I've seen people in Europe living in homes with mold everywhere and it just doesn't bother them. Not all molds are toxic. Not knowing what mold abatement firms or labs to test for toxins exist in France if they do exist I wouldn't know who to recommend you to get the mold tested. That would be my first step, know what you actually have.

When in Rome............

Good luck. Wish I could be of more help.

Mold loves to grow inside drywall. I hate to say it but I think you will have to replace the drywall. Covering it will only keep the mold in it.

Before you get far along, realize that some people are very allergic to some molds and you should take the appropriate safety measures.

When you take down the drywall, treat the studs and frames in the wall with a mold treatment chemical. I used BoraCare with mold care on my subfloors. Let it soak in and repeat the application.

Also, here in the USA there have been lawsuits regarding Chinese and some German made drywall that contains high levels of chemicals that will cause the household wiring to corrode and create a fire hazard. Keep that in mind when you buy the new drywall.

If you want someone else to do the mold treatment, many pest control companies and water damage repair companies will do it.

Jcalhoun,

We're talking France, in Europe, drywall and studwalls are not very common, it's stone, block, plaster almost everywhere. Many, many layers of plaster. New construction maybe studs and drywall. 4 2x4's in England a few years back came shrinkwrapped, $30.00 usd.

Hopefully you're dealing with drywall vs plaster.
I have a hobby room that flooded and I found mold was growing behind the baseboard and also in the drywall, but only in the area directly behind the baseboard. I had to cut out the drywall about 8" from the floor before I no longer saw any mold growing. After cutting out the drywall I treated the studs and let the area dry out for several days. Drywall was patched and painted and no problems since.

So, I suggest you start at floor level and cut out some drywall to see if there's any mold.

You said drywall so I agree with annz. Take a sharp blade and cut a small square or hole in a spot where the odor is strong. make it a plug so that you can put glue on it an replace it in the event that you find nothing. Do this a few times and see if there is any evidence. Also, take a straw or chopstick and cover it with cotton (tape it but let the end be just cotton) and swap the inner hole. see what comes out.

You might consider a home test kit you mail them in for testing so may not matter your location. Here's a link to several kits. Never used one myself.

Here is a link that might be useful: Test kit

Cutting a hole in drywall and replacing it isn't a big deal, just a pain.

What if you were to cut a hole in the drywall, get a dehumidifier, and run it for a few days and completely dry it out?

You are a renter. I don't know what the landlord/tenant laws are in France, but I wouldn't do anything to the walls without the landlord's permission in writing.

You are a renter. I don't know what the landlord/tenant laws are in France, but I wouldn't do anything to the walls without the landlord's permission in writing.