Polythene And Polyethylene Sheet

Polythene And Polyethylene Sheet

Polythene or polyethylene sheet is usually used as a damp-proof membrane with oversite concrete for all however severe conditions of dampness. It's endorsed that the sheet needs to be at the least 0.25 mm thick (1200 gauge). The sheet is supplied in rolls 4 m large by 25 m long. When used below 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 partitions, under the dpc for the thickness of the wall.

The place 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 completed with a
polythene jointing tape as illustrated in Fig. 29.

For this lapped joint to be successful the sheets must be dry and clean else the jointing tape will not adhere 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, visqueen sheeting this type of joint should be only used where there is unlikely to be heavy absorption of ground moisture.
Where 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 formed by folding the sides of sheets collectively after which making a welt which is flattened.

The plastic sheet is successfully not possible to fold and so stiff and elastic that it'll at all times tend to unfold in order that it requires a deal of persistence to fold, hold in place and then contrive to fold along the joint. By using the maximum dimension of sheet available it is possible to minimise the number of joints.

The sheet must be used in order that there are solely joints one way as it is impractical to kind a welt at junctions of joints.

The place the extent of the damp-proof membrane is under that of the dpc in partitions it is mandatory to turn it up towards partitions in order that it may overlap the dpc or be. turned over as dpc as illustrated in Fig. 31. To maintain the sheet in place as an upstand to walls it is necessary to preserve it in place with bricks or blocks laid on the sheet in opposition to walls until the concrete has been positioned and the bricks or blocks removed as the concrete is run up the wall.

At the internal 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, providing they aren't punctured or displaced during subsequent building operations.

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