Chopped strand mat, also known as fiberglass mat is the most popular type of fiberglass compared to fiberglass cloth. Chopped strand mat is less expensive. It comes in weights such as 3/4 oz., 1 oz., 1.5 oz., 2 oz. and 3 oz. The weight has figured out per square foot, not per square yard.
Chopped strand mat is often used as the first layer when making a mold. It is a layer against the gel coat. This helps prevent print through. Print through is the pattern of the fiberglass fabric is visible on the surface. When making a mold solely out of that, you will want to use 5-8 layers.
The matt is often used in between layers of cloth to build up thickness. The thicker the part, the stronger it is. Use matt when weight is not a factor. If a lightweight part is desired, do not use Matt.
Mat is made up of randomly-oriented fibers that are held together by a resin binder. This binder is typically a polyester resin which makes it incompatible with epoxy resin systems. Only use polyester or vinyl ester resins with it.
Mat does not need to be cut. It easily rips apart, leaving a feathered edge. The feathered edges can be laid on top of each other to avoid seams in the laminate.
How chopped strand mat conforms to a surface?
Here, we will laminate a piece of chopped strand mat to a plastic Halloween pumpkin. We chose the pumpkin to demonstrate how well chopped strand mat conforms to a complex surface.
Working with fiberglass will be hazardous. So, remember to wear safety equipment before you start. Safety glasses, latex, vinyl gloves, and a respirator are all vital to keeping you safe from the fiberglass and resin. To protect your skin and clothes wear Tyvek coveralls. Also, work in a well-ventilated area.
First, clean the surface with acetone to remove any dirt or grease.
Second, apply molder lease to the surface. Wax it on as you would wax your car. Let the mold release dry then wipe off. Apply 4-5 coats to assure good separation. For larger applications or when working with brand new molds, also use part all #10. It is a spray film that will add extra protection when removing your part.
Next, mix your resin. We are mixing 2 oz. of ortho laminating resin at 1% MEKP. Be sure to mix thoroughly for several minutes.
Lay the chopped strand mat on the surface to be laminated. For this part, we will start by adding resin to the middle and work outwards. Working with resin can be messy. Lay down a drop cloth or other material to protect the area from spills and drips.
As the chopped strand mat saturates with resin, the binder dissolves and allows the short strands of fiberglass to easily move and conform to various complex shapes.
A chopped strand mat will now conform to the part with the use of a brush or roller. The excess fiberglass can be trimmed once the resin has reached the green stage. This is when the resin has somewhat hardened but is still tacky, use scissors or a razor blade to trim the fiberglass. Allow the part to fully cure.
When removing the part, typically a wedge is used to help force the two pieces apart. It isn’t necessary on this part.