Epoxy resin problems and how to fix them

After the stated cure time, the mix is still liquid, soft or dips when you touch it.

Epoxy resin cures through a chemical reaction between its two parts, not by evaporation. If the A:B ratio is off, if it was undermixed, or if the room is below 18 °C, the reaction never completes and the material never hardens.

1. Confirm the product ratio (2:1, 3:1…) and whether it should be measured by weight or by volume: they are not interchangeable.
2. If only the top layer failed, sand it, clean with isopropyl alcohol and pour a fresh, well-mixed layer on top.
3. If the whole piece is soft, there is no chemical rescue: remove the mix and start over with exact proportions.
4. Keep the room at 20-25 °C during the entire cure; heat drives the reaction.

Weigh each part with a 0.1 g precision scale, stir for 3-5 minutes scraping the cup walls and bottom, and always work above 20 °C.

The piece has hardened inside, but the top face is still sticky or greasy to the touch.

It is usually amine blush: ambient humidity reacts with the hardener at the surface during cure. It also happens when the last layer was undermixed or poured at humidity above 70 %.

1. Clean the tacky layer with warm soapy water, or with isopropyl alcohol, to remove the amine blush.
2. Dry-sand with 220-400 grit until the surface is matte and no longer sticky.
3. Apply a thin fresh layer of well-mixed resin in a dry environment (humidity < 60 %).

Always pour with humidity below 70 %, avoid working outdoors on humid days, and mix the final layer with the same care as the rest.

Air bubbles appear inside the piece or on the surface once it has cured.

Air gets in from stirring too fast, pouring from too high, cold (more viscous) resin, or air escaping from a porous substrate such as unsealed wood.

1. While the resin is still liquid, pass a torch or heat gun 15-20 cm away with quick strokes of no more than 2 seconds.
2. If it has already cured, sand the affected area and pour a thin fresh layer over it.

Bring the resin to 22-25 °C before mixing, stir slowly with folding motions, let it rest 2-3 minutes before pouring, and seal wood with a thin first coat.

A clear piece takes on a yellow tint, especially in areas exposed to light.

UV radiation degrades resins without a filter. It also yellows from overheating during cure (too thick a layer) or from using a low-quality resin with no UV protection.

1. Yellowing is permanent: it cannot be reversed in the affected layer.
2. On flat pieces, sand and pour a fresh layer of UV-protected resin to restore clarity.

Choose resins with a declared UV filter, respect the maximum depth per layer to avoid exotherm, and keep pieces out of prolonged direct sunlight.

The resin smokes, gets very hot, cracks, shrinks or forms craters during cure.

Runaway exothermic reaction: pouring a layer thicker than the product maximum traps heat, the temperature spikes and the piece cracks or yellows.

1. A piece cracked by exotherm cannot be repaired: it has to be redone.
2. Split the pour into layers within the product limit and wait 16 to 24 h between each.
3. For pours deeper than 2 cm, use a dedicated deep pour resin (such as Wood PRO).

Respect your resin maximum depth per layer and plan the layers before pouring. The calculator splits the pour into safe layers automatically.

The piece cured but stays rubbery, marks with a fingernail or gives under pressure.

A small ratio mismatch (a little too much hardener or resin) or too much pigment alters the chemistry of the mix and leaves an incomplete, elastic cure.

1. There is no chemical fix once cured: the piece has to be remade.
2. Review your measuring method and reduce the amount of colorant on the next attempt.

Always measure by weight with a precision scale, never by eye, and keep pigment below 5-6 % of the total mix weight.

The resin forms small round dips or pulls away leaving uncovered spots.

Contamination from grease, dust, silicone residue or release agent on the surface. The resin will not bond to those spots and retracts, forming craters.

1. Let it cure, sand to level and clean thoroughly with isopropyl alcohol.
2. Pour a fresh layer over the clean, degreased surface.

Always clean and degrease the surface before pouring, keep silicone sprays away from the work area, and handle with clean gloves.

The mix loses clarity and looks whitish or hazy.

Moisture or water in contact with the mix, resin too cold when mixed, or excess microbubbles that never escaped.

1. If it is from cold, warm the bottle in a water bath (without letting water in) before mixing the next batch.
2. A piece that is already cloudy will not clear; on flat surfaces, sand and pour a fresh layer in dry, warm conditions.

Bring both components to 22-25 °C before mixing, avoid any contact with water, and work in low humidity.

Decorative pieces, dried flowers or wood rise to the surface instead of staying in place.

Resin is denser than many materials, so it pushes them up while liquid. Unsealed wood also releases air that makes it float.

1. While the resin is still liquid, hold or weigh the objects down until it gels.
2. For wood, fix it with screws or weights before pouring the channel.

Seal porous objects with a thin coat of resin before the main pour, and fix or weigh down anything that can float before you start.

Resin escapes through the mold or formwork joints during the pour.

Insufficient sealing between mold walls, tape that cannot hold the weight of the resin column, or an unlevel mold.

1. Stop the pour, let what is there gel, and reinforce the sealing before continuing.
2. Wipe drips with alcohol before they cure; once hard they have to be sanded off.

Seal every joint with silicone or strong packing tape, test the seal with water before pouring, and level the mold with a spirit level.

Particles, lint or insects get stuck on the final layer.

Liquid resin acts like a dust magnet during the hours it takes to gel, especially in unprotected spaces.

1. If the resin is still liquid, lift the particle out carefully with a clean toothpick.
2. If it has cured, sand the affected spot and apply a thin fresh layer.

Cover the piece with a box or dome while it cures, work in a clean, draft-free area, and avoid clothing that sheds fibers.