# Professional Finishing

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# Dry Mil Thickness Calculations?

11/14/18
 DanShaf Member

Magnalac has at most 30% solids by weight and also 24% solids by volume. If I spray 3 applications, each of them 4 - 5 wet mils, will I achieve 3.9 - 4.5 dry mils or will I achieve 2.88 - 3.6 dry mils? That is to say, to do the math on my dry mils should I be using the percentage of solids by weight or by volume.

11/14/18       #3: Dry Mil Thickness Calculations? ...

My guess is the later,,,with a wet film gauge you're measuring volume not weight,

11/15/18       #4: Dry Mil Thickness Calculations? ...

Use volume for your calculations. Weight doesnt matter for the intended use. Mfg put weight on as it shows a higher percentage so looks better....marketing crap.

Also dont forget when you scuff sand between coats, you are removing some material, so you will be less than calculated.

11/15/18       #5: Dry Mil Thickness Calculations? ...
 Collin Parker

Website: heritagewoodwright.com

your numbers looks funny. should be .24*(4 or 5)= .96 or 1.2.

dry mil= wet mil * %solidsvolume

11/15/18       #6: Dry Mil Thickness Calculations? ...
 Brian Member

The coating manufacturer should be able to run a dry mil check for you on a finished panel if you are trying to determine if you are applying their system to the correct millage. Check with your distributor.

11/15/18       #7: Dry Mil Thickness Calculations? ...
 DanShaf Member

Collin, then multiply that by 3 applications. Not how much per application. 3 applications, each one 4 - 5 wet mils.

The percent of solids by weight is important for EPA considerations, i.e., what is the weight of the material that you are expelling into the air. If a shop is a large quantity generator, they want paperwork filled out by you so they can see on paper the amount of waste that you might generate. But I'm not asking any EPA questions or VOC questions, only questions of calculating total dry mils.

Measuring it after the fact isn't what I'm after. Only the math because when I'm deciding on a finish schedule to play with, I need the details. That would include if I plan to do a washcoat, anywhere from 3% - 12% solids depending on the amount of sizing I want to introduce into my finish schedule.

11/16/18       #8: Dry Mil Thickness Calculations? ...

Buy a positester from gaurdo and be done..... that is the only true way to know....

11/16/18       #9: Dry Mil Thickness Calculations? ...
 DanShaf Member

A testing tool will measure the thickness of the coating but it does not tell me whether to make my calculations using the solids as a percentage of volume or to make my calculations as a percentage of weight.

My inclination is this, we mix up a quart of finish without regard to weight. We know that one quart of water weighs 32 ounces. We are not mixing water. In most cases a quart of finish will weigh in at more than 32 ounces, yet it will still only be one quart of that material.

The question arose at work, volume versus weight. We aren't looking to measure what we are laying down, we are looking to calculate it properly in the first place.

11/16/18       #10: Dry Mil Thickness Calculations? ...
 Collin Parker

Website: heritagewoodwright.com

Sorry about that Dan, didn't realize you did the multiple coat X. Anyways, I've actually switched to making my spreadsheet for paint needed per sqft based upon tested values AFTER reduction etc. You can attempt calculating based upon the % solids, % efficiency of spray equipment, % reduction... but its all a crapshoot. Time tests on multiple jobs is much better in my opinion. Just track how much raw paint you use and divide by sqft and get yourself a baseline to move forward with. Only takes a couple jobs to get decent numbers for all of your frequently used primers, stains, basecoats, clears. KISS (keep it simple stupid) p.s. not calling you stupid haha

11/21/18       #11: Dry Mil Thickness Calculations? ...

To calculate your mill thickness, you use volume solids. Using round numbers, if you have a 25% volume solids finish, that means 75% of the material are solvents that will evaporate as it is sprayed, drys and cures. If you put down 1 coat that is 4 mills
wet, it will dry to 1 mill because 75% is solvent that will evaporate. To get a 4 mill dry film you would need 5 coats if you are sanding between coats.(because you remove material with sanding) 4 coats if you don't sand. To figure coverage - if you had a finish that was 100% solids and you applied it 1 mill thick it would cover 1644sq ft. So if your finish is 25% volume solids it will cover 25% of 1644 sq ft. in 1 coat.

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