Primer Question

[rabidsheeep]

Ok, maybe im doing somethiung wrong... i always thought when priming sometghing it was

sand>prime>sand>prime>sand>paint>seal

now, i was using krylon primer and krylon paint and when i sanded the primer it all basically just scratched off... i was sanding so lightly and i was using a light grit sandpaper...

should you not sand this stuff?

 

[swimmer]

rabidsheep,

It was completely dry, right? High humidity will prolong primer cure rates. The primer is soft until it is dry and can easily be scratched off. Was it "sandable primer?. Should say on the can. What grit sandpaper are you using?

I always use wet sandpaper anytime I sand primer, Krylon or otherwise. Water gives the sandpaper some lubrication.

 

[rabidsheeep]

it wasn't at all humid that day, i know i checked, and i let it dry for 1/2 hour... i dont know the grit, but i know it barely sands balsa so its gotta be light... i guess it was either not dried or it isn't sandable

 

[HeadHunter]

Was it PML QT?

If so I have found it helps to rough it up w 320 grit before the 1st coat of primer. If not, very strange. Must be a bad can.

 

[Omega_D]

I'm recently back into rocketry after a 5 year hiatus. Back then I would swear by Krylon red oxide primer. Drys fairly quickly and dry sands and fills pretty well.

I recently picked up Krylon gray & white primer (Wal*Mart didn't have the red oxide), it says right on the can to sand lightly with 320 grit paper when dry. So I'm thinking this primer can be sanded right?

So I prep my rocket and spray a couple of coats of the gray primer and let it dry overnight. I know it was a little humid so I thought it best to let it sit.

The next day it still wasn't dry. The next week it still wasn't dry, nor the week after. I've had the same luck with the white primer on another rocket as well.

I ended up wet sanding it carefully (cardboard tube). I covered it with Krylon color and let it sit for another week.

Everything seemed dry so I taped off some areas for a different color using auotmotive striping tape. Wouldn't you know it the tape pulled off the color?

To make a long story even longer, I dislike Krylon primer and won't use it anymore. I just bought some Rustoleum automotive primer but have yet to use it. I hope it works better!

On the other hand, I love Krylon paint!

Good luck!!

 

[lalligood]

Originally posted by rabidsheeep
it wasn't at all humid that day, i know i checked, and i let it dry for 1/2 hour... i dont know the grit, but i know it barely sands balsa so its gotta be light... i guess it was either not dried or it isn't sandable

The instructions on the label for Krylon primer are: Recoat anytime. Dries to the touch in 7 minutes. Fully dry in one hour. Can be sanded after 2 hours.

As has been recommended here countless times: be sure to shake the can for a minimum of two minutes before spraying.

As far as drying time goes, I prefer to let it dry overnight or at the very least after 8 hours of sitting in a very hot garage (very easy to do in my neck of the woods this time of the year!) before sanding. Krylon does NOT sand well (read: gums up the sandpaper) nor does it fill very well (at least the white & gray primers...haven't tried the red one). However, when applied properly, it provides an excellent surface for the final glossy coats.

As long as you don't have a problem with those limitations, Krylon primer has done a super job for me.

HTH,