Membranes Under Paving & Bases
Water permeable/free draining membranes are essential barriers, laid over a compacted sub- grade beneath the base or sub-base layer of either MOT Type 1 (for standard paving projects) or MOT Type 3 (for those projects designed to be free draining or water permeable (larger patios, car parks or driveways) to prevent the base material from being pressed into the soil.
Although we are trying to avoid mentioning Brand names, the one product that is universally recommended is Terram, which is a non-woven geotextile fabric, available in large rolls up to 450 sq metres (4.5m x 100m) sold as T1000. Ensure to over-lay the material, bringing it up to and over the finished size, and trim off afterwards, to ensure 100% coverage.
It is also used in drainage systems, as a trench liner or for wrapping soakaway crates, due to its’ permeable properties. Very versatile, as floor stabilization, ground protection and to prevent migration of fines, it may be used for rainwater harvesting (SuDS compliant) and for preventing rootzone soil from being washed into the sub-base in planting pits.
Other fabrics are often black, and are woven, which, oddly enough, does not allow water to drain through it efficiently, and are unsuitable as membranes under paving projects.
