You need more arms than Vishnu to fit it without wrinkles . Bloody sticky stuff, but ridiculously bombproof, and excellent for a 1st floor install. Get more of it if funds allow and finish the room, with upstands, to get it utterly waterproofed. Is it 610? The stuff Impey give you in a mastic tube? It is the anti-Christ of sealants, and is STILL on some old combats and STILL wet / tacky to the touch!