Guide boat repair with polyester resin or epoxy resin advantages and disadvantages

A GRP boat (glass fiber reinforced boat) can be repaired with both polyester resin and epoxy resin. We would like to briefly examine the advantages and disadvantages of boat repairs with polyester resin or epoxy resin. There is also a short guide for boat repairs.

When repairing a boat, the different types of synthetic resin are selected based on a number of criteria. For example, epoxy resin should also be used for the repair on a boat made of epoxy resin. This is because polyester resin does not adhere particularly well to an epoxy resin laminate. In principle, one can assume that epoxy resin adheres to both a polyester laminate and an epoxy laminate. Polyester resin, on the other hand, adheres best to a polyester resin laminate, but less well to an epoxy resin laminate.

Epoxy resin also has the advantage that it is resistant to osmosis. Osmosis is an acid-alcohol reaction that occurs in polyester resin as water diffuses into the laminate. This process is more common in boats that are permanently in the water than in boats that are dry/out of the water. Osmosis is indicated by bubbles in the laminate and gelcoat layer. Osmosis bubbles usually contain a yellowish-brownish liquid. Newer, high-quality polyester resins and the associated improvement in processing have led to a significant reduction in osmosis damage in recent years. Today, polyester resin, provided it is of good quality, can also be used for underwater areas. However, epoxy resin remains the first choice when repairing osmosis.

When repairing a boat, you can work selectively or extensively. The flat work requires that the hull is repaired with a flat layer of reinforcing fiber on the hull after sanding and cleaning. Here it is recommended to use glass filament fabric when using epoxy resin. When using polyester resin, you can work with both glass fiber mats and glass filament fabric. In contrast to glass filament fabric, glass fiber mat is held together with a binder that is dissolved by the styrene in the polyester resin.

The selective repair is usually done by repairing the damaged area by applying reinforcing fibers and synthetic resin.

Now how is the repair done? At the beginning, the damaged areas must be cleaned, the damaged parts removed and the damaged areas cleaned. Broken spots should be filled. This should not be done underwater with polyester filler, since polyester filler can have a hygroscopic effect. Damaged areas can be filled with filled epoxy resin (e.g. with micro glass balls, glass fiber flakes or cotton flakes), or by using epoxy putty. After filling the damaged areas, the area or the boat is laminated. This can be done with epoxy resin or polyester resin. After lamination, the laminate is either sealed with a fine layer, i.e. top coat, or filled and varnished with epoxy putty.