Resin and Epoxy Fills

Finish Type

Epoxy resin is a two-part thermosetting system used as both a filler material and a surface element in wood furniture. It fills voids, stabilizes cracks, and creates the glass-like river channel in river table designs.

Chemistry

Epoxy is a two-part system consisting of a resin and a hardener. When mixed at the correct ratio, typically two parts resin to one part hardener by volume, they trigger an exothermic chemical reaction that forms a dense, crosslinked thermosetting polymer network. This reaction generates heat, which accelerates curing but must be managed carefully. A 1.5 gallon mix poured into a large mold generates minimal heat, but the same volume in a smaller container can reach 86 to 104 degrees Fahrenheit internally, enough to cause yellowing, bubbling, or cracking. Deep-pour formulas are engineered to cure more slowly than tabletop epoxy, typically with a 30 to 60 minute working time, allowing trapped air to rise out before the resin gels. The cured material forms a rigid, glass-clear solid that bonds tightly to wood fibers. Quality formulas include UV additives and HALS stabilizers to prevent yellowing from light exposure over time. Initial cure takes 36 to 48 hours at room temperature, with full cure at 72 hours before the piece can be safely removed from its mold and worked.

Characteristics

Cured epoxy is hard, strong, and optically clear, creating a glass-like mass that contrasts with the organic texture of the surrounding wood. It fills voids completely and bonds to irregular surfaces including bark, punky wood, and rough-sawn edges. The material cures with minimal shrinkage, so it holds its shape and does not pull away from the wood as it hardens. Tinted epoxy can be colored to match or contrast with the wood, and metallic pigments create depth effects within the resin itself. The trade-off is repairability. Shallow scratches in cured epoxy can be polished out, but deep damage requires sanding back and repouring, and matching the color of an existing pour can be difficult.

Best Use Cases

Epoxy is the standard solution for filling cracks, knot holes, bark inclusions, and voids in live edge slabs, where it stabilizes the wood and turns natural imperfections into design features. River table designs use larger volumes of epoxy to create a continuous channel of colored or clear resin between two matched slab halves. Spalted or punky wood zones that need structural stabilization before finishing also benefit from epoxy penetration. Reclaimed wood with insect damage, nail holes, and checking becomes usable and visually intentional once the voids are filled.

Wood Compatibility

Best on: Epoxy works as a fill system across a wide range of wood species. Walnut is the most common pairing for river tables because the dark wood creates strong contrast with clear or tinted resin. Oak, maple, and other domestic hardwoods all bond well with epoxy when the surface is clean and properly prepared. Wood moisture content should sit between 8 and 12 percent before pouring to avoid bubbles and cloudiness in the cured resin.

Use caution on: Oily tropical woods and species with high extractive content may resist adhesion, so always run a test pour on a sample before committing to the final piece. Wood must be fully dry and acclimated to its intended environment before epoxy is applied, because moisture trapped under cured resin causes clouding, delamination, or finish failure. Differential movement between wood and rigid epoxy is a long-term consideration, especially on wide slabs that experience seasonal humidity changes.

Browse all species in our wood species guide.

Application and Prep

Make sure the wood is stable, dry, and acclimated before starting any epoxy work. Seal voids and knots with epoxy using a syringe to prevent leaks and stabilize defects. Apply a thin seal coat to porous live edges to prevent air bubbles from forming during the deep cure. Seal the edges and underside of the pour area to contain the resin. Mix the resin and hardener at the manufacturer’s specified ratio using a two-cup method: combine in one container, pour into a second container, and mix again to ensure thorough blending. Pour slowly to reduce air entrapment, and use a heat gun or torch to pop surface bubbles during the open working time. For deep pours, build the fill in layers of two to four inches, allowing each layer to reach a semi-solid state before adding the next. Subsequent layers must go on within 24 to 36 hours while the surface is still tacky for chemical bonding. If more than 72 hours pass, scuff with 220 grit before the next pour. Once fully cured, sand through progressive grits and polish to the desired sheen.

Maintenance and Care

Clean epoxy surfaces gently with a soft cloth and mild soap. Avoid abrasive cleaners and scouring pads, as these can haze the glossy surface. For river tables and large resin areas, plan for an occasional polish to restore clarity if light scratching develops from daily use. Deeper scratches respond to wet sanding with fine grit followed by polishing compound. Protect epoxy from prolonged direct sunlight exposure, even with UV-stabilized formulas, because extended UV bombardment can eventually cause yellowing.

Daily Care

• Dust with a soft, dry cloth or microfiber.
• For routine cleaning, use a slightly damp cloth, then wipe dry.
• Avoid abrasive sponges and harsh chemical cleaners, especially ammonia-based or silicone-containing products.
• Wipe spills promptly. Use coasters and trivets for heat and water protection.

Environment

• Maintain indoor humidity around 40 to 60 percent to reduce seasonal movement in solid wood.
• Avoid placing the piece near heating vents, fireplaces, or prolonged direct sunlight.

Maintenance Schedule

• Oil-finished surfaces: Refresh (clean, lightly abrade if needed, reapply oil) once or twice per year depending on use.
• Film-finished surfaces (water-based clear, polyurethane, lacquer): Clean gently. Refinish generally only after visible wear or damage.

Repair

• Oil systems: Minor scratches can often be blended by light sanding and re-oiling.
• Film systems: Small scratches may be spot-repaired. Deeper damage may require sanding and refinishing the affected area.

Outdoor Furniture

• Outdoor exposure increases stress on finishes.
• If maintaining original color: plan periodic UV-protective oiling (often annually). Otherwise, allow natural silvering and focus on cleaning and inspection.
• Avoid pressure washing. High-pressure water can erode surface fibers, increase splintering, and shorten finish life.

For more details, see our care and maintenance FAQ.

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