Good morning, 

Thank you for getting in contact. With the resin being cast at 15-20mm thick you have 2 options for this. As you are going to be suspending the aluminium in the resin I would recommend using the GlassCast 10, the reason for this is that it is slightly faster curing that the GlassCast 50 but can be built up to the 20mm thick in 2 pours. Of course, this would be the same for the GlassCast 50 but it would take a considerable amount of time longer to cure.

When pouring in layers, you will need to wait for the previous to reach its b-stage of curing before pouring the next layer. The b-stage is when the resin is firm but slightly tacky.

As for the quantity, I have worked out that you will need 4.5kg of resin if you wanted to cast 20mm but would only be 3.37kg of resin for a 15mm thick pour.

If there is anything else I can help you with, please let me know.

Best Regards

Tom