Case study
Watsons Bay: Sandstone Basement With Three Problems
The Property
A very old terrace in Watsons Bay with a basement level on a sloping block. The lower level is solid sandstone block, which is common in Sydney, rendered and painted on the inside. The floor was travertine over underfloor heating, recently laid, and the owners wanted to keep it.
Below-ground rooms rarely have just one problem. This one had three.
What I Found
Inside, there was a salt band and blistering paint along the base of the walls, with a power point sitting in the wet zone. Outside, the paving, deck and fence footing were at or above the internal floor and window sill level. A side passage sloped up towards the front of the block, and a downpipe was discharging right at the footing.
The sandstone sills and lower courses were scaling and flaking. Above and below one window, a short piece of embedded metal, around 300mm long, was rusting in layers like stacked paper and pushing the render off.
What was causing it
Rising damp through most of the basement. Water coming in sideways through the walls on the uphill pathway side. Rusting metal expanding and blowing the render off around the window. And salt weathering of the sandstone on top of all of it. Each one needed its own fix.
What I quoted:
- Injection to about 31 lineal metres of 400mm thick sandstone wall
- A negative side membrane on the uphill external walls
- Tanking to the wall in line with the bathroom
- Removal of about 54 square metres of render
- Salt resistant render to the areas not waterproofed
The lesson
A below-ground room needs every water source identified before anything is quoted. Treat only the rising damp and the side-on water keeps coming. More on heritage and sandstone walls.