This seems very unusual. Fast set joint compound, in my experience, will even set (on the inside anyway) under water, as my buckets have proven.

Yet I needed a hearty amount to plug a deep hole, and it's literally been 4 days and the surface is still wet to touch, and visually you can tell it's still wet (though the dry part is slowly growing day by day).

What could be causing this? (Should I be worried about effects later on. E.G. after priming & painting)

UPDATE: It dried after 1 week, I had a dehumidifier on but didn't get a chance to put in a fan/heater yet. The day it dried it was raining a lot, ironically.

  • Lack of heat to cause evaporation (IDC what the humidity is; if you shoot 10k BTU at a wall... it will dry). It's 'set'. Double the number on the bag and I guarantee you it's long since set. It's just still too wet to sand.
    – Mazura
    Commented Mar 16 at 20:27
  • How thick a layer did you put on at once? Quicker dry still takes time to release the water, and a thicker layer will dry slower. Many things layer is more hassle than few thick layers, but each layer dries faster and the result is more predictable. I think the pros did about six plaster-dry-sand-examine cycles on my living room before they felt it was ready to prime and paint
    – keshlam
    Commented Mar 16 at 21:08

3 Answers 3


Two possibilities:

  1. There is too much humidity in your building. This can often be the case with new construction in humid areas. It can take many days for the HVAC system to remove enough humidity. In existing construction you still may have excess humidity depending on the location, such as a bathroom. You might find a dehumidifier helpful.

  2. The compound is old. In this case it may never dry. If you don't know its "vintage" scrape it off and get some new compound from a sealed container.

  • So I should clarify... I used the same compound elsewhere on the wall in a hole almost as deep, and it did dry, nonetheless I did put a dehumidifier in the room. If there aren't down the line concerns about this compound after painting & priming, then I will continue to just be patient
    – james
    Commented Jan 1, 2021 at 21:48
  • also @jwh20 is there a point at which i should just stop waiting and remove it and redo it? i'm worried the continued moisture may damage something? nearby dried mud?
    – james
    Commented Jan 2, 2021 at 3:54

I would redo it--you didn't choose to use hot mud to wait a week for it to dry. Second reason to redo it: the way it's supposed to dry is a chemical reaction. If that didn't happen I believe the chance of failure definitely increases, be it shrinkage, cracking, weak bond, pounding on the wall could easily compromise the bond as well.

  • Drying and setting are two different things. The way it sets is a chemical reaction. The way it dries is the same as everything else: evaporation. - Need both of those to have happened. OP is still waiting on the second one because they're too cheap to run the building 74f. Or this is in FL.
    – Mazura
    Commented Mar 16 at 20:31

Scrape off the areas that did not dry and seal the entire area with Shellac. I use the Shellac from Sherwin Williams , but Lowe's also sells Shellac . Then you can mud your walls again. I feel it is a humidity issue . And not all the areas of the wall will react either ! Best of luck !

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