Pros and Cons of Polyester, Vinylester & Epoxy Resins

The importance of the pros and cons of various marine resin types depends on external factors such as the nature of the job, the conditions the resin will be exposed to, and the task it must perform once cured.

For example, in the case of an area of fiberglass topside needing repairs, the marine resin offering the strongest bond might seem like the best choice. However, if a different resin offers better UV and water resistance, it may be a better choice despite its slightly weaker bond. Here are the advantages and disadvantages of polyester resin, vinylester resin and epoxy resin.

Polyester Resin

Widely considered the all-purpose marine resin, polyester is used for everything from boatbuilding and fiberglass repairs to manufacturing boat hulls, topsides and decks and making molds.

It’s easy to apply, and clings well to vertical surfaces to prevent drips and runs. Polyester resin cures fast, and provides good resistance to UV, water, weather and chemical corrosion. It ages relatively well too, but its adhesive, bonding and stretch properties are not as strong as other resins. Although it’s perfectly suitable for most boats, polyester resin is not recommended for use on high-performance watercrafts.

Pros

• Least expensive 
• Best UV resistance
• Bonds well to gelcoat
• Easy to use
• Excellent for whetting out fiberglass
• Cure rate easily controlled by adjusting the amount of catalyst used

Cons

• Weakest adhesion and bonding properties 
• Short shelf life
• Poor elongation and stretch qualities
• Uses a highly toxic catalyst to accelerate the rate at which it cures

Vinylester Resin

Vinylester resin falls somewhere between polyester and epoxy resins in terms of price and strength. However, vinyl ester offers the highest resistance to corrosion and heat, as well as to water penetration, making it ideal for hull repairs. It also has the best elongation properties among the marine resins.

Vinyl ester resin is used to make repairs and modifications to all types of boats. Because of its durability when exposed to heat and elongation, it’s being more commonly used in the manufacture of high-performance boats.

Pros 

• Best water, heat and corrosion resistance 
• Best elongation properties 
• Better adhesive and bonding strength than polyester resin 
• Cheaper than epoxy resin

Cons

• Very short shelf life
• Not as strong as epoxy resin
• More expensive than polyester resin
• Uses a highly toxic catalyst to accelerate the rate at which it cures

Epoxy Resin

Epoxy has been used in the marine industry since the 1980s. It’s known for having the strongest adhesion and bonding properties of all the marine resins, and adheres to a wider range of materials, including wood, metal, and cured polyester, vinylester and epoxy laminates.

Because of its strength and durability, epoxy resin is used for everything from hull or deck repairs, to strengthening older boats and manufacturing new boats. Epoxy is used less in the marine industry because it’s the most expensive, but the price has somewhat decreased as consumer demand for higher performance boats has increased.

Pros 

• Best adhesion and bonding properties
• Bonds to most materials and surfaces
• Lowest shrinkage rate
• Best resistance to damage
• Uses less toxic hardeners
• Longest shelf life

Cons

• Most expensive 
• Poor resistance to UV
• Doesn’t bond well with gelcoat 
• More sensitive to atmospheric conditions during application
• Requires more precision for mix ratio between resin and hardener 

Whether it's for maintenance or repairs on your boat, a better understanding of the pros and cons of each type of marine resin puts you in a better position to choose the best one most suitable for the job.