Fiberglass resin....

Butters · Post by **Butters** » Fri Dec 31, 2010 1:32 am

Can Bondo Fiberglass resin be used for casting? If so, what are some of it's characteristics? Good for small stuff? Big stuff? Or is the most horrible substance I can use?

I got some on sale from a going out of business sale.

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Fri Dec 31, 2010 2:32 am

I used to use it.
It is is often brittle like glass...

You know like "those kits"...

You don't want to use it in large pieces, it can generate
a lot of heat while curing. Small pieces are okay, but still,
it can be brittle.

Rogviler · Post by **Rogviler** » Fri Dec 31, 2010 1:37 pm

If you use it by itself, then yes it will be brittle. It's not intended to be used like that though. If you reinforce it with either fiberglass mat or cloth, or polar fleece, it's tough stuff.

If you were casting something with a lot of detail and really wanted to use fiberglass, I'd basically fill in all the detail in the mold with fiberglass gel and then lay down your resin with cloth/mat/fleece. The gel is essentially already reinforced resin that's finer-textured than the next step up, which is the type with "hairs" of fiberglass in it.

Either way, I wouldn't use it for something with really fine detail as it's not going to flow very well into that.

-Rog

Butters · Post by **Butters** » Sat Jan 01, 2011 1:31 am

Thanks fellas.

AbsoluteSciFi · Post by **AbsoluteSciFi** » Mon Jun 13, 2011 3:02 am

Fiberglass: polyester resin, is good for several things, casting is one of them... if you understand how to use it. If it is tiny detail you need, paint the mold with several layers or resin, then use the fiberglass to "embed" it into the walls of your casting then put a coat down then some cloth, then coat, then cloth... by doing this it gives the shell incredible strength. It is true the resin by itself is a bit brittle, but if there is less than a 1/4 inch above the reinforcing layers, it will be fine, just don't use the model as a hammer. The most important part of using polyester resin is to mix it up in the right amounts, with the right percentages of catalyst to resin. Too much and you have a very brittle casting, and it could crack under its own molecular shrinkage, not enough and you have a sticky rock that never fully cures. Mix thoroughly. It pays to experiment first on a block of wood.

It helps to mix in a cup or deep container that you can easily stir the mix in. The Bondo brand resin will cure in about five minutes, so you can't spend more than a minute on mixing. Chill the can of resin if you want a longer curing time, but this makes it harder to mix.

Tankmodeler · Post by **Tankmodeler** » Wed Jun 22, 2011 8:52 am

And, being polyester resins, they are as stinky as h*ll. Do it outdoors or in the garage with the door open. Doing it inside will certainly result in consequences from anyone you live with plus the fumes are NOT good for you.

Once it's cured, it will be fine.

Paul