How can I calculate the amount of paint needed?

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Discussion Overview

The discussion revolves around calculating the amount of paint needed to cover 500 rectangular pieces, each measuring approximately 0.85 m², with a specified thickness of 50 microns. Participants explore the implications of overspray and the practical aspects of achieving uniform paint thickness.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes a calculation method based on the formula: (number of pieces) * (area) * (thickness), suggesting a conversion to liters afterward.
  • Another participant corrects the area calculation for each piece, indicating it should be 0.423 m², and provides an estimate of 10.58 liters without overspray.
  • A different participant agrees with the initial volume calculation but suggests that including a 30% overspray would result in approximately 27.6 liters.
  • One participant mentions that paint shrinks as it dries, emphasizing the importance of consulting the manufacturer's specifications for coverage area.
  • Concerns are raised about achieving a uniform thickness of 50 microns, with one participant noting that it can be easy to apply too much paint.
  • Another participant shares their experience with a painting system that typically achieves the desired thickness, mentioning the use of a percometer for measurement.

Areas of Agreement / Disagreement

Participants express differing views on the calculations and methods for estimating paint volume, with no consensus reached on the correct approach or final estimate.

Contextual Notes

Some calculations depend on assumptions about the area and thickness, and there are unresolved questions regarding the accuracy of the area measurement and the impact of overspray on the final volume needed.

NMGMarques
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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.
 
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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
 
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.
 
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.
 
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.
 
Right now I'm just trying to get a rough estimate so I am adding 30% over-spray just to be safe.
 
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.
 
phyzguy said:
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.

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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