Case study
Federation House: A Bitumen Damp Course at the End of Its Life
The Property
A Federation-era house showing the full progression of rising damp, from first signs to serious damage. It is one of the clearest examples I have of what happens when an original bitumen felt damp course reaches the end of its life.
Bitumen felt was a common damp course in this era. It lasts a long time, but not forever.
What I Found
When I opened up the base of the wall, the bitumen felt damp course had broken down into a fibrous residue. I found the same residue at the same height on the inside and the outside of the wall, which confirmed what it was and where it sat.
Above it, the render had come away from the wall in sheets, the paint was pimpling, and in places the bricks themselves had lost so much face that they would likely need replacing.
What was causing it
Rising damp through a failed original damp course. With nothing left to stop it, ground water had been climbing the wall for years, leaving salt behind as it dried. The salt broke the render bond and then started on the bricks. See bitumen damp course failure for how and why these damp courses break down.
What the repair involved:
- A new chemical damp course injected above the failed bitumen layer
- Removal of all salt-damaged render
- Sounding the bricks to find which ones need replacing
- Replacing the worst bricks
- Re-rendering with a salt resistant system
The lesson
The longer rising damp is left, the more of the wall it takes with it. Caught early, it is an injection and a re-render. Caught late, it can mean replacing brickwork as well.