Help, Rondo not hardening

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Chewbacca

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Hey guys hopefully someone can help me out.

Currently I'm in the process of building a set of ODST armor
I got to the stage where I used rondo to harden the inside of my armor but 3 days later the rondo still has not set all the way. If you press on it, it will leave a finger print that will disappear about an hour later and the armor does not have a hardened quality to it.

I used epoxy resin which has worked on the rest of the armor exterior curing fully within 8 hours and bondo which also has cured fully on its own. I mixed the epoxy resin parts A and B together for 5 minutes and mixed the bondo and cream hardener together for 2 minutes in separate containers. I then mixed them together in a 1 part resin 2 part bondo mixture and mixed again for 3 minutes and poured/ brushed the rondo over the armor.

Any ideas on how to either make the rondo cure at this stage, or what I did wrong in the process that caused the rondo not to cure?

Here is the bondo I used:

IMG_20150106_122714929.jpg

Here is the resin I used:

IMG_20150106_122827678.jpg

Here is how the rondo appears on the ODST shoulder pauldron
IMG_20150106_122729932.jpg
 
I may be wrong but isn't bondo polyester based? And therefore should be mixed with polyester resin?
i could be wrong so someone please correct me if needed.
also, what is the temp where the piece has been left to cure?
 
It looks like you used Bondo Glass, it not the same as what everybody else uses. Bondo Glass has strands of fibgerglass in it. I have never used Bondo Glass with the Rondo method and it could be that it should be used exclusively on it's own.

If you would like to try and fix it, I would personally put another layer of Bondo on top of it, but with a much larger amount of hardener to compensate for the rest.
I've done something similar to this method but with Fiberglass Resin.

It could also be the resin and bondo brands not mixing well. Anyways, let me know if this helps at all.
 
I may be wrong but isn't bondo polyester based? And therefore should be mixed with polyester resin?
i could be wrong so someone please correct me if needed.
also, what is the temp where the piece has been left to cure?

I read somewhere on the forums that people have used epoxy resin with bondo to make rondo and it has worked. That's why I mixed them separately before putting them together, so the individual hardeners would have time to react with the resin and bondo.
Also its about 45F where I'm working (which may be an issue) but the resin and bondo are hardening perfectly when used separately



It looks like you used Bondo Glass, it not the same as what everybody else uses. Bondo Glass has strands of fibgerglass in it. I have never used Bondo Glass with the Rondo method and it could be that it should be used exclusively on it's own.

If you would like to try and fix it, I would personally put another layer of Bondo on top of it, but with a much larger amount of hardener to compensate for the rest.
I've done something similar to this method but with Fiberglass Resin.

It could also be the resin and bondo brands not mixing well. Anyways, let me know if this helps at all.


Alright thanks. I'm going to add a layer of bondo on top of the rondo with a ton of hardener and see if that does the trick
 
Remember when you combine them, you're halving the concentration of both resin and hardener of each mixture within the overall mix, so curing drops to 1/4 efficiency at best. With curing, that delay may be exponential. Might be wise to leave it a week.

Second, you say the fingerprint disappears. Is that the cured rondo mix behaving like a foam, or is it still wet to the touch and that's the epoxy self-levelling?

I'm not a composites expert just yet and don't have too much information to go on here, but I think what I'd try to do here is scuff up the surface a bit with a sanding sponge or something, then brush on a thin layer of epoxy hardener. Then after a day or two, wipe off any excess hardener that's still on the surface (hopefully the whole thing will be marginally more rigid now) and then lay a 1/8" Bondo layer over that. Then scuff that up and go over the top of it with fibreglass cloth and epoxy. If the whole thing isn't rigid and more or less cured by then, it's probably a write-off. Unless it's rigid enough to expanding foam fill and then brush-mould and cast in urethane, but that vs re-peping is a cost/time equation only you can answer.

Edit: Yeah your 45F is the problem. Bring it inside at 70-80F and it'll be done in a day or two. Can't push the temperature boundaries when you're watering down those concentrations like that. Maybe if you were using polyester resin instead of epoxy.
 
The first time I use rondo, I ended up with the same thing. The piece finely hardened to the point where it wasn't really sticky. But that took a very long time (a couple of weeks I think, maybe more).

I just recently rondoed another test, but this time I added a lot of extra hardener (about 1/2 more I think, about 15-18 drops per ounce of resin, and a good amount of paste to make the bondo pink, but not red) And it worked out superb! almost fully cured in just a few hours (got harder after a couple of days)

For mixing, I mixed the resin and bondo together really good first, then I added each hardener, and mixed that in fast. And used it before it started hardening beyond pourable. Beware: it gets super hot! Make sure it's not sitting it on anything flammable, or somthing with a low auto ignition temp.

From the looks of it, you used a lot of bondo hardener (a lot more then you need that is), and probably not enough resin hardener? (I see it's a 2 part) I've never used any other resin than bondo's fiberglass resin.

You could possibly do a coat of resin on top of that to make it workable. And hopefully it will harden up over time.
 
Remember when you combine them, you're halving the concentration of both resin and hardener of each mixture within the overall mix, so curing drops to 1/4 efficiency at best. With curing, that delay may be exponential. Might be wise to leave it a week.

Second, you say the fingerprint disappears. Is that the cured rondo mix behaving like a foam, or is it still wet to the touch and that's the epoxy self-levelling?

I'm not a composites expert just yet and don't have too much information to go on here, but I think what I'd try to do here is scuff up the surface a bit with a sanding sponge or something, then brush on a thin layer of epoxy hardener. Then after a day or two, wipe off any excess hardener that's still on the surface (hopefully the whole thing will be marginally more rigid now) and then lay a 1/8" Bondo layer over that. Then scuff that up and go over the top of it with fibreglass cloth and epoxy. If the whole thing isn't rigid and more or less cured by then, it's probably a write-off. Unless it's rigid enough to expanding foam fill and then brush-mould and cast in urethane, but that vs re-peping is a cost/time equation only you can answer.

Edit: Yeah your 45F is the problem. Bring it inside at 70-80F and it'll be done in a day or two. Can't push the temperature boundaries when you're watering down those concentrations like that. Maybe if you were using polyester resin instead of epoxy.

I just encountered this. I took out my heat gun and pretty much boiled the rondo. It hardened within a few hours. Epoxy resin is heat activated so getting that to cure while the bondo does it's chemical evaporation should be enough to get it workable in short order.
 
I just encountered this. I took out my heat gun and pretty much boiled the rondo. It hardened within a few hours. Epoxy resin is heat activated so getting that to cure while the bondo does it's chemical evaporation should be enough to get it workable in short order.

Hey man, this post was 8 months old... would've been best to leave it dead and start a new thread with your problem/solution. Posting on a thread over 3 months old is generally frowned upon on forums, as it bumps down newer content.

Since its been bumped though, might as well share a little insite on this.

The reason rondo works well when fiberglass resin and bondo brand body filler are used, is because they are both polyester resin- based. In other words, you can use liquid hardener for fiberglass resin, and it will cure both the resin and the body filler (which is essentially powder enriched polyester resin). When you try to cure both polyester and epoxy resin mixed together, you are using multiple materials which react differently with different hardeners.... which will not have an ideal result.
 
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