On my project, I had to sand a front fender and the hood down to bare metal to get rid of some surface rust. I'm doing all of this in my class at the community college. When all the metal work was done and we were going to shoot the primer, I asked my instructor if there was something that I needed to wipe the bare metal down with before we shot the primer. He said no, and we primered it. Last night I finished the hood and one of the other people in the class with some experience asked me if I was going to use a primer was before primering. I told him that the instructor told me there was nothing to put on it. He was slightly shocked and said that it had to be primer washed. Anyway, I asked the instructor about it later and he said to definitely primer wash it before primering. And now I had to sand the fender completely down again to put the wash on. Apparently there has been some problems with the instructor before and I was told that it came down to brand loyalty, he's chevy, I'm ford, and I was told that his attention is divided up according to projects. I've heard of brand wars, but this is rediculous. I'm getting the paintucation dvd's so at least I have an idea of what is going on.


So, what is the primer wash used for? I was told it was best to primer wash, epoxy primer, sealant (i think), primer, block sand, and paint. But later I was also told that I didn't need the epoxy primer. Can someone set me straight on this stuff. Thanks.

 

Wash primer? or primer wash? Wash primer is only sprayed on bare metal for primers that can not stick to bare metal so they require a wash primer in the system for adhesion. I don't bother with those types of primers at all simply because its expensive, I just use a 2k urethane surfacer for my work, which does a good enough job because im just gonna sand it anyways.
I think you should paint with every type of paint you can like Urethane, enamel, base/clear, 1k primers, 2k primers, sealants. That way you can watch 'n see what the paint does in differant situations such as hot or cold, humid or dry. Thats how you get good at painting, and shoot the paint differantly also because enamels are not shot the same as a base/clear or urethanes, so just practice practice practice while its not costin you much.

 

In general, a wash primer is used to re-establish a chemical bond between bare steel and any subsequent primers/paints.

Wash primners are generally alot thinner (read: runny) than other types of primers- particularly primer/surfacers. They don't need to carry inert solids, because they aren't designed to be sanded afterwards.
They are strictly a sealer and adhesion promoter.

Many wash primers contain an acid that etches bare metal to provide the primer with a "bite" into the metal.

In general, wash primers are designed to be topcoated "wet-on-wet" with another primer sealer or primer surfacer (within an hour or so).

Most wash primers have an extended window, in which you can spray over them without experiencing any adhesion problems (usually 24-48 hours). However, after the wash primer has cured, it must be etched with sandpaper or abrasive pads before it can be sprayed over or coated with plastic filler without encountering any possible future problems with peeling, etc. Sanding wash primer usually results in a tear or breakthrough to the bare metal, becasue it is by design, so thin. For this reason, wash primer is usually coated over with an epoxy primer, to provide a base to which primers and fillers can be applied, and then sanded.

Epoxy primer is generally an excellent primer/sealer. Although it doesn't aggressively etch into bare metal, epoxy is by nature, very sticky, and will glue itsself to just about anything, including clean, raw steel and aluminum. It too, is low in solids, and designed to be sprayed over top of in a wet-on-wet manner, and not sanded. However, epoxy is more versatile than a wash primer. You may use epoxy sealer over bare metal, polyester filler, fiberglass, and over any primer, just before painting. Epoxy primer provides a great surface for color basecoats to adhere to. It even promotes even color hiding before clearcoat.


2k urethane primer/surfacers are best sprayed over a sealer- not over bare metal- and are designed to be sanded smooth after drying. These primers generally may NOT be topcoated wet-on-wet, and must be allowed to dry, and be sanded thoroughly before being coated over with anything. Urethane primers are best used to fill low spots, pits, waves, etc.- and can be sanded silky smooth. Primer surfacers are used to block-sand for straightness. It is possible to paint directly over sanded urethane primer, but is not ideal.

Using an epoxy or urethane sealer (not a primer/surfacer) seems like an extra unneeded step before paint, but will actually save you money by reducing the amount of basecoat color needed. (Paint is wayyy expensive as you know). It can also significantly cut down on the amount of shrinkage in the final spray job by keeping the amount of paint & solvent to an absolute and efficient minimum.

hope this helps

 

Oh, sorry- I saw your question and just went off without really reading it thoroughly.

To answer your question directly- Yes, you probably should use a wash primer first.
You can get away with just epoxy sealer if the car is really prepped well, and the metal is really clean.
...but in a learning environment, it's probably best that they have everyone do things according to the manufacturer's guidelines.
What brand of products are you using??

 

One of the hardest things to tumble to in a auto paint education is decoding
the confusion about the term "primer". It is used differently and
in different context by almost everybody. The manufacturers have
no qualms about about calling their product what ever it takes to
make you think it is what you need.

In general terms the high end paint system manufacturers will market
something like this:

Self etching primer...super thin..not really a paint..applied over bare metal
for rust protection issues. Often called wash primer.

Primer surfacer....high solids,high build..kind of a "filler" for surface prep issues.

Primer sealer...top coat adhesion and bleed through issues.

My experience is that the only time window is between bare metal sanding
and application of your etching primer or wash primer. Some paint systems just give
you a couple of hours before your supposed to resand.

Congratulations on taking the college paint course. Since there is almost
no more union apprenticeship auto paint training it is one of the best ways
to learn the trade. Keep us posted on what you learn.

Good Luck!

 

Thanks everyone for the replies. Even if some things weren't asked by me, the information provided means alot. As for products, I'm using stuff that I get at my local PPG dealer. I did get the wash primer today (it is wash primer and not primer wash, my mistake) That is some expensive stuff. The primer that is provided by the school is primer surfacer, I'm guessing. From the description provided it sounds about right. Is there a time limit that the wash primer and the activator can sit before being used? Because I don't want to mix it all up and then find that I only used some and need more later.

 

The guys at the paint store should have Technical data sheets for every product they sell-or just ask them.

Also, you can go to the manufacturer's website, PPG.com's refinish site.

http://www.ppg.com/cr-refinish/phase...indProduct.asp

http://www.ppg.com/cr-refinish/phase...indProduct.asp

Good luck, bro.

 

Back in the day - and that really hurts me to say that. When I was in HS working on my first car I was told to hit all the bare metal with a weakened solution of muratic <sp> acid and allow it to dry before I put on the primer. It created a lite white film that I hit with a tack rag and primed. I have had some paint fail but never the primer using this method. The bonus is that you can get the acid at almost any hardware store for $5 cut it by 75% and have enough to do about 3 cars.

 

Right On...muratic acid is still main component of wash primers. Thats why wp's
must be stored in plastic jug and not metal can.