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Epoxy primer - is using the wrong Wax & Grease Remover my only issue?

Let me start my post with a confession - I learned only after I received the SPI epoxy primer that I am supposed to use the SPI Wax & Grease Removers. Since I was in a hurry, I used Klean-Strip Prep-All, to clean the parts.

The first batch I sprayed turned out just fine:

Today, I sprayed a second batch, what turned out to be a complete fail:

I am now wondering, if using the wrong cleaner is my only problem (I will order SPI cleaner tomorrow morning) or if I have something else going on?
The only two differences, I can think off compared to the first batch, are aluminum instead of steel as material, and that I removed some markings with MEK, prior to cleaning with Prep-All, 80 grit sanding and cleaning with Prep-All again.

Three steel parts, which I had media blasted, instead of sanded, showed similar defects.

Any ideas?



Paint Fanatic
Staff member
Now not talking down to you as I will pretend your new at this and just want to cover all potential causes.
It is contamination for sure and fisheyes.
First, did you dry the Wax and Grease remover as soon as you applied it doing a 3-foot section at a time with a clean rag?
Second did you even though dry let the solvents get out of metal for 30-60 minutes?
Either way, there is a contamination problem caused by cleaning, contaminated rags or epoxy applied too soon.


Paint Fanatic
Staff member
First parts look great, so something has changed??? Could it be oil vapors coming from compressor because maybe the second set you sprayed the compressor had been running a lot before and heated up?
Do you have a desiccant system?
Hello Barry,

Thank you very much for you response and advice.
You are right – I am new to solvent based epoxy primer. So far, I have only painted aluminum parts for a kit plane with Stewarts Systems waterborne epoxy primer. For that, I would however just scuff and clean the surface in one step with a purpose made cleaner, rinse it with water and let it dry.
While I am glad that you confirmed that I only have a contamination issue, I have to admit, that I am a bit embarrassed.
I exactly followed the instructions (except of using the wrong cleaner), including the required dry times and wiped off the wax and grease remover while it was still wet.
I have a water separator installed on the spray gun, but will also look into that.
Sleeping on it, it occurred to me that the paper towel might have also been an issue – I’ll order the SPI Wax & Grease Remover and also appropriate towels to wipe it off.
I really can’t tell what was different than with the first batch. After stripping the bad part in the picture above and cleaning and painting it the exact same way again, the paint actually turned out beautiful.
Anyways, I’ll get the correct products and make extra sure to not accidentally contaminate the parts while handling them.

Thanks again for your help, I really appreciate it!
I think that besides any contamination issue, the material was applied too wet and/or without enough air pressure. I can sometimes make epoxy look something like that by accidentally over-applying it, this can happen if gun is set wrong, lighting is poor, etc.
i was going to say the same thing as crash. if you apply it to heavy it will look just like that. #1 dont use a big tip gun for primer. use whatever gun your using for base or clear. dont dry spray epoxy. you want a wet coat but a very thin wet coat so a gun with a 1.4 tip and maybe bump up the psi 5lbs to give you a nice fine atomization.
Thanks again for your replies.

After I stripped the messed up parts last night and sprayed them again, they turned out just fine:

The first coat was a bit dry, what led to the rougher than it possible surface, overall I however think that it looks good, particularly for primer and considering that I sprayed them under less than optimal conditions (not so great lighting, hanging parts). Same painter, same settings.

I run a small water trap, which is directly attached to the gun and thought that this might be the problem. When I tried today, I was however not able to make it spit out any water, even when I held it upside down.
It therefore appears as whether I either did not clean the parts sufficiently or contaminated them in the process.

I ordered today SPI cleaner, additional black and white primer as well as proper towels. I am confident that this will solve the issues I had.

Also, a big shoutout for Barry + SPI: I spoke with him today, to place a new order and he was super friendly, helpful and spent quite a bit of time troubleshooting with me.
Since I ordered white primer today, I figured that I wanted to have one of the previously black primed parts rather primed white. I tried to strip it today with MEK, only around 20 hours after I painted it: Absolutely nothing, except of a little bit of black on the towel. I then tried Rustoleum Aircraft Remover, with what I so far had great results, but all it did was to soften the SPI epoxy primer. Even after two application and 20 minutes of waiting, all it did was to soften the primer. I had to scrape if off! This stuff is super tough!!!