OK Gary, I didn't realise that bgl was there for a reason.
I checked again and I do indeed see a layering where the afcad has a wet surface on top and it's dry around the edges of taxiways where the afcad hasn't reached. Maybe it doesn't look so bad to me as I have Rex2.0 installed and it replaces some of the default ground airport textures. The textures also seem to retain their alignment. i suppose I just have to decide what look I want. Thanks for your reply.