Bumps in epoxy primer... what am I doing wrong?

S

ssanto

I'm finding many little bumps/bubbles after laying down SPI black epoxy primer (see pictures). It is mainly happening on horizontal surfaces. Almost never happens on vertical surfaces. I'm not sure what the problem is or how to cure it. I figure I'd post as much information as I can here to hopefully find a solution. I apologize in advance for all the detail. I tend to be verbose :)

Here is my setup...
- 60 gallon Husky compressor
- 3 ft rubber hose connected to 20' of black pipe
- Black pipes runs up and down the wall next to my compressor
- On the final vertical leg of the pipe, I have a T that that connects my Kobalt regulator and water separator
- 50' of harbor freight air hose
- I can shoot air through my blower nozzle against a flat piece of metal and not see any water blowing out

... I've been running this setup for about 10 years while doing random projects on and off in the garage. Not used daily or anything like that.

Here is how I prep the panel...
- blow off with compressed air
- spray W&G remover with spray bottle
- wipe with a clean lint-free towel
- blow panel dry with compressed air
- (maybe repeat process if the towel I used to wipe it came out too dirty)
- mix paint
- tack cloth right before shooting
- garage and metal are on the colder side.... 62-65 degrees. Which is right at the lower limit of the tech sheet. But I figured this would just cause longer curing time which I'm OK with since I'm doing about one panel a week.

Here is how I prepped the paint...
- 22 month old batch of SPI primer (both parts)
- the paint was split into four 1-qt cans and I'm nearing the end of using up the 2nd can
- stir the can with a paint stick being sure to get everything that has settled onto the bottom mixed up into the paint
- pour a bit of paint into a small paper cup with a line on it
- pour a bit of activator into a second cup with a line on it (same height as the first cup)
- mix them together in one cup with a small paint stick
- (this is my "small batch" process to avoid cleaning cups)
- let induce for 30 minutes
- go and prep the panel while waiting
- after induction, stir again
- pour through filter cone (not sure what size) into paint cup

Here is my paint gun...
- 10 year old HF gun
- the outside is not that clean... paint runs and such on it
- the inside is also not that clean... when I fully disassemble it, I can see a coating of black inside the cavity where the paint comes through (like looking inside through where you remove the tip). I've tried cleaning in there but it doesn't seem to get spotless
- I am NOT using one of those filter/strainers that go under the cup
- 50 psi on the gun regulator with the trigger pressed
- using the standard tip which is 1.4
- new DevilBiss Whirlwind in-line air filter on the gun

Here is how I paint...
- gun is adjusted so that I don't get any runs
- I still get some orange peel
- I've shot a bunch of epoxy before and I can lay it on thick without getting any runs
- I try to go light on my first coat but I end up having a mix of places with nice full coverage and some spots that you can tell that it went too light on

Here is when I see the bubbles...
- after the first coat, mainly in the places that got full and thick coverage
- the bubbles are mostly on horizontal panels, I hardly see any on vertical panels
- I'm just over-coating filler and places where I sanded through to bare metal and giving a fresh cover over the old epoxy primer that I shot a couple years ago
- when the paint is still tacky, I can rub them down with my thumb. they appear to be filled with air/gas... nothing comes out of them and there isn't a "grit" or something hard inside of them

Here is where I am in my restoration process...
- doing metal and filler work
- I'm spot priming over those areas as I complete them
- once all the filler work is done, the car will get SPI high build primer
- the garage is dusty

Here is what I've tried so far...
- the first time this happened, I had my filter/dryer right on my compressor and not after the black pipe. And when I did the "blow air onto glass" test, I got water coming out of it. Since then I've added more black pipe to condense the water and put the filter/dryer at the end of it. Now I get no water, but the problem remains.
- the first time this happened, I did a very thorough cleaning and blow-out of the garage. I am confident at that time that I wasn't kicking up dust. This time I didn't clean thoroughly (other than the decklid I painted). But the bumps showed up right after I got done spraying the panel and I was away from sources of dust when I painted so I don't think these bumps are caused by stuff falling from above.

Here is what I think could be the problem...
- insufficient filter/dryer ($40 Kobalt setup)
- old air hoses
- not-perfectly-clean paint gun
- issue with the 22 month old SPI primer/activator that has been opened/closed probably 12 times
- poor atomization or something with the HF gun
- lack of filter/strainer in the gun (but the cup was clean and I strained the paint as I poured it into the cup)

Other notes...
- I've got a new (never used) DevilBiss Plus gun. I bought it for basecoat and clearcoat. I was hoping to do all the primer work with the HF gun. I may shoot some of the epoxy with the new gun next to see if that solves it.
- I don't really mind the bumps in the epoxy. It is getting sanded anyway. My main concern is that the problem keeps coming back and affects my BC/CC.


If you've made it this far, I owe you a big thanks!

Looking forward to your thoughts...
 

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If similar to fisheyes/craters epoxy too thick. If sprayed like a medium base coat and not too heavy these should not appear.
 
- the garage is dusty
- lack of filter/strainer in the gun (but the cup was clean and I strained the paint as I poured it into the cup)

I say its dust, lint, or both.

I find that no matter how good I tack or wipe I still get bumps that look similar to what you have. It is especially bad on fresh blasted metal that is rough. I found a tip on here that suggested when blowing off the panel before tacking use a scotch brite lightly in the area you are blowing on, it helps loosen anything that might be stuck down in the pores.

Some other concerns, do you wear a paint suit, clean the air hose off with W&G remover? Is this in a booth? How much air movement? You mention you have a water separator but do you have any type of air filter? You might try a toilet paper filter as a starting point. Motor Guard M30, or M60 are popular and relatively cheap. 10 years of light use with black pipe might have rust started as well.

