Dimple Drainage Membrane 8 mm with Geotextile (HDPE Drainage Board)

What it is

A dimple drainage membrane is a plastic sheet pressed into rows of small studs. Set against a wall, the studs hold a gap open, so water that seeps through the backfill runs down to a drain instead of standing against the waterproofing. Kitovu ordered this one for foundation walls, laid vertically.

The gallery shows a black studded sheet on a roll, sheets laid out on a slab, and one sheet fixed to a foundation wall under a profile strip, with gravel at its foot. None of these pictures shows a fabric layer. The geotextile face and the 8 mm stud height in the product name are therefore still being confirmed with the supplier, as is the maker.

Until then, only other makers’ data are available. On the PM DRAIN-TEC 400 data sheet, PMI-Plast describes a drainage board with geotextile: an 8 mm HDPE dimple sheet with polypropylene fabric bonded to the studs. The fabric filters the water and stops fine soil from silting up the channels, while the flat back spreads the load over the sealing behind it. PMI-Plast gives about 400 kN/m² in compression and a range of −30°C to +80°C; both are figures for a similar product, not confirmed for this item. Boards, mats and drainage cells are compared on the dimple drainage membrane page.

How it is used

For a basement or foundation wall, PMI-Plast gives these steps for its PM DRAIN-TEC 400; they are written for a similar product and are not confirmed for this item.

1. Cut sheets across the roll to the wall height and hang them from the top down, geotextile facing out towards the soil.
2. Let each sheet stand roughly 15 cm higher than the waterproofing. Overlap neighbouring sheets, lifting the fabric at each joint, and close the run with an overlap of at least 30 cm.
3. Fix the sheets only for the time being, with wooden battens for example, since the backfill will later press them to the wall.
4. Stand the bottom edge on the drain pipe that runs round the building, which PMI-Plast wants wrapped in no less than 15 cm of gravel that will not wash into it. Trim the top at soil level when the trench is full.

The studded sheet protects the wall’s waterproofing but does not replace it. For that layer, Kitovu stocks the APP Torch-On Waterproofing Membrane, Mineral Finish, a torch-on bitumen roll that Kitovu offers for foundations as well as flat roofs and terraces. The gravel-and-pipe drain at the foot of the wall is explained in the French drain guide.