ᐅ Eliminating Odors and Soot from a House with Clay Plaster – Any Suggestions?

Hello Forum,

Last year, we bought a house in Hungary and plan to renovate it. The house was probably built around 1950. It is solidly constructed from fired bricks (40cm (16 inches) exterior wall), unplastered on the outside, with walls and ceilings inside fully covered with clay plaster. The floors are tiled, except for two rooms which have wooden floors.

At the time of purchase, the house was unfortunately completely cluttered—sometimes up to 2 meters (6.5 feet) high—and the floors were almost entirely covered with PVC, newspapers, furniture, laundry, carpets, and garbage bags. The walls were completely blocked with cabinets and trash, so there was no ventilation anywhere. In the kitchen, moisture was present under the PVC on the tiles but dried within two weeks. In one of the rooms, the wooden floor partially disintegrated under piles of trash, PVC, and carpets; this floor will be replaced soon. We hope to save the other wooden floor by sanding it. In one room, black moldy marks formed on the exterior walls behind the cupboards. The roof had two major leaks, through which the interior of the house was consistently exposed to moisture 🙁
It is unknown how long the house had been empty before the purchase, but we estimate at least 1–2 years.

We have completely cleared out the house and have now let it dry for eight months. Fortunately, the windows and front door are currently quite drafty, which provides some air exchange. A critical damp spot on an exterior wall was traced back to a faulty gutter and is now dry as well.

Now we have two problems and are unsure how to proceed:

1. In the kitchen, the previous owners heated the room for years with a defective wood stove. The room smells unbearably of smoke, like after a major fire. The ceiling and walls are BLACK!

2. The entire house has a very strong musty smell and other unpleasant "leftovers."

Basically, we need to clean all surfaces from dirt, soot, and mold.
For the tiled floors, we plan to use baking soda as an odor absorber and possibly a steam cleaner. Wooden floors, doors, and windows will be sanded. We have also considered an initial ozone treatment to kill mold spores and eliminate some of the odors.
What do you think?

How should we approach the clay plaster on the walls?
We thought about removing the top layer (maybe 2mm (0.08 inches)) with a floor grinder and then applying a new fine clay plaster. The walls will be repainted anyway. However, I worry that sanding will push the mustiness and especially the black soot layer in the kitchen deeper into the plaster (I would like to avoid removing the full 2–3cm (0.8–1.2 inches) of clay plaster). We also considered cleaning with steam, but that would add a lot of moisture to the house...
How would you do it?

Thanks for your tips and suggestions.

Although I was impressed by how much a small ozone generator can neutralize in the bathroom, I’m afraid you won’t be able to avoid gutting the space.

The mold has probably already penetrated deeply into the plaster, where ozone can’t reach quickly. The smoke smell has certainly soaked in completely.

But I’m just an amateur. Maybe someone with restoration experience will weigh in...

A friend of mine helped clear out a mold-infested apartment a few years ago and was exposed to harmful mold spores. With lung function reduced to nearly 50%, the infestation was eventually stopped. His life was permanently changed and, unfortunately, ended far too soon. Last summer, in his early 60s, he passed away. I miss him.

Please be careful and wear protective clothing. It’s better to completely gut a building than to keep any mold contamination. Cutting corners in this area would worry me.

For sanding the walls, we will definitely use FFP3 masks and a vacuum cleaner with dust class H or exhaust air directed outside. Do you think 2-3mm (0.08-0.12 inches) is enough here? The walls will be painted with lime paint afterward, which, as far as I know, strongly inhibits mold growth.

No, I don't think it's enough, as I said. Take it all down.

The smell of smoke can only be removed by completely removing the plaster. A persistent musty odor would concern me and prompt a close inspection of the structural timbers in the floors and ceilings. What is the floor construction in the ground floor?