Hood prep, primer, sanding help needed.


Apr 3, 2005
I am starting this thread to get some insight on proper procedures dealing with sanding primer. I have an aftermarket hood that I scuffed up, wiped down with grease and wax remover, tack raged it etc. but I am having problems with sanding down the primer that I have sprayed on using many coats with an HVLP gun. Should I have prepped the hood with something else? On the side of the cheap-o spray gun it says 20 psi max. This might have something to do with it. Is 35-40 psi max more like it? I have a huge compressor to push the paint through the gun. I think I need to invest in a better gun. Any recommendations? The tip from what I can read is a 1.7. A 1.4 to 1.7 is okay for Primer right?

In the pictures as an experiement you can see what grit paper I used and what the primer was doing to the sand paper. I also used guide coat to help me along. Long story short, the 180 grit on the DA was doing much better than the 320, 220 on the sanding blocks and 240 on a non DA air in line board sander. ( I just had to try it). I blocked the primer using Dura Blocks. I used the "X" pattern and the paper in a matter of 3-6 strokes builds up the primer in small balls or rolls up into foot ball shaped pieces and sticks to the sand paper and it sounds like small rocks digging into my hood. I have to use a lot of compressed air to remove the small chunks from the paper to move on. I did let the hood dry over night and even in one case for a week. Still got the same sanding results.

I am testing with Dupli-color paint system and the lacquer primer they offer. This might be the problem too. I have tried to find PPG Shopline JP 285 primer which I have read works well. But I can't find it in Portland/Vancouver so here we are. I don't know a lot about primers, reducers, urethanes, and mixing ratios but the JP 285 is a urethane high build surfacer and I was wondering if I do find this procuct or an equal substitute will it go over the lacquer Dupli-Color primier? Or will there be a bad reaction? Can someone recommend a good high build primer for a beginner to experiment with? With most primers you have to use a hardener?

So I have asked an expert in body and paint to look at this thread also, give his insight and some pointers. This is not just a thread me but for everyone that reads this that wants to learn and practice body and paint. I can't get over the exceptional work this guys does, his name is Jeff and I only hope my work comes out half as good as his. His son's Mustang looks amazing and his 03 Cobra will look great very soon too. Reading his threads is better than watching any movie I have seen in a long time. Iron Man 2 comes out tonight so you might be in trouble Jeff.


Black 1991 GT - complete refinishing thread - Corral Forums

All over refinishing of a DSG 03 Cobra - SVTPerformance










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Ben, thank you for the kind words. I don't really think I am much of an expert. There are many painters working in the field every day that would run circles around me. I like to think I know just barely enough to get into trouble with a few tools.

I have not worked with the primer you are using but I bet that is the problem with your sand paper loading up. Many surfacers will be marketed as "easy cut", I would look for something along that end. The professional products will work much better than many of the over the counter items at the local auto parts store. I have used some of those types of primers and had similiar issues with paper clogging.

I think you are on the right track. I would try to stay away from the laq. primers if possible as they will shrink and are not as durable as the ones that use hardners. Unless you will be using a laq. base paint. If that is not possible try Dupont Fill & Sand. That primer cuts like butter and can be purchased at a fair price. A good primer will set up quickly and can be hand sanded without clogging within the hour. The paper will still load but not to the extent you are talking about. I like to hit the paper with a soft sanding block several times to loosen the primer that is sticking to it.
1 thing to do is loose the lacquer primer. Its shrinks and doesnt have enough build. You need a good 2K primer.

I would start by sanding off all the old primer with some 180 on the DA, Wipe the hood down, spray 3 coats of 2K primer.

Let it sit for a few days to dry and shrink. A week would be best. Mist it with some black spray paint then start blocking with a long, hard block by hand with some 180 grit. Stop sanding before you cut in to the fiberglass's gel coat. Ant black spots left are low areas and need either a 2 part putty ( I like EverCoat metal 2 metal) or more primer if its not that deep., spray a few more coats of primer and block again with 320, There shouldnt be any low spots this time and you can either spray over the 320 marks or spray a few thing coats (thing the primer out with reducer) and wet sand with some 600.
I second loosing that laquer primer. That stuff is JUNK!!! It balls up on the sand paper, it will not flatten out, and it shrinks like crazy still months after your paint job. I would get some Nason 2K Urethane primer. It's an activated primer that sprays thick and sands so so nice!! Keep on blocking and priming.
Ha. Just got back in town will hit the hood this weekend. I did play with the new primer and it fell off like baby powder. So much better to work with. I will post pics this weekend too. That lacquer crap just wasn't cutting it for me. I still need to work on setting up my cheap-o paint booth.
Thanks I will deff. try the Nason 2K Urethane next time. Always looking to try new stuff and learn. Yeah the U-Poll just fell off and didn't ball up at all.




Will post more pics of progress when available.