Looking for recommendations - filler material

[Re-Bar Ricky]

Hey all - I've got several rockets in the final build stages before going to primer. I've got a couple of rockets that have cut tubes attached to the main tube to simulate engine intakes (Estes Lynx and Scorpion, among others). I am looking for recommendations on the best filler material to fill the gaps between the cut tube and main tube to make more smoother appearance. I can do regular glue or epoxy on fin fillets with no problem, but I haven't had too many kits where I've had to cut tubes like this. And, I am working on a Fliskits Decmi8 which will need that same kind of filler on the tube joints. I've seen bondo filler, wood filler, etc but I'm not sure which would work best in this situation. Your expert opinions are always welcomed! Thanks!

 

[Rob Campbell]

I recommend light weight spackle from the hardware department at Walmart. It's easy to shape when wet, it sands easily, and I haven't found a primer it isn't compatible with.

 

[neil_w]

I would normally use CWF in such situations.

I have some lightweight spackle but haven't used it in rocketry yet. Doesn't seem to adhere all the well in general, although maybe it would be fine for non-structural use.

 

[Titan II]

After you adhere the parts with adhesive, this is great for filling minor gaps, etc. Make sure you get the 907...NOT the two part version.

 

[prfesser]

After you adhere the parts with adhesive, this is great for filling minor gaps, etc. Make sure you get the 907...NOT the two part version.

It's not too cheap but it dries SO much faster than water-based fillers. Squirt some into a glass or polypropylene container, add some talcum, add acetone or lacquer thinner to get a proper texture, and it paints on balsa just fine as a filler.

 

[neil_w]

If you care about odor, the Bondo is extremely… fragrant. That’s why I rarely use it, despite the fact that it is very good stuff.

 

[David Schwantz]

The bondo in the tube shrinks as it dries. I like to use the 2 part stuff in the can. No shrinking with that.

 

[Titan II]

If you care about odor, the Bondo is extremely… fragrant. That’s why I rarely use it, despite the fact that it is very good stuff.

Actually, I think it smells great.

Regarding the two Bondos. As I mentioned...minor gaps. It looks like that is what you may have in the models you mentioned. I also use it for body spirals and to smooth out any minor irregularities in filets, for example. It is not for something thick. In that case, I also use two part.

 

[neil_w]

Actually, I think it smells great.

It’s not what *I* think of the smell that matters here, if you catch my meaning.

 

[Hobie1dog]

Bondo Spot & Glazing putty in the tube. dries quick, sands easily, tough stuff, all hardware and auto stores usually have it in stock.

 

[Cape Byron]

Bondo is harder to get in Oz than it should be, and as a result ridiculously expensive. Antipodeans can use Septone blade putty, ~$20 AUD a 375 gram tin and available at Repco. One part, dries in minutes, sands well.

 

[Hobie1dog]

Bondo Spot & Glazing putty in the tube. dries quick, sands easily, tough stuff, all hardware and auto stores usually have it in stock.

And by all means heed the warning label on it which says causes eye irritation, as my eyes are half swollen shut, and feel like somebody threw sand in them. use goggles

 

[caveduck]

If the joint can be made to sit level, I usually just use some good 5-min epoxy like West G-5 for the fillet. It lays out very nicely and can be made absolutely smooth via a very short application of a heat gun from some distance. You do not want to heat it enough to accelerate the cure much, just reduce the viscosity. Spot putty fills any dimples.

BTW be aware that the Bondo spot putty and 2-part polyester filler are VERY different products with dramatically different properties. There are other threads around here discussing the differences in detail. TLDR: spot putty must be kept in a thin layer, cures by solvent evaporation, and is structurally very weak. The 2-part filler can be applied in bulk, is a lot stronger, cures by catalytic reaction, is harder to sand, and has extremely short working time. Both will accept nearly any type of primer.

 

[GlenP]

Good suggestions already, for larger gaps I like indoor light spackle. You could also try Titebond quick and thick for that body tube to cut body tube joint in those particular kits, It will shrink a bit but you can add another layer to build it up. You can put a healthy fillet on there and it will stay put pretty well.