I went through a similar horror after a toilet leaked from the first floor onto the ceiling of a basement stall shower.

The plaster fell off, the mold collected, the paint bubbled and buckled.

Call the plumber, as I did, and if you are lucky, he can also tear off/down the damaged wall stuff, repair and repaint. It took months since he needed to caulk and then let the walls dry several times.

He did, of course, start with the source of the water damage, which required a new toilet (and some work on the floor it stood on.)

Nasty, brutish, long and expensive.

Contact someone that is a specialist, get quotes and get more than one quote. Do not try to do it yourself, you could end up in hospital with things growing in your lungs or nose.

You definitely need to contact a mold abatement team, do not try to open up the wall or try to fix the problem yourself. Black mold is extremely toxic and can make you very sick (even in the state that it’s currently in, behind the walls).

Here is some info about how to hire a mold abatement team without getting scammed. Info

You definitely want to get multiple estimates and check the credentials of anyone who is going to do the work. There are companies that specialize in mold abatement, so just a regular plumber (unless they are also have special qualifications to do mold abatement) is not the right person to hire, at least not initially, for the mold abatement part of the situation.

You might want to consider staying at a motel during the mold abatement process.

Good luck and sorry for your problem.

Mold specialists often rip people off. They know they get called because most of the time people are terrified of the mold and they take advantage charging extra high prices. I recommend getting a contractor to tear the walls out, he has to cut back way beyond the mold to make sure the area is free of mold and then reconstruct the area. You will want to have the area kind of sealed off with plastic so if any mold spores do fly around they are contained in the area. If it is black mold once it is fiddled with the spores can release and get into the air. The air can get thick fast. You certainly can price the project with a mold specialist type company and with a regular contractor (who knows what he is talking about) and see if there is a price differential. People who renovate and do construction deal with these sort of things more often then one would think.

A friend of mine works for Belfor Property reconstruction and I am pretty sure that do that type of work and are nationwide. If you want I could get in touch with her and ask her about your area, but FYI I have not personally used their services.

Contact a mold remediation specialist company. They have the equipment and expertise to deal with it.

Stop the water, (fix the leak) remove damaged drywall, remove any loose organic matter (in my business we never use the“M” word,) spray any other discolored areas with 50/50 bleach water solution, let it dry, (you may want to put an electric heat with a blower in front of it for a couple of days.) replace drywall, paint, and never speak of it again.
If your insurance company even hears the words mold or water damage they will try to cancel you. Mold abatement companies will try to scare the crap out of you and charge an arm and a leg. Unless you have a close friend or relative that you trust in the business, avoid them like the plague.
You may want to wear some sort of mask when removing the affected materials. You can get them at Lowes or Home Depot.
Edit: my husband is certified to do mold remediation.

Get references from recent clients to whom you can speak for whom the contractor did somewhat similar work.

If the contractor tries to avoid getting cit of luck!esty permits for the work, then fire them right away. Inspections to the work protects you, the client!

Best of luck!

Haven’t read any of the previous replies, so I apologize for repeating any info.
As a GC, who often deals with these sort of issues, here’s my advise.
So, there are three components to this repair process.

1). a GC. (who’ll do the demo, and once the testing and remediation is complete will rebuild the damaged areas.
2). A Mold testing specialist. (a specialist who’s independent, certified tester who will test the affected areas for mold & write up a remediation protocol for the Remediation Co to follow). And lastly,
3). a Remediation Co. (guys who’ll come in and clean up the mold per protocol).

A good GC should have a list of the other two, (any two can work under/through the other), so you’ll only be dealing with one individual/entity. It should be a given that everyone is licensed, insured etc.

First thing you want to do is NOT call your insurance company! The reason for this is that in my experience, insurance companies do not like to deal with mold issues (in particular) unless they are forced into addressing them, provided that they are liable for such an issue. So read your policy carefully, and make sure they do not have an ‘out’ clause.
Your independent tester will come in handy, once you’ve established that the insurance co is obligated to address the mold issue.

Get a good GC who’s done this sort of thing before, Angie’s List is a good resource to start. If you cannot find one look for a Tester, or a reputable Remediation company. They’ll each have lists of the other two qualified Sub’s.

If you have any further questions, please feel free to PM me or you can reach me at “info at sasvs dot com”.
Best of luck to you!

PS. do not let anyone do any demo until you get a remediation protocol from a qualified tester. The reason for this is that if the mold is dangerous, and demo is done, (without proper containment) it will get airsolized and spread throughout the house. Right now, it’s probably pretty well contained.