Film thickness of the wet film.
To determine how thick the wet film will be, first convert 0.12 gal./sq. yd. to sq. ft./gal. following the formula.
1 ÷ 0 .12 = 8.33 sq. yd./gal.; 8.33 sq. yd./gal. x 9 = 74.97 (call it 75) sq. ft./gal.
- 1st coat = 0.12 gal./sq. yd. = 75 sq. ft./gal.; 1604 ÷ 75 = 21.39 mils
To determine wet film thickness of the second coat, again convert 0.08 gal./sq. yd. to sq. ft./gal. 1 ÷ 0.08 = 12.5 sq. yd./gal.; 12.5 sq. yd./gal. x 9 = 112.5 sq. ft./gal.
- 2nd coat = 0.08 gal./sq. yd. = 112.5 sq. ft./gal.; 1604 ÷ 112.5 = 14.26 mils.
- Total wet film thickness of two coats = 21.39 + 14.26 = 35.65 mils.
Film thickness of the dry film. Multiply the wet film thickness by percentage of solids by volume (Chart 2).
- 1st coat = 21.39 mils. x 39.4% = 8.43 mils,
- 2nd coat = 14.26 mils. x 39.4% = 5.62 mils,
- Total dry film thickness of two coats = 8.43 + 5.62 = 14.04 mils.
Note that the film thickness of the cured film in Job B is only two-thirds of the correct film thickness and that might cause performance problems, including premature failure. The above examples demonstrate the importance of adhering to mix design recommendations and the specified coverage rates.
- If the coverage rate is specified in terms of concentrated sealer: Use the specified number for calculating the amount of sealer needed for the job. But for actual application of the mixture, multiply the coverage rate by the ratio between the mixture and the concentrated sealer. So if 100 gallons of sealer concentrate makes 150 gallons of total mix, multiply by 1.5 (i.e. 150 ÷ 100).
- If the coverage rate is specified in terms of the final mixture (sealer, water, aggregate, additive, etc.): Calculate the percent of sealer in the mix and use that number for calculating total gallons of sealer, water, sand (measured by the pound), and additives. Then apply per the application rates of the mixture.
Should you have any questions about sealer mix designs, coverage rates, or any other aspect of sealcoating contact your sealer supplier or the manufacturer.
Girish C. Dubey is president of STAR Inc., Columbus, OH, which has affiliate sealer producing operations throughout the U. S. States.