Raw PolyUrethane parts painting. Epoxy reacting with adhesion promoter.


Promoted Users

I have some raw polyurethane parts that I am trying to paint. I properly sanded and cleaned the parts. I sprayed a coat of Bulldog adhesion promoter then Epoxy Primer with 10% reducer and the primer starts to react creating a cracked look. It happens within 5 minutes of spraying the epoxy.

When I spray the epoxy over the adhesion promoter with no reducer added there is no issues at all, however the epoxy is orange peeled. I need a smooth surface.

I am manufacturing these parts and I want my customers to have a nice smooth epoxy primer surface. I also like the idea of having the open window time that if a customer wants me to paint the items for them. I can pull from inventory if its in the window time and simply denib the epoxy and base/clear.

I have the waterborne version of Bulldog adhesion promoter also available that I haven't tried yet. Would that make any difference?

There is also the debate about not needing adhesion promoter which would be even better because it would eliminate a step and cost. But then other people say I absolutely must use it. I can't risk paint failure or my reputation would be destroyed.

Any ideas ?

Here is a link to the pictures:








Trying to be the best me, I can be
First off I would not use the Bulldog products. I've had issues similar to what you are having in the past using Bulldog. To me it looks like the reduced epoxy is causing the ad-pro to lift.
Here's what I would try if I was in your situation.
1. Don't sand the parts , use a grey scotch brite pad and some Presta "ScuffStuff" or equivalent sanding paste and go over entire piece.
2. Only use a water based wax and grease remover. SPI 700 would be perfect. Avoid using any solvent based W&G remover.
3 Get some of the SPI 600 adhesion promoter, activate it with SPI 6501 activator at a ratio of 5:1 (5 parts ad-pro to 1 part activator)
4. Apply ONE medium wet coat. Wait 30 minutes, then proceed with epoxy. As for Epoxy I would only use SPI as well.

By activating the adhesion promoter it should "lock it down" and not allow subsequent coats of epoxy to cause any lifting etc.


Promoted Users
Great advice. Didn't know you could activate adhesion promoter!

What you described should solve all problems. I thought the bulldog adhesion promoter was bullet proof and didnt react with anything. Now I know to retire it.

Thanks for advice.


Paint Fanatic
Staff member
What Chris said!
Also, adheision promoter can cause this (any brand ) and not uncommon and here is why.
Allways caused by getting on the adhesion promoter to soon, it can cause cracking but usually, it will cause wrinkling in the later coats of paint such as
2nd coat of base wrinkling or the first coat of clear wrinkling.


Combo Man
Are the parts polypropylene or polyurethane? Because if they really are polyurethane, they shouldn't need adpro at all.

Jim C

this will happen with almost any adhesion promoter, even spi. in addition to what barry said you have to remember that adhesion promoter is a 1k product. when you spray a solvent product on it, it will soak up the solvents and basically re-liquify to some extent. the wetter and heavier you spray on top of it the more it rewets the adpro. now if you combine that with a product that flashes fast then what happens is the primer, base, etc on top hardens up a bit as the adpro soaks up the solvents. when the adpro soaks those up it swells up a bit and makes the wrinkles. now if you leave it alone, once all the solvents come completely out of all the layers then it will tend to lay back down and the wrinkles can go away by anywhere from 50-100% depending on products. there are a couple key factors to eliminate this. #1 the less adpro you use the better. you want a solid coat of it but as thin as possible. 1 coat is better than two. #2 when spraying anything over adpro NEVER hammer it. spray one light to med light coat at a time, let flash off twice as long between coats as you would normally wait. remember what you spray on top may seem dry but thats because the solvents went into the film not out. the heavier the adpro is the more it will soak up.


Combo Man
It's really important to know what kind of plastic it is, because adpro used inappropriately doesn't help, and can hurt.


Top Banana
Being u make these pieces, how bout making a few of anything simple shapes for testing.
Sand one, ad pro one, sand & ad pro one & epoxy all at same time.
Days? later put packaging tape on them, rub tape real good & pull.

I tried same ad pro u did. Smelly smelly burning plastic rubber smell on some of my 93 caddy bare black stripped with heatgun & tape, razor blade bumper fillers.
I said the heck with that stuff & sanded the rest of fillers & based right on em. Still holding fine. No i'm not trying tape pull lol.
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