Description
The Sika AP861 epoxy filler is a trowelable two-part system built for fairing large surface imperfections on marine vessels. It works on aluminum, steel, fiberglass, and wooden hulls, and it can go on above or below the waterline. The white resin and light brown SikaBiresin AP861-1 hardener mix at a 1:1 volumetric ratio, so measuring is straightforward at the workbench instead of a jobsite guessing game.
Where the Sika AP861 epoxy filler gets used
Boatyards reach for this filler when a hull has low spots, gouges, or transitions that need building up before fairing and paint. Because it applies up to 1 inch thick without sagging or shrinking, a single pass often covers repairs that would otherwise take several thin coats of a lighter-bodied filler. The color-coded mix gives a visual check that both components are blended evenly before the paste goes on the surface, which matters on a below-waterline repair where a soft spot in the cure is not something you want to discover later.
The mixed paste trowels smooth and stays workable through the pot life window, then sands and finishes cleanly once cured. Shops that also handle fiberglass repair on tanks, decks, or transoms use it for the same reason: a hard, sandable fill that accepts primer and topcoat without bleed-through.
How the Sika AP861 epoxy filler holds up
Cured hardness lands in the Shore D 76 to 81 range, hard enough to sand fair without chipping at the edges. Service temperature tops out at 136°F, which covers hull temperatures in direct sun in most climates. The system carries 0% VOCs, a point that matters in yards running under tighter air-quality permits or working in enclosed sheds without heavy ventilation.
| Property | Value |
|---|---|
| Technology | 2-component epoxy |
| Hardener | SikaBiresin AP861-1 |
| Mix ratio | 1:1 by volume |
| Mixed color | Light brown |
| Shore D hardness | 76 to 81 |
| Pot life | 42 to 48 minutes |
| Max service temperature | 136°F |
| Below waterline use | Yes |
| Max application thickness | 1 in, no sag or shrinkage |
| VOC content | 0% |
Order by the quart for smaller fairing jobs or step up for full hull projects. Pair it with the matching AP861-1 hardener and keep both components at room temperature before mixing so the pot life runs true. For related epoxy systems and fillers for marine and composite repair, browse Chemical Concepts epoxy adhesives. Sika publishes full cure schedules and surface prep guidance for the AP861 system on its technical data sheets, available through Sika.
Need Help?
Need help matching hardener quantity or working time to your repair size? Call (800) 220-1966 or email [email protected].
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