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Old 10-18-2013, 08:55 PM
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Is it OK to mix paint/activator/reducer by weight?

I know that when they mix paint it us usually mixed by weight, but is it OK to mix the paint/activator/reducer by weight.

I am using the Dekups System and have a small digital scale that reads to tenths of an ounce.

I can put the Dekups container on the scale and zero it out and then add X ounces of paint, X ounces of activator and X ounces of reducer.

This requires less cleanup, results in much less waste and seems much more accurate than pouring each product to a line on a container and then mixing them all together.

Does an ounce of paint have the same volume as an ounce of activator and the same volume as an ounce of reducer?

If not, is there a formula/s to use to get the same volumes?

I am using all SPI products, but I would be curious if the same "rules" apply to different brands also.

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Old 10-18-2013, 10:46 PM
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Volume and weight are 2 separate measurements. If you know the ratio for weight, you can do it that way. But, using the same ratio for volume will not give you the correct ratio.
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Old 10-18-2013, 11:12 PM
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Paint company's are now using the digital scale to manage their materials...these computerized digital scales do mix paint, hardner and reducer by weight and if a technician over pours a toner, he can correct it, but, it's recorded in the front office...the same goes with any other additive...so if a color is off....the front office can check the computer for that mix and determine if it was mixed properly....scary...talk about big brother.

The problem doing this with your your gram scale is that every mix is different in weight...an average quart mix for PPG Deltron solvent base is just over 900 grams (US quart) but...each toner has a different weight, so if you have a color with light weight toners, your mix ratio of hardner to reducer to paint will be different than if you had a color with heavy weight toners.

The only way to safely do what your thinking is to either have the computer program (real expensive) or if your using SPI products, make your self a system...for example, if you want to mix 1 quart of Epoxy, get your stick out and weigh out 1/2 quart of primer, write down the weight, add the activator up to the line, write down the weight and now you have a weight formula for SPI Epoxy primer to activator using your gram scale. With a calculator and a bit of math skills, you could increase or decrease that 1 quart formula to suit what ever you need...and you could do this for all SPI products...just not with color that uses different toners....because of the difference in weight from toner to toner.

Hope this explains.

Ray
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Old 10-19-2013, 12:25 PM
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it all comes down to the specific gravity and density of the paint material, and they're all different as mentioned, so it would all need to be empirically determined. It's the exact same thing as when I mix different chemicals in the lab; if I do any mix by weight I have to know the specific gravity.

By the way, what is up with measuring sticks? I saw someone say you could make your own measuring stick by putting a mark at one inch, and a second mark at 2 inches to make your 1:1 ratio. This would only work if you were measuring in a cylinder. Any bowl or paint cup widens the farther up you get so you're putting a lot more of one component in than the other.
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Old 10-19-2013, 03:46 PM
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those responses are correct, do not mix by weight. The only time you mix by weight is with a mixing bank system where the computer already knows the weights of all of the products and compensates on the scale. Just mix by volume, being inacurate isn't that critical when mixing reducer and activator.
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Old 10-19-2013, 09:53 PM
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By the way, what is up with measuring sticks? I saw someone say you could make your own measuring stick by putting a mark at one inch, and a second mark at 2 inches to make your 1:1 ratio. This would only work if you were measuring in a cylinder. Any bowl or paint cup widens the farther up you get so you're putting a lot more of one component in than the other.

Lizer, the measuring sticks were mainly used when everyone was using siphon feed guns. You can still use them if mixing in a container with straight sides and a flat bottom (IE: metal paint can). You are right about the mixing cups having a taper that would alter the measurements and give you an inaccurate mix. I usually use metal cans to mix everything because every mixing cup on the market will be slightly off in the markings. If anyone doesn't believe me, use a mixing cup on a whole gallon of 4:1 primer, and be exactly to the marks each time. You will end up with a little primer and no activator or a little activator and no primer depending on which brand of cup used.


"being inacurate isn't that critical when mixing reducer and activator.

Branhar, I am not trying to be argumentative, but it is always critical to be accurate when mixing modern paints. With today's paint systems, the amount of reducer and activator is a lot more critical. A lot of paint/primer failures are because of improper mix.

Kelly
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Old 10-20-2013, 03:13 AM
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Quote:
Originally Posted by bran1har View Post
those responses are correct, do not mix by weight. The only time you mix by weight is with a mixing bank system where the computer already knows the weights of all of the products and compensates on the scale. Just mix by volume, being inacurate isn't that critical when mixing reducer and activator.
being off by more than 3% when mixing ratios can start to have adverse effects.
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Old 10-20-2013, 03:20 AM
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Quote:
Originally Posted by carolinacustoms View Post
By the way, what is up with measuring sticks? I saw someone say you could make your own measuring stick by putting a mark at one inch, and a second mark at 2 inches to make your 1:1 ratio. This would only work if you were measuring in a cylinder. Any bowl or paint cup widens the farther up you get so you're putting a lot more of one component in than the other.

Lizer, the measuring sticks were mainly used when everyone was using siphon feed guns. You can still use them if mixing in a container with straight sides and a flat bottom (IE: metal paint can). You are right about the mixing cups having a taper that would alter the measurements and give you an inaccurate mix. I usually use metal cans to mix everything because every mixing cup on the market will be slightly off in the markings. If anyone doesn't believe me, use a mixing cup on a whole gallon of 4:1 primer, and be exactly to the marks each time. You will end up with a little primer and no activator or a little activator and no primer depending on which brand of cup used.


"being inacurate isn't that critical when mixing reducer and activator.

Branhar, I am not trying to be argumentative, but it is always critical to be accurate when mixing modern paints. With today's paint systems, the amount of reducer and activator is a lot more critical. A lot of paint/primer failures are because of improper mix.

Kelly
I'm apprehensive of those measuring cups too. Barry has tested them before and he usually finds several percent variability. One time, one brand of mixing cup had so much variability it was causing the product he was testing to fail QC because the ratios were too far off. Once a better cup with more accuracy was used, the tests worked just fine. I was using DuPont cups and figured they probably had to be ok because they had DuPont's name on them, but now I have the Smart brand, which is the house brand that Finishmaster carries, and is just what they gave me when I asked for mixing cups and I don't feel as confident in them, though I haven't noticed anything.

Of course, in the lab we use calibrated methods of delivering highly precise and accurate volumes, so the fact that I leave that and come home to measure in a plastic cup with some markings with no statement to the accuracy is kind of a mind****. What I should be doing is taking a mixing cup into work and measuring volumes into it with a graduated cylinder to see how accurate it is
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Old 10-21-2013, 02:18 PM
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I apologize. I meant it is ok to be slighly over the lines when mixing, but if your goal is to mix 4:1 and you mix 3:1 that is stretching it and you may have a problem. Be as precise as you can, that is the way to go.

Also, you make a good point in the fact that all mixing cups are not spot on, and if you add that error to sloppy measurements then you will have big problems. I'm glad you brought that up because I never thought of mixing cups being inaccurate, I just assumed that they are all accurate. I will do some tests for my self to see if the cups I use are accurate. I have ended up with clear coat and no activator left, but maybe it was imprecise measurement of the material in the containers and not the measurements. I don't know, but I am curious to find out.
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Old 10-21-2013, 02:34 PM
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depending on the brand paint and acc does not always come out even. so if you have a little acc left over it does not mean your mix was wrong. cups are close enough .
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