Client: Asda Walsall
Type of works: supply of Delta-NP Drain.

Damp problems that might occur in a below-ground level bakery at an Asda store in Walsall have been overcome by using Delta-NP Drain from Delta Membrane Systems.
The bakery and car park for the store have been placed below ground level on a very wet site where severe water ingress and soil erosion were inevitable.

To overcome these problems, Delta-NP Drain membrane is fixed to the piled foundations of the store and apartment structure. In total, some 1,500m2 of Delta-NP was used on this project which is a mixture of Grade 1 and Grade 3 basement constructions.

The soil and between the piles is bound and held back by the Delta-NP Drain. Water is allowed to pass through, and this is drained down in the void in the middle of the membrane, into a channel cast into the ground slab for disposal.

Delta-NP Drain features a two-layer design. The first is a polyethylene drainage sheet with a dimple profile pattern – giving it high strength, durability, and increased drainage capacity. The dimple sheet keeps incoming water away from the structural sealing layer.

Layer two is a polypropylene geotextile mat securely bonded to the dimple crowns by thermal welding. The rot-resistant geotextile removes suspended soil particles and prevents clogging of the flow passages in the dimple texturing.

As Delta Project Manager, Paul Durham explains: “BS 8102 dictates how to keep water out of basement structures. Grade 1 is a car park where there is an acceptable amount of water ingress allowed.

With Grade 3, for health reasons, no penetrating water or damp formation is permissible – and this is the grade that was demanded for the bakery.”

Apart from controlling the damp ingress, Delta-NP Drain is also being used to give stability to a 100mm dense concrete block wall.