Help with Bondo Molds

[Rafael]

As the thread title implies, I'm at a loss here.

First off, let me state that I live in a country where the vast majority of implements, substances and equipment every modeler here uses may see as a given, do not exist here. Even kits are no longer on sale here. I have a good stash from old, better days. Almost all airplanes.

So I want to cast some things. I already do with plaster molds and automotive body repair resin, and the results have been mediocre (i.e. surface detail nor registering well, resin wrinkling, etc.)

I can't find, aves, sculpey or any other magic putty/sculpting substance. But, in my endless exploration of alternate materials, I have found useful things as sawdust, papier mache, balsa, and.....Bondo!

I bought it (a grey thing with a smaaaall tube of blue hadener) very cheap and used it in one of my builds (very defficiently, but I have to climb the learning curve).

Then I stumbled upon an article written by one of our members, Ward Shrake, at internetmodeler.com, and ideas are coming randomly to my head.

I would like to mold/cast (if possible) some kits I have to produce several new "designs". Of course, I would avoid casting pieces with undercuts, and complicated shapes.

Several questions arise, before I even attempt to plaster a valuable (here) little piece of plastic with the stuff:

- Does bondo register detail in molds fairly good?
- Does vaseline work as a release/demolding agent?
- Can bondo castings be made in bondo molds?

Your inputs very appreciated.

Rafa
(eager scratchbuilder)

[Mr. Badwrench]

I don't know the answer to any of those questions, but it would cost very little to find out. Try casting up something you aren't going to use, like a cheap gumball machine toy, or a plastic spoon, and see how it behaves.

[Johnnycrash]

Other than trying to do what you mention, may I suggest these two options;

1) Export your parts/kits to somewhere where the materials used (RTV/Resin) are readily available and have a modeler/caster do them for you, and then ship them back.

2) Import the materials you need (RTV/Resin) and do a bang-up job with the right material.

Both wil be a litle costly. But, you can't beat the results. Bondo (or other rigid materials) don't make the best molds for this. Unless the parts a very simple, NO under cuts, and are open face (the part is one sided). WHile you can get good detail with the Bondo, it's very hard to get it to cover the part completely with out any voides on the surface.

Not the best help, but hopefully some.

[Shinnentai]

Bondo can be cut with fiberglassing (polyester) resin to improve its viscosity for use in moldmaking. IIRC thats how some FX artists used to build molds for casting silicone based makeup appliances.

If all you have available is hardware materials, look for tubes of silicone bathtub caulking. This can be thinned with naphtha and used to create a flexible mold by brushing it on in coats/layers, essentially the same techniques as in creating latex rubber molds. Here's a nifty tutorial link Google turned up when I plugged in "latex molds":
http://www.wetcanvas.com/Articles2/22248/366/
Silicone caulk gives much better results than latex IMO, though it does take a long time to dry/cure and is fairly fumey. Although the tutorial shows Magic Sculpt (epoxy putty) being used for the mother mold, you can use pretty much anything rigid. Plaster is what's most commonly used for this sort of thing, (or you can use... Bondo).

If you really have no better options than just Bondo, look around for a ceramics/pottery workshop. Casting rigid materials in rigid molds is SOP for ceramic arts, so it's a good way to learn the techniques involved.

Ultimately these methods/materials are workable, and can produce quality results. The problem is they're a lot more time, skill, and labor intensive than working with dedicated moldmaking rubbers and casting resins. Like Johnnycrash says, if you can order these online and have them shipped to you, even if you have to have them shipped from another country, the extra cost is likely worth it.

[Rafael]

Thanks for your inputs.
Sadly, I can't order anything out from my country due to severe restrictions on currency change and internet buying.

So I will stick to what I can find to do my molds the cheap way. I understand now that there is no "ideal" substitute for the expressely created materials for molding and casting, but some solutions are "less than ideal", but equally workable

Bondo can be cut with fiberglassing (polyester) resin to improve its viscosity for use in moldmaking. IIRC thats how some FX artists used to build molds for casting silicone based makeup appliances. I used this formula for my casts, but they are sticki to the touch (takes too long to cure. So I went with polyester resin alone. worked like a charm
If all you have available is hardware materials, look for tubes of silicone bathtub caulking. This I did. This can be thinned with naphtha and used to create a flexible mold by brushing it on in coats/layers, essentially the same techniques as in creating latex rubber molds. I have to test this thinning formula Here's a nifty tutorial link Google turned up when I plugged in "latex molds":
http://www.wetcanvas.com/Articles2/22248/366/
Silicone caulk gives much better results than latex IMO, though it does take a long time to dry/cure and is fairly fumey. I molded and cast an old revell Hurricane, a very small item in 1/72 for a building project I have. Without thinning the silicone, and of course, my poor first-timer technique, I had incredibly crisp detail transferred to my mold, only marred by a lot of bubbles, but I believe that Thinning and thin layers will cure this ill. The resin casts are only different from the master for the bubble-riddled surface. The detail transfered exquisitely, though. Although the tutorial shows Magic Sculpt (epoxy putty) being used for the mother mold, you can use pretty much anything rigid. Plaster is what's most commonly used for this sort of thing, (or you can use... Bondo).I went the Plaster way...

If you really have no better options than just Bondo, look around for a ceramics/pottery workshop. Casting rigid materials in rigid molds is SOP for ceramic arts, so it's a good way to learn the techniques involved. I liked the fexible mold the better

Ultimately these methods/materials are workable, and can produce quality results. The problem is they're a lot more time, skill, and labor intensive than working with dedicated moldmaking rubbers and casting resins. I have time. Labor and skills are something I can practice. Like Johnnycrash says, if you can order these online and have them shipped to you, even if you have to have them shipped from another country, the extra cost is likely worth it.

Thank you very much.

If you have more info and advise, I'd be glad to hear.

Rafa