Yesterday Cement on Epoxy, Today Epoxy on Cement

I keep going back and forth with the casting materials to determine which product is the right surface for the exterior and which product is the right material for the interior. Although there are many considerations, including but not limited to resistance to weathering and exposure to sunlight, finished detail and strength, cost and ease of use and ability to release from the molds, as well as, to adhere to the frames with minimal hardware and labor. Cement or a hybrid of cement, like surface bonding cement may be the best exterior coating that I have come up with and epoxy is the best chemical mixture that works well for bonding and sealing a piece to a wood or aluminum frame.

My previous experiments were almost settled with a combination of epoxy on the outside and cement on the inside, but no matter what I do I have to worry about the epoxy on the outside looking worn from exposure to heat and cement on the inside releasing from the frames and falling on the interior of a structure. Over the last week I made a veneer of cement that measures less than a quarter of an inch and I liked the amount of detail that it preserved. Bonding to it immediately wasn't successful, but I think I can work with a thin veneer of cement on the exterior as a better surface for weathering and use an epoxy cement type of mixture to bond the top layer and adhere the whole piece to a frame. I don't like the idea of drilling through the thin veneer of cement for bolting the frames together, but I think the top surface needs to be finalized and then I will work around the problems that are created as a result of using these materials once it is finalized.

Cement can be painted and should resist the absorption of heat more than the epoxy and by resisting the heat this should create a more stable temperature for the bonding layers and reduce the shrinking and expanding more than if I used epoxy on the top layer. The plastic finishes like epoxy and polyester resin seem to create very hot surfaces and in some cases that will crack sooner than I think they should. Although the fragility of the cement layer is potentially the weakness with a thin layer of that material, I am hopeful that if I back it up with more rigid and solid materials I can make it strong enough for the job at hand, which is to make weather resistant frames that can be used like tiles and shingles to build a dome like structure.