Polythene sheet for use as a dpc should be black, low density polythene sheet of single thickness not less than 0.46 mm, weighing approximately 0.48 kg/m2. Polythene sheet is flexible, can withstand distortion due to moderate settlement in a wall without damage and is an effective barrier against moisture. It is laid on an even bed of mortar and lapped at least the width of the dpc at running joints and intersections. Being a thin sheet material, polythene makes a thinner mortar joint than {bitumen} dpc, and is sometimes preferred for that reason.
Its disadvantage as a dpc is that it is fairly readily damaged by sharp particles in mortar or the coarse {edge}s of {brick}.