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Whether you are repairing or bonding boat components, a marine putty can be a versatile option. Each marine putty has different performance capabilities that largely depend on its chemical makeup.
Choosing between a polyester marine putty and an epoxy marine putty requires an understanding of their differences and how they fit into the real-world requirements of your application. At Gluegun.com, our team reviews the similarities and differences between polyester and epoxy putties for the marine industry, as well as when each chemistry may be the better choice.
Polyester Marine Putty
Polyester marine putties are made from a polyester resin thickened with mineral fillers, lightweight fillers, fibers, or a combination of reinforcing materials. The exact makeup will determine the performance capabilities, but polyester marine putties are generally fast-curing and cost-effective. These properties are great for manufacturers looking to shorten cycle times and stay on budget.
Marine polyester putties are compatible with fiberglass, wood, gelcoat, and some metals. They are widely used in fiberglass boat manufacturing because they easily integrate with polyester and gelcoat production processes. They can also be easily sanded for a smooth finish.
Epoxy Marine Putty
Epoxy marine putties are best known for their great structural strength and durability. They are made from an epoxy resin, fillers, and a curing agent. Marine epoxy putties also commonly have good moisture resistance and resist water damage. Some can even be used for below-the-waterline applications.
Marine epoxy putty can bond to wood, metals, prepared fiberglass, and previously cured laminates. They are commonly used for secondary bonding, repairs, restoration work, and other marine applications that require dimensional stability.
Similarities and Differences
To choose the right putty for your application, it is important to understand the similarities and differences between the two types of products and how they tie into real use cases.
Our team highlights some of the key similarities and differences between polyester marine putty and marine putty epoxy.
| Property | Polyester Marine Putty | Epoxy Marine Putty |
|---|---|---|
| Substrates | Compatible fiberglass (FRP), gelcoat, exterior-grade wood, and properly prepared metals | Compatible fiberglass, gelcoat, wood, and most metals |
| Cure speed | Generally faster | Generally slower |
| Cure shrinkage | Generally higher | Generally lower |
| Resistance to water exposure | Varies | Generally good adhesion and resistance to water damage |
| Relative cost | Usually lower | Usually higher |
Both polyester and epoxy putties are broad product categories. While putties may have the same base chemistry, their properties can vary greatly from one product to another. Always compare the technical data sheets for specific products to ensure they match your application requirements.
1. Adhesion and Substrate Compatibility
Polyester putty works well in compatible polyester laminate systems for bedding, filling, and bonding fiberglass components, but it may have lower secondary-bond strength on some cured surfaces. On the other hand, epoxy typically bonds to a wider range of properly prepared materials, including cured fiberglass, wood, steel, and aluminum. This versatility makes it a strong choice for repairs and mixed-material assemblies.
2. Shrinkage and Surface Appearance
Polyester putties generally shrink more during cure than epoxy putties. This shrinkage may cause distortion or print-through. Because epoxy putties generally shrink less, they tend to be better suited for precision fairing and profile-sensitive applications.
3. Production Speed and Cost
Compared to epoxy marine putties, polyester putties often cure faster and cost less. This combination makes polyester marine putties great for high-volume boatbuilding. Pumpable formulas can also streamline production. While epoxy marine putties tend to cure more slowly and cost more, their adhesion and low shrinkage may reduce rework in demanding applications.
When to Use Each Type of Marine Putty
When determining which type of marine putty to use, it is important to look at the full picture. Your specific application, substrates, finishing requirements, service environment, and production requirements should all play a role in your marine putty selection and help you narrow down your choices.
In general, you should choose a marine polyester putty over an epoxy putty when:
- Your production process primarily uses compatible polyester resins and fiberglass laminates.
- You need a fast-curing material to support high-volume production.
- Lower material cost is a priority.
- The putty will become part of a compatible polyester laminate or finishing system.
Polyester putties can deliver an efficient, economical solution in compatible production environments, especially for fiberglass assembly. They are advantageous when cure speed and throughput are priorities. Some common applications are production fairing, core bedding, gap filling, and composite assembly.
In general, you should choose a marine epoxy putty over a polyester putty when:
- The application involves secondary bonding or repair work.
- Strength and durability are key considerations.
- Low cure shrinkage is a high priority.
- The repair or assembly requires strong adhesion to an existing structure.
- Fairing and sanding requirements are minimal.
Epoxy putties are often the better choice when adhesion and dimensional stability are higher priorities than fast production speed or initial cost. Common applications for an epoxy marine putty include secondary bonding, repairs, fairing, filleting, and bonding dissimilar substrates.
Product Examples
While these recommendations can lead you toward the right formulation type, specifications can vary from product to product, and the right putty will depend on your unique needs and application requirements. Our team shares a few tried-and-true marine putties that may be worth exploring.
Low-Shrink Marine Putty
The POLYFILL 1050 polyester putty is designed with reduced shrinkage characteristics to minimize print-through and gelcoat stress during fabrication. It supports applications with tight radii and offers good vertical stability for corners, transition lines, complex contours, and vertical filling applications.
Lightweight Marine Putty
Manufacturers looking for a reliable lightweighting option should consider the POLYFILL 4000 marine putty. It weighs less than 5 pounds per gallon and has a low-exotherm formula. It is ideal for hardtop bonding, sandwich panel assembly, and composite fabrication applications.
High-Strength Marine Putty
For demanding and critical bonding applications, the Infinity Bond POLYFILL 7000 is a great option. It is designed for high-stress and high-vibration marine environments. Common applications include bonding hull-to-deck joints, stringers, bulkheads, and liners.
Before selecting a product, confirm its intended function and performance capabilities match the application requirements by reviewing its technical data sheet. You should also test the putty under your real-world conditions before fully incorporating it into your production process.
Need More Help?
Polyester marine putty and epoxy marine putty each have their own unique strengths and weaknesses. They also tend to be better suited to different applications. You can explore our collection of marine filler putties, or speak with one of our adhesive experts to get a personalized product recommendation and find the best marine putty for your needs.
