Ask the Expert: Calculating the Density of Coating Solids

Q: I'm trying to determine the weight that is added by painting a surface with CARC paint. Our specifications call for a Finish: Chemical Agent Resistant coat in accordance with MIL-DTL-53072 (REF. FED-STD-595) with a surface treatment in accordance with chemical conversion coat per MIL-DTL-5541 Class 3. From what I can tell from MIL-DTL-53072 and lower specifications, it indicates an approximate dry film thickness of .6 to .9 mils for the primer and a 1.8 mil thickness for the top coat of coarse some of the specifications indicate top coat thicknesses up to 2.5 mil. What is the dry film density of the recommended primer and topcoat? Are these thicknesses a good assumption?

A: From an MSDS you should be able to determine the % wt. solids and the % volume solids. Also the MSDS will give you the density of the coating expressed as WPG (weight per gallon) or S.G. (specific gravity). To convert SG to density multiply by 8.34 lbs water/gallon water.

Calculate the density of the solids as follows:

Wt solids (lbs solids/gallon of coating) = % wt. solids * WPG (lbs of coating/gal of coating)

To convert % volume solids to actual volume simply change the percentage to a fraction. Therefore 42% volume solids = 0.42 gal solids.

Density of the solids = Wt of solids (lbs)

Volume of solids (gal)

Best wishes,