Painting a car not stripped to bare metal?

[karls59tr]

Is it possible to get a reasonably good paint job on a TR4 (that has many coats of paint on it) by sanding the old finish with increasingly fine paper and then applying a compatible sealer,primer,finish instead of stripping the car to bare metal?

 

[TR3driver]

I am by no means an expert; but I believe the answer depends greatly on what paint is already on the car as well as what you put over it.

I had "professionals" paint over the apparent gray primer on my TR3 without first stripping it, and two years later the paint started simply falling off the car.

 

[DougF]

There are limits to the thickness of coats. I don't have that info at hand. As Randall said, it depends on what was put down previously. If your current paint has imperfections such as small bubble marks, flaking, etc., you'll want to sand it off.
Epoxy primer is a good base over old paint. It's pretty nasty stuff too, if you don't have proper respiration equipment. When sanding the old, if you finish with a 400-600 grit, you should be ok.

 

[jimstr4]

You can repaint a car without stripping to bare netal but, as I've found, there is almost always rust beneath the old Bondo as they used to bondo over bare metal in the past. Nowadays they primer then fill.
The rust usually comes through again.
I have repainted several vehicles and have found that the first thing to do is figure out whether the underlying paint is a lacquer, enamel or two pack.
If two pack or enamel then use an etch primer between the old and new paint as well as sanding the heck out of it.
The etch primer has acid in it that will etch into the old paint and help with adhesion.
If lacquer then repaint with lacquer and don't use anything but lacquer based paints underneath it, as the lacquer will crocodile over two packs and emanels.
Using an epoxy under a two pack is also good but put an etch on first.
Two packs top coats usually have isocyanates in them which rot your lungs so use good breathing gear.
I used a black truck topcoat made by Ameron, much much cheaper and no isocyanates. Lasts just as long.
The truck paint had the same chemical backbone as the expensive car paints, and painting everything black means that its much easier to get the correct colour.

 

[hondo402000]

what ever you do best to read the directions carefully. And there are some plastic fillers that are required to go on bare metal still today, I dont think you can even purchase laquer paints anymore, just ask the paint store guys how to proceed, I would think that a two part urethane would work, there is also a product that Wayne on here steered me to when I had lifting issues, its called Barcoat, spray it on as a primer, then a sealer coat and top coat

Hondo

 

[karls59tr]

Thanks for the info guys.I looked up Barcoat and it's described as "a quick drying isolator that prevents lifting and bleeding of existing paint film sensitive to solvent attack" That sounds like what I'm looking for. I'm going to get in touch with a supplier up here called Rondex to see if they have a similar product. I think solvent based paints have been banned here and if the solvents are what causes the lifting of the old paint maybe the waterbourne paints would not react with the existing finish to cause it to lift? I'll check with the supplier.

 

[tdskip]

Depends on the older finish and how well the primer is still attached. Generally you'll want to do a sealer on whatever is left to prevent the issue that Randall and other have had. Bare metal repaint is a big job, so be aware of what you are asking about.

One last tip - stay with the same family of primers, sealers and top coats.