Dont ever put a strainer in your gun. And rip the one out of the cup system if you use one. If the cup is clean and you strain when pouring into the cup there is no reason to have another strainer in the gun, all it will do is plug up and wreck what you are painting.
 
Couple comments:

50 psi is way too high imho. 30 psi or so....
Don’t spray your first coat thick. Nice thin coat or it will crater....
Wait at least 30 minutes after wax and grease remover
Lint free cloths usually are not when used over rough bare metal, especially blasted metal
Don’t get aggressive with your tack cloth. Gently roll it, don’t rub it in...

Don
 
Also, at the lower temp you my want to let the w&g remover longer than 30. I've had issues with it no being flashed off fully at lower temps.
 
An air compressor that is barely putting out enough CFM to run even a low end gun. Couple that with a worn out HF spray gun that was in my opinion junk to start with, using a ton more air pressure than necessary and you are wondering why the paint isn't spraying right?

Sorry but I think you already know why you are having problems. If you are going to do this type of work please invest in a compressor and spray gun that will get the job done correctly. Putting $200-$800 per gallon paint through a $15 gun has never made sense to me.
 
PartA sounds like pigment out of suspension, take to ace, Lowes or HD and they will put on the shaker for 5 minutes and that should take care of it. if not activator could be getting weak but unlikely. ALL of this is assuming all the other advice or questions are covered.
 
An air compressor that is barely putting out enough CFM to run even a low end gun. Couple that with a worn out HF spray gun that was in my opinion junk to start with, using a ton more air pressure than necessary and you are wondering why the paint isn't spraying right?

Sorry but I think you already know why you are having problems. If you are going to do this type of work please invest in a compressor and spray gun that will get the job done correctly. Putting $200-$800 per gallon paint through a $15 gun has never made sense to me.

My compressor was fully pressurized from the day before and I only painted one panel so the compressor did not have to cut on. So I don't see why the CFM of the compressor would make a difference in this case. I only shot 1/4 of a cup.

I was under the impression that the bumps I was seeing were due to contaminants. I don't see any relationship between a cheap gun and contaminants... is that a correct assumption? Or are you saying that the bumps I'm seeing is because the gun isn't properly atomizing the paint?
 
Also, at the lower temp you my want to let the w&g remover longer than 30. I've had issues with it no being flashed off fully at lower temps.

When I blow the area off with compressed air, I see the surface drying and I see the W&G remover blowing off. So I believe it is pretty dry. And then I let it sit for the 30 minute induction time.
 
Question about solvent popping...

- Could it be that I'm getting solvent pop on the first coat?
- Does solvent pop show up immediately after laying down a coat?
 
PartA sounds like pigment out of suspension, take to ace, Lowes or HD and they will put on the shaker for 5 minutes and that should take care of it. if not activator could be getting weak but unlikely. ALL of this is assuming all the other advice or questions are covered.

I'll get things stirred up (unstuck from the bottom) with a stick and then take it to HD for a good shake. I'll start with a new can (quart #3 of 4) because the can I've been using is almost empty.

I don't think the activator has gotten weak. The paint still dries and gets hard overnight. And the bit I left in the bottom of the cup turned into a hockey puck after a few days.
 
black is the only one i have any trouble with. i use a mixer blade in my screw gun to stir with. then do the fat man shake on it .
that hf gun at 50 lbs is blowing a lot of dry spray out while your painting. northern tools sells vaper guns cheap. they are much better than the hf purple junk .
 
My compressor was fully pressurized from the day before and I only painted one panel so the compressor did not have to cut on. So I don't see why the CFM of the compressor would make a difference in this case. I only shot 1/4 of a cup.

I was under the impression that the bumps I was seeing were due to contaminants. I don't see any relationship between a cheap gun and contaminants... is that a correct assumption? Or are you saying that the bumps I'm seeing is because the gun isn't properly atomizing the paint?

Not trying to offend you. I started out with a similar setup and eventually upgraded and all the issues when away. If I have a problem now, I know it is operator error. LOL
 
I'm thinking of getting the Devilbiss QC3 dessicant/dryer. Maybe instead of the Motorguard M30 or in addition to?

So far, all I've got for drying is 20 feet of pipe followed by a Kobalt water separator. I recall reading in another post on here that Barry said "ONLY 100% cure is Desiccant or refrigerant cooler."

If I get the QC3, is the Motorguard M30 overkill? And if I do both, which order would they go in? And I suppose I'd keep the Kobalt water separator as a first stage, right?

https://www.amazon.com/DeVilbiss-13...&qid=1517842610&sr=8-1&keywords=devilbiss+qc3
 
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i would install M30 10ft down the line from compressor and install QC3 at the end before rubber air line.
that with a 20-30 degree angle down towards the tank with your hardline will help draw moisture back to tank.
i had this setup for years before i went all out on a $700 filtering system.
 
I read some reviews about the QC3 needing its (expensive) filter replaced very soon. But I'm guessing that those folks were using that QC3 for general air and not just paint.

I plan on running a separate air hose connection (and a separate hose) for paint. I hope to get one car's paint job out of it (1 gallon primer, 1 gallon paint, 1 gallon clear). Does that sound reasonable?
 
With the M30 first in line it takes most of the moisture out giving longer life to the QC3.
Plus you can buy a pack of unscented toilet paper real cheap to use as a replacement filter
 
I am far from an expert or even novice but when I painted my Coronet I used the black epoxy for most of the brackets/shields/etc and had a hell of a time getting it to lay down flat. It always had pin holes or ripples in it. The grey that I used for the body would go on like glass but I struggled with the black every time.
 
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