Theoretical coverages are those calculated for glass-smooth surfaces with no allowances made for loss. Manufacturers publish theoretical coverages instead of actual coverages because they cannot anticipate job or surface conditions. Therefore, published coverage rates should only be used as a guide for estimating material requirements for a given job.
Actual coverage will be less than theoretical coverage. When coatings are applied over concrete, many factors such as the surface texture, overspray loss, container residue, equipment characteristics, and applicator technique will directly affect the amount of coating material required to meet the designed in-place dry film thickness (DFT). Therefore, it is very important that additional material be added to the theoretical quantities to ensure that the proper coating thickness is applied. Items to consider are:
Shot-blasted Concrete: Even though the surface texture appears to be fairly smooth, this surface may require 5%–15% additional material than the theoretical amount.
Wind Loss: During spray applications, up to 30% of the coating may be lost due to wind. Consider using wind screens and add wind loss to your coating calculations.
Miscellaneous Loss: A miscellaneous factor must be added to the theoretical coverage rate to cover losses due to material left in containers, equipment problems, etc. Use a percentage factor of between 3% to 10%, depending on the contractor’s experience and efficiency.
Calculating Theoretical Coverage
Any liquid, when applied at a thickness of one mil (1/1000 inch) will cover 1604 square feet per gallon. Another way to state this is that one gallon of any liquid, applied over a 100 square foot surface, will be 16 mils thick when wet. To determine dry mils (or how much is left when the solvents are gone), multiply 16 (wet mils) times the solids content (by volume) of the particular liquid. Solids by weight should not be used in this formula.
50% solids by volume = 16 (wet mils) x 0.5 (50% solids by volume) = 8 dry mils.
To determine how much total material is required to cover 100 square feet, divide the total system thickness (expressed in mils) by the number of dry mils per gallon.
System = 32 dry mils total
Material (50% solids by volume) = 8 dry mils per gallon
32 divided by 8 = 4 gallons per 100 square feet
% Solids by Volume X 1604 ÷ Desired Dry Mils = Coverage Rate
Calculating Actual Coverage
To determine total material requirements for a job, add estimated losses due to field conditions to theoretical coverages. Depending on jobsite conditions, up to 50% additional material may be required to meet the designed in-place dry film thickness (DFT).