I have PPG DP40LF Epoxy Primer. Over that, I will be applying Delstar Polyurethane Acrylic Enamel. Metal surfaces have been stripped bare. I work slow, and to keep pieces from rusting, I had given them a quick coat of SEM self etch primer. Today, the PPG rep told the guy I buy paint from that the DP40LF primer should never go over the SEM product. He says that I should sand back to bare metal with 80 grit before priming. Is the issue here that the primer requires a strong mechanical bond to the metal? Or, is there some chemical thing between the SEM and the primer? On a somewhat related subject, can I put polyesther glazing putting over the DP40LF? I have already puttied over the bare metal prior to dusting it with the SEM stuff. Can I prime over this putty, or should I strip that back down to metal as well? I assume that if I do putty over the primer that I can squirt more primer over the puttied spots as long as it's within the time period prior to applying the acrylic enamel.

 

IMHO, PPG would be the one to answer your question.....

 

With Beechkid here---anytime you mix system brands your potential for failure increases significantly.

Its too easy thinking PPG and others specify their products as a profit motive but the fact is they do a lot of work developing that system for maximum performance.

SEM is a good product line but it might not be compatible with PPG for any number of reasons. Proceed at your own risk of all your work being for nothing if/when non-compatible materials are used.

Typically PPG would have a help line but a local body shop using their system would be the best source. They'd be hands on every day and not much better info than that.

 

Thanks Beachkid & JWA. I'll do some asking around about compatibilty of the various products. I don't mind sanding off the SEM self etch, but I don't know how I'm going to get rid of all of it without blasting again.

 

This SEM

SEM Products :: Self Etching Primer


The word glazing is not used anymore today. Polyester is a body filler versus the old lacquer glazing putties. What brand are you using? Evercoat Rage is a regular polyester body filler and Evercoat Easy Sand is a polyester putty. Those are an example.

 

I'm using "Evercoat Polyester Glazing Putty". The product # is 100 400

 

Hi jvmcc,

Hopefully you're sorting this out. As to your question about the bonding between the 2 different primers (epoxy vs. self-etch):

Self-etch uses an acid to chemically score the metal and bond to it. Then the regular hi-build primer you spray on next bonds to the self-etch layer. So the self-etch acts as a middle man between the bare metal and regular primer.

For self-etch, be sure to do all your bodywork first including bondo/filler because (for most brands) you can't put it on top once you've sprayed self-etch.

The epoxy you originally bought from PPG is meant to go on bare metal too but it lacks the acid so you have to sand/scuff the surface of the metal to provide the rough surface it needs to "grip" onto. One advantage of epoxy for DIYers is that you can put bondo/filler over it.

Because many of us are weekend warriors flash rust is always a problem so you can spray your car with epoxy to seal it from rust and then tackle all your problem areas at your pace. Then simply re-spray the areas you worked on. I know some people like to spray epoxy first, then bondo, and cover that bondo again with epoxy to encase it in sealer - it's really about personal preference. Just be sure to pay attention to the recoat window - if you pass it then you have to scuff the epoxy layer before picking up where you left off.

In general (depends on brand), you choose either epoxy or self-etch primer to apply on bare metal and not both so your rep is probably right about having to start over.

Let us know how you make out! Paint can be pretty confusing because although there are general rules, each brand has their own idiosyncrasies.