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 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 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.

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.

A visible line or milky band appears between two pours, or the layers actually come apart.

The previous layer cured too much before the next pour. Once the bonding window closes, the fresh resin no longer bonds chemically to the old one and just sits on top. It also happens when amine blush, dust or moisture is left on the intermediate surface.

1. If the line is superficial and the piece can still take another layer, sand the area with 220-400 grit, clean with isopropyl alcohol and pour a thin fresh layer.
2. If the layers are physically separating, there is no reliable repair: remove the loose layer and pour again.

Pour the next layer within the window stated on the product datasheet, usually once the previous one has gelled but is still tacky to the touch. If you miss it, sand and clean with isopropyl alcohol before continuing.

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.

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.

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.

Color settles at the bottom of the piece, or patches and streaks appear where you did not want them.

Too much pigment, or a dense pigment in a resin that takes a long time to gel: while the mix stays liquid, heavy particles sink. In deep pours the effect is stronger because curing is slower.

1. While the mix is still liquid, stir again gently to redistribute the color.
2. Once cured, the distribution is permanent: sand and apply a thin pigmented layer on top.

Stick to the pigment dosage (rarely more than 5-6% of the mix weight), blend it thoroughly before pouring and, on deep pieces, pigment layer by layer instead of all at once.

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.

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.

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.

After sanding out a defect, the surface stays dull or covered in micro-scratches and never regains its shine.

Sanding leaves micro-scratches that scatter light. Gloss does not return on its own: you have to step up through the grits and polish, or seal it with a fresh layer.

1. Wet sand stepping up through the grits without skipping: 400, 800, 1200, 2000 and, for a mirror finish, 3000.
2. Polish with compound and a soft pad at low speed so you do not overheat the resin.
3. The fastest, most reliable route: pour a thin fresh layer of resin, which restores the gloss without polishing.

Work in a dust-free area and cover the piece while it cures: most sanding is done to fix dust or bubbles that could have been avoided.

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.

The resin sticks to the mold, is very hard to pull out, or the piece cracks when you force it.

A rigid mold with no release agent, shapes that lock the piece in, or demolding too early: at 24 h the resin is hard to the touch but has not reached its final strength.

1. Wait for a full cure before insisting: between 3 and 7 days depending on the product.
2. Put the silicone mold in the freezer for 20-30 minutes: silicone and resin contract differently and the piece usually releases.
3. Run hot water over the outside of the mold: the silicone becomes more flexible and the piece slides out.

Use flexible silicone molds whenever the shape allows, apply a release agent on rigid molds, and do not demold until the datasheet considers the piece cured.

The contents look cloudy, crystallized or grainy, and do not flow as they should.

Cold. Below roughly 15 °C many resins crystallize in storage. It is a physical change, not chemical degradation: the product is not spoiled.

1. Place the sealed bottle in a 50-60 °C water bath for 10-15 minutes, stirring occasionally until it turns clear again.
2. Let it return to room temperature (20-25 °C) before mixing: using it warm shortens the working time considerably.

Store bottles above 18 °C and never on the floor of a cold garage or workshop. In cold climates, bring the resin up to temperature the day before you work.