Why a resin pour stays sticky

Resin that is still tacky three days later has almost never gone wrong on the table. It went wrong in the cup, in the first two minutes, and in most cases the mistake was measuring the right ratio in the wrong unit.

By weight and by volume are different mixes

A resin sold at 100 to 45 is specified by weight. One sold at 1 to 1 is usually by volume. Read either one as the other and the mix is off before you stir.

The reason is density. Resin and hardener do not weigh the same per millilitre, with the hardener typically lighter, so a 1 to 1 mix measured on a scale is not a 1 to 1 mix measured in cups. Depending on the product, pouring equal volumes of a system specified by weight can leave you a tenth off the correct ratio, which is enough to leave the surface permanently tacky.

The label always says which. It is usually in small print beside the ratio, and it is the single most important line on the bottle.

How far off is too far

Epoxy is more forgiving than people fear and less forgiving than they hope. Within about 2% of the stated ratio, most systems cure normally. Past roughly 5%, the surface often stays soft, and the piece may never reach full hardness no matter how long it sits.

That tolerance is why small batches fail more often than large ones. Mismeasuring by 2 ml in a 500 ml pour is nothing. The same 2 ml in a 30 ml batch for a pair of earrings is a 7% error, and it will not cure. Work out the batch before you pour it with the epoxy resin calculator, which splits the total into part A and part B at whatever ratio your product uses, rather than eyeballing a small mix.

Surplus hardener does not help

It is worth saying plainly because the instinct is so common. Adding extra hardener to a mix that seems slow does not speed it up or firm it up. Epoxy reacts in fixed proportions, and anything beyond that proportion stays in the cured piece as unreacted material, which usually shows up as a soft surface and a yellow cast within months.

Mixing is a separate failure from measuring

A correctly measured batch still fails if it is not properly combined, and the signature is different. A ratio error gives a uniformly soft or tacky piece. A mixing error gives a hard piece with soft patches in it.

Scrape the sides and the base of the cup, not just the middle. Unmixed resin clings to the wall of the container, and a stir that only turns the centre leaves it there until you pour it onto the work. Two cups help, mixing in the first, then pouring into a second and stirring again, so anything stuck to the first cup never reaches the piece.

Then give it longer than feels necessary. Three minutes of slow, deliberate stirring is the usual guidance for a moderate batch, and fast stirring mostly buys bubbles.

Temperature decides whether any of it matters

Epoxy cure is a chemical reaction, and like most reactions it slows sharply as it cools. Most tabletop systems want 75 to 85 F, around 24 to 30 C, during the pour and through the first 24 hours.

A garage at 60 F can leave a perfectly mixed pour rubbery for a week. Warming the room is the fix, not warming the piece with a heat gun, which cures the surface before the depth below it and traps the problem underneath. Cold resin and hardener are also thicker, which makes accurate pouring harder and drags more air into the mix, so bringing the bottles indoors the night before solves two problems at once.

If the room genuinely cannot be warmed, that is an argument for a slower-curing system rather than for pushing a fast one through a cold night.