeric roof coating.
Take it out vertically and notice that the deepest teeth are painted, the next taller teeth are not.
The true wet film thickness is somewhere between these two readings. Clean gauge after each use.
Determine the dry film thickness (DFT) after finding the wet film thickness:
Many roof specifications and warranty policies require a certain number of dry film thickness mils to be on the job. A wet density meter gives you one of the numbers needed in the formula for determining dry film thickness. Another number you need to know is the volume solids of the elastomeric roof coating. Here is the formula:
Wet film thickness x percent volume solids = dry film thickness (DFT)
Let's take the National Coatings specification as an example. The specification calls for 24 mil DFT Elastomeric Roof Coating AcryShield A503 primer and AcryShield A400 topcoat. Let's start by taking a look at the AcryShield A503 primer. It has 54% solid material - contractor will need to apply 1 ½ gallons (these amounts are based on good conditions, good spray equipment, no wind, etc...see "Things to Consider" below) per square Up to about 24 wet mils. Using the above formula we will take 24 and multiply it by 0.54 to find that the DFT equals 12.96. When the primer dries, the AcryShield A400 topcoat also needs to be sprayed at 1 gallon per square meter to reach 24. This topcoat has a solids content of 52%, so we need 24 mils and multiply by 0.52 to find that the DFT equals 12.48.
Things to consider:
When measuring wet film thickness, this needs to be done immediately after the roof coating is applied. If the coating contains high concentrations of volatile solvents (liquids that evaporate at room temperature), they evaporate immediately, giving false readings.
Wind Loss: With winds up to 20 mph, you can lose 20%-30% of your coating.
Miscellaneous Losses: 3% to 10% added to total coat required (additional coats required due to coat grinding between coats and coats trapped in lines and empty barrels/drums)
