Polythene And Polyethylene Sheet

Polythene And Polyethylene Sheet

Polythene or polyethylene sheet is commonly used as a damp-proof membrane with oversite concrete for all but extreme situations of dampness. It is suggested that the sheet needs to be a minimum of 0.25 mm thick (1200 gauge). The sheet is equipped in rolls four m wide by 25 m long. When used beneath concrete oversite the sheet should 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 walls, beneath the dpc for the thickness of the wall.

Where site conditions are reasonably dry and clear, 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 visqueen sheeting this lapped joint to achieve success the sheets must be dry and clean else the jointing tape will not adright here to the surface of the sheets and the joint will rely upon the weight of the concrete or screed pressing the joint sufficiently heavily to make a watertight joint. As clean and dry situations on a building site are rare, this type of joint should be only used where there's unlikely to be heavy absorption of ground moisture.
Where site conditions 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 formed by folding the edges of sheets collectively after which making a welt which is flattened.

The plastic sheet is successfully inconceivable 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 endurance to fold, hold in place and then contrive to fold alongside the joint. By utilizing the utmost size of sheet available it's potential to minimise the number of joints.

The sheet must be used so that there are only joints a method as it's impractical to type a welt at junctions of joints.

Where the level of the damp-proof membrane is below that of the dpc in walls it is vital to turn it up against walls in order that it could actually overlap the dpc or be. turned over as dpc as illustrated in Fig. 31. To keep the sheet in place as an upstand to partitions it's essential to maintain it in place with bricks or blocks laid on the sheet towards partitions till the concrete has been placed and the bricks or blocks removed as the concrete is run up the wall.

At the inner angle of partitions a minimize is made in the upstand sheet to facilitate making an overlap of sheet at corners. These sheets which are commonly used as a damp-proof membrane will serve as an efficient barrier to rising damp, offering they don't seem to be punctured or displaced throughout subsequent building operations.