Primer and topcoat in the same session?

Discussion in 'Techniques' started by neil_w, Mar 31, 2017.

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  1. Mar 31, 2017 #1

    neil_w

    neil_w

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    Can I safely lay down one (or even two coats) of primer and then do the top coats in the same session? If I leave (say) 10 minutes between coats, I have plenty of time to apply all necessary coats within the recommended recoat window of 1 hour. All paint would be Rustoleum, so there should not be compatibility issues.

    A related issue is spraying a shot of clear or base color to seal the masking tape before applying a second color coat. I would certainly *want* to do that all in the same session.

    I asked Rustoleum directly about this and they seemed to say this was OK to do as long as I stay within the 1 hour window, but their response was a bit cryptic so I'm not quite sure what to make of it.
     
  2. Apr 1, 2017 #2

    Woody's Workshop

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    Primer typically requires sanding for proper adhesion.
    If it's lacquer based, you can use a lacquer based adhesion promoter.
    I've used a cold lacquer thinner spray before to create adhesion on hard to sand areas like on door jams and hinges.
    What is the purpose of the primer if your not sanding out imperfections? If you don't mind me asking?
     
  3. Apr 1, 2017 #3

    neil_w

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    I'm not convinced that the purpose of primer is specifically to sand out imperfections. That would be true for filler/primer, but not the regular stuff. Anyway, I have two separate circumstances in mind:

    1) My upscale Quinstar. This is a mixture of bare balsa, basswood, and papered parts. Although I painted my regular Quinstar as recommended by JumpJet (no primer, just a few coats of paint, for lightness), I believe this one needs some primer to ensure a consistent topcoat given the varied surfaces. I also note that Rustoleum (I think?) specifically recommends primer when painting on bare wood. I wasn't planning to sand the primer; there are many nooks and crannies in that crazy thing that are nigh unsandable. There are a few areas that could be sanded, conceivably, but certainly not the whole thing. Anyway, if I'm *not* going to sand, then it would be nice to do two light coats of primer and then go right to the topcoat. If that works.

    2) Starship Avalon (see my avatar). This will have a black basecoat followed by a set of fluorescent green highlights. For the green, then, I must mask the heck out of the rocket, then I will spray a coat of clear to (I hope!) seal the masking tape, then one or two light coats of white (not necessarily primer, maybe just regular white paint) then the green. In this instance, there is *absolutely* no sanding during this sequence. If I'm disciplined, I believe I could do all the necessary coats within an hour. Alternatively, I'll need to do the clear and the white, then wait at least a week or until next painting opportunity to do the green. I'd prefer to get it done all at once. If that works.

    Note: I have thought about it a lot, and it is not practical to do the green before the black on the Avalon, in keeping with the theory of starting with the light colors and finishing with the darker. I have done a test and a layer of white followed by a couple coats of green looks great on top of the black. Wait, I have a picture of that somewhere.... ah yes here it is. It's very messy because it's all done by hand, but it proves the point.
    [​IMG]
     
  4. Apr 1, 2017 #4

    CORZERO

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    Maybe try it out on a test panel and then decide?
     
  5. Apr 1, 2017 #5

    manixFan

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    I have done it with Duplicolor primer and paint on the same day, if that counts. The weather has to be right. The Duplicolor primers are lacquer based with can be top-coated with either lacquer or enamel. Some dry in as little as 12 minutes.

    I've shot primer, let dry, wet sanded, let dry, hit it will surfacer, let dry, and hit it with topcoat all in the same day. Generally I'll try for a day when the temps are near the top of the range - high 80's and humidity is in the 50-60% range. I've pushed it in the low 90's if the humidity isn't too high.


    Tony
     
  6. Apr 1, 2017 #6

    jimzcatz

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    In short, absolutely. I prime, sand, paint, wet sand, and paint second coat, all the same day. Allowing days between coats is totally unnecessary.
     
  7. Apr 1, 2017 #7

    blackjack2564

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    Yes I do it also with rattle cans.
    Prime & top coat all done in an hour. Soon a primer is tacky..on goes finish.
     
  8. Apr 1, 2017 #8

    Nathan

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    For all wood surfaces the primer should be sanded. After spraying primer, shine a flashlight across the fins at a low angle. You will probably see a lot of grain. Sanding after primer gets rid of some of that and makes the surface smoother before painting.
     
