David G

Well-known Member
I have 2 coats of urethane on a pair of rims. I used 220 between the coats. Would you use 320 or 400 for the finish coat?
 
You should not be spraying and sanding urethane. that;s the old school method for lacquers.
Read the spec sheet on your paint. If you are not using hardeners you need to wait 6 weeks or so to sand and repaint urethanes. I think you had a light tack coat for your first one so you got away with that. You can't put a topcoat on those first two for a long time. That should have been done in 45 minutes.
And when you do sand 400 would be good. Wet.If you see little "balls" of paint STOP. Your paint is not hardened.
 
I color sand and buff the last coat of urethane (1200-2000 grit) on sheet metal, but only to remove the "cooties" that I can't prevent from getting in the paint. Rims have enough roughness in them that you really need to mess up to have to sand them, the cooties are hard to find and blend in with the texture of the metal. Put on 3 normal coats of urethane with hardener with 5-15 minutes between coats, using the right reducer for the temperature and they will be nearly perfect. As Gordo says sanding between coats is reserved for lacquer, IMO the worlds worst paint. Also if you sand single stage urethane you can remove the clear in it which gives the UV protection, as it "floats" to the top. Since I usually have to sand, I use base-clear, which give a better finish and the ultimate in UV protection.
 
In single stage the clear is added to the paint during mixing (by the dealer) according to specifications given by the manufacturer. In base clear, the base is dull when applied, the clear is applied over the base and brings out color. That system has been used on all cars and trucks since the late 80's, was probably around before that. It adds one more step to the painting, but is worth it to me. If you can keep the crud out in your painting enviornment, you really don't need base-clear, except it does give a somewhat brighter finish, probably the most important feature is the added UV portection. You can also put clear over single stage, but I see no advantage to that when compared to base clear. I believe you can add more clear to single stage in the last coat, also.
 
Next time, shoot a good coat of epoxy primer on the sandblasted parts. Maybe some light block sanding if you have some orange peel. Then a good heavy coat of high build primer. Block that down to the epoxy with 360.
Now shoot a tack coat and then topcoat withinn 45 minutes of your urethane. And have the paint store print out the app sheets for you.
 
I wouldn't sand the urethane between coats. I sanded these wheels and then sprayed them with an epoxy primer, then sprayed them with a surfacer and then used acrylic enamel with about 3 coats. Hal
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Not trying to Hi-Jack the thread, but this is what I use for primer (recommended by Auto Paint Store). I put 2 coats down, and then wait a few days....around a week minimum, to take and Wet-Sand it with 320 paper. Once that is done....wash with soap and water. After it's dry I paint it with Acrylic Enamel with Hardener (Case/IH Ironguard or Valspar...just whatever I have on-hand).

Is this the right method to use? Is that a good primer to use? Am I sanding the right way and in the right times? I get a decent to good finish.....still not like a mirrored glass finish though.



(reply to post at 21:39:13 12/05/12)
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PPG Omni epoxy can can have surfacer or topcoat applied after 30 minutes. Surfacer over the epoxy I usually wait until the next day to sand, although it can be done the same day. The Omni MP 182 surfacer uses hardener, thus it is sandable very soon. Up to you but you are wasting time with the products you are using. Use quality products from PPG, DuPont, Martin Senour, etc and follow the spec sheet. They ALWAYS work as long as you follow insructions. Yes they are expensive, and some of them require supplied air to protect your lungs, but you get what you pay for. CaseIH does not sell acrylic enamel, it is an acrylic modified alkyd enamel, it's ok but not as good as urethane.
 
@RTR, You might want to try using 400 grit before your topcoat. It should help your gloss retention. 320 is a little too coarse unless you are hardblocking out imperfections in your metal or primer and you are going to recoat.

Acrylic enamel has less viscosity than the synthetics and can open up your sand scratches a little. You probably won't see it with your eye, but it kills gloss retention. Also the Acrylic enamel reducer has a little more bite than the older synthetic enamel reducer. That bite from the reducer can also react on larger sand scratches.

If you are using urethane you should be using 400 or even 600 as a final sand or you might see sand scratches in your base under your clearcoat. .02
 
Thank you !!!


(quoted from post at 21:20:48 12/07/12) @RTR, You might want to try using 400 grit before your topcoat. It should help your gloss retention. 320 is a little too coarse unless you are hardblocking out imperfections in your metal or primer and you are going to recoat.

Acrylic enamel has less viscosity than the synthetics and can open up your sand scratches a little. You probably won't see it with your eye, but it kills gloss retention. Also the Acrylic enamel reducer has a little more bite than the older synthetic enamel reducer. That bite from the reducer can also react on larger sand scratches.

If you are using urethane you should be using 400 or even 600 as a final sand or you might see sand scratches in your base under your clearcoat. .02
 

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