Primer or sealer after sanding car in 220

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PostPosted: Wed Aug 21, 2019 8:00 pm
If covering with a two pack high build primer then P220 (even P180) is no real problem. The primer won't shrink back into the scratches. But, using just a sealer (even a "high build") over P220 is, in my opinion, fraught with danger.

Sealers are intended to go on thin and just provide intercoat adhesion and (in some cases) shading. They're generally not designed to fill big scratches and they're not intended to be sanded, so any scratch marks can, and will, show through.

P400 really is the best base for a primer or sealer. Old school was that your bodywork needed to be good because the primers didn't have the hardening or the solids content that they have now. The high build of current generation primers means that you can block out imperfections and get a really nice finish that in the old days had to be in the metalwork or filler.

In the case of OP in this thread, his plan was to just sand with P220 and then seal and paint. No problem if the panels are new or perfect but they wouldn't be, so the consensus recommendation has been to high build and block back down, taking out all those little imperfections that would have spoiled the job. Unfortunately his inexperience got him in the end with a load of dust, so his primer/sealer needs to be sanded anyway. I expect that it won't be thick enough to take up all the variations in his panels so he'll end up with a very ordinary job unless he bites the bullet and high fills over the sealer, before guide coating and blocking down. A lot of extra work that I think he was trying to avoid, but painting just doesn't work like that - the quality of the job is highly dependent on the quality of the preparation.
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PostPosted: Wed Aug 21, 2019 10:49 pm
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PostPosted: Thu Aug 22, 2019 7:47 pm
Thanks for the explanation. Even though I've been more or less out of body and paint for about 15 years or so I've kept my fingers in it and I wanted to make sure I still had a general idea of how to do it correctly. When I started we had acrylic lacquer and synthal enamel. I loved to paint and learned to do body work just so I had something else to paint. I appreciate your answer. Thanks



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PostPosted: Mon Sep 09, 2019 6:46 pm
NFT5 wrote:If covering with a two pack high build primer then P220 (even P180) is no real problem. The primer won't shrink back into the scratches. But, using just a sealer (even a "high build") over P220 is, in my opinion, fraught with danger.

Sealers are intended to go on thin and just provide intercoat adhesion and (in some cases) shading. They're generally not designed to fill big scratches and they're not intended to be sanded, so any scratch marks can, and will, show through.

P400 really is the best base for a primer or sealer. Old school was that your bodywork needed to be good because the primers didn't have the hardening or the solids content that they have now. The high build of current generation primers means that you can block out imperfections and get a really nice finish that in the old days had to be in the metalwork or filler.

In the case of OP in this thread, his plan was to just sand with P220 and then seal and paint. No problem if the panels are new or perfect but they wouldn't be, so the consensus recommendation has been to high build and block back down, taking out all those little imperfections that would have spoiled the job. Unfortunately his inexperience got him in the end with a load of dust, so his primer/sealer needs to be sanded anyway. I expect that it won't be thick enough to take up all the variations in his panels so he'll end up with a very ordinary job unless he bites the bullet and high fills over the sealer, before guide coating and blocking down. A lot of extra work that I think he was trying to avoid, but painting just doesn't work like that - the quality of the job is highly dependent on the quality of the preparation.


Hey, So when I shot the sealer, I gave it two semi-strong coats. I really made to lay it on in the second coat. According to the HOK technical sheet, the ratio I used yields a high build sealer, or a medium build surfacer. I let the primer cure for a week before guide coating and sanding with 400, and I'm very happy with how smooth the panels came out. I did hit bare metal in some spots, and I plan to redo the body filler on my passenger side front fender. I also plan on reshooting high build primer on the passenger front fender, then guide coating and blocking with 400, then shooting base. My question is; should I be good with shooting a light coat of sealer over all my panels before base, or should I do another coat of high build primer? basically, is it okay that i hit bare metal in some areas after blocking my guide coat. Thanks!

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PostPosted: Mon Sep 09, 2019 9:17 pm
That depends whether the metal is higher than the surrounding filler or primer. If higher then it needs to be knocked down a tad and probably skimmed with filler, then primed/sealed. Guide coat should tell you what the situation is.

Once you have it straight then a light coat of sealer will be fine. It's what I was saying above. Too many thick coats of paint may look good to start with but won't last. The trick is to get the substrate straight first and then keep the paint thickness as low as possible.
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PostPosted: Sat Sep 14, 2019 9:43 pm
FWIW I am doing a repair on a Mazda 3. I sprayed 2-3 coats of high build primer then wet sanded with 320 and durablocks. I thought it was perfect. I then applied guidecoat and sanded with 400 grit. I was shocked how much more sanding it needed and even found a door ding and a hail ding I had previously missed. After fixing these I eventually wet sanded to 600 grit. Then base and clear. Although there is clear coat orange peal left to deal with, the body work looks absolutely perfect. The moral of the story is guide coat is essential and also lets even a beginner like me achieve perfect bodywork. Do not neglect this step.



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PostPosted: Fri Sep 20, 2019 3:11 am
David Edwards wrote:FWIW I am doing a repair on a Mazda 3. I sprayed 2-3 coats of high build primer then wet sanded with 320 and durablocks. I thought it was perfect. I then applied guidecoat and sanded with 400 grit. I was shocked how much more sanding it needed and even found a door ding and a hail ding I had previously missed. After fixing these I eventually wet sanded to 600 grit. Then base and clear. Although there is clear coat orange peal left to deal with, the body work looks absolutely perfect. The moral of the story is guide coat is essential and also lets even a beginner like me achieve perfect bodywork. Do not neglect this step.
NFT5 wrote:That depends whether the metal is higher than the surrounding filler or primer. If higher then it needs to be knocked down a tad and probably skimmed with filler, then primed/sealed. Guide coat should tell you what the situation is.

Once you have it straight then a light coat of sealer will be fine. It's what I was saying above. Too many thick coats of paint may look good to start with but won't last. The trick is to get the substrate straight first and then keep the paint thickness as low as possible.

Yeah after looking at the guide coat on my "repaired" fender I was very unsatisfied. ended up redoing the bondo and it looks a lot better now. Plan to do a little more body work on the rear bumper then prime/guide again before sealing and base. Prep on the rest of the car is something I'm proud of. I'm glad I guide coated.
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