I have a patio I'd like to remove in order to place decking. I don't want to lose out on height what with the 30cm limit, sO I'd like to replace the patio brick with top soil, I'd like to leave the patio bedding (hardcore and sand) where it is. Can I do this? Can around 6" of topsoil be laid on top of what is essentially non organic matter? I won't be growing anything and it will all be covered by a membrane. I can dig the post holes deeper into the established soil. will the topsoil just blow away if it's too shallow?