Thanks K. But can I just use regular mud to fill in the cracks, and do I really have to clean it out.
Can't I just leave it the way it is, and then try to fix it with mud?
Thanks for your advice.
No you cannot do it with regular mud. It shrinks too much, cracks and takes too long to dry. But a bag of hot mud, mix in a 1 gallon bucket, clean bucket immediately with brush and sponge while it is still super easy to do so. Pre-fill the gaps and cleaned out break outs and then you will find the rest of the job is much easier.
It is also, NOT "just as good" to make the many patches. You have a much higher probability of a crappy looking job and cracking down the road. Much better to span with full sheets.
If you haven't already addressed the stud, what is going on on the backside and will that be a future problem? If not, just rip a piece of plywood and shim it out.