A composite is a material that contains more than one component. On a boat, this is typically fiberglass, which is made up of fibers and resin. The orientation of the fibers is key to the strength of the component.
The resins used and the density of the resin used also determine the strength of the component. As a general rule of thumb, the least amount of resin used in a part yields the strongest part.
Other composites can include glues, which can be made up of resins and fillers. Different resins and fillers have different properties. Epoxy resin makes for a great glue to bond to most any substrate. Using the same resin that was used in the substrate is another excellent way of making a good bond.
Many glue applications require filling, and some glues function better when there is a void to fill, while some glues, like wood glue function better with less material.
The two types of bonds made, when applying a resin to a substrate, are chemical bonds and mechanical bonds. Chemical bonds occur on a chemical level - make sure that the resin is compatible with the substrate. Mechanical bonds occur by roughing up the substrate by sanding and grinding. A smooth, polished surface has no mechanical bond. In every case, bonding is best done by optimizing both chemical and mechanical bonds to the substrate.
There are many types of composites, each having different properties:
- fiberglass is an excellent all round material for building boats
- epoxy is an excellent material for building and glueing things together.
- fiberglass matt is an excellent first layer to use in any construction''
- fiberglass biaxle cloth is an excellent layer for strength
- fiberglass finishing cloth is an excellent last layer for a smooth finish
- kevlar produces a very tough part that can absorb energy because it can distort then regain its shape
- carbon produces a a very strong part
What the final resin, and cloth or filler is used, is determined by the strength requirements of the part.