DM25-Drainage Board-400

DM25 Drainage Board


Radmat DM25 Drainage board is a geocomposite drainage layer ideal for structural drainage applications on roofs and podiums requiring vehicular access or high volumes of pedestrian access, including motorised wheelchairs and mobility scooters. Specially designed to be compatible with structural waterproofing DM25 provides optimum performance over the whole life of the structure.

Consisting of a high strength flexible polyethylene cuspated core with a non-woven geotextile bonded onto one or both sides.

The geotextile filters a wide range of materials allowing water to perculate into the core to be efficiently drained away to a discharge point. The geotextile is bonded to the core to ensure that it does not deform into the drainage passages under the load of the backfill material allowing continuity of the drainage void. The single cuspated HDPE core forms a high-performance drainage layer with clear void to allow flow in all directions. The compressive strength and creep resistance properties of DM25 ensures that the core maintains its drainage capacity, even when subjected to compressive loads. DM25 is durable and sufficiently robust to resist the mechanical stresses imposed during installation and throughout the design life. Use of DM25 will eliminate the need for further protection of the waterproofing.


Unroll over waterproofing membrane or protection fleece overlapping side and end laps by one cuspate.

MGO Boards

Magnesium Oxide (MgO)

Unsuitability of Magnesium Oxide (MgO) building boards

As you will be aware through our Blue Notes, at the end of 2018 changes were made to the Building Regulations requiring external wall materials on buildings that contains flats, hospitals, residential care premises and student accommodation above 18 metres in height to be European classification Class A1 or A2.

This has resulted in the use of some relatively new type of building boards, commonly known as MgO (Magnesium Oxide) board, being used as either sheathing or as a backing board to render systems.

The NHBC have raised concerns that some of the products they have come across do not have suitable verification of performance and that similar products are known to have failed overseas, and specifically the NHBC has received reports from Denmark and other countries of defects in walls built using MgO building boards, typically as either sheathing or as a backing board to render.

Until such time as these issues have been resolved, and Radmat have conducted compatibility tests with specific manufacturers MgO products, it is our belief that they are not suitable for use with our waterproofing systems and are not acceptable for Warranty.

Cement Particle Building boards are proven as a suitable substrate for Radmat waterproofing systems and are available with European classification Class A1 or A2 and BBA Certification.  Where a sheathing or render system backing board is required these products should be used and are acceptable for Warranty.

The full NHBC statement can be read using the link below, but the key parts of the statement are detailed below.