When laying up a fiberglass mold or repairing a structural component, selecting the right reinforcement is critical. Two of the most common materials are Chopped Strand Mat (CSM) and Woven Roving. But when should you use which?
Chopped Strand Mat (CSM)
CSM consists of short fiberglass strands randomly dispersed and bound together. It is incredibly easy to work with, soaking up resin quickly and conforming perfectly to complex, tight curves. It is the go-to material for the initial skin coat and for building bulk thickness quickly.
Woven Roving
Woven roving looks like a heavy, coarse fabric. The continuous glass strands are woven together, providing immense structural strength and impact resistance. However, it doesn't conform to tight corners as easily as CSM and can leave a rougher surface finish.
The Perfect Combination
In most heavy-duty applications (like boat hulls or storage tanks), the best approach is to alternate layers. A layer of CSM provides a good bond and smooths out the surface, followed by a layer of Woven Roving for sheer strength. This alternating laminate schedule ensures maximum durability and prevents delamination.
