Damp-proof membranes (DPMs)

Damp-proof membranes (DPMs)

DPMs are sheet or liquid membranes designed to resist damp
caused by capillary action. They do not have to perform as
well as tanking membranes, which must resist water pressure.
DPMs may be positioned under site slabs providing the hardcore
is smoothed with 25 mm minimum rolled sand or preferably
25 mm smooth blinding concrete. This position is more
vulnerable to damage than placing them over smooth finished
site slabs. In this position the membrane can prevent
satisfactory bonding between slab and screed, so a thick
screed is needed, ideally at least 63 mm.
DPMs must be carried up to lap or join DPCs in walls. Brushapplied
membranes are better than sheets in this respect.
Care must be taken not to penetrate membranes when laying.
Any pipe ducts must be in position before screeds are poured,
as any subsequent chasing could well damage the DPM.