Chopped Strand Mat (CSM) is the reinforcement layer. This is saturated with roofing resin to form the GRP laminate.
There are two main specifications of mat: 450g per sq metre which is the standard weight of mat for most roofs 600g per sq metre which is used for more demanding applications, such as walkways and balconies.
For tanking applications (pools, ponds, green roofs etc) two layers of 450g per sq metre are recommended.