Case study
Victorian House: Brick Wall on a Sandstone Plinth
The Property
The side passage wall of a Victorian house. Solid brick sitting on two to four courses of rock-faced sandstone, with layers of old paint over the brick, the stone and the damage. There were terracotta vents to a suspended floor, a garden strip along the base and a downpipe running into the soil at the corner.
The paint was pimpling in a band two to five courses above the top of the stone.
Reading the Wall
The key question on a wall like this is where to put the new damp course. The sandstone plinth carries water up into the brickwork above it, so the injection has to go into the first continuous brick bed joint above the stone. