Dampness in prefabricated structures

1. Dampness penetration through joints

Prefabricated elements, such as walls, beams, ceilings and columns, are manufactured in a factory, then transported to the construction site and assembled there. A building can be built entirely from prefabricated elements, or from a mix of prefabricated elements and concrete poured on site.

Wherever two prefabricated elements meet, a joint forms, and that joint has to satisfy two requirements: functional ones, such as watertightness, thermal insulation and acoustic insulation, and structural ones that keep the building stable.

Several methods exist for sealing these joints, and getting the seal right is essential. Where the sealing falls short, dampness gets into the joint between the prefabricated elements and causes two main kinds of damage: it can damage the thermal insulation, leading to condensation and mold on the inner face of the walls, or it can work through the joint into the apartment and swell the plaster.

Patching the outside of the joint with a crude external seal does not help, since it does not address the source of the problem. The repair has to happen inside the joint itself: expose it, then redo the internal seal properly.

2. Dampness penetration from windows

In buildings built using an industrialized method, dampness commonly gets in through the seam between a window's blind frame and the surrounding concrete, whenever that work was done poorly.

The water gets in because the blind frame was not properly sealed to the concrete around it.

Done correctly, sealing (with EPDM sheets, for example) goes over the concrete wall and the blind frame before the exterior stone cladding is applied to the window reveal, the term for the section of wall the window sits in. But if the cladding on the reveal goes on before the concrete is poured, that sealing step becomes impossible, leaving a failure point for water to get in between the blind frame and the concrete.