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Typical problem: iron ocher

Iron ocher that attacks French drains results from either a chemical reaction or a biological process:

Chemical reaction
When the soil contains iron, it migrates with water to the drain and forms, in contact with the air, an iron hydroxide sludge.

Biological process

When ferrobacteria is present in the water table, it produces, following the oxidation of iron in contact with air, a gelatinous mass. The result of both is the formation of a viscous deposit on the walls of grooved drains and it is this deposit that is called “ferrous ocher”.

The first symptoms caused by iron ocher

The phenomenon of iron ocher is pernicious because it can cause significant damage even before the owner realizes it. Vigilance is also required if there are precursory signs such as:

An abnormally high humidity level in the basement Reddish deposits on the concrete slab of the basements. Deposits of ocher-colored mud in the catch basin


Possible remediation of existing buildings to mitigate iron ocher symptoms varies by location, but may require:

The modification of the slope of the ground Sealing at the junction of concrete wall and concrete slab Installation of cleaning chimneys Drainage under the slab The installation of a waterproof coating The installation of a waterproofing membrane The raising of the slab of the basement Condemnation of the basement

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