Regardless of the material your boat’s hull is made of—whether it is a new build or a second-hand purchase—boats are subjected to harsh conditions while sailing, and the hull is the part that requires the closest attention. Constantly immersed, it needs regular maintenance and must be repaired quickly in the event of an accident.
While major repair work requires professional intervention, it is worth noting that some minor repairs can be carried out by yourself, provided you use the correct techniques and appropriate products. For small boat hull repair jobs, many people therefore question the use of two types of resin: epoxy resin and polyester resin. Which one should be used and in which situations? What are their characteristics? Our specialists explain.

Epoxy and polyester resins: what are the characteristics of these repair fillers?

When a crack or hole is detected in a boat hull, repairs are carried out using a specific filler whose binder can be either epoxy resin or polyester resin. This filler can be more or less thick depending on its filler content; however, the thicker it is, the more robust the final result will be. Nevertheless, a very thick filler is also more difficult to sand afterwards.

It is also important to know that these repair fillers combine two components supplied as a kit containing the base and the hardener. The hardener acts as a binder but also enables the mixture to cure and provides excellent strength.

Although curing time varies depending on the environment in which the product is applied, it should be noted that mixing the resin (epoxy or polyester) with the hardener must not be carried out in a humid environment, as this may result in excessively high viscosity and poor filler quality. If you wish to achieve faster curing, the room temperature should be high.

Boat hull repair: why use epoxy resin?

Epoxy resin is renowned for its excellent durability and outstanding resistance. As a result, it can be used in many fields, not only in the marine industry. Workable in liquid form, it can be applied at temperatures between 20 and 25°C. Below 15°C, the product begins to cure and can no longer be worked.

While epoxy resin is used in many sectors such as construction, decoration and furniture manufacturing, it is particularly valued in the marine field and more specifically for boat hull repairs, as it is not affected by water—unlike polyester resin. This advantage makes it a highly sought-after product in this industry.

Watertight, epoxy resin can also be used for hull repairs located below the waterline. Another advantage of epoxy resins is that they do not shrink during curing, allowing for very precise repairs and eliminating the need for corrections once the mixture has cured.

Boat hull repair: why use polyester resin?

Polyester resin is a convincing alternative to epoxy resin for repairing a boat hull. Often chosen because it is less expensive than epoxy resin, this is not its only advantage. It is also very easy to apply and generally easier to work with than its counterpart. In addition, it tolerates inaccuracies in the resin-to-hardener mixing ratio better.

Easier to sand than epoxy resin due to its relative softness, polyester resin also offers a much faster curing time. Indeed, around ten minutes are sufficient for the mixture to reach its final state.

In terms of drawbacks, it should be noted that polyester resin is not watertight and is therefore better suited to repairs located above the waterline. However, it can be coated with a treatment such as gelcoat to make it waterproof. Furthermore, after curing, noticeable shrinkage of the filler is often observed, sometimes requiring additional finishing work.

Finally, note that epoxy and polyester resins are not always compatible. While polyester resin can be overcoated with an epoxy filler, the reverse is not true.