Different Types of Primer - Explain?

[mokid]

I'm re-doing a dart that was primed with Urethane (yellow) and painted with base/clear. During blocking and filling, some areas are down to bare metal. This car is going to just be a driver, but I want it to look nice.
1) Is it OK to temporarily prime bare spots with lacquer primer and later cover the whole car with Urethane?
2) Is it OK to prime the whole car with lacquer primer and just apply base/clear over that? (I have 2 gal of lp on the shelf and $ is tight right now)
3) How serious a problem is "shrinkage"? I have painted cars in the past using only lacquer primer and acrylic enamel and had no problems.

I've been reading a lot of posts here, but am still confused. Comments, recommendations, and experiences would be appreciated.........james

 

[oneway71]

For #1 It is best not to mix the two; it will cause delamination. Or in other words the lac will soften and begin to peel up.

I had a customer, 2 years ago, that wanted to mix lac and newer uro's The lac softened, cracked and peeled up. I had to do the job twice because I tried it his way first.

Check out this forum for paint questions; they are the real experts.

http://www.kustomkulturelounge.com/forum/index.php

 

[sscuda]

I'm re-doing a dart that was primed with Urethane (yellow) and painted with base/clear. During blocking and filling, some areas are down to bare metal. This car is going to just be a driver, but I want it to look nice.
1) Is it OK to temporarily prime bare spots with lacquer primer and later cover the whole car with Urethane?
2) Is it OK to prime the whole car with lacquer primer and just apply base/clear over that? (I have 2 gal of lp on the shelf and $ is tight right now)
3) How serious a problem is "shrinkage"? I have painted cars in the past using only lacquer primer and acrylic enamel and had no problems.

I've been reading a lot of posts here, but am still confused. Comments, recommendations, and experiences would be appreciated.........james

To answer your questions;

1) no - lacquer primer is porous, it doesn't protect the metal from moisture. Lacquer primer acts like a sponge pulling moisture into the primer.

2) no -lacquer primer has a tendancy to A. sink, B. lift, C. peel, D shrink, E wrinkle. And in most cases all of the above.

3) " shrinkage " can range from a little shrinkage, leaving just slight pinholes or sanding/grinding marks to a major flaw in the finish. It depends how lucky you are and the environment you live in.

I honestly don't know why the paint companies still sell this s***.

Use the urethane primer and forget about it.

Good luck with your project and provide us with good quality pictures when you are done.

sscuda
8)

 

[dgc333]

I made the mistake of spraying urethane primer/filler over some lacquer primer and the urethane caused the lacquer primer to wrinkle up and lift, made a real mess and I am glad it was only in some spots since I had to sand it off to bare metal.

Now when I am doing spot repairs I use SEM self etching primer on the bare metal then cover it with SEM urethane primer filler. These are aerosol sprays that you can get at the local autobody supply house specific for this type of work.

As others have mentioned primers are porus and will allow moisture through so they are not appropriate for long term storage where the car is exposed to the elements. You need to use epoxy primer to seal the metal up from the elements.

 

[mokid]

Thanks for the replies. I'll follow your recommendations and get some aerosol urethane(ur) to cover the areas I'm re-working. Then I'll apply a complete coat of ur. It will probably be a few weeks before I get the car painted. Just gotta get it done before cold weather.