Visible indicators consistent with iron ochre activity, visual-inspection limitations since the drain is buried, and when specialist verification is recommended. Regional defect documented mainly on the South Shore, in clayey Lanaudière, and on Île-Perrot. Educational page — not engineering expertise or legal advice.
Iron ochre is a gelatinous orange-reddish deposit produced by bacteria (notably Gallionella and Leptothrix genera) that develop in iron-rich soils when groundwater is present. When these bacteria colonize a French drain, they produce an iron precipitate that progressively clogs the drain's perforations and stone bedding. Typical consequence: the drain loses its drainage capacity, hydrostatic pressure increases against the foundation, and basement infiltration appears — often accompanied by excessive sump-pump activity. Not all soils contain enough iron or the favourable conditions for this process. This is why iron ochre is concentrated in certain Greater Montreal regions — primarily the South Shore, the clay lowlands of Lanaudière, and Île-Perrot — and much rarer elsewhere. Regional context is therefore a key factor for risk assessment.
Here are the visible indicators we document during a pre-purchase inspection. Each is a sign to investigate, not a confirmation of iron ochre. Confirmation requires specialist verification of the buried drain.
Viscous, gelatinous substance, orange to red-brown in colour, observed at the accessible drain outlet, around the sump pit, or on exposed drainage system components. The gelatinous texture is characteristic — distinct from simple dry rust.
Orange-reddish rings on sump-pit walls, deposits on pump components, coloured traces at the surface of residual water. Particularly visible if the sump pit has not been cleaned recently.
Recent fill marks in the sump pit, pump cycling often even in dry weather, signs of wear or recent pump replacement. A sign that the drain is struggling to evacuate.
Moisture halos, paint flaking, water traces at the wall-slab junction, particularly after a wet spring or heavy rain. A drain clogged by iron ochre lets water accumulate against the foundation.
Ferrous, slightly metallic odour, sometimes reminiscent of marshland, in the basement or near the sump pit. May accompany other visual indicators and orient the hypothesis.
Seller documents mentioning repeated drain interventions, recent drain camera cleaning, prior basement backups. Historical context is a strong indicator in at-risk areas.
Important: these visible indicators do not conclusively confirm the presence of iron ochre. Several other conditions can produce orange staining (rust from galvanized plumbing, water sediment, oxidation of stored metal) or sump-pit activity (high water table alone, deficient exterior drainage, misdirected gutters). Confirming the presence and assessing the extent require a camera inspection of the drain by a qualified drainage contractor.
Our visual inspection follows the InterNACHI standard. For iron ochre specifically, the limitations are significant because the defect is primarily in the buried drain.
We recommend specialist verification by a qualified drainage contractor in the following situations — ideally before removing the conditions on the purchase offer.
Unlike many defects that affect all regions, iron ochre is concentrated in specific areas with favourable geological conditions (iron-rich soils, high water table, sensitive drainage). It is not a universal Greater Montreal defect.
Iron ochre is rare or undocumented in other regions we serve (downtown Montreal, Laval, North Shore, Laurentides, Estrie/Mauricie). Case-by-case verification remains relevant if the specific lot context (soil, water table, drainage history) justifies it.
If the pre-purchase inspection reveals visible indicators consistent with iron ochre in an at-risk area and the condition-removal deadline is short, several options are available depending on your risk tolerance and the seller's cooperation.
What is documented during an inspection, what is not, and when to verify further.
Pre-purchase inspection in Greater Montreal. Report within 24h*. InterNACHI certified · IBC Network. Thousands of inspections.