Why is my resin sticky, bubbly or yellow?
Eight failures, eight causes, and an honest answer about which pieces are recoverable. Most of them were decided before anything was poured.
Permanently tacky resin is almost always a ratio error — and the commonest one is reading a ratio the bottle stated by volume and measuring it by weight, which is about 7% out on the hardener. Soft patches are under-mixing. Bubbles are cold resin, fast stirring or wood outgassing. Yellowing is UV and a resin with no inhibitor. And a piece that got hot, cracked or smoked was poured past its depth ceiling, which is 1/8 in for a coating epoxy and a hazard rather than a finish problem.
Resin fails in a small number of ways, and almost all of them were decided before the pour rather than during it. That is the useful thing to know when you are standing over something tacky: the fix is rarely something you can do to the piece, and it is nearly always something to do differently next time.
The one worth putting first, because it is the commonest and the most expensive, is the ratio. A permanently tacky pour is almost always resin and hardener in the wrong proportion — and the usual cause is not carelessness but conventions. 2:1 by volume is 2.20:1 by weight, because resin is 1.1 g/ml against hardener's 1. Weigh out the by-volume figure on a 500 ml batch and you are 11.1 g of hardener out, which is comfortably enough.
And the thing that makes it worse: The ratio is not a recipe you can lean on. Epoxy and hardener react in fixed proportion, so anything left over after the reaction has finished has nothing to bond to and simply stays in the piece as a soft, sticky contaminant. Extra hardener does not speed the cure up and extra resin does not make it harder — both give you the same result, which is a surface that never stops being tacky.
Eight failures, and whether the piece survives
The last column is the question people actually arrive with, and the honest answer is usually no — which is why every fix here is really a change to the next batch. The exceptions are amine blush, which washes off, and bubbles, which are fixable for about twenty minutes and then are not.
The three that account for most of it
On a 500 ml batch of a 2:1 system, weighing to the by-volume figure gives 177.8 g of hardener where 166.7 was needed. The excess has nothing to react with and stays in the piece as a soft contaminant. The mix ratio calculator converts either way; check which convention your bottle states.
Unmixed resin clinging to the sides and the bottom of the cup goes into the pour along with everything else and stays soft where it lands. Stir slowly for three full minutes, scraping the walls and the bottom repeatedly, and turn the stick over and scrape that too. Then pour into a second cup and stir again — whatever was left unmixed stays in the first one.
Cold resin is thick and holds air; fast stirring folds it in; porous wood releases it for hours. All three are dealt with before the resin thickens. After about twenty minutes nothing will rise through it, and whatever is in there is in there for good.
Every failure, and what actually caused it
Either the proportion was wrong, or it was right in the wrong convention. Brands quote ratios both ways and often do not say which, and the gap is about 7% of the hardener. Extra hardener does not help: it makes exactly the same failure. There is no rescue — the piece has unreacted material through it. Scrape it out, check the data sheet, and remake with a scale.
Different from the above and much more common than people think: the pour cured everywhere except where a streak of unmixed resin landed. Three minutes of slow stirring with repeated scraping, then transferring to a second cup and stirring again, eliminates it almost entirely. If the patch is on the surface, it can sometimes be scraped back and recoated; if it is inside, it cannot.
Cold resin holds bubbles, so stand the bottles in warm water for ten minutes first. Whipping the mix folds air in, so stir slowly. And porous substrates — wood, MDF, concrete, dried flowers — outgas for hours, which is what a seal coat is for. Then torch the surface in a sweeping pass. All of it has to happen in the first twenty minutes.
A property of what you bought and where you put it. Resin without a UV inhibitor yellows in daylight over months; uv resin yellows sooner than a good two-part epoxy, which is why it is for pieces that get replaced. Nothing reverses it. Buy a resin that states a UV inhibitor for anything that will live in a sunlit room, and accept that no clear plastic is permanent.
Moisture is the usual cause and it does not take much: a damp mold, a wet stir stick, humid air on a cold day, or a water-based pigment. Resin stored cold also crystallises in the bottle and goes cloudy — that one is reversible by standing the bottle in warm water before mixing. Cloudiness inside a cured piece is not reversible.
Two causes that look identical. Either it has not finished — full cure is 3 days for a coating epoxy and 7 days for a casting one, and a cold room stalls it further — or there is too much in it. Nothing you stir into resin takes part in the reaction. Every particle of pigment, glitter or powder is inert filler that the curing resin has to build a solid network around, so there is a load past which there is simply not enough resin between the particles. It does not fail loudly — the pour just stays faintly soft, and the usual response is to wait another week for something that is already finished. Mica powder stops at 6% by weight and the loads add up across everything you added.
Epoxy cures by a reaction that gives off heat, and that heat makes the reaction go faster, which makes more heat. In a thin film the warmth escapes into the room and nothing happens. In a deep mass it cannot, so the pour climbs to a temperature it was never meant to reach — the piece cracks and yellows, the resin smokes, the mold distorts, and a large enough mass of the wrong resin can scorch the surface it is standing on. This is why a coating epoxy and a casting epoxy are different products, and it is the only figure on this site where being over is a hazard rather than a disappointment. If it is happening now, get it outside if you safely can and ventilate the room. There is nothing to salvage. The pour depth guide covers the ceilings and how to build depth in lifts instead.
A waxy or greasy layer on the surface of an otherwise cured piece, caused by amines in the hardener reacting with moisture and carbon dioxide in humid air. It looks exactly like a failed cure and is not one. Wash it off with warm soapy water and dry properly — and do it before recoating, or the next layer will not bond.
Preventing the next one
The single change that removes the commonest failure. Check whether your bottle states its ratio by volume or by weight while you are at it — the calculator converts, and the gap is 7% of the hardener.
Mix in the first, transfer to the second, stir again. Whatever clung to the walls of the first cup stays there instead of becoming a soft patch. It costs one cup and removes an entire category of failure.
Ten minutes standing in warm water thins the resin and lets bubbles rise before you mix. Warming the mixed batch does the opposite of what you want — it shortens the working time in a mass that is already generating its own heat.
Wood, MDF, concrete, dried flowers and unglazed ceramic all release air for hours after the resin goes on. A thin brushed coat of the same resin, cured, closes the pores. This is the fix for the bubbles that appear an hour after you stopped watching.
A pour deeper than the resin's ceiling fails no matter what else you do right. Table top / coating epoxy is 1/8 in per coat and deep pour / casting epoxy 2 in per lift; UV resin will not cure through more than 3 mm at all. The calculator checks it against whichever system you picked.
Full cure is 3 days and 7 days respectively, and a cool room stretches both considerably. A great many "my resin did not cure" posts are about a piece that was two days into a seven-day cure in a cold garage.
Check the mix before the next batch
Most of the failures on this page start with the ratio or the depth. Put your bottle's stated ratio in and it gives both conventions; put your project in and it checks the depth against the resin you own.
Open the mix ratio calculator →Print the pour-depth card
Maximum pour depth and cure windows by resin type — the number that cracks a casting. Free.
Estimates, not advice. Every figure on this page is computed from published reference values and standard measures, so your own inputs, equipment and conditions will move it. Nothing here is professional advice — talk to a qualified professional before acting on it.