Polyester: Advantages and disadvantages

Benefits:

• Price: Polyester is generally cheaper than epoxy, making it an attractive choice for budget-conscious projects.
• Shaping: Polyester is easy to shape and work with, especially when used with reinforcement.

Disadvantages:

• Curing temperature: Polyester requires a relatively high temperature (20-30°C) to cure properly, which can be difficult for most of the year here in northern latitudes.
• Steering fumes: Emits steering fumes which can be harmful and requires good ventilation.
• Shrinkage: Shrinks significantly during curing, so remember to either "overfill" any holes on e.g. gelcoat on deck or freeboard, or refill.
• Mechanical properties: Polyester has lower strength and durability, especially when used as an adhesive to repair or join parts that are already cured.
• Osmosis protection: Requires longer curing time for optimal protection against osmosis.
• Poor adhesion: Polyester does not adhere well to epoxy, which can create weaknesses in the structure.
  
  

Epoxy: Advantages and disadvantages

Benefits:

• Strength and Adhesion: A quality marine epoxy that WEST SYSTEM is extremely strong with excellent adhesion properties.
• Mechanical properties: Epoxy has very good mechanical properties and high resistance to moisture penetration, making it ideal for osmosis treatment.
• Applications: Epoxy can be used on many different surfaces including wood, metal, aluminum, cured polyester laminates and concrete.
• Low shrinkage: Epoxy shrinks very little during curing, which means you can count on a more precise and stable shape.
• Chemical resistance: Epoxy has good resistance to chemicals and water ingress.
• Working conditions: Epoxy can be used at temperatures down to 5°C and contains no solvents, making it more user-friendly. It doesn't smell strong, but always remember to wear nitrile gloves and quality safety goggles. It's a mess to get cleaned off your fingers.
• Longevity: Epoxy has excellent durability and can remain usable for many years.

Disadvantages:

• Price: Epoxy is more expensive than polyester, but the extra cost is often outweighed by the many benefits.
• UV degradation: Epoxy is degraded by UV light and must be protected with varnish or paint to prevent degradation.
• Amine veil: A surface film (amine wax) may form, which must be washed off before further processing.
  
  

Examples of Applications

Use of Epoxy

1. Repairing fiberglass damage: If there is a hole or crack in the boat's hull, epoxy is the best choice for the repair. The strong adhesion of epoxy ensures that the repair will be durable and waterproof.
2. Reinforcing Structures: If you want to reinforce a rudder or, for example, a mast foot, you can use fiberglass mats impregnated with epoxy. This provides a strong and rigid structure that is resistant to water ingress and mechanical stress.
3. Osmosis treatment: Epoxy is used to coat the bottom of the boat and protect against water penetration (it's not the bottom paint that makes the hull waterproof, it's the epoxy primer!) The high resistance to moisture makes epoxy ideal for this task.

Use of Polyester

1. Small repairs and molds: Polyester can be a good solution for minor repairs where costs need to be kept down. For example, if you have a small superficial damage to the tire, polyester can be sufficient and economical.
2. Reinforcement projects: If you need to make a larger shape that doesn't necessarily require extreme strength, polyester can be easier to work with due to its moldability. This could be the case when making seats or interior panels.
3. Budget projects: For projects where cost is an important factor and extreme strength requirements are not necessary, polyester can be a sensible choice.

Application techniques for Epoxy and Polyester

Epoxy application techniques:

1. Preparation: Make sure the surface is clean, dry and free of oil, dust and other contaminants. Sand the surface lightly to ensure good adhesion.
2. Mixing: Follow the manufacturer's instructions carefully to mix the epoxy resin and hardener in the correct proportions. Use a clean container and tools to avoid contamination.
3. Application: Use a brush, roller or spray to apply the epoxy. For larger areas, a roller may be more effective, while a brush is good for details.
4. Layering: Apply epoxy in thin layers to avoid runners and bubbles. If multiple coats are required, wait until each coat is tack dry before applying the next.
   NOTE: if you use epoxy before bottom paint, do this wet-on-wet with the last coat of primer to get the bottom paint to adhere well
5. Finishing: Once the epoxy has cured, the surface can be sanded and painted or varnished to protect against UV light and provide a smooth finish.

Polyester Application techniques:

1. Preparation: Clean and sand the surface thoroughly. Make sure all areas are dry and free of dust and oil.
2. Mixing: Mix the polyester resin with the catalyst (hardener) in the correct proportions. Please wear protective equipment as styrene fumes are toxic.
3. Application: Apply the polyester resin with a brush or roller. Work quickly as the polyester starts to harden relatively quickly.
4. Reinforcement: Use fiberglass mats or cloth to reinforce the structure. Fully impregnate the reinforcement with polyester resin.
5. Curing: Allow the polyester to cure at the recommended temperature (20-30°C). Avoid low temperatures as this can negatively affect the curing process.
6. Finishing: Once the polyester has cured, the surface can be sanded and painted to improve the appearance and possibly waxed to protect against the elements.

Conclusion