While it’s not a good idea to continuously freeze and thaw your drywall compound, you may occasionally end up with a frozen pail — either through storage or cold-weather delivery. Not to worry.
First, thaw it out… slowly. Don’t try and speed up the process by blasting it with extra heat or by adding hot water to the mix. Let it warm on its own at room temperature.
Now, thawing is only the first step. Once it’s all warmed up, you’ll find the liquids and solids have separated and the compound itself is no longer smooth. Actually it’s a yechhy, lumpy mess, apparently useless.
So now you need to mix it.
You could simply pour off the water and add it back in later, but you can save yourself the trouble, by turning the container upside down for 20 minutes or so. This will mix the two a bit, but not completely.
So turn the pail right side up, and mix the compound thoroughly. Attaching a mixing tool to your electric drill does a good job. Run it at low speed, because if you go too fast, you’ll add a bunch of air to the compound. Keep mixing till it looks normal and you can’t detect any more lumps.
And get some on your hock and get to work.
A final note. Use it up fairly quickly. For some reason, previously frozen mud will start to smell nasty after a few days. If you’re not going to use it all, stick it in the freezer till the next time you need some.