Sanding Grit Progression

[61 Silver]

The 65 is stripped of its Glen green Lacquer. The polly-fill and the original GM (red) primer are left. I tried to block the lacquer off (220G) but started to sand trough to the fiberglass and stopped (hood only). Some of the polly-fill edges lifted during the stripping process so I am currently block wet-sanding the entire car with 200G-wet/dry paper. What should be the progression of grits and finial grit prior to re-finishing? Is there any other hidden problems or correct procedures that I should look for (follow) before I start the paint process AGAIN!



John M. and Paintdaddy help would be appreciated.

Ray

 

[John Mcgraw]

Ray,

I would not stop at the primer. I would take it all the way to bare glass.
I just would not trust the primer that has had stripper soaking into it. I feel pretty strongly, that once you start stripping a car, you should not stop until you see bare glass.


Regards, John McGraw

 

[IH2LOSE]

Ray how did you get the green (top coat) off? did you paint strip it? or block it off.

 

[61 Silver]

re-paint 65

IH2LOSE



I started by block sand using 220-Grit wet/dry. I was not happy with the results, so I stripped the entire car using fiberglass safe stripper. The stripper removed everything except the polly-fill and the original GM red primer. I wash the car thoroughly with lacquer thinner and have started to sand off the polly-fill and most of the original primer. I would like to know if I could go courser than 220-grit to remove the polly-fill, I worked for over 6 hour today and only have the top of the front fenders and the hood done. After removal of the polly-fill, what should be the progression of grits prior to primer?



Thanks for any help!



Ray

 

[IH2LOSE]

Ray with the history of this car poping thru the paint all ready,I would highley recomend that you finish with the chemical stripper and get this car down to bare glass. Then let it gas off in a heated garage. I say heated because I am not sure if its an old wifes tale or not,but I have heard if your below a certain tempiture the chemicals are dormant and will not pull out of the glass.

How many time have you heard of a car being painted and then brought out in the sun only to have solvents come back out.

I think it will take you forever to sand thru that poly fill by hand.

 

[Tom Bryant]

Also sanding has the potential of rounding over sharp edges like the fender peaks and door edges. if any paint or primer is lifting at the edges when you try to feather it, it must be removed. If you don't it will do it for you at a later date. I would never paint over any paint, primer or spray filler that had stripper on it. If you start to use stripper the only place to stop is the bare glass.

Also follow the strippers instructions on how to thoroughly clean the stripped surface before priming. Whatever you do to wash the glass down go to the Home Depot or Lowes and get a few of those cheap clamp on heat lamps. It really is unlikely that you will ever get the glass too hot considering how hot this stuff is when it is press molded. The heat lamps will drive out any solvents or moisture in the glass..

I use heat lamps to quick cure fiberglass repairs. Just lay it up and put the lamp on it til it gets too hot to touch. Let it cool and you're done. You will be able to tell if it's about as hot as it would be sitting out in the midday sun during a summer car show. That will be good enough.

tTm

 

[paintdaddy]

I would sand the rest off with a da sander (held flat ) with some 100 grit or 180.The chmical stripper soaks into the fiberglass like a sponge sometimes and I think thats where the problems start most of the time.From there put some epoxy primer down to seal off everything then do any bodywork thats needed then poly fill.Just my 2 cents.

 

[vette]

I have always (20 years now) finished taking the red primer off with coarse steel wool or scotch brite pads. Put a thin coat of stripper on a small area at a time and scubb off with steel wool and warm water. The water will break down the stripper. I never had any paint problems doing it this way. Sanding can ruin edges and body lines real easy. Even pros ruin a line or two. When you have the car down to bare glass clean with warm water. Then I like to sand the car with soft pads with 100 grit. This gives your primer good tooth. And then prime and keep on sanding. And as stated above before you prime let the car sit in the sun or some type of heat source. These cars where cooked at 250 when the where built. The more heat the better, and as long as possible.

 

[John Mcgraw]

I agree with Vette. That is the way that I allways remove the primer, A scotchbrite pad and a little stripper. Scrub until you see bare glass, and then scrub the bare glass with warm, soapy water after the stripper is all gone. I then follow with a lacquer thinner wash after it is dry. It is labor intensive, but better than rounding off the sharp edges with sandpaper.

Regards, John McGraw

 

[61 Silver]

Ready for primer?

I agree with Vette. That is the way that I allways remove the primer, A scotchbrite pad and a little stripper. Scrub until you see bare glass, and then scrub the bare glass with warm, soapy water after the stripper is all gone. I then follow with a lacquer thinner wash after it is dry. It is labor intensive, but better than rounding off the sharp edges with sandpaper.

Regards, John McGraw

Hi! John,



I have been reading many post on this and other sites on sanding grit progretion prior to primer. Through my readings I respect your views and application the most. Could you please correct the procedure that I have followed to this point;



1. Stripped using fiberglass friendly strip

2. Washed with hot soapy water

3. Washed with lacquer thinner

4. Sanded 80 grit dry

5. Sanded 120 grit dry

6. Sanded 150 grit wet

7. Sanded 180 grit wet

8. Sanded 220 grit wet

( I have sanded for so long that I have no fingerprints left, some fingers are bleeding and my arms feel like they want to fall off)

9. Wash with warm soapy water

10. Dry in heated garage



Should I use the heated spray booth to insure that the fiberglass is completely dry and if so, at what temperature and for how long.



This will be my first attempt at painting with something other then lacquer. I will be using PPG, what products and procedure would you recommend?



Thanks for all your help!

Ray

 

[John Mcgraw]

Hi Ray,

I like PPG DCC (Concept) for a single stage urethane. I think that if you want a finish that looks like lacquer, then a single stage urethane is pretty tough to beat. A lot of people use K-36 PPG primer, but I have used NCP-271. I don't think that there is any real difference in the primers, the NCP product is a self-etching primer that is used on metal panels. I paint both glass and steel panels, so it has just been easier to stick with only one product. Both of these products are high-build primer/surfacers, and will block down nicely. I have used other products over the years like Featherfill and SlickSand, but find tha the PPG products perform just as well, and you don't have to worry about incompatible products. The DCC urethane will color-sand and buff out looking like lacquer, but if your finish is going to be metallic, you might be better off with a basecoat/clearcoat system. Metallics have a real problem when you try and color sand them. It is allways nice on metallics to leave the color coat alone and do all the sanding and polishing on the clearcoat.

I would prime and block with either K-36 or NCP-271 until you are happy with the straightness of the panels, work your way up to 600 grit for the final sand, and then shoot your color coats. You are going to find that with urethanes, you will need no more than 2-3 coats to get plenty of material to color sand on.

Regards, John McGraw