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chachybaby

Bondo Products Clarification

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hey guys,

sorry to be such a newb on this one, and its probably been answered somewhere in the mass of replies... but I've been trying to read and understand the numerous posts/discussions regarding Bondo and how to make one and two piece molds. The more I read, the more its confusing me. Body filler, polyester resin and fiberglass resin need to be broken down better since I'm a bit on the slow side.

I see on the Bondo website, that the body filler and fiberglass resin are different products. Reading the discussions on this forum people are making molds using a) both products on their own or b)a mixture of the two at the same time (my understanding for durabilty, higher resistance to heat and distortion??) Can anyone clarify the difference between polyester resin and body filler?? Is polyester resin esentially fiberglass resin? Cuz I keep seeing polyester resin pop up alot.

Thanks,

C

Edited by chachybaby
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technically there is no such thing as "fiberglass" resin. it is polyester resin (fiberglass is the material the resin is soaked into). Bondo is a brand, not a product.

polyester is a thick liquid resin that when mixed with a liquid catylist (mekp) will harden like a rock

Body filler is a thick paste type material, also polyester based, that you mix with a cream catylist.

you are going to have best results if you mix the 2 together 50:50 and use the liquid hardener with it. becareful with the hardener as too much will create too much heat and warp or crack the mold. use just a little less than recommended on the resin can.

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I've never tried to mix the two, and only use bondo as a filler in making cranks, so I'm far from an expert. My surfboard making is many years in the past. But I've used bondo to fill dings in one of my sons' surfboards, and it holds up fine. I just coat it with crazy glue after it sets up.

However, I did sleep in a Motel 6 last night, so here goes.....

The resin used with fiberglass cloth is like a glue or binder, and is meant to be applied in thin layers. That's why it cracks when poured thick. It has no tensile strength on it's own, and shrinks when thick. The fiberglass cloth provides that tensile strength, like the steel in steel-reinforced concrete. If you've ever mixed some pure cement, and then let it set, you'll see it cracks, too. The sand and gravel in a concrete mix provide a matrix, and the cement is the binder. Too rich a mix (too much pure cement) will shrink and crack.

Bondo has some kind of filler added to it, which allows it to be applied thick without shrinking and cracking.

I don't use bondo for making my molds.

I make my one and two part molds for plastics out of POP, reinforced with drywall fiberglass mesh tape, and coated with diluted D2T to seal the plaster once it's dry.

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ok thanks guys, its maknig much more sense now. As always, very good explanations.

If not using other materials(pop etc), I'm reading a fiberglass resin mold is probably better suited for an open pour mold, that sound right?

also, I know this should be in the wire baits posts, but anybody have experience pouring lead into a (2 part) D2T sealed POP-mold ?? Does the D2T,pop handle the heat or is this idea a recipe for disaster? Obviously I'd make sure the pop was completely dry and sealed properly. It'd be a mold for small batch production, not expecting it to last forever.

I was leaning towards the bondo mold from what I read for this application and hence my question on the clarification.

thanks,

C

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