Q: I used an unopened tube of DAP 3.0 (stored in my basement for a couple of years) to fill a joint in a wood mantel that I had primed for painting. The caulk is supposed to be paintable after three hours, but it was sticky even the next day. I waited a few more days before applying the oil-base finish coat (even though the caulk was a bit tacky). The caulk is still kind of soft after two weeks. Will it eventually harden? - Bruce Edwards, Des Moines, IA
A: You are wise to store caulk in a conditioned space; temperature extremes could contribute to the problem you're describing. The issue in this case is probably shelf life. "For best performance, new product should be used within 12 months from the date of purchase," says Jason Toth, DAP's technical-department supervisor. Unlike latex (water-base) sealants that most people are familiar with, chemically curing sealants begin slowly curing in their unopened containers, gradually becoming thicker and less workable over time. Once opened, a tube should be used or discarded within a few weeks.
If you're not sure about the state (or date) of a stored product, Jason recommends testing it. Apply a bead of the caulk to a wood scrap or cardboard; it should gun out easily. Then tool the bead to check for smoothness, letting it dry according to the label's instructions. Although silicones, polyurethanes and advanced-polymer-base sealants are designed to stay indefinitely pliable, they should not feel excessively gummy or appear to transfer when touched (after 12 to 24 hours).
On your mantel, the caulk may continue to cure and feel less tacky over time. You could wait a few more weeks to see if that's the case, or just remove the caulk and apply fresh material and repaint. (The DAP 3.0 instructions say to use an acrylic primer before applying oil-base paint. Some products are directly paintable with oil or latex, so be sure to check the manufacturer's instructions.)
To dispose of outdated caulks and sealants, Jason recommends gunning out the contents onto some newspaper and letting the material fully dry. Then roll up the paper and discard it in your household trash. In many areas, the empty tube will be accepted for recycling as "2 PE."
To avert DIY disasters caused by applying expired caulk, use a permanent marker to write the purchase date on the cartridge so you'll know when it's past its prime. - HANDY