The short answer to why your resin is still sticky is that you have not mixed the resin and hardener in the correct proportion. That’s all. Epoxy resin is a chemical, that undergoes a chemical reaction when mixed with the hardener, which is why you CANNOT eyeball proportions and have to calculate them.
To illustrate, 3 parts of resin, need only 1 part of hardener. What happens if you put in extra hardener, those particles have nothing to combine with and therefore, they will remain sticky and uncured.
Adding extra hardener will not make your piece cure faster.
This is a very common myth. Mixing the two incorrectly will leave cause the resin to remain sticky!
An important note is that you must mix resin and hardener by WEIGHT and not by volume.
The ratios that are calculated, are based on measurements by weight. That is to say, when mixing the two substances, make sure to weigh, with the help of a scale.
Sometimes, in high humidity environments, or in the rainy season- moisture from the environment affects and hampers the process. This causes the resin to remain sticky. Ideally, wait for the rain to stop before you pour.
In winters, resin takes longer to cure. The solution to this is, putting the resin bottles in a warm water bath. This allows the resin to cure properly.
Unfortunately, if you’ve mixed the resin wrong, and it is not curing there is nothing you can do except discard and start over. However, if it’s only a slightly sticky, you can use a sanding machine to sand it out and pour a fresh layer on top.