Ask the Expert Question-and-Answer Archive

by Ron Joseph

March, 2004

VOC for the Lube

Q. Please show me the stepwise calculations to calculate the VOC's minus water

% True VOC's = 2.23 lb/gal
% Wt Water = 53.0%
% Wt Solids = 20.8%
Density = 8.52

A. Thanks for sending me the information. For reasons that I don't have time to explain right now, the equation for calculating VOC (lbs/gal) less water is as follows:


VOC (g/L)
(less water) = (100 - %Wt. solids - %Wt. water) x Dc
                                   {1 - %Wt water x Dc}
                                                   Dw

Where Dc = Density of the coating (g/L). This is the same as the weight per gallon, (WPG)

Dw = Density of water (G/L) = 8.33 lbs/gal

VOC (g/L)
(less water and exempt) = (100 - 20.8 - 53.0) x 8.52
                                              {100 - 53.0 x 8.52}
                                                               8.33

                            = 223.2
                               45.79

                            = 4.87 lbs/gal less water

This is the answer that your vendor gave you and by sheer coincidence

it is just more than double the VOC of the coating including water.

If you need to perform these types of calculations often and want to understand why we do what we do, then you might want to take my Calculations Class which will be given again in the last week of September in Rhode Island.