  9. Apr 2, 2017 #9

    neil_w

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    I decided to try it. 2 coats of Rusto 2x white primer follows by two coats of Rusto blue metallic. Looks ok while wet, we'll see how it dries.
    ImageUploadedByRocketry Forum1491165850.476536.jpg
     
  10. Apr 3, 2017 #10

    hornet driver

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    Yea, I've done it before as an experiment.It does work. That whole wet over wet over wet thing. The initial product can look really good if you avoid runs. The down side comes a month or so later as the product finally begins to cure ALL THE WAY. The paint shrinks over time(don't know how many times I've said this).( ANY ) flaw you had before will re-appear.
     
  11. Apr 3, 2017 #11

    farsidius

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    Also, look at the directions of the paint too. I'm not in my garage right now, but I know that I have some primer that specifies something like "apply topcoat within one hour of drying to the touch or after 24 hours" So, definitely may have some options.
     
  12. Apr 4, 2017 #12

    Micromeister

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    I've said it before I'll add it here again.

    Finishing: Any Finishing takes much longer then the building or construction. When in finishing mode: Haste always makes Waste! What's the hurry? Primer should be applied, allowed to "Sniff Test" dry, Dry Sanded to no finer then 360grit. Then, and only then should a base and/or color coat(s) be applied.

    Rushing to apply High Gloss Color coats; as the unlaying primer begins to cure in a week or so, the color or base coat(s) having trapped the outgasing thinners and solvents usually crack, craze or wrinkle.

    Truely: It's YOUR Rocket so finish it however you wish.. Just be fore Warned! Haste in the Finishing phase of a build almost always makes Waste.
     
    Last edited: Apr 4, 2017
  13. Apr 4, 2017 #13

    neil_w

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    I was willing to take a risk with this one, we'll see what happens. Rustoleum (company) implied it should be OK, but time will tell. Total application time for all four coats was about 50 minutes.
     
  14. Apr 4, 2017 #14

    Marc_G

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    Back in my lacquer paint days, I did what you propose, with usually good results. I was careful to keep it to one coat of primer, one thin and one medium coat of color, and then lacquer based clear. Listen to what John said though: you risk shrinkage and cracking when the thick paint layers finally finish out gassing and get fully hard (brittle). I had some instances of this in corner-type places and even a couple tighter fillets. Flat surfaces where I was careful no problem. All of this experience was on top of well dried / sanded Rusto auto filler primer. I used a white lacquer-compatible primer, and lacquer color coats, and lacquer clear.

    I learned the hard way not to put lacquer over enamels, but also I found it's bad to lay down enamel over WET lacquer. You will get odd effects, sort of like fish eye on steroids. Actually I considered doing this purposefully with black lacquer base and blue/green/orange metallic enamels to get a weird organic skin looking effect.

    In the end I switched to water-based acrylics and never looked back.

    Marc
     
  15. Apr 4, 2017 #15

    neil_w

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    I will post back my results here in a month or two, good or bad.
     
  16. Apr 17, 2017 #16

    neil_w

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    At the two week point, the paint appears to be curing just fine, with no unwanted crinkling. Only visible problems are due to my crappy rattle can technique, couple with a metallic paint that likes to run a bit.

    Of course, things could change as it continues to cure but I've personally never had anything change noticeably after about a week. For now I'll call it a success.
     
  17. Apr 17, 2017 #17

    Trident

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    I'm with Micromeister on this one. I often spend more time on painting than building.

    I'm not sure why you'd even bother with primer if you're not going to let it dry, and sand. Just go for the final color you want.
     
  18. Apr 17, 2017 #18

    neil_w

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    The metallic paint instructions specifically recommended primer if painting on bare wood.

    This technique is not one I expect to use often (or maybe even ever) but it seems to have worked out OK this time.
     
  19. Apr 19, 2017 #19

    SCIGS30

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    Well, after letting the nose sit for a few days, the red was getting worse so I decided to strip the paint. I used Testors ELO and that stuff worked great, the paint just peeled right off. I then sanded the nose cone to roughen it up and now she is ready for paint. Looking at the model cars forums this seems to be an issue over there and there is an article on this subject. The cure is to use black primer, allow to off gas followed by grey primer and allow to off gas. Then I will shoot flat white followed by glossy white. This is definitely going to set me back on my finished project but the pink nose was going to bother me.
     
  20. Apr 19, 2017 #20

    neil_w

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    Wrong thread? :)
     
  21. Apr 19, 2017 #21

    AfterBurners

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    I totally agree...what is the rush? It's not like you're gonna launch tomorrow. I've seen so many people on here build this awesome rockets and then rush the finishing only for it to look terrible.
     

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