I have a gallon container of premixed Dap Lightweight Wallboard Joint Compound (composed of calcium carbonate, water, aluminum oxide and attapulgite clay) in an unopened plastic container with a tight fitting plastic lid. I am wondering if it is still good (I haven’t opened the container as I don’t wish it to start drying out if it hasn’t done so yet as I don’t plan to use it immediately). Does the water evaporate out after a while even with the tight-fitting lid or otherwise create an unusable mess?
I’ve had a half-used gallon bucket sitting around for a year. Every few weeks I open it up to schpackle some nonsense that the previous owner of this place left for me. It’s as good as new.
I used a 5 gallon bucket for well over a year after it was opened. I once had a smaller bucket, probably a gallon, some time after it was opened it hardened on top. I scraped off the crust and the stuff underneath was fine.
The old trick with drywall mud (in the 5 gallon pails) is to leave a couple inches of water on top of the mud. It will keep indefinitely this way, when it is time to use it, pour off the excess water, mix and its good. An unopened container is good for a long time.
The mud is probably (as in, used to be) in a plastic bag inside the tub.
Make sure the plastic is twisted down tightly after each use, and it should be good for a year or so.
The standing water trick sounds good - especially if the water is on top of a twisted bag.