Polythene And Polyethylene Sheet

Polythene And Polyethylene Sheet

Polythene or polyethylene sheet is often used as a damp-proof membrane with oversite concrete for all however extreme situations of dampness. It is suggested that the sheet should be no less than 0.25 mm thick (1200 gauge). The sheet is supplied in rolls 4 m extensive by 25 m long. When used under concrete oversite the sheet ought to be laid on a blinding layer of sand or compacted fuel ash spread over the hardcore.

The sheets are spread over the blinding and lapped one hundred fifty mm at joints and continued throughout surrounding partitions, below the dpc for the thickness of the wall.

Where site situations are reasonably dry and clean, the overlap joints between the sheets are sealed with mastic or mastic tape between the overlapping sheets and the joint accomplished with a
polythene jointing tape as illustrated in Fig. 29.

For this lapped joint to be successful the sheets have to be dry and clean else the jointing tape won't adhere to the surface of the sheets and the joint will depend upon the burden of the concrete or screed urgent the joint sufficiently heavily to make a watertight joint. As clean and dry situations on a building site are rare, this type of joint ought to be solely used the place there's unlikely to be heavy absorption of ground moisture.
The place site situations are too wet to make use of mastic and tape, the joint is made by welting the overlapping sheets with a double welted fold as illustrated in Fig. 30, and this fold is kept in place by weighing it down with bricks or securing it with tape till the screed or concrete has been placed. The double welt is shaped by folding the sides of sheets together after which making a welt which is flattened.

The plastic sheet is effectively not possible to fold and so stiff and elastic that it'll at all times are inclined to unfold in order that it requires a deal of patience to fold, hold in place after which contrive to fold along the joint. Through the use of the utmost size of sheet available it is attainable to minimise the number of joints.

The sheet should be used in order that there are solely joints a method as it is impractical to form a welt at junctions of joints.

The place the extent of the damp-proof membrane is under that of the dpc in walls it's essential to turn it up towards walls in order that it may possibly overlap the dpc or visqueen dpm be. turned over as dpc as illustrated in Fig. 31. To keep the sheet in place as an upstand to partitions it is essential to keep it in place with bricks or blocks laid on the sheet in opposition to partitions till the concrete has been positioned and the bricks or blocks removed because the concrete is run up the wall.

On the internal angle of partitions a reduce is made within the upstand sheet to facilitate making an overlap of sheet at corners. These sheets which are commonly used as a damp-proof membrane will function an efficient barrier to rising damp, offering they don't seem to be punctured or displaced during subsequent building operations.