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Spray-up is similar to hand lay-up but uses special equipment—most notably a chopper gun—to cut reinforcement material into short fibers, add them to resin and deposit the mixture (called chop) on to a molding surface. Spray-up is more automated than hand lay-up and is typically used to produce large quantities.

SPRAY-UP, or chopping, is an open mold method similar to hand lay-up in its suitability for making boats, tanks, transportation components, and tub/shower units in a large variety of shapes and sizes. A chopped laminate has good conformability and is sometimes faster to produce than a part made with hand lay-up when molding complex shapes.

In the spray-up process, the operator controls thickness and consistency, therefore the process is more operator-dependent than hand lay-up. Although production volume per mold is low, it is feasible to produce substantial production quantities using multiple molds. This process uses simple, low-cost tooling and simple processing. Portable equipment permits on-site fabrication with virtually no part size limitations. The process may be automated.


As with hand lay-up, a gel coat is first applied to the mold and allowed to cure. Continuous strand glass roving and initiated resin are then fed through a chopper gun, which deposits the resin-saturated “chop” on the mold. The laminate is then rolled to thoroughly saturate the glass strands and compact the chop. Additional layers of chop laminate are added as required for thickness. Roll stock reinforcements, such as woven roving or knitted fabrics, can be used in conjunction with the chopped laminates. Core materials of the same variety as used in hand lay-up are easily incorporated.


These are the same molds as hand lay-up: simple, single cavity molds of fiberglass composites construction. Molds can range from small to very large and are low cost in the spectrum of composites molds.

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