a good filling compound

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Well-Known Member
Sep 20, 2003
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I need advice on an appropriate filling compound.
Is Bondo appropriate as far as sanding properties are concerned for rocketry applications? I'm looking for something that will fill in seams and sand (wet or dry) easily.

I have experimented with CA, Elmers' and Elmers wood filler for that matter already. Y'all got any good alternatives?

you could try the ready patch I mentioned in my last post
I have tried bondo. It works okay but sometimes flakes off, and it is hard to get the mixture right as there is no accurate way of measuring the parts
The difficulty here is that it all depends on what you are trying to fill--particularly what is the material that needs said filling--and then can be complicated further by the depth that that item needs to be filled.

I think that first & foremost, the most important things you can do are A) select the best components/materials you can find & B) develop good build techniques.

I rarely need more than Elmer's Fill 'n' Finish (tyically diluted to make it easier to spread) but I only use it on wood surfaces. I wouldn't expect it to work very well on other surfaces (plastic, fiberglass, epoxy, etc.) About the only other filler I have use for is a high fill primer, but I even use that sparingly & rely more on good sanding & prep work (because I initially selected good components to build with) to accomplish the same goal.

That's what works for me anyway...

I'm working on plastic to paper transition areas. So I need a low shrink formula appropriate for both media.

Bondo (the two part stuff used with creme hardener) works fine but it helps to have some experiance working with it. It hardens quick wich can make working with it a pain unless you've slapped some up on a few car fenders before.
For smaller rockets (LPR) or smaller areas on larger rockets the Bondo spot putty is good stuff. No mixing, has longer working time, sands easy. The only real downside is it leaves a fine red dust all over the place. I usaually use one of the Elmer's products first then finish off with spot putty just to cut down on the dust.
I usually use fill-n-finish for balsa fins, epoxy resin for plywood fins, and bondo spot putty ( in the tube) for plastic mold lines in nosecones, etc. on both model and HP rockets.

I usually fill tube spirals with a few good coats of lacquer primer. It dries very fast so I can sand quickly between coats.

I have had good luck with both bondo spot putty and lightweight drywall spacle (did I spell that right?)depending on how much had to be filled and where.
I've tried the bondo out of the tube and have found that it can be "painted" by first thinning with a bit of acetone. It appears to give a smoother finish with less effort required for sanding and less shrinkage. The disadvantage with bondo is clean up, again with acetone. Elmers is water based and washes easily but seems to be a bit more gritty?

Thanks for your suggestions.