My kid is bugging me about turning our basement into an underground movie theatre. But I want to have it tanked and damp-proofed first before we even begin furnishing the interior. I found this damp proofing experts based on London, and I have already kept in touch with them. But before I close the deal, I want to make sure that I’m getting the right and fair priced service. So is there anyone here who knows the average cost of such a service? I would appreciate some ranges. TIA.