Types of Fillers: Structural, Fairing & Glazing

Marine fillers and putties are formulated for different stages of repair, from rebuilding damaged structures to achieving a smooth paint-ready finish.

Structural Fillers

• Reinforced compounds designed for strength

• Used to rebuild damaged areas or bond components

• Often contain fibers for added durability

Fairing Compounds

• Lightweight materials used to smooth surfaces

• Ideal for shaping and contouring hull repairs

• Easy to sand for a uniform finish

Glazing & Finishing Putties

• Ultra-fine compounds for filling pinholes and minor imperfections

• Applied as the final step before painting or gelcoat

• Produce a smooth, cosmetic surface

Selecting the appropriate filler type ensures both performance and appearance.

Polyester vs Epoxy Fillers

Different resin bases offer distinct advantages depending on the repair requirements.

Polyester Fillers

• Fast curing and easy to sand

• Common in traditional fiberglass repairs

• Typically used for cosmetic or non-structural work

Epoxy Fillers

• Superior adhesion and strength

• Excellent moisture resistance

• Suitable for structural repairs and bonding dissimilar materials

Epoxy-based systems are often preferred for critical repairs due to their durability and versatility.

Above- vs Below-Waterline Use

Environmental exposure plays a major role in filler selection.

Above-Waterline Fillers

• Focus on appearance and sandability

• Suitable for topsides, decks, and interior repairs

• Designed to withstand UV exposure

Below-Waterline Fillers

• Require excellent moisture resistance

• Used for hull repairs and blister treatment

• Often part of a barrier coat system

Choosing a filler rated for immersion helps prevent water intrusion and long-term damage.

Material Compatibility: Fiberglass, Wood & Metal

Fillers must bond securely to the underlying substrate.

• Fiberglass: Compatible with most marine fillers after proper preparation

• Wood: Requires flexible compounds that accommodate movement

• Metal: Needs corrosion-resistant formulations and thorough surface prep

Ensuring compatibility reduces the risk of cracking or delamination.

Structural vs Cosmetic Repairs

Fillers serve both strength-critical and appearance-focused applications.

Structural Repairs

• Restore integrity to damaged components

• Often combined with fiberglass reinforcement

• Used for cracks, holes, and bonding tasks

Cosmetic Repairs

• Address surface imperfections and minor damage

• Improve appearance prior to finishing

• Typically involve fairing and glazing compounds

Understanding the repair goal helps determine the appropriate product and application method.

How to Choose the Right Filler

Selecting a filler depends on several project factors:

• Location of the repair (above or below waterline)

• Structural vs cosmetic needs

• Substrate material

• Desired sanding characteristics

• Compatibility with coatings

Matching the product to the repair conditions helps ensure durable resul

Application & Sanding Guidance

Proper application techniques improve adhesion and surface quality.

Typical process:

1. Clean and prepare the damaged area

2. Mix filler according to manufacturer instructions

3. Apply with a spreader, slightly overfilling the repair

4. Allow material to cure

5. Sand to the desired contour

6. Repeat as needed for a smooth finish

Progressive sanding produces the best results prior to painting or coating.

Cure Times & Working Time

Fillers begin curing shortly after mixing, making timing an important consideration.

• Working time determines how long the material remains usable

• Initial cure time indicates when sanding can begin

• Full cure time reflects maximum strength development

Temperature, humidity, and batch size can all influence curing behavior.

Estimating How Much Filler You Need

Material requirements depend on repair size and depth.

Factors affecting quantity include:

• Surface area of the damaged region

• Thickness of application

• Number of layers required

• Sanding losses during shaping

Purchasing sufficient material helps avoid interruptions and ensures consistent results.

Choose the right marine filler or putty for your application.

Marine putties and fillers are used under paint to create a smooth surface. One major difference between these products is whether they can be used below the waterline. Another difference is whether the marine filler or putty filler is one-part or two-part. One-part putty fillers tend to be less waterproof than two-part epoxy fillers or two-part polyester or polystyrene fillers. Examples of marine-grade putties and boat hull fillers include Travaco’s Marine-Tex® Epoxy Putty, Interlux’s Watertite Epoxy Filler and Pettit’s Splash Zone EZ-Fair Epoxy Fairing Compound. Custom, marine-grade fillers and fairing compounds can be created by mixing WEST SYSTEM Two-Part 105 Resin with a variety of thickeners and fillers.