I have a concrete slab as a base in my shed,ive laid a Wickes liquid dpc all over it and it has taken absolutely ages to go off and still feels a little moist to touch.The solution was given three good coats to floor and up on the two coarse brickwork,but the brickwork feels bone dry and the floor as i say feels a little damp still,when i run my hand over it i'm getting a black mark on my skin from it but not the case when i do the same on the brickwork,is this normal?it feels like the floor is sweating somehow?