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Polyester Resins
All polyester resins and gelcoats are divided into different groups and to enable the reader to better understand these, we have included a brief description of each type.
Waxed - A waxed resin or gelcoat will cure to a hard and tack free surface when fully cured. This type of material is used when only a single coat is applied or when it is used as a final coat.
Unwaxed - All unwaxed resins and gelcoats when fully cured remain slightly sticky and tacky. These materials are used for multiple laminations, such as building up thicker laminates or when doing molding work.
Orthophthalic - Orthophthalic (ortho) resins and gelcoats are the basic chemistry of polyester resins. It is a type of molecular structure that is considered the standard in the industry. All general purpose resins are orthophthalic.
Isophthalic - Isophthalic (iso) resins and gelcoats are a step up from the ortho resins in that the molecular structure is denser. This makes the isophthalic material, stronger more flexible and more water proof than the orthophthalic materia.
Epoxy Resins
Epoxy resins are classed as "thermosetting" resins as they too cure by internally generated heat. Epoxy resins have greater bonding strength, less shrinkage and better weathering end physical characteristics than polyester resins. Epoxy resins require greater care in use. If you are to use an epoxy resin follow the manufacturer's recommendations explicitly. Epoxy resin is higher in cost, slow curing ( normally 24 hours before subsequent work can be performed ) and problems with handling.
GEL-COATS
Gel-Coat is a glossy, opaque, and (usually) colored surface of a fiberglass product. Its purpose is to protect the product as well as make it attractive to the eye. It also eliminates the need for painting the product after it has been built.
Although the Gel-Coat is on the "top" or surface, of the fiberglass product, it is applied first during its construction, usually by spraying it on the walls of the mold. The remaining fiberglass reinforcements are
then laminated onto the Gel-Coat, permanently bonding it to the molded product.
Gel-Coats consist of a complex mixture of several materials, including a curable polyester resin, a colorant, and a catalyst, which are formulated according to specific requirements.
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