Waterproofing and damp proofing in the Free State

Heaving clay: keep water away from the walls

Researchers from the Central University of Technology in Bloemfontein and Tshwane University of Technology, writing about raft foundations on Free State clays, describe how expansive soils cause visible cracks, jammed doors and damaged floors. They recommend an apron around the foundation that slopes away from it, to stop extra moisture moving underneath.

Their work also found that the north-facing side of a house, which gets the most sun, shows the greatest moisture changes. In dry periods large cracks open in the clay on that side, and when rain comes, water runs fast and deep into them and causes heave.

For waterproofing and damp proofing, that means the work around the house matters as much as what's applied to the walls:

• Ask the contractor to check for missing, cracked or back-sloping aprons, especially on the north side.
• Make sure downpipes discharge onto channels that carry water well away from the walls.
• Don't let flower beds or lawns that get watered sit hard against the house.
• Repair wall cracks with flexible fillers and coatings that can take some seasonal movement.

Different rainy seasons, east and west

A Water SA study of the Free State's rainy season found it starts earliest in the north-east: in Thabo Mofutsanyane and most of Fezile Dabi it has begun by mid-November in four years out of five. In central and western Lejweleputswa it starts around early December, and western Xhariep has the shortest season of all. Thabo Mofutsanyane, around Bethlehem and Harrismith, has the longest.

If you're in the eastern Free State, plan flat-roof membranes, parapet repairs and exterior wall coatings for winter and early spring, and aim to finish by October. In Welkom or the drier west you have a few more weeks, but the same rule applies: membranes need a dry surface, and a leak found in the first big storm is harder to fix.

Telling clay damage from rising damp

On heaving clay, cracking and damp often turn up together, and it's easy to blame one for the other. Cracked walls, jammed doors and lifting floors point to soil movement. A horizontal tide mark with salt deposits at the base of a wall points to rising damp. If you see both, have the soil movement looked at as well as the damp, so you are not paying to treat only a symptom. Our waterproofing page explains the different kinds of damp.