Case study
Waverley Federation Terrace: Why the Last Injection Failed
The Property
A Federation terrace in Waverley, around 20 metres long, double brick with no cavity. The house was mid-renovation with a builder on site, and the walls had already been injected twice before. The damp kept coming back.
The question was simple: why had two treatments failed?
What I Found
I laser-measured the ground levels. The neighbour’s ground and tiles sat 200 to 250mm above the internal floor level along the full common wall. Both earlier injection lines were below that.
I also tested the old injection. The original liquid treatment was still repelling water, so the product itself had not failed. Other findings: skirtings wet at the rear and dry at the front, rotting subfloor bearers, sections of concrete internal floor, blue metal packed against the boundary wall, and a cut in the boundary gutter dumping water against the wall. The owner had also painted a membrane on without a primer, and it was peeling.
What was causing it
The damp course was bridged. Water was going around the earlier injection lines, over the top, through the raised ground next door. The failure was geometry, not chemistry. The concrete floor sections made it worse by stopping the ground drying out under the house.
What I recommended:
- Injection at about 400mm along the full common wall, above the bridging
- The same, plus render removal and a negative side membrane
- Full perimeter treatment over two days
- Fix the boundary gutter so it stops feeding the wall
- No warranty on any membrane applied over existing paint
The lesson
A damp course in the wrong place is the same as no damp course. The injection line has to sit above the highest point where ground, paths or paving bridge the wall. See rising damp explained.