Wet laminating (wet lay-up) is a widely used technique for making composite parts. Wet lay-up usually involves impregnation of dry reinforcement with a low viscosity thermosetting resin using hand lamination but can also be done using one of many other automated techniques. The dry reinforcement may be impregnated on/in the mold or on a flat surface and then transferred to the release coated mold and placed in wet. Once the layup is complete, the part can be cured open to the environment, press cured, or cured under a vacuum bag. Depending on the cure process and desired cure rate, the selection of the resin is critical. Fiber volume and void content are significantly affected by the lamination process and technique as well as cure process. While wet-laminating is often thought of as a technique for making low cost composites, the performance does not have to be sacrificed.
Laminating resins are generally two-part thermosetting systems (Part A resin/Part B curing agent) which have the necessary viscosity and wetting characteristics for impregnation of dry reinforcement. These resins require thorough mixing of the two parts before lamination. The selection of the laminating resin depends on the mixing technique and method of resin application, cure process (heat or ambient) and rate, and desired final properties. It is important to know that epoxy resin systems that are made to cure fast, and therefore remove from a mold or handle in short time, also have a short pot-life and gel time. Wet laminating resins are offered with range of cure rates and temperatures, and properties from high elongation to aerospace mechanical performance.