Powder crawls away

[PatrickMcGovern]

I'm trying to powder coat a fan housing for a late model (72-79) VW Bus.
I cleaned it, blasted it, and coated it with another company's powder. It covered nicely but I didn't like the color (gray) so now I'm trying to coat it with Super Wet Black.
I lightly sandblasted the gray powder coat to rough it up a little, blew the dust off with compressed air, wiped it down with denatured alcohol and a lint free rag, and then blew it off again.
Satisfied with the cleanliness of my part, I applied the super wet black. First I hit the nooks and crannies and then moved on to the large, flat areas.
On one of the flat areas the powder seemed to crawl away and leave an exposed crater. Is this what y'all in the powder coating business call a fisheye? I've sprayed lots of cabinets, etc. with liquid paint (painting contractor, 15 years) so I've heard the word fisheye before. My craters look kinda like fisheyes but it's the crawling powder that has me stumped.
So, I saw it happening but I stuck it in the oven and cured it anyway. I was hoping the craters would magically dissappear in the oven but they didn't.
At this point I figured the problem was caused by dirt or something on the surface. No problem, I'll just sand it with some 400 grit and coat it again.
I also entertained the possibility of moisture coming through the air hose so I drained the compressor, checked the filter, and used a different hose that I knew was dry. I also cleaned the gun and used fresh powder.
When I applied the second coat of black powder,the craters came back in the exact same places!!
I blew the powder off and cleaned the part again.
Same craters, same places.
The first coat of gray powder was perfect.
I'm not exactly sure what the fan housing is made of. It looks like aluminum to me, but I'm no expert.
Ok, I've described the problem as thoroughly as possible.
What am I doing wrong?
Please don't tell me I have to strip the powder coat off.
Thanks.

[sswee]

You say it apears to be aluminum, would it be a cast part? What size is the crater?
SS

[hvac36]

If the part was Powder Coated already before you did the black it sounds like you my have to pre-heat the part to 150-170 degrees. The static charge my not be coming thru the Gray PC.
If the crater is big enough I'm sorry to say you may need to reblast the part.
Now you tried the Other Powders No try the Best!! Caswell all the way...

Jim S...

[ShelbyCSXT]

It sounds to me that the static cling thing isn't working in those spots. At this point, it looks like you don't want to strip it down to bare metal, so i'd suggest heating it up to 150f and shoot it while it's hot. From what i understand, you'll see the powder melt on contact, so it wont matter that you cant get the static cling.

[PatrickMcGovern]

Ok, sorry it took so long for me to respond. Had some trouble logging in.
sswee, yes, i'm pretty sure the part is cast aluminum and the craters are about 1/8 to 1/4 inch diameter.
hvac, i am using powder from Caswell. The gray stuff is from another company - it worked fine. I should have just left it alone.
Shelby, yes, it's the static cling thing that you mentioned. Very strange. I can actually see the little powder grains rolling away from the spots.
I'm going to try a light sand blast to rough it up a bit, then heat it up a little bit, and then pc it again.
Thanks for the advice. I'll let you know how it turns out.