It is rare in Ireland where a building defect can cause the structure to rise. In the UK, heave is quite common when the moisture content rises in areas of shrinkable clay soils. This post relates to corrosion of steel lentils, particularly those constructed during the last century.
Lentils are required to provide support above the opes of the building such as windows and doors. These lentils are usually constructed in either reinforced concrete or steel – the choice of material will normally depend on the finish of the external leaf. So for buildings finished in brick, steel lentils are required as they can be designed to incorporate the brick finish. Nowadays, these lentils (see photo) are galvanised in order to provide protection for the design life of the building, usually 50-60 years.
During the last century, anti-corrosion measures were not always fit for purpose leaving the steel to inevitably come in contact with moisture and rust. Lentils which were not maintained were even more vulnerable. Unprotected steel will rust in the presence of moisture – this can result in a four to six increase in volume.
The lentils on the subject property have increased in thickness by about two-fold resulting in moderate vertical and horizontal cracking along the bonds of the brickwork on either side of the window. Remediation in the form of repair or replacement should only be completed by competent tradepersons under the direction of a consulting engineer.