eli5 What is the difference between Dry, Cured and Set?


eli5, While I would like a general answer, the concept that brought this question up was drywall compound, specifically “hot mud”. “five minute hot mud” sets in five minutes but takes longer to dry. What is the difference?

In: 4

Dry is a generally useful term, meaning “not wet anymore”. In compounds, it means it can no longer be adjusted and it is reasonable to expect the compound to stay there unless it is damaged. If the compound is water soluble, getting it wet can undo the drying. If it is not, getting it wet might undo some of the compound’s final effectiveness.

Cured means time (and often something else, like heat) has taken its course, and the thing will stay in its new, changed form for a long time (this definition also sort of works with curing meats and other things). In compounds, enough time has passed that the compound has changed almost entirely from its starting form into its final form; e.g. instead of concrete, it is now sidewalk. It is reasonable to treat the compound as if it is another part of the wall at this point. Water will no longer do anything special to the compound.

Unfortunately, I don’t have a good answer for set. From my hobby level knowledge, I’d say it’s a similar word to dry but the compound can still be mildly affected. Something set will not change if left alone, but it is not finished curing so it is weaker than its final stage. If it is specifically not dry yet, then touching it will probably disrupt the process as well. Perhaps it can still be lightly molded for a few finishing touches, but if left alone it will cure as it is.

Real dry wall compound will create a very strong material when you mix it with water. It creates a chemical reaction with the water and forms a new compound from the water similar to the way cement and water make concrete. It doesn’t dry, if it simply dried then they’d be water soluble and mixing them with water would make it dissolve. Set just means it’s firm enough to work with, but the chemical reaction hasn’t finished yet and it’s not at it’s full strength.

Dry = The solvent has evaporated completely.

Set = It has hardened enough to hold its shape or in the case of a glue, it is functionally sticky to hold the bond together, but it is not at its full strength.

Cured = If the substance you’re using undergoes a chemical reaction, this means that the reaction is fully complete.

Some products dry, some cure, and some do both. If you can just mix the dried stuff with some solvent and then use it again, it dried and did not cure. For example, (if I understand how clay works correctly) if you use clay to make a bowl or something, you can let it dry, and it is still possible to turn it back into wet clay. However, once it is fired, it undergoes a reaction and is cured. then it is not possible to turn it back into wet clay.

Set = how long until the material is no longer workable. You need to have any mixing, molding, shaping, and positioning of things complete prior to this time.

Dry = How long it takes the material to dry out. Normally refers to compounds containing water. Prior to being dry, the material may be set and appear solid on the surface, but will have portions that are still wet. For dry wall, wet filler compound will gunk up your sand paper and not result in a smooth surface. It can also result in chunks breaking off while you sand.

Cured = How long it takes the material to reach its full strength. I’ve normally seen this in regards to compounds that involve chemical reactions such as epoxies. An epoxy can set pretty quickly, but the material is still very weak until the chemical reaction has had time to complete and the compound cures to its full strength.