Why is my paint job doing this?

Always been a mechanical guy, never wanted to deal with paint and body (and now I remember why).

Attempting to paint a plastic Suburban grille with poor results. Here is my process:

I sanded it to bare plastic, can sprayed high build primer to fill in low spots, sanded again to keep relatively smooth finish 

Cleaned with wax and grease remover, blew dry with compressed air in my 70F heated garage

Sprayed custom mixed base coat through Amazon HVLP gun with the following result 

Going on 3 days of priming, sanding, cleaning, priming, sanding, cleaning, so the frustration level is high. 

What is the issue?

Chemical contamination?

Moisture?

Still drying paint under it?

I'm thinking incompatible coatings.  Your primer and your paint are not friends.

In reply to SkinnyG :

My thoughts as well. When I painted my wheels with spray bombs, I was very tempted to use the cheaper Rustoleum primer, then the good Duplicolor top coat. Instead, I ate the difference. Primer, base, and clear all by Duplicolor because I feared what happened to nsogiba.

What primer and top coat brands are you using?

Could also be solvent issues. What are your wait times between rounds? 

Do you have a filter on shop air? 

How long are ypu waiting after wax and grease remover( never liked that stuff. Prefer windex or isopropyl alcohol myself)

My guess is that the solvent in the paint is reacting with  the primer. 

Besides non-compatible materials, it might be a case of primer  being "dry to the touch" but not "cured". Most paint products have an "open" time frame where they can be re-coated and they chemically blend. This could work against you if the next topcoat is not the same. It is one of the reasons why sealers are used before topcoats when painting a car.

I will never not be afraid of painting; more ways to go wrong than right.

I used this for cleaning before painting ...

We did this with Rustoleum primer and spray cans ....it was about a week between each stage as we did it on weekends so paint was definitely dry between stages...

Sanding to Bare Plastic:
Good start, but some plastics need a plastic adhesion promoter before applying primer. Sanding alone may not be enough to ensure proper paint adhesion.

High Build Primer:
Using high-build primer is appropriate for filling low spots, but ensure it’s compatible with plastic. Some primers can shrink or fail to bond properly over time on flexible materials.

Sanding Again:
Sanding the primer for a smooth finish is a great step. Make sure you’re using progressively finer grits (e.g., 400-600 grit) to avoid deep sanding marks that show through the paintCleaning with Wax and Grease Remover:

Excellent step, but ensure the remover is completely dry before proceeding, as any residue can interfere with adhesionTemperature Control:Your 70°F garage is within an ideal range, but make sure there’s minimal humidity, as moisture can cause issues during painting.

It sounds like you're putting in solid effort, but painting plastic can definitely be tricky. A few things to consider:

1. Adhesion Promoter: Bare plastic often needs an adhesion promoter before primer. Without it, the primer might not bond properly, leading to poor results.
2. Primer Coats: Make sure you’re applying thin, even coats of high-build primer and giving each coat time to cure fully before sanding.
3. Surface Prep: Your cleaning process sounds good, but ensure no residue from the wax and grease remover remains—it can sometimes interfere with adhesion.
4. Spray Technique: Keep the spray can about 6-8 inches away from the surface, and use light, overlapping passes to avoid uneven coverage.

Plastic parts can be frustrating, but with patience and proper prep, you can get great results. Don’t give up—you're on the right track!