Marine Resin Types: A Quick Guide
Polyester, vinylester and epoxy marine resins all have their pros and cons, which we covered in great detail in the past. Here at the Boats.net blog, we'll sometimes publish "Quick Guide" versions of past subjects for more easily digestable reading, like we're doing here.
Deciding which resin to use for a given purpose will be a compromise, often coming down to choosing the one with the least disadvantages. If you aren’t sure which marine resin type to use, here’s a quick guide to polyester, vinylester and epoxy resins.
This marine resin type has been used for boatbuilding and repair projects for decades, and there are very few applications it isn’t capable of handling.
When to use it: For anything from minor repairs to fabricating parts, reinforcing components, or building a new hull or an entire boat. Although it’s not as corrosion-resistant as vinylester or as strong as epoxy, its ease of use and low cost make it the top choice for most people.
Why use it: It’s easy to use and inexpensive, which is why it’s the go-to resin for boat builders and owners who use it for maintenance and repairs. Polyester resin has the highest resistance to UV rays and is ideal for topside and deck repairs, as well as any work that will be exposed to prolonged sunlight. It’s also the best resin to use for repairs that bond to or will be finished with gelcoat.
Why not use it: It doesn’t bond well to vinylester or epoxy laminates. Polyester resin also shrinks more than other marine resins, so it may not be ideal for repairing large surface areas. Its poor elongation and stretch qualities make it not so suitable for high-performance boats.
This marine resin type is the “middleman” of resins used in the industry, falling somewhere between polyester and epoxy in the pros and cons department.
When to use it: For repairing hulls blistered by water damage, and for adding or strengthening existing stringers or bulkheads. It’s the best resin to use for components such as water tanks and other parts that are prone to corrosion.
Why use it: Its adhesive/bonding strength is somewhere between polyester and epoxy resin, as is its price range. Vinylester resin is often overlooked in favor of the stronger epoxy or cheaper polyester resins, but it’s just as effective for most tasks and sometimes better for certain applications. It excels in resistance to water, heat and corrosion, and has the best elongation properties, making it less likely to develop cracks. Vinlyester’s adhesion/bonding strength is greater than polyester resins.
Why not use it: It’s not as strong as epoxy resin, and has a short shelf life. Once purchased, vinylester needs to be used relatively quickly, so there’s no point in buying it in bulk for projects way down the line.
This marine resin type is the strongest, but also the most expensive. However, its price has dropped significantly since it was first used in the 80’s.
When to use it: For making repairs, or bonding additional parts to a boat such as stringers or cores, and for repairing large areas.
Why use it: As mentioned, epoxy is the strongest marine resin type. It has the highest adhesive/bonding strength and provides better resistance to damage. Epoxy resin also bonds to more materials, and has the lowest shrinkage rate among the rest. Its ability to bond to most materials including wood, metal and cured polyester or vinylester makes it the perfect choice for repairs or fabrication when bonding together dissimilar materials. Epoxy also has the longest shelf life, making it safer to buy in bulk.
Why not use it: It’s the most expensive by far, but it’s not very resistant to UV light and deteriorates faster with prolonged exposure, making it the least ideal for external top layers. Gelcoat doesn’t adhere to epoxy, so it’s not the best choice for gelcoat repairs. However, there are UV resistant paints and varnishes that can be applied over epoxy to protect it, so don’t rule it out for external use.