Bad fillet goof...can it be fixed???

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Well-Known Member
Apr 8, 2004
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Alright I don't think pics will be needed but if you want them ask and ill get them.

Its been awhile since i have looked at this roc. started it some time ago but goofed on the butt end fins with the epoxy heres the problem..

as it was my first MPR attempt and i didn't know very many epoxy techniques
(i rushed it ..oops) so using my 5min epoxy and some popsicle sticks i bought at crafts 2000 i tried to make my epoxy fillets...well i messed them up....BAD
the epoxy started to set before i could get off all the runny spots and put epoxy all over the BT. this was done on plastic tubing BTW. But i couldn't really see much of the epoxy goofs so i sanded to what i though was alright and primed it... :eek:

Well as you can imagine everylittle spot showed up...and everylarge spot too.
so now the bottom end looks horrible! not to mention some of the epoxy didn't get mixed right and never cured so on top of that i tried to put another coat (paint AND epoxy).....that helped minimally.

Ive tried everything sanding, scraping... is there anyhope for this roc? or is it pretty much trash? have you guys had this problem?

everytime i try to scrape it off i leave dings in the plastic..that looks even worse and sanding goes nowhere because of the uncured epoxy and the paint peels....

and advice would be great, insults are welcome also seeing how this has to be the dumbest thing anyone has ever done.

thnx in advance.

Ahh grasshopper, you have learned a valuable lesson...don't use 5 minute epoxy for fillets. I had somewhat similar problems many years ago, but mine may even have been with 20 minute. :eek: No rocket is all are :)

I am not terribly worried about the bumpiness, as my Big Brute will show. The original job was reasonable but I have made many quick fixes to the non-TTW fins and I'm sure they look worse than yours.

Some ideas:

The worst issue with non-mixed epoxy is that it is not strong. I'd try to carefully scrape off as much as possible. You can either sand the hardened bumps or use a dremel to knock them down. The idea here is to lower them to a point when you can re-fillet with fresh well mixed epoxy. They don't have to be smooth if you are recoating. I have also had good success overcoating with a sandable epoxy filler like SuperFil from Shadow Composites. Search this forum and you will see many other filler recommendations.

Good luck!
thnx. I think i may try the dremel and then fill or level of the cratches with epoxy...that sounds like the best way to go right now....theres gonna be alot of ( dremel sanding :p ) of this
The point is to avoid the sanding by grinding and filling :cool:
... I have a few rockets with crummy fillets like this. my kids try to console me by saying they look great from 30 feet away.
hahah thats great.....thats the same thing my dad said to me.
mines a 10 footer. :rolleyes:
Bah, good from 10 foot...that's my criteria...quit complaining and build something else ;)
Can you use a dremel or other rotary tool and grind out the old stuff? Doesn't have to be pretty, just lay in another layer of "Good" epoxy.
yeah I've grinded off most of the old stuff hopefully enough then ill go get the RIGHT epoxy and try to make it a little better this time.
I'd cut it off, using an Xacto as a scalpel. I'd expect to cut the tube, and so do so on purpose and very carefully. Then I'd patch the plastic tube by filling in the dings. Having practiced with epoxy for a while now, that's what I'd use (slow cure, painted on) to fix the tube. You'd end up with a thick layer, thicker than the BT down there. Go with it. Take a look at an Acme fin can, and go for that look.
is there any certain epoxy you would recommend for this?
obvoulsy something that adheres to plastic...but a brand? or a kind that finishes or sands well?
thanks for all the advice! ;)
Originally posted by moocrew
is there any certain epoxy you would recommend for this?
obvoulsy something that adheres to plastic...but a brand? or a kind that finishes or sands well?
thanks for all the advice! ;)

As far as I'm concerned, no epoxy sands well. It'd have to be painted on quickly and smoothly. A stiff sponge might do well here. For painting, they all seem to take paint fine.

I now use strictly 5 minute Devcon. I plan out what I'm going to do before I ever mix it, even practice with the tools I'll use, then I work fast enough so that if things really go south I can get most of it back off. Mostly all I need is rubber gloves and paper towels, and a bamboo skewer for fine placement (a syringe would be better).
I have found the thinner epoxies are easier to use for fillets. I often use Bob Smith (hobby store type) 20 minute and have used West. (for fillets) Like DynoSoar says, I don't find any epoxies easy to sand. However, if you get a good epoxy filler, it will sand nicely.
I find that the longer the cure the better it sands. I can't sand five minute epoxy at all. West Systems epoxy sands reasonably well, and much better if you add filler.
what about that epoxy "putty" from aerotech?
anyone tried that?
thou it seems a bit dumb just to buy putty for $6 and pay 6 for shipping...anything "like" this avable in some sort of store... home de-pot lowes? hobby lobby?
most things ive tried that are similar either don't dry or aren't strong enough to use as a sub.
I use an epoxy putty from a hardware store, but forget the brand. I sets hard and sticks well, but it is impossible to get a good fillet with it. It's hard as a brick. The fillers I'm talking about are very light and sand easily. They will adhere to anything epoxy will, including epoxy itself. I haven't tried the putty from apogee (I assume that's who you mean, I don't know of anything from aerotech)

I have to retract what I said earlier. I don't use fillers often. hokkyokusei was right about West with fillers added. I haven't had good luck with fillers in 20 minute epoxy (tried it once). You have to use the longer setting epoxies for these.
yeah i meant apogee oops. :eek:
I might just try 20 or 5 min to fill in all the dings and gaps left. I might even try this "Foam Finish" stuff. sands well and takes a while to set but it works very well. Besides i don't need to worry about strength in these areas.