Interlux Watertite Epoxy Filler

What Is Interlux Watertite Epoxy Filler?

Interlux Watertite Epoxy Filler is a two-component epoxy fairing and filling compound formulated specifically for marine use. It combines a base (YAV135) with a curing agent (YAV136) in a simple 1:1 ratio by volume, producing a high-strength, water-resistant filler that bonds reliably to fibreglass, metals, epoxy substrates, and rigid wood constructions.

Unlike polyester-based fillers, Watertite does not shrink after curing, which is a critical advantage when repairing osmotic blisters or filling voids below the waterline. Its 100% volume solids formulation and zero VOC content mean the cured film retains its full applied thickness with no solvent evaporation loss.

Key Applications: Blister Repair, Fairing, and Filling

Watertite is especially recommended for the prevention and repair of gelcoat blisters below the waterline. When osmotic blistering has occurred, the filler can be applied after the damaged area has been properly prepared, restoring a fair, watertight surface before barrier coat application.

Beyond blister repair, Watertite functions as a versatile fairing compound. Its superior spreadability makes it an effective glazing compound for filling small nicks, scratches, and surface imperfections. It can be applied in a single pass up to 3/4" thick without sagging, which reduces the number of build coats needed on deeper repairs.

The product is suitable for use both above and below the waterline, making it a single solution for hull repairs from the keel to the topsides.

Drying Times and Working Window

Watertite cures quickly relative to many marine epoxy fillers, and drying times vary with temperature. At 23°C (73°F), the product reaches touch-dry in approximately 35 minutes, becomes sandable in about 5 hours, and is ready for immersion after 2 days. At cooler temperatures typical of spring and autumn boating seasons, such as 10°C (50°F), touch-dry time extends to 50 minutes, sandable time to 8 hours, and immersion readiness to 5 days.

Pot life at 23°C is approximately 15 minutes, extending to 25 minutes at 10°C. This relatively short pot life means mixing only what can be applied promptly. The product should not be used below 7°C (45°F), and both product and ambient temperatures should remain between 7°C (45°F) and 35°C (95°C) during application.

Once sandable, Watertite accepts a long sanding window, allowing thorough preparation before overcoating with compatible epoxy primers and barrier systems.

Compatible Overcoats and Application System

Watertite is designed to be used within a broader epoxy barrier system. It is recommended for use with the Interprotect 2000 Epoxy Barrier System or VC Tar2, and is compatible with a range of Interlux epoxy primers and barrier coats.

Compatible overcoats include:

Watertite must be sanded before any epoxy primer is applied. It is important to note that topside finishes, polyester materials, and vinyl ester materials must not be applied directly over Watertite. Gelcoat should also not be applied directly over the cured filler.

• Epoxy Barrier-Kote
• Epoxy Primekote
• Interprime 820
• Interprime 880
• Interprotect 2000E
• Interprotect 3000 / 3001
• Pre-Kote
• Primocon
• VC Performance Epoxy
• VC Tar2
• Yacht Primer

Surface Preparation and Application Method

Proper surface preparation is essential for adhesion. On bare fibreglass, the surface should be cleaned with a suitable fibreglass solvent wash and sanded with 80-grit paper before application. For osmotic blister repairs, any blistered, cracked, or gelcoat-removed areas should be treated with an epoxy resin prior to applying Watertite. On metal surfaces above the waterline, a primer wash coat followed by an epoxy primekote is recommended before applying the filler.

Watertite is applied using a trowel, spatula, or putty knife. The two components must be mixed thoroughly in a 1:1 ratio by volume until a uniform colour is achieved. Do not thin the product. After curing, wash the surface with fresh water and sand with 80-grit paper before proceeding with overcoating.

Coverage is approximately 25 ft² per gallon at 1/16" dry film thickness. The recommended dry film thickness is 63.5 mils. No more than 3/4" should be applied in a single application.

Storage and Shelf Life

Watertite has a typical shelf life of 2 years when stored correctly. Containers should be kept firmly closed between uses, stored away from direct sunlight, and kept at temperatures between 5°C (40°F) and 35°C (95°F). Exposure to air and temperature extremes should be avoided to preserve the full shelf life of both components.

The product is available in two sizes: 500 ml (Binnacle SKU #13071, MFG part YAV135KIT500CA) and 1 litre (Binnacle SKU #13105, MFG part YAV135KITLCA).

Specifications

• Colour: Light blue
• Finish: Matte
• Specific Gravity (mixed product, TDS): 1.8
• Volume Solids: 100%
• Mix Ratio: 1:1 by volume
• Curing Agent: V136 (YAV136)
• Typical Shelf Life: 2 years
• VOC (as supplied): 0 g/L
• Unit Sizes Available: 500 ml, 1 litre
• Maximum Application Thickness: 3/4" (per application)
• Recommended Dry Film Thickness: 63.5 mils
• Coverage (theoretical): 25 ft² per gallon at 1/16"
• Application Method: Spatula / putty knife / trowel
• Touch Dry at 10°C (50°F): 50 minutes
• Touch Dry at 23°C (73°F): 35 minutes
• Sandable at 10°C (50°F): 8 hours
• Sandable at 23°C (73°F): 5 hours
• Immersion Ready at 10°C (50°F): 5 days
• Immersion Ready at 23°C (73°F): 2 days
• Pot Life at 10°C (50°F): 25 minutes
• Pot Life at 23°C (73°F): 15 minutes
• Minimum Application Temperature (ambient/substrate): 7°C (45°F)
• Maximum Application Temperature (ambient/substrate): 35°C (95°F)
• Flash Point (base component): 146°C (294°F)
• Base Product Code: YAV135 (YAV335)
• MFG Part Number - 500 ml: YAV135KIT500CA
• MFG Part Number - 1 litre: YAV135KITLCA
• Binnacle SKU - 500 ml: #13071
• Binnacle SKU - 1 litre: #13105
• Compatible Substrates: Fibreglass, metals, epoxy, rigid wood
• Cleaner / Solvent: Fiberglass Solvent Wash 202

Key Features 

• Above and below waterline use: a single product handles repairs anywhere on the hull, from the keel to the topsides
• Non-shrinking formulation: maintains its applied volume after curing, ensuring repairs stay flush and fair over time
• Gelcoat blister prevention and repair: specifically recommended for addressing osmotic blistering below the waterline before barrier coat application
• Suitable for osmosis damage: extreme water resistance makes it reliable for restoring hulls affected by moisture intrusion
• Fast cure with a long sanding window: reaches a sandable state in as little as 3 hours at warm temperatures, giving a generous window for shaping and fairing
• Applies up to 3/4" thick without sagging: deep voids and repairs can be filled in a single pass, reducing labour and build time
• Superior spreadability: works as a glazing compound for fine surface imperfections such as small nicks and scratches, as well as larger structural repairs
• Zero VOC content: no solvent evaporation means the full applied thickness is retained in the cured film
• Simple 1:1 mix ratio: equal parts by volume eliminates guesswork and reduces the risk of mixing errors
• Broad substrate compatibility: bonds to fibreglass, metals, epoxy, and rigid wood, making it versatile across different hull and deck construction types
• Compatible with major Interlux barrier systems: integrates directly into Interprotect 2000E and VC Tar2 application systems for a complete repair programme