Drywall....The morning after...discolored areas in newly dried mud

[stevegeneral]

HOW COME WHEN I.... Had a loose panel with some cracks... Fixed it with new drywall screws or mesh tape... Washed it with mild detergent... Wiped it with clean wet rag... Let it dry... Then applied two coats of brand new mud from a brand new bucket over three days (low 70s, 50% RH)....

SO WHY....When the mud dried there were small (Less than 1/4") discolored areas (greenish) with tiny cracks in the middle of each little blob? I'm thinking there must be some kind of a chemical reaction happening that is making the mud shrink. Any ideas? These are not tool marks, and they are not air bubbles. ( Believe me, as a newbie, I've seen plenty of both) These are different.

Thanks for any suggestions

steve

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[mucker111]

How much mud did you have to use? Was it a big hole?

[Phisherman]

Mud shrinks as it cures and it may crack especially in areas where the mud is applied too thick. The drying process will pull any dyes or ink in paper. A good mud job takes a few thin layers progressing from a 4", 6", and 10" knives, waiting a day between coats if you can. You can pre-spot the greenish areas with some PVA or shellac to help stop the color transfer. Mud drying is a physical reaction.

[Phisherman]

LOL!!!!!!!!!!!!!!!!!!!