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Old 07-29-2011, 12:17 AM   #1
69SSC5
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Default how far do i sand down the paint

started on sanding my 88 C4 today,,, man block sanding is alot of work... i sanded off the clear coat, sanded off the stock red paint... under the red paint is a dark grey color then under that is a light grey (i assume that is primer)... do i sand past the light grey or do i just sand away all the dark grey till its light grey....

i am using a block and 80 grit paper

URL=http://imageshack.us/photo/my-images/638/c4paint.jpg/]Click the image to open in full size.[/URL]

Last edited by 69SSC5; 07-29-2011 at 12:32 AM.
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Old 07-29-2011, 09:10 PM   #2
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That light gray stuff appears to be raw glass. Stop sanding when all the red is gone. then try lacquer thinner and a coarse Scotchbrite pad to see if that will take off the dark gray. If you continue to sand 80 grit untill all is a uniform light gray it looks to me like you'll have trouble with making the glass thin in spots. What are you using for a block? The reason I ask is if your sanding technique is good, the factory panels are really wavy since all the light gray is not leaving at the same rate. They're never perfect from the factory, but my experience is they ought to strip more uniformly.
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Old 07-29-2011, 09:18 PM   #3
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Im using dura blocks. I don't really have a technique I was just sanding. Is there a proper way to sand to remove paint? First car I've sanded and painted
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Old 07-29-2011, 09:46 PM   #4
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The best way to remove paint using sanding is to try and remove it all at approximately the same rate meaning trying to go to all the edges, in all the curves and as far into all corners as possible evenly and smoothly. Long sanding strokes carried all the way to, but not lapping over the edges of panels are most effective and easiest to keep uniform. You must remember that the glass substrate is soft as well, and if you press harder or sand longer/less in any spot you will remove panel thickness as well as paint. This will make getting things straight as you prime and reblock(yes you will have to sand the entire car two, three or possibly more times again before you apply color). On you hood I would now carefully try and remove just the red from those areas it is still visible and hope for the best when you prime/resand. For the rest of your removal pay close attention to how uniformly the topcoats are coming off ( you'll be able to tell if you look closely) and modify your technique to getit as close to even as possible.

Last edited by markids77; 07-29-2011 at 09:47 PM. Reason: spelling
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Old 07-30-2011, 02:26 PM   #5
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thanks for the tips... The goal is to get all the paint and primer off and get down to EVEN bare glass, is this correct? i also read that i am supposed to seal the bare glass right away?
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Old 07-30-2011, 04:11 PM   #6
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IMHO there is no reason to remove the primer on a C4 unless you want to apply polyester filler to the whole car to make it "show car straight". If you just want to block it and make it better than it was you can apply urethane primer surfacer directly on top of the factory primer and block that as needed.
Blocking with 80 grit on the bare glass is going to make some deep scratches that are going to need filled by polyester filler prior to applying primer. Most paint manufacturers recommend sanding with 180 or 220 before priming.
I would use 180 to strip it and then apply the primer and then block the primer. This will save you quite a bit of work.

Good Luck
Craig
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Old 07-30-2011, 04:59 PM   #7
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Quote:
Originally Posted by CF6873 View Post
IMHO there is no reason to remove the primer on a C4 unless you want to apply polyester filler to the whole car to make it "show car straight". If you just want to block it and make it better than it was you can apply urethane primer surfacer directly on top of the factory primer and block that as needed.
Blocking with 80 grit on the bare glass is going to make some deep scratches that are going to need filled by polyester filler prior to applying primer. Most paint manufacturers recommend sanding with 180 or 220 before priming.
I would use 180 to strip it and then apply the primer and then block the primer. This will save you quite a bit of work.

Good Luck
Craig
the plan was to try my best at a show quality paint job, i was planning on doing a poly filler (some spots on the car needed it already anyway) on the entire car and removing almost all the body panels for final prep before painting. i have alot of time on my hands right at the moment and i dont mind the work out (sanding that is)
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Old 07-30-2011, 05:29 PM   #8
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I now understand what you want to accomplish, but you still do not want to cut into the glass with 80 grit. If you look at the directions on most sprayable poly fillers you will see that 180 -220 and finer is recommended.
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Old 07-30-2011, 10:56 PM   #9
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I now understand what you want to accomplish, but you still do not want to cut into the glass with 80 grit. If you look at the directions on most sprayable poly fillers you will see that 180 -220 and finer is recommended.
I will be buying 180 or 220 on monday and use that to remove the primer. Is it ok to use the 80 grit to strip off the clear and some of the red paint? Also I noticed that the primer seems to be alot thicker in some areas than others, is that normal?
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Old 07-30-2011, 11:21 PM   #10
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Broken down to simple terms all paint prep consists of is making progressively finer scratches in the body panels, then filling them and repeating until the topcoat is so smooth the scratches no longer show to the naked eye. It is OK to start with 80 grit, and I always try and use the most coarse paper which will not ruin the job at hand... it saves time and energy to cut as aggressively as practical early in the paint removal process.

