This guide will cover the basic techniques used for fiberglass repair work for your boat. The techniques used here will cover the majority of projects you would encounter when repairing cracks, sagging decks, delaminated decks or patching holes.
The fiberglass deck of your boat is most probably composed of fiberglass strands encased in polyester resin and covered with a layer of protective gel coat. When repairing a fiberglass structure, we typically are either repairing the cosmetic look of gelcoat layer or patching the structural fiberglass underneath.
- Epoxy & Polyester Resin
- Surface Preparation
- Gel Coat
- Simple Bonding
- Laying Fiberglass
- Patching a hole
Epoxy & Polyester Resin
Most sailboats are made of polyester resin because polyester resin is much cheaper than epoxy resin. For small projects the advantages of epoxy may outweigh the price advantage that polyester gives. Epoxy has the advantage of being stronger and does not have as strong of an odour. Epoxy also has the advantage of bonding or sticking well to existing polyester or wood. Polyester on the other hand will only bond to other polyester or wood and will not make a good strong bond to existing epoxy. Which you use is up to you. I personally prefer epoxy but don’t let that discourage you from using polyester if that is what you prefer.
Your boat was most probably built by spraying the loose fibers into a mold. In our repair projects we will typically build up layers of fiberglass cloth mat saturated with the resin. The fiber used comes in various assortments of cloth mats and weaves. The strength comes from the combination of the resin and mat working together to cure into a strong hard plastic. In situations where the hardened plastic must be made even stronger, we sandwich the fiberglass around a solid core. Balsa wood and plyboard were a popular affordable material for core however for our smaller repair projects, modern synthetic foam cores may be preferred for their light weight, resistance to water and rotting.
Clean the surface of existing fiberglass with a wash of acetone. This rinse will remove any wax coating that that may have been left over from when the boat was originally removed from its mold, and would later cause a problem for your new fiberglass work to properly bond to. Interlux sells a product specifically for this, named appropriately enough “Interlux Surface Prep”. There are similar products from West Marine or Awlgrip but they are more expensive. Use lots of fresh cloths so your not smearing the wax around. The surface prep products from Interlux and Awlgrip have other chemicals that may help paint adhere better but if you want to save money, acetone will do the job.