What is iron ochre?
Iron ochre is the result of a chemical reaction or biological process, both of which can occur individually or simultaneously :
- Chemical reaction: when the soil contains iron, it migrates with water to the foundation drain and forms an iron hydroxide mud in contact with the air.
- Biological process: when ferrobacteria is present in the groundwater, it produces, following the oxidation of iron in contact with air, a gelatinous mass.
When the biological process is added to the chemical reaction, the oxidation effect is considerably increased.
In both cases, the result is the formation of a viscous deposit on the walls of the grooved drains. This deposit is called iron ochre.
This deposit of iron ochre can clog the foundation drain with time especially if it is covered with a geotextile. This can reduce the effectiveness of foundation drainage, or even completely obstruct the drain, and crushed gravel may lose its filtering properties, which may promote excess moisture in the basement, or even seepage of water that could seriously damage the putrescible components of the building.
What are the signs of ochre?
Very high humidity level in the basement is often the first sign. The appearance of yellowish, orange, brownish and even reddish water in the holding tank and / or ditches may be a sign of its presence. In case of doubt, contact a specialist who can perform an analysis to confirm the presence or not. Note that only a laboratory analysis can confirm the presence of ochre.
Is it problematic?
Yes, iron ochre can obstruct the drainage of foundations. Water accumulated near the foundation could thus infiltrate into the basement through cracks as well as between the foundation and the floor slab. This water could create reddish, orange and / or brownish deposits in the basement and in the holding tank which could affect the effectiveness of the submersible pump, or even render it inoperative. In addition, this problem could scare some buyers and could even affect the resale price.
How to eliminate iron ochre?
There are no methods to stop the phenomenon that creates the formation of iron ochre, because to do this, it would need to eliminate the presence of air and water that are naturally present in the soil. Various options are available such as the installation of cleanouts in order to have a good access to clean the foundation drain. Chemical treatments are possible to reduce the impact related to ochre too. If the situation is extreme, the raising of the building or the complete waterproofing of the foundation could be considered. In this case, the fees can be very expensive.
Several factors will be considered for corrective actions :
- The type of soil
- Soil pH
- Annual variations in groundwater level
- The concentration of iron or ferrobacteria in the soil
- The type of drain and filter, etc.
When the iron ochre test is positive, it is very important to check the foundation drain regularly to make sure that it is working properly. A telescopic camera inspection costs about $ 300 (if easily accessible by a cleanout and/or by the retention pit) and allows checking its condition. If the drain is clogged, the installation of exterior cleanouts is recommended to allow periodic pressure washings. The time between each cleaning depends on several factors and can vary from a few months to several years.
Several cases have been reported in these cities: Otterburn Park, Mercier, Granby, Mont Saint-Hilaire, Saint-Jean-sur-Richelieu, Saint-Lazare, Bromont, Eastman.