Even the factory uses a "build" primer to eliminate waviness in new car panels, so yes some variance in thickness is normal. If your car has already received a professional strip/refinish then the thickness of primer substrates can be greater than original as well... fiberglass "moves" as it ages and can get wavy due to environmental exposure, chemical changes and careless prep; all of which require more "remediation".... either thicker primer coats, or actual body filler/resin application followed by a surfacer.
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Old 07-31-2011, 11:24 AM   #11
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Like Markids stated it would be OK to use 80 but you will want to eliminate the 80 scratches with something finer prior to any poly or urethane filler.
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Old 08-12-2011, 11:02 PM   #12
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ok i finally got all the clear coat and red paint sanded off of the car with 80 grit paper and dura blocks. now how do i get rid of the dark grey color primer? i tried 3m pad and laquer thinner but that didnt do much.
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Old 08-13-2011, 09:24 AM   #13
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220 grit wet is a good next step if thinner won't take it off. You do have to smooth the 80 grit scratches anyway, and my personal opinion is 220 grit scratches are unlikely to telegraph through at least 2 coats of fill priming sanded progressively finer, and they give a good "tooth" for the first coat to grab onto. Again, be careful with your technique, and I would not stress too much about leaving some small patches of factory primer in the low areas on the car.

EDIT: Be sure to let the car dry preferably 48 hours before applying paint after wet sanding... the bare glass will soak up some of the water. And yes... please seal the bare surface as soon as practical after sanding it raw.
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Old 08-13-2011, 09:05 PM   #14
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Quote:
Originally Posted by markids77 View Post
220 grit wet is a good next step if thinner won't take it off. You do have to smooth the 80 grit scratches anyway, and my personal opinion is 220 grit scratches are unlikely to telegraph through at least 2 coats of fill priming sanded progressively finer, and they give a good "tooth" for the first coat to grab onto. Again, be careful with your technique, and I would not stress too much about leaving some small patches of factory primer in the low areas on the car.

EDIT: Be sure to let the car dry preferably 48 hours before applying paint after wet sanding... the bare glass will soak up some of the water. And yes... please seal the bare surface as soon as practical after sanding it raw.
what should i seal the bare glass with?
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Old 08-13-2011, 09:56 PM   #15
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I am using a catalysed epoxy primer as the only base under paint on my 1977. It seals well but does not build very rapidly, but my car is pretty straight after I did all the body repairs required. I recommend you choose a paint supplier now, and follow that manufacturer's techline recommendations as to which product should be applied in what sequence for best result. I see you live in Kalifornya, so what is legal here in Georgia is probably not in LA. I suspect you will be required to purchase low or no VOC refinish products... to almost cetainly include water borne color coats. I can still purchase "traditional" paint systems here, so my experience will differ.
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Old 08-14-2011, 12:20 AM   #16
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I am using a catalysed epoxy primer as the only base under paint on my 1977. It seals well but does not build very rapidly, but my car is pretty straight after I did all the body repairs required. I recommend you choose a paint supplier now, and follow that manufacturer's techline recommendations as to which product should be applied in what sequence for best result. I see you live in Kalifornya, so what is legal here in Georgia is probably not in LA. I suspect you will be required to purchase low or no VOC refinish products... to almost cetainly include water borne color coats. I can still purchase "traditional" paint systems here, so my experience will differ.
Yeah I need real paint not the stuff they sell here in cali... im going to order it online and have it shipped to my fathers house in texas. I would like a thick primer, one that hides imperfections well. Can u steer me in the right direction as to places to start looking or as to which manufacturer to choose?
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Old 08-14-2011, 10:11 AM   #17
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I have no experience with mail order materials so I can't advise you there....I like Sherwin Williams products myself... get them at the local NAPA. Perhaps another member has ordered their stuff online and had the job turn out well?
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Old 08-14-2011, 05:17 PM   #18
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I would like a thick primer, one that hides imperfections well.
PPK K36. It's a 2K Urethane primer with some build to it.
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Old 08-14-2011, 10:15 PM   #19
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If you want a substantial filler I would use Slick Sand by Fiberglass Evercoat. It is a sprayable polyester filler.
You will need a spray gun with at least a 2.0 fluid tip to spray the stuff but it will fill small waves and scratches. It is also quite a bit less costly than urethane primer.
After this is blocked you can just apply sealer and then paint.
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Old 08-18-2011, 02:14 PM   #20
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ok im frustrated at this point... i tryed to sand the dark grey primmer off with 220grit but no luck, so i switched to 180 gritt, no luck... this primer is thick as all get up and doent want to come off.... ive spent 30+ hours hand sanding this car and now im tired (much respect to those that due this for a living). im thinking about breaking out the DA sander and goen at it with 220 grit on the DA. what do you think,,, how do i get this dark grey primer off....... if i create some waves in the glass will a thick high build primmer fix the waves?
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Old 08-18-2011, 02:14 PM
 
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