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Polyfelt Underlay Installation

Polyfelt Underlay Installation


Subgrade preparation

Level the subgrade to remove ruts, potholes etc., with a depth greater than 100mm. If rutting occurs after a period of use, re-grade the sub-base layer by filling these ruts with fresh aggregate or substrate. Do not simply level out with a grader.

Laying the geotextile Roll out the geotextile over the prepared subgrade.

Overlapping Overlap adjacent rolls by at least 150mm. Increase the overlap to at least 250mm if the subgrade is very uneven or soft.

Or Welding

Welding of the laps is preferable over very low bearing-capacity subgrades. The geotextile is overlapped 100-200mm and heated with a propane burner or a blowlamp to soften the fibres and allow them to fuse when pressed together. Care should be taken not to overheat the geotextile. It is sufficient for the person unrolling the overlapping layer to walk over the heated lap to weld the two sheets together. If the geotextile is damp and welding is difficult, the overlap dimension should be increased to 300mm.

Overlay Protection

Placing of the gravel or other material if Polyfelt is being used as a protective overlay. Plant equipment should not be driven directly over the geotextile as this could damage the geomembrane beneath; the aggregate should be back dumped. The required depth of the fill material depends in the application ,bearing capacity of the subsoil or gradient but should not be less than 100mm.


Spreading should be carried out by hand or with tracked plant from outside the pond or lake installation. Should tracked plant be required we recommend that protective boards or similar be placed on top of the geotextile for both stabilisation purposes and to ensure no damage is caused to the geotextile or geomembrane layers.

Capillary Action

If using Polyfelt an a protective overlay application, ensure that the overlay and the underlay do not come into contact with each other in the anchor trench,as sometimes there may be a capillary or wicking effect through the material – as such the water could continually wick between these two layers

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