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914World.com _ 914World Garage _ Painting question - inside and underneath

Posted by: tracks914 Dec 9 2006, 10:08 PM

On my last resto I took the entire outside of the car down to bare steel. The underside and inside the trunks I just scratched it up with scotch pads (abrasive cloth). That was alot of work but it did the trick because the paint inside there was pretty good.
This car I am working on doesn't appear to have as nice a paint on the inside. Acid dipping is not an option but I was wondering if anyone has used a product that, when sprayed on and wiped clean, would etch the old paint enough to get a good adhesion to the new paint???

Posted by: SGB Dec 10 2006, 01:37 AM

Doug-
your resto project effort was pretty amazing. Thanks for the link. Oh, I don't know about the paint etching, but that is a damn fine job on the yellow car.

Posted by: highways Dec 10 2006, 02:55 AM

Umm, ok I'm not an expert but I have been studying bodywork alot lately and the first time I prepped my car for paint went really well, so I'll give it a shot.

Etching is only done on bare metal as far as I know, not paint. Either your existing paint is on the body well or it's not. If it flakes off like with a fingure nail test- it's no good. If it takes alot of sanding and elbo pressure to get it off- then it's on there. In that case all you need to do is a little prep to make the new paint stick to the old. You don't need to remove solid old paint- it's probably more in your favor to use it... considering it to be a stable base coat. However if it's flaking off easily- you better flake all of it off (sander time!).

For your inner surfaces which don't require a mirror finish, just good adhesion- I think you just need to clean (car wash), clean again, degrease, rough up, clean and paint. Notice the word 'clean'.

After normal washing, you would use a quality degreaser, such as something from the PPG brand. Sorry don't know the name but it will be a three digit number such as "PPG 550" for example only. After degreasing you might do a little scuff sanding to create a good 'footing' for the new paint (assuming you're not going further down the perfection road with it- i.e. block sanding, filling, block sanding, ect). Just like you did with the scotch bright pads... I used sand paper propably in the 150 (worn soft)- 320 grit range to rough up my old paint surface before priming. If you don't degrease it before you sand- then you will effectively sand the grease deaper into the paint. Degreasing is an art in itself so check out the forum below.

http://www.autobody101.com/forums/

Posted by: Ted914/6 Dec 10 2006, 11:23 AM

After the prep work, try using a sealer or an adhiesion promoter before the top coat. Make sure to stick with the same product line. Mixing products is a good way to see paint failures.