Quote Originally Posted by rjustice View Post
Thanks for the insight... When you say that the abrasive nature of the concrete deteriorated the mold, were these deep draws, that shrunk down around the Delrin?... what i am considering, is something that would have more of a flat surface to it, maybe more like the concrete stamps just make it look like a natural rock surface. It would be perhaps .8 of depth, because that is what our machines will do in one shot. The sides of the blocks, would be formed with plywood, and just cap the bottom with this decorative carved face.

Thoughts?....

PS, it probably would be a very good time to buy stock in Dawn, there are going to be a lot of greasy birds that will get cleaned up!...
Basically what happens with the delrin is it gets scratched up. Those scratches will hold material no matter how slick the plastic is. This will make the mold stick to the concrete. With that, even though it's hardened it's not fully cured and can still break depending on the mix. It just needs to be greased properly even with that kind of slick material. The mold sounds good. If you're planning on using the ply more then a few times. Put a few thick coats of poly on the ply. They'll last a lot longer.