[RiverMan]

I was using the "bondo" luresmith but have only built a couple of molds with it. I also had a considerable amount of mold shrinkage. The stuff is tuff tho!


Hey Red,

Have you tried the standard two-part silicone/water mold with the foam? If not, do you see any reason why it would not work? I thought this would be a good quick option for me before going to the epoxy.

Thx.

[redg8r]

Sure, like I said, the 100% silicone & RTV only really differ in catalyst. they will still exude silicone oil for natual release properties.

I did try the rigid foam on a 100% silicone mold & it released fine.
I also sprayed some primer on the mold before pouring the foam & the primer pulled free along with the foam, pretty neat, time saver.

Good tips guys, interesting stuff huh?

[RiverMan]

Yes it is some good stuff, thanks Red. I haven't used the 100% silicone long enough to know how it will hold up over time. I was originally using it for the Featherlite and it was causing some problems in the curing process. I will give it another try and see what happens with the foam.

RM

[luresmith]

Hi Riverman,

I guess bondo is a brand name, haven't seen it in this neck of the woods. Look for an auto body filler designed for finish applications. They have finer solids, which results in less bubbles and a smoother surface in the cavity. They are also formulated to shrink less. The stuff is definately tough, you'll get lots more castings out of them than you will from RTV. I've been experimenting with some of the metal impregnated epoxies but haven't been happy with the results so far. These formulations aren't far short of real metal, but don't seem to give the smoothness that standard epoxies do.

A tip for anyone planning on using silicone (RTV or 1 part) - make the molds thicker than you would for soft plastics or non-foaming resins. This helps prevent the mold from being pushed out of shape as the foaming urethane expands. Learnt that one through bitter experience!!

Cheers
Greg

[RiverMan]

Greg,

I have no idea where "bondo" falls in the scheme of epoxy finishes. It would be interesting to know how close this stuff is to what your used to using. When dry it has a rust-brown color. To be honest "Bondo" is the only brand/type that I have found available but will take a closer look at what's available next time. I too tried experimenting with an epoxy/metal a couple of years ago without good success. As I recall the stuff was quite spendy and didn't give me the detail I was hoping to find. Thank you for the advice!

Red,

I built a silicone mold last night and had forgotten just how easy it is to build them with the water catalyst. I layed the bait into clay first and then built the first half, 20 minutes dry time then the other side, worked great! The mold took most of one tube of silicone to make so it cost me about three bucks. I'm sure the mold won't hold up like the epoxy but sure covenient and easy to build.

RM