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Building Tips and technical articles. => Paint and finishing => Topic started by: Clint Ormosen on February 27, 2009, 06:43:41 PM
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I'm under a time crunch to make it to VSC (as usual). How long should I let the color dopes cure before shooting the Omni clearcoat? I know there is probably an ideal amount of time, but I need to know what the minimum safe time is. Thanks.
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I don't do auto paint but from what I've read it's hours.. The colors seem to dry pretty fast and won't even look good till the top coat is on.
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Clint,
Good question. I shot the catalyzed clear on my Cobra about 2 hours after finishing the trim colors (trim color in dope). Like you, I was in a bit of a time crunch. Seemed to work fine and the finish, while it had all sorts of other wonderful problems, didn't seem to suffer from this. Ideally, I'd want to wait a bit of time, maybe a couple of days to a week, to allow the lacquer to gas off a bit. But it hasn't seemed to be a critical issue.
Maybe Mark will chime in on this.
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Boy, I was guilty of what I see allot on the forums.. Not reading the question throughly... Ya over dope I would wait several days..
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You can shoot as soon as its dry (4 or 5 hrs). I have done it with no problems. Results may vary according to experience.
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Thanks guys, that's what I needed to know. 8)
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When I use Brodak dope I wait 7 days. Once I put the auto clear on after 3 days & it bubbled all over.
Sig is different. Takes longer to gas off. I wait 21 days.
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one very important thing people tend to forget with air dry products,, well all products actually is the rule of 15,, if its 15 degrees cooler it takes twice as long to dry, if its 15 % higher humidty it takes twice as long to dry. To make across the board statements about dry times without taking into account the number of coats of material, the temp , the solvents, and the humidity is a bad idea!!!
Ok so to anwer the question, first statemtent,, ( i have to say it) urethane over clear isnt a great idea,, but,, if your going to do it,, then, I would test my laquer for being dry enough by lightly scuffing a spot of solid color , the last color sprayed,, you shouldnt really smell any solvents after you lightly scuff it. think scratch and sniff,, In other words, take some 600 grit paper and smell a small spot, then scuff it wet, dry it and sniff again, there should not be an appreciable difference in the aroma.
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Mark, so you're saying that I should not shoot a coat of clear dope over the plane after all the trim is done? Just shoot urethane directly over the color dope?
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While I would never think of disagreeing with Mark ( ;D ), I would shoot a highly thinned coat of clear over the colors. It tends to lock things down and keeps unpleasant things for happening. I've done this without problem (now, if I could just keep bats out of my shop, I won't have 3 coats of catalyzed polyurethane on planes and they won't weigh a ton).
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Ok so I knew what I was saying even if I didnt say it,, sigh,, something about having a fever for the last three days,, maybe?
Ok so what I meant to say is my same old mantra about mixing products,,, laquer and urethane,,, so what that sentance should have said was,,,
""Ok so to answer the question, first statement,, ( i have to say it) urethane over DOPE isn't a great idea,,
but,,""
Yes I agree that putting a coat of clear laquer/dope over the top of your colors IS a good idea definitely. I totally agree with what Randy said there.
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I admit my data base is small.
I have built 9 stunt planes using dope then Dupont Nason clear top coat.
My 3 day wait burnt me. Bubbles started once the plane sat in the hot summer months.
The planes I waited to gas off, no bubbles.
If you live in a desert, start clearing. Otherwise wait a bit.
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OK guys, I think I got it. I'll wait as long as possible to shoot the clear.
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You can also use the rule of 15 (although I aalways heard 10) to your advantage.
If you can raise temperature and/or lower humidity (within reason), outgassing will happen faster.
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You can also use the rule of 15 (although I aalways heard 10) to your advantage.
If you can raise temperature and/or lower humidity (within reason), outgassing will happen faster.
That's what I'm doing. I have the shop at about 80 deg (or pretty close to it) and am letting the plane sit for as long as I can. The "lock down" coat of clear was shot 2 days ago.