In the past, I have experimented with home casting of 80 and 90 Duro two-part polyurethane with the intention of making repro Weasel track bands and grouser pads.
What I found was the stuff has quite different properties to natural rubber, and sadly not all of them good. The worst thing was that home-cast PU splits quite easily along small cracks. Very easily in fact. Natural rubber can withstand lots of small splits without breaking. The other thing was the water absorption affected the material. A friend left one sample I cast out in the rain and it went from a translucent honey colour to an opaque brown. Although it returned to its original state after drying out, we agreed it was not a good sign.
Also the pigment seems to affect the strength. Even adding the tiniest bit of black pigment to the PU seemed to produce weaker material. The other main problem was that of air bubbles, they are difficult to completely remove unless the job is placed in a vacuum chamber (which I don't have).
If going the PU route for retreading tracked MV wheels and bogies, I strongly suggest getting it done professionally by forklift wheel repair places where they use something much better than the 2-part stuff. Perhaps it's thermosetting, or perhaps done in a vacuum but whatever it is, it is much better and IMO the only way to get reliable and strong PU casting.
Steve.
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