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Old 06-17-2010, 04:40 AM
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Clear coat on old paint

Hi can anyone help ? are you able to shoot clear on paint that has been on for 2 to 3 months ? will a light sand say 800 grit do the job, ready for a clear coat ? do I need to use a cleaner to help get rid of any unwonted Greece and grime from the roads?

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Old 06-17-2010, 10:22 AM
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If the old paint does not have clear on it, you will sand with 400, then shoot more color on top. You never want to sand a color before clearing. If you have to, then always shoot another coat of color before the clear, or you may end up seeing splotches where you sanded.

Assuming the paint on there is good quality, and already has some clear on it....

First wash it down with wax and grease remover.

Sand with 600 or 800.

I would recomend you put on a thin coat of Dupont 222S clear adhesion promotor 30 minutes before you start spraying clear. It is very thin, so you just want to mist it on.

Follow with 2-3 coats of catalyzed clear. Allowing that brands drying time between coats.

If you have runs or dust, find out how long it needs to dry before you can sand those out and buff. Depending on the brand and conditions.... this can be anywhere from "overnight"... to a couple months later!!! (PPG Concept) ....unless you can force dry it at a body shop.
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Old 06-17-2010, 10:35 AM
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Quote:
Originally Posted by TucsonJay
If the old paint does not have clear on it, you will sand with 400, then shoot more color on top. You never want to sand a color before clearing. If you have to, then always shoot another coat of color before the clear, or you may end up seeing splotches where you sanded.

Assuming the paint on there is good quality, and already has some clear on it....

First wash it down with wax and grease remover.

Sand with 600 or 800.

I would recomend you put on a thin coat of Dupont 222S clear adhesion promotor 30 minutes before you start spraying clear. It is very thin, so you just want to mist it on.

Follow with 2-3 coats of catalyzed clear. Allowing that brands drying time between coats.

If you have runs or dust, find out how long it needs to dry before you can sand those out and buff. Depending on the brand and conditions.... this can be anywhere from "overnight"... to a couple months later!!! (PPG Concept) ....unless you can force dry it at a body shop.
the adhesion promotor, do u have to sand the surface before applying promotor? any thoughts in bull dog adhesion promotor? compared to duponts
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Old 06-17-2010, 11:25 AM
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jeetkunedoground, thanks for that just the advice I needed
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Old 06-17-2010, 11:58 AM
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jeetkunedoground, thanks for that just the advice I needed

oh! thats TucsonJay advise but i wish i made that advise
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Old 06-17-2010, 12:02 PM
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Bodyshops spray clear over existing old paint everyday.
Anytime they blend into a panel, clear is extended onto the old
existing clear and all that is ever done to prep it was to
take a gray Scotchbrite pad and scrub the panel down first real
good. I've never seen an adhesion problem when done this way.
As long as it's clean it adheres just fine.
It's standard practice.
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Old 06-17-2010, 03:47 PM
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doe sorry TucsonJay thanks anyway mate !!!!! just put down the clear coat and it's looking good !!
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Old 06-17-2010, 05:36 PM
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Depends on what paint is on there. If its a clearcoat finish, it could probably be sanded, and new clear shot over the existing clear. This is basically how majority of repairs are done in a bodyshop these days. Base color is sprayed over the repair area, and blended into the existing paint for match, then the rest of the panel cleared, so essentially part is only clear over old sanded clear. But manufacturers might really skimp on material (not all but some may not really have much clear on there to play with) and could break thru the clearcoat into the base color, then more color would need to be sprayed first, at minimum over any break thru areas. Be real carefull around edges and corners when sanding. When doing a repair, areas that will only be receiving clear, I usually wetsand with around 800. Some go courser then this, while others finer. I never use an adhesion promotor, never needed it, do a thorough job sanding and you shouldn't have a problem, I never did.

If its a singlestage, no clearcoat on it and when you sand your sandpaper turns the color of the car-instead of white like clear when its sanded, then probably real iffy if you just cleared without spraying more color first. Metallics and pearls really not advisable, the sanding will most likely disturb the metallic, leaving you with a blotchy or streaked appearance. If a solid color, maybe, but same thing could happen where the eveness of the color is effected.

If the clear coat is failing, leaving the base exposed, no you cannot just clear over it, it should really be stripped at least down to the primer and more color and clear applyed.
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Old 06-17-2010, 06:36 PM
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I recommended the adhesion promotor as "an insurance policy" to ensure the best possible chance to avoid problems. Not everyone does it, but I don't like to paint things twice, so I do it for "peace of mind".

The bulldog seems quite different from the DuPont 222S.

The dupont is very thin... like lacquer thinner. It seems to really penetrate the sanded surface, and leaves a thin coating that almost anything will stick to.

I have used the Bulldog on flexible plastics like quads. It is thicker, more like paint. Of course the big advantage on those is that it is not only an adhesion product, but when added to every layer of paint, it chemically crosslinks each coat, AND makes the entire paint job flexible "top-to-bottom"!

...of course you don't need that on this project.
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Old 06-18-2010, 02:41 AM
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I put down a pearl finish but was not able to shoot the clear coat right away, now it has been 3 months can i just shoot the clear or do i have to start again?
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Old 06-18-2010, 06:38 AM
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NO. This is a basecoat right? If by chance its an unactivated enamel product, then other possible problems could occur on recoat.

Read the tech sheets for the product you are using. These answer a lot of questions on how to properly use the product, and should be read because there is a lot more information then you'll ever find written on the back of the can.

After so much time, most base coats I've seen say something like 24 to 72 hours, it would need to be scuffed well and reapplied and then cleared within the open time window stated. Plus you can't just sand a pearl (without a clearcoat already over it that your sanding protecting the pearl) and clear over it, you would have to shoot another coat or two of color before clear, or the color would look uneven from the sanding.

If it happens to be dupont or sw brand you used, check out these threads and make your own decisions (get a little heated) if you should go further then just sanding and reapplying the base before clearcoating.
Clearing Chromabase Base Coat
Interesting test on sanding base coat paint (against the data sheets recommendation)
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