Q&A Ref: Using Automotive Body Filler / Spot Putty On Rockets

[lakeroadster]

I want to use some automotive body filler / spot putty on my Lifting Rocket to fill some areas on the body tubes and transitions.

Do you folks that use this product apply it directly over the as sprayed primer, or do you sand the primer then apply the filler?

If you sand first, what grit sandpaper?

I'm using Rustoleum Automotive type primer and have applied one coat thus far.

Thanks in advance.

 

[Uncrichie]

I use it over the unsanded primer. I feel the solvent in the spot putty melts into the primer and helps give a better bond. Just my opinion.

Kurt

 

[lakeroadster]

I use it over the unsanded primer. I feel the solvent in the spot putty melts into the primer and helps give a better bond. Just my opinion.

Kurt

Thanks Kurt. What brand spot putty are you using?

 

[Nytrunner]

I am not Kurt, but theres a 70% chance he'll answer bond spot and glazing putty (the 1-part red stuff, not the 2-part white stuff) use ventilation appropriately, it is quite chemical

 

[prfesser]

I use 1-part auto body spot putty, straight-up or diluted with lacquer thinner, on the bare paper/phenolic/FG/CF. Sand after it dries, check if there are any apparently-deep places to refill. If not, then I go with the sandable primer. That's just me.

 

[manixFan]

When I’m using spot putty I generally sand with 150 first to make sure I have good surface adhesion. I never thought about the chemical bond but that’s a good point. Once I have the initial coat of filler, I sand most of it off and go back over with a thinner coat. I typically wet sand to only 400 grit but for some birds I’ll go higher if I’m going for performance. FWIW I’ve always used Bondo part red putty.

I always sand between coats of different primer. If I’m putting on a couple of coats of the same then I don’t. I alternate colors, typically between white and gray, sanding between to reveal the high spots. I wet sand since I’m always using fiberglass tube of some sort. (Although I have also wet sanded phenolic with no ill effects.)

My wife is amazed at how much time I can spend sanding. I call it the Zen of sanding.

Tony

 

[neil_w]

I have some Bondo spot and glazing putty but rarely use it because of the stink. Use Elmer's CWF for almost everything whenever possible.

 

[Uncrichie]

Bondo spot and glazing putty. I try to use it outside, contains very flamable solvents.

Thanks Kurt. What brand spot putty are you using?

 

[Banzai88]

I use it over the unsanded primer. I feel the solvent in the spot putty melts into the primer and helps give a better bond. Just my opinion.

Kurt

My paint and body guy tells me that's how it's supposed to be used.

 

[SammyD]

+1 on Bondo spot putty over unsanded primer - works like a champ for spirals in airframes, depressions in epoxy fillets, clam-shell mismatches on nosecones, and more...

 

[rharshberger]

+1 on Bondo spot putty over unsanded primer - works like a champ for spirals in airframes, depressions in epoxy fillets, clam-shell mismatches on nosecones, and more...

It also happens to be how the instructions say to use BS&GP, it goes on a primed surface. [emoji3]

 

[lakeroadster]

Bondo spot and glazing putty it is then. Thanks for the help.

Have I said recently I love this site!