Can I use chopped strand mat (CSM) with epoxy resins?”
The simple answer is ‘no’ – for two reasons. Firstly CSM is used to reinforce the resin in GRP structure, where the resin usually makes up two thirds of the GRP and takes as much of the load as the glass fibre. The reverse is true with epoxy resins. The fibres usually make up two thirds of the volume of the laminate. The primarily role of the epoxy is to hold the fibres in place and transfer the load evenly across the fibres, which bear the majority of the load. The CSM can only effectively be used with an “excess” of resin, because of its structure. The open nature of CSM means that it is very difficult to achieve a high fibre volume fraction. Secondly, the glass surface in CSM is treated to bond well to polyester resin. It can bond to epoxy but it is not so compatible and in some cases a cloudy resin results because of this incompatibility.
