Can't comment directly on your questions, but I made my tombstones out of Polystyrene Insulation Board. It is fairly easy to work with (and cheaper), and gives a good finish, if sharp blades are used.
I think the US board is has finer 'particles' than the UK version. I say this because people seem to use 'Dremmel' type equipment on it to engrave it, whereas on UK board, it seems to shoot polystyrene balls everywhere! But that might just be my poor DIY skills!
Drylok as far as I can tell is a waterproofer that is added to paint or concrete in the US. Again I used exterior grade masonary paint on my tombstones, mix with acrylic colour of your choice. They have survived three years with little damage, mainly caused by knocking edges off. This isn't a bad thing, as they were made with the intention of looking worn!
HTH
Iffy
I think the US board is has finer 'particles' than the UK version. I say this because people seem to use 'Dremmel' type equipment on it to engrave it, whereas on UK board, it seems to shoot polystyrene balls everywhere! But that might just be my poor DIY skills!
Drylok as far as I can tell is a waterproofer that is added to paint or concrete in the US. Again I used exterior grade masonary paint on my tombstones, mix with acrylic colour of your choice. They have survived three years with little damage, mainly caused by knocking edges off. This isn't a bad thing, as they were made with the intention of looking worn!
HTH
Iffy