White efflorescences of saltpetre on the walls, and an acrid – ammoniacal, sour – smell settling into the house. Many owners are puzzled: « a 1980s house, modern – how can it smell like a barn? ». The explanation lies in the ground, and it is more common than you would think in our rural and peri-urban communes.
The mechanism: fertilisers rising with the water
Land that carried crops (vines, orchards, field crops) was fertilised for decades with nitrogen fertilisers. Nitrates accumulate in the soil, often deep down. When a house is built on top and the damp-proofing is imperfect – no or aged capillary break, no drainage – water rises by capillarity, dissolving these salts. It deposits them on the walls as white blooms: saltpetre. And these nitrates, in the presence of constant damp and organic matter, release acrid, ammonia-like smells that flare up in wet weather and fade in summer.
Why the smell is the symptom that matters
Saltpetre alone is harmless – it is an indicator. The smell signals that the dampness is ACTIVE and the soil’s nitrate load is high. It is the combination that should trigger a diagnosis: without treating the cause (capillary break, drainage, ventilation), neither anti-saltpetre surface treatments nor repaints will last. The smell will return, season after wet season.
How we work
Further reading: Origin of Damp at the Base of a Wall – Vence – Case Study · Ammonia Smell in a Newly Renovated House: Likely Causes
Hygrometry measurements at the base and top of walls (telling rising damp from condensation), examination of the blooms, soil-history analysis (past agricultural use), ventilation check. The written report names the cause, its severity and the correct scope of works – so you don’t pay for surface treatments that will fail. Free quote, report within 2 to 5 days of the visit: 04 22 46 06 04 – English spoken.
Survey carried out by Frédéric Faucouneau, independent building expert – Antibes, Alpes-Maritimes (06), Var (83), Bouches-du-Rhône (13). Find out more
📅 Last updated 25/09/2026 - Cassini Expertise, independent building expert – departments 06, 83 and 13.