How long does UltraClear epoxy last after the bottles are opened?

It depends on the product.

UltraClear Bar & Table Top Epoxy: opened or not, it has a one-year shelf life from purchase when stored at room temperature in the closed box. Cap the partially used containers, keep them indoors, and use them within that year.

UltraClear Deep Pour Epoxy: use it within two months of opening, and within one year of purchase even if unopened. Past that window, treat it like expired product: test a small batch first or order fresh.

If opened Deep Pour Epoxy stays tacky or gel-like, check three things before blaming its age. It only cures when mixed at exactly 2:1 resin to hardener by volume; it will not cure at any other ratio, and adding extra hardener does not speed it up. Each layer must be at least 1/4" thick, because it can't cure properly any thinner. And Deep Pour is slow by design: pours under 1" deep can take 24 to 48 hours just to feel dry, and the full cure takes 3 days, so don't troubleshoot a pour until 72 hours have passed. The curing process can't be shortened.

If you'd rather not have leftovers sitting open, use the coverage calculator on each product page to buy the size that matches your project.