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How can I calculate the amount of paint needed?

  1. Mar 22, 2014 #1
    Hi all.

    So I need to calculate the approximate liters of paint needed to paint 500 pieces about 0.85m2 (580mm by 730mm rectangular pieces, 2 sided) each. The specifications allow thickness of 50 microns. Also I'd like to add 30% over-spray just in case.

    How do I calculate the amount of paint needed?

    I am not very good at math. But I did think it might be something along the lines of (number of pieces) * (area) * (thickness) then 1liter / result.

    So basically 500*.85m^2*(50*0.001) = 21.25
    followed buy
    0.1m^3/21.25

    But this gives me something so small I just don't understand which probably means it must be way off base.
     
  2. jcsd
  3. Mar 22, 2014 #2
    number of pieces * area * thickness gives you the volume of paint in cubic metres. Multiply this answer by 1000 to convert to litres and you have your answer. I didn't understand your last step. I think the area you calculated for each piece may also be wrong .... 0.58 * 0.73 = 0.423 sq metres. Maybe you typed in a wrong number. I think the answer is 10.58 litres without overspray
     
  4. Mar 22, 2014 #3

    phyzguy

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    Science Advisor

    I don't understand why you did the second step. The volume of paint is just:

    500 pieces * 0.85 m^2/piece * 50 microns * 10^(-6) m/micron * 1000 liters/m^3 = 21.25 liters

    If you take into account your 30% overspray, it will take 21.25 * 1.3 = 27.6 liters.
     
  5. Mar 22, 2014 #4
    Thanks both.

    @nmf77: 0.423sq meters x 2 sides = aprox. 0.85 sq meters.

    @phyzguy: honestly, I don't know either, but I saw that somewhere, and thought I needed that to convert the result from an area or whatnot into liters or cubic meters and then liters.
     
  6. Mar 23, 2014 #5

    Nugatory

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    Staff: Mentor

    Paint shrinks as it dries (the solvent evaporates) so you can't just calculate the volume of liquid paint needed from the volume of the finished coat.

    The paint manufacturer will have a spec sheet somewhere that gives you the coverage area that you can expect for a given volume of liquid paint, and your best bet will be to work from those specs.
     
  7. Mar 24, 2014 #6
    Right now I'm just trying to get a rough estimate so I am adding 30% over-spray just to be safe.
     
  8. Mar 24, 2014 #7

    phyzguy

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    Science Advisor

    Well, if we're getting practical, the other thing you need to pay attention to is the thickness of paint. How will you guarantee a uniform thickness of 50 microns? It is easy to accidentally spray on 2-3 times as much as you want.
     
  9. Mar 24, 2014 #8
    Yeah, it happens from time to time. But fortunately we haven't had many issues with this. Our current painting system, 2 component based, yields a 40 to 50 micron cover for each layer. We can usually achieve the 50 microns per pass quite easily. SO considering 50 for the primer and another 50 for the paint, we get a total 100 which is within desired specs. We use a percometer to measure the paint thickness.
     
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