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Old 07-02-2005, 02:31 PM
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Reduced Acrylic Enamel Shelf Life ?

I am in a major hurry to get some painting repairs done to my Malibu, and have a need to paint two colors on both of two different days each.

I am spraying Martin Senor acrylic enamel I have to custom mix for the main yellow color, and I am spraying PPG acrylic enamel for the black stripes- this looks GREAT when I mask the stripes in the proper measurements.
I started the whole job with a set of incorrect measurements and immediately played with them to get the right look, and I am pleased with them.
I now have the incorrect stripe dimensions to fix, and repaint another panel completely to fix a centering error, the center of the hood does not line up with the center of the header panel.


1. Can I reduce the necessary amounts and store them in a sealed container for two days max without problem?

2. Can this reduced mix be stored longer if need be (as in: I don't use it all)?

3. Should I just mix as needed each day?
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Old 07-02-2005, 04:37 PM
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Acrylic enamel should store fine reduced, the only thing you'll have to watch out for is pigment settling. Just use extra care and better than normal agitation to make sure you get any pigment settling up off the bottom of the container, then strain well before use. (In this situation, you'd be better off with a good motor-driven agitator rather than just hand stirring. Use care, however to avoid flammability dangers with a motor-driven stirrer). Due to the possibility of pigment settling, it would be prudent to use an extra-fine mesh strainer.

Note for other readers: In contrast to the above situation, a catalyzed acrylic urethane will definitely have a limited potlife, and is a completely different situation.
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Old 07-02-2005, 06:41 PM
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powderbill is correct . As long as it's NOT catylized the paint will stay good for quite awhile. I use AE's for airbrushing and they do settle which will require remixing to get pigment back in correctly. Rember model car paints when you were a kid? Same deal basically.
If you have some Kemwipe's,drop one between 2 paint strainers or a good paper towel,wife's clean old panty hose, anything fine mesh to strain the paint. Being it's only a few day's, a double, fine paint strainer's deal will be good.
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Old 07-02-2005, 08:19 PM
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Quote:
Originally Posted by powderbill
Use care, however to avoid flammability dangers with a motor-driven stirrer).
No problem, I can use the air drill with lower input pressure to slow it down.

Quote:
Originally Posted by powderbill
Note for other readers: In contrast to the above situation, a catalyzed acrylic urethane will definitely have a limited potlife, and is a completely different situation.
I happened to have two ounces of the yellow fully mixed that wouldn't siphon out of the gun, and I was done with painting the hood at the time. It sat for two days and had gelled up about 50%, I had another not-so-noticeable part to need some yellow coloring to it for effect- I strained it and used a 50/50 mixture of that junk with reducer, mixed quite vigorously, and it sprayed OK.

I knew I was pushing the catalyzed mixture, but I blew the entire concoction onto a part that is not that noticeable anyway. Learning experience.

I have determined that I will only need to mix up 1 batch of yellow for the entire job, and the same for the black.

It's 10:15pm now and I plan on at least a couple more hours, besides the wife isn't home yet for dinner (she said to get something out of the freezer, so I think she is in for the long night with me).

She's cool about the hotrod thing, late nights/ all day in the sun/ a couple hours drive/ and NO TROPHY, with another long drive home.
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Old 07-02-2005, 09:22 PM
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M&M,
I'm a tad confused by your comment, and think we need to make sure we have our nomenclature correct in order for the advice to be correct.

Your initial question sounded like you were using a single component acrylic enamel. This would be defined as a colored component which does not use an isocyanate hardner or curing agent. By reduced, I assumed you meant reduced to spray viscosity with solvent only. If this is what you were using, then my earlier advice is correct.

However, your last post made it sound like you were indeed using a 2K or catalyzed product. This would consist of a pigmented acrylic base component to which an isocyanate hardner or curing agent his been added, typically followed by solvent reduction to spray viscosity. If this is the case, then once the viscosity starts to increase too much to spray without adding additional solvent, then it is not a good idea to try to spray the product. The application properties will be relatively poor, and if it gets too far over the hill the film properties such as chemical resistance and adhesion may begin to suffer. How severe this effect might be is highly formulation specific, so its hard to generalize. In any event, for catalyzed products, adding isocyanate curing agent to more material than you can spray within its potlife is to be avoided.

One of the things that makes for confusion in this terminology is that some acrylic enamels can either be sprayed as a single component product or can alternatively be catalyzed with isocyanate and used as a 2K product. The same thing is true for certain alkyd products as well, incidently.
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Old 07-03-2005, 09:04 AM
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I am using Martin Senor acrylic enamel requiring 8 parts color, 4 parts reducer, & 1 part hardener for the yellow but the custom mix to get the color correct to match the rest of the car I have to use the following mix.
5 parts bright yellow pigment, 3 parts (paint shop mixed with as much bright yellow pigment as he could fit in the can to make more "yellow") GM #56 1975 Corvette Bright Yellow, 4 parts reducer, and 1 part hardener.

I use a container with ounce gradations to mix for the spray gun, and a medicine dropper for spraying with the air brush when doing smaller parts not requiring large amounts of paint.

The PPG black I am spraying requires a mix of 8 parts color, 6 parts reducer, and 1 part hardener. I spray the black straightforward as-is so I have no need to play with it's mix ratios.

To reduce confusion further, with the information given above, can I mix the color with the reducer and store it for a short period of time, and add hardener later?
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Old 07-03-2005, 09:27 AM
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Thanks for the clarification, M & M. The component that limits potlife once it is added is the hardner. You can mix the colored base component with reducer and have an indefinite potlife (although you might get some pigment settling).

If you're interested in the chemistry of what's happening here, the pigmented base component will typically contain an acrylic resin with hydroxyl groups on it. (With some acrylic enamels, it can alternatively be an acrylic co-polymerized with other ingredients that give it some oxidizing cure capability). The hardner has isocyanate groups that will react with the hydroxyl groups of the acrylic. These isocyanate groups will also react with water, which is why urethane grade solvents need to be kept dry. The solvents for these systems are typically selected to be chemically inert, that is not capable of reacting with either the acrylic base component nor the isocyanate hardner. That's why you can get away with adding reducer, but not hardner.

Best of luck on your project!
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Old 07-03-2005, 09:29 AM
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Yes you can store reduced paint for awhile if you haven't added the catalyst, as previously mentioned it will require a thorough mixing when you go to use it.
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Old 07-03-2005, 12:03 PM
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That's what I thought but would have rather had at a second opinion.

I fuly understand that the reduced pigments will settle more so than the paint without the reducer.

No problem shaking it up a little more.
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