Surface damp-proof membrane

• Floor finishes such as mastic asphalt and pitch mastic that are impermeable to water can serve as a combined DPM and floor finish
• A DPm placed above the concrete bed is the easiest method

Sandwiched damp-proof membrane below floor screed

• An alternative method is to place the DPM between the floor screed and the concrete bed
• THe floor screed should be at least 50mm thick to minimise the possibility of folding , due to unrestrained shrinkage
• A sandwiched DPM will delay wet floor screed over it drying out to the concrete below and will prevent adhesion of the floor screed to the surface below

Damp-proof membrane below concrete

• DPM is placed on a blinding layer over the hardcore
• Being impermeable to water , DPM will delay the druing out of wet concrete to ground.
• A DPM placed below the concrete bed has 3 advantages :

1. It will be protedted from damage during sussequent building operation
2. It will keep the concrete bed dry and make it a better thermal insulator
3. During construction , it will act as a separating layer preventing leakage of the cement matrix into the harcore layer, which could result in a weak concrete mix