Which primer?

I've got the front fenders,hood and trunk lid off of my 72 convertible. I know it will be a couple of months before I paint the car. I want to do the minor body work on the pieces while they are off the car and use epoxy primer to protect them. When it's time to paint can I sand and use a 2K urethane primer? The real question is, will the epoxy primer be good to go after a couple of months.


Art

RTR

 

You need to put a SEALER over the primer. Primer itself will let moisture through, and you will have to sand it down AGAIN.

 

The answers will be more interesting than just that, in fact I don't believe sealer necessarily applies to epoxy primer, as once cured it's already waterproof and can be used as a sealer itself. The bigger question is how long can you wait before you topcoat a modern epoxy primer? The older stuff had a fairly short window before it was advised against topcoating. I'm interested in hearing if the modern epoxy primers have the same limitations. It's been quite a few years since I used the stuff.

Devon

 

The vast majority, if not all, of the epoxy primers have a "recoat window" of 7 days or less I believe.

After that they typically instruct you to clean the old surface, sand or scuff it and then apply one wet coat of the same epoxy prior to going to your next coating.

That should not be a large enough roadblock to keep you from using an epoxy. I'm sure there are plenty of people that have sprayed a bare fender, etc with epoxy, had it sit for months, etc and instead of following the instructions they may have just cleaned and scuffed and then sprayed on a urethane build primer. Probably came out fine....but it's your $$ and your paint job and you have to decide whether you want to risk the chance something happens if you don't follow the manufacturer's instructions.

Look into Southern Polyurethanes's products (SPI)...they make epoxies, urethane build primers, etc and sell them at VERY reasonable prices compared to the big name stuff. They have a good rep and have A LOT of people using their products on some very nice cars. Very "user friendly" company with lots of knowledgeable tech support (typically provided by one of the owners of the company.....no "phone center" people reading from some catalog without the ability to develop an independent thought).

 

I would be one of those guys. I use Dupont 2580CR epoxy and the tech sheet states:

"Dry to nib sand 30-60 minutes
Dry to topcoat 20-30 minutes (1 coat)
Dry to topcoat 40-60 minutes (2 coats)
Scuff sanding is required if primer has been allowed to dry more than 2 days. For optimum appearance, sand with 400-600 grit until smooth"

 

its easier to shoot the u primer the same day you shoot the epoxy. then it can sit until you are ready, and you dont have to deal with the epoxy re scuff

 

I'll have to look at that. I thought the 2k primer didn't want to be exposed for long periods of time.
Thanks all.

Art

RTR

 

It depends a lot on the conditions. Primer absorbs, which is the reason why most don't like it to be exposed for long periods of time. You certainly don't want it to sit outside exposed to the elements but if your garage is closed up and dry I wouldn't worry about it. Personally, I'd rather have it sit with just epoxy on it until I'm ready to do the finish work on it even if it takes a little more time to scuff it.

 

epoxy primer does not absorb moisture and is the primer to use if you are going to let the panels sit for an extended period of time......when ready to prime with urethane primer you treat the surface as you would a repaint......thoroughly scuff the paint as you would before repainting the car and then apply your primer.......the worst thing you can do is to apply the epoxy primer then apply your 2k primer and then let the panels set out to the elements the 2k primer not only absorbs moisture but also absorbs impurities which could show up in your final paint job......i have had panels that were primered with epoxy and were not touched for 3 years while the was being finished and this was in a garage that was unheated in the winter [condensation] and was in the worst location you could want the atlantic ocean was 200ft infront of the garage and the marsh was 50ft behind the garage [very damp salty air] the paint job on this car is now approx 10 years old and still looks new

 

If the car will be inside dry no problem just scuff and prime when ready .Dont leave a car outside in primer even epoxy will start to rust very soon.

 

What brand of epoxy is it? If its PPG after 24hours it must be scuffed and re-applied, or scuffed and top-coated. If you're planning on using a sealer before paint, I would highly recommend a product like Super Build, to straighten things out, its great building and sands super easy. It's a polyester based products, so it's like "spraying putty" and is much better than using multiple heavy coats of acrylic urethane primer, less possibility of shrinking etc. But should be sealed before painting.