Paint prep for 30 year old oem automotive

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  #1  
Old 12-14-03, 09:52 AM
bronco427
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Paint prep for 30 year old oem automotive

I have a thirty year old Bronco top that I am ging to paint. I have removed the seam sealer and treated it with Skyco OSPHO rust inhibitor. Do I have to remove all the paint from the top due to the age of the paint? There are many areas of the top[inside and out] that I can't use my DA sander on. When hand sanding , what grits should I use to bring it down to bare metal and what grits should I use where bare metal is not necessary? What type of sand paper is best and is there anything that will strip metal better than a DA sander with Gold papers. What grits should I use in the DA sander for bare metal and for repaint.?
 
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  #2  
Old 12-14-03, 10:05 AM
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Location: Pittsburgh,Pa
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If the paint still is in fair condition not cracked or peeling sand with 360 and repaint.Old paint is the best surface for new paint to adhere to according to my autobody teacher.I would sand it, paint it with high build epoxy primer, sand then apply the final finish coats.I'm not a body man though,but this is what they do where I work.
 
  #3  
Old 12-16-03, 07:01 AM
jimmymc
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I would try to remove all of the old paint if I could. Although this is sometimes difficult...it will produce a better paint job in the long run. Prep work is always the key to a good paint job.

Removing the old paint to bare metal cuts down on priming and blocking and removes the possibility of the newly applied paint dulling because of trapped solvents.

I usually use 80 grit on a DA for stripping. For really serious stripping on metal, I use a 8" stripping pad and a electric buffer...with 40 grit green stick-it paper.

Always use sharp/clean sandpaper...sandpaper that is used past it's use-able life creates un-necessary heat which can warp panels.

You might consider professional media blasting...although this can sometimes do more damage and requires that you do additional repairs.

Stripping chemicals can be spot used as a last resort and with all appropiate caution. Read the label and don't get where it's not supposed to be...cover all areas that you don't want the stripper to get on. Tops are especially difficult because the stripper wants to run down.

I have used an abrasive plastic wheel on a drill at times...and then there is always muscle power...sometimes there is just no easy way.

Take the top a section at a time...and don't jump around. When you get a section done...it's done and you can see some progress.

It sounds like you are off to a good start...hang in there and the end results will be worth it.

jimmymc
 
  #4  
Old 12-16-03, 07:43 AM
bronco427
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Thanks for the info. I have been hand sanding some small areas and have run into a problem I hadn't expected. It appears as though there has been some runnoff from the rust inhibitor onto the paint and it has lifted the paint. I'm pretty sure the paint is oem. Do you know if this is a problem when using OSPHO? Any info is Helpfull.
 
  #5  
Old 12-17-03, 03:24 PM
jimmymc
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Phosphoric acid is the usual ingredient of products for metal/rust treatment...and yes it will dis-color/damage paint as you have already discovered.

Only use this as a last step before priming...if you want...although it is not necessary

If you have rust problems...If possible, I would get a spot type sand blaster and remove as much of the rust as possible.

There is no real way to treat seams without something like acid dip...but if you seal the seams good and cut off the oxygen to the rust...It may be while before it comes back.

jimmymc
 
  #6  
Old 12-17-03, 05:02 PM
bronco427
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Thanks JIMMYMC. I'm taking your advice and removing all the paint. Things should speed up when I get to the outside where I can use a da sander. I'll probubly have more questions later and look forward to your help. Ken
 
  #7  
Old 12-20-03, 12:38 PM
bronco427
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Jimmymc, I'm using PPG DP 50LF primer with DP 402LF hardner on the bare metal. Is this ok? Can I put Feather-rite Filler on top of this primer? Before painting , what grit of sandpaper should I use on this primer? Thanks KEN
 
  #8  
Old 12-22-03, 07:55 AM
jimmymc
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I haven't used PPG's primers recently...so I'm not familiar with their specific product use-ability...but PPG products are great and have worked well for me in the past.

The primer should be a filler type with high build properties...and two part primer is definitely the way to go.

Plastic filler should adhere to it with no problems...just make sure when you are sanding the filler, it feather edges well. Feather edge quality is always a good indicator of adhesion.

If it won't feather edge...then it won't stick.

Sanding/blocking is a very important step in paint prep...don't ignore "blocking" particularly. Blocking with a trace coat, levels the surface and indicates areas that need more work (highs and lows).

A trace coat is a contrasting color applied to the primer after it drys to indicate defects or areas that need more attention. The trace coat is usually intirely removed during the blocking/ sanding operation.

Some people use paint spray bombs for trace coating...usually black. I have used this also...but keep in mind...lacquer products are not compatible with 2k urethane products and may cause problems if not intirely removed (Sanded off).

A neutral powder is availible for trace coating...this is what is use now.

I usually dry block with 180 grit gold stick-it paper on a 8" yellow plastic 3M block...some people use a paint stick wrapped in sandpaper. I don't like the paint stick deal...because I think it is too flexible. Blocking is hard enough without added headaches.

Let the block and sandpaper do the work and don't apply excessive pressure to the block as this may deform the contour of the blocked area and give false information about the "straightness" of the area. When the paper becomes clogged or dull clean it with compressed air or change it as necessary.

Curved areas sanded with a block require particular finese with the block to avoid "flat spots".

Re-prime and block with 180 grit as many times as necessary until you are comfortable with your work.

When you are satisfied with your blocking...re-prime all the area to fill the 180 scratches.

You can re-block with 320/400 if you like and want a particularly "Straight Job". Or water sand/dry sand with 320/400 with a soft foam pad or your hand. I use my hand...but this requires some experience...not to leave finger marks in the sanded area.

I prefer water sanding on the final sanding...others dry sand... either is OK. You may have to re-mask if you have to spot prime any areas...(plastic or metal showing). The idea is to have a consistant surface ready for paint or sealer.

jimmymc
 
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