First some background. After getting back into rocketry several years ago and doing the usual Internet research at the time, I settled on Kilz spray cans as my primer of choice. It was readily available (if not cheap), and others seemed to be getting good results with it. My daughter was taking an auto body class at the time, and schooled me in the art of sanding most of the primer off between coats. I was building mostly 3 to 4 inch diameter rockets, I had no complaints with the primer. I considered my paint jobs better-than-average and didn't think that the effort to achieve the results was unreasonable.
Later, I began building more of the smaller, more detailed, scale rockets. I started to get annoyed when I would carefully apply a coat of Kilz, only to find what I describe as "pinhole bubbles" when I started sanding. These bubbles look like a multitude of pin pricks and extend through most (or all) of the primer coat. To make it worse, I would occasionally take the time and effort to sand these bubbles away, only to hit previously undiscovered bubbles in the layer beneath, requiring still more sanding!!! I found that I was spending more time sanding out imperfections in the primer coat that imperfections in my rocket. Not good.
Finally, a couple weeks ago I decided to do some testing. Since these bubbles didn't always show up, I was sure it was something that I was doing wrong, and since the bubbles seemed to often appear in longitudinal strips, I thought it might have to do with recoating too quickly as I rotated the rocket and started to prime areas of the rocket that had already been primed moments before (if that makes any sense). I decided that the variables were 1) distance from the surface being primed, 2) amount the can had been shaken (could shaking too much be causing the bubbles?), and 3) time between coats (were lower layers out-gassing and causing the bubbles?). I did the test where I normally paint my rockets, in the back of my closed garage. The temperature was near 70 and low humidity. I grabbed a crumpled piece of naked BT-50, and started priming. First with the can hardly shaken at all, from close, medium, and far distances, then with the can shaken like I would normally do, 30-60 seconds, from all three distances, and then shaking the can for a full five minutes, from all three distances, followed by some recoating of the previous samples.
The result, after drying overnight??????
Every freaking sample showed signs of bubbling, to some extent or another!!! The "best" sample looked to be the hardly shaken, close, immediately recoated sample, but I think that additional sanding would probably just start hitting additional layers of bubbles that were hidden under the sloppy coat of primer. Even the well shaken, single coat of primer applied from a "finish coat" distance of nearly two feet had bubbles. Unbelievable.
I headed for the hardware store and grabbed a can of Rustoleum 2x flat white primer and tried it on my current build, which had already been through a couple sessions with Kilz. I was a very skeptical because it went on much more like paint than the thicker Kilz primer I was used to. I didn't think it would cover imperfections (like tiny bubbles from the Kilz) very well, and was actually worried about sanding it. I couldn't have been more wrong. After three coats of 2x primer (waiting my normal 24 hours between priming and sanding) sanded with 220, then 320, then 400 grit sandpaper, the model looked great. It was wonderful to quickly sand away surface imperfections, and not be confronted with underlying gotchas. I found I could be much more picky with the overall surface smoothness, since I wasn't spending so much time dealing with dreaded bubbles. I followed this with three coats of Rustoleum 2x gloss white (15 minutes between coats), and the rocket still looks fantastic.
It's been 48 hours and tonight comes the masking and my first attempt with Rustoleum Industrial Choice Florescent Red-Orange, but that will be a different thread...
Later, I began building more of the smaller, more detailed, scale rockets. I started to get annoyed when I would carefully apply a coat of Kilz, only to find what I describe as "pinhole bubbles" when I started sanding. These bubbles look like a multitude of pin pricks and extend through most (or all) of the primer coat. To make it worse, I would occasionally take the time and effort to sand these bubbles away, only to hit previously undiscovered bubbles in the layer beneath, requiring still more sanding!!! I found that I was spending more time sanding out imperfections in the primer coat that imperfections in my rocket. Not good.
Finally, a couple weeks ago I decided to do some testing. Since these bubbles didn't always show up, I was sure it was something that I was doing wrong, and since the bubbles seemed to often appear in longitudinal strips, I thought it might have to do with recoating too quickly as I rotated the rocket and started to prime areas of the rocket that had already been primed moments before (if that makes any sense). I decided that the variables were 1) distance from the surface being primed, 2) amount the can had been shaken (could shaking too much be causing the bubbles?), and 3) time between coats (were lower layers out-gassing and causing the bubbles?). I did the test where I normally paint my rockets, in the back of my closed garage. The temperature was near 70 and low humidity. I grabbed a crumpled piece of naked BT-50, and started priming. First with the can hardly shaken at all, from close, medium, and far distances, then with the can shaken like I would normally do, 30-60 seconds, from all three distances, and then shaking the can for a full five minutes, from all three distances, followed by some recoating of the previous samples.
The result, after drying overnight??????
Every freaking sample showed signs of bubbling, to some extent or another!!! The "best" sample looked to be the hardly shaken, close, immediately recoated sample, but I think that additional sanding would probably just start hitting additional layers of bubbles that were hidden under the sloppy coat of primer. Even the well shaken, single coat of primer applied from a "finish coat" distance of nearly two feet had bubbles. Unbelievable.
I headed for the hardware store and grabbed a can of Rustoleum 2x flat white primer and tried it on my current build, which had already been through a couple sessions with Kilz. I was a very skeptical because it went on much more like paint than the thicker Kilz primer I was used to. I didn't think it would cover imperfections (like tiny bubbles from the Kilz) very well, and was actually worried about sanding it. I couldn't have been more wrong. After three coats of 2x primer (waiting my normal 24 hours between priming and sanding) sanded with 220, then 320, then 400 grit sandpaper, the model looked great. It was wonderful to quickly sand away surface imperfections, and not be confronted with underlying gotchas. I found I could be much more picky with the overall surface smoothness, since I wasn't spending so much time dealing with dreaded bubbles. I followed this with three coats of Rustoleum 2x gloss white (15 minutes between coats), and the rocket still looks fantastic.
It's been 48 hours and tonight comes the masking and my first attempt with Rustoleum Industrial Choice Florescent Red-Orange, but that will be a different thread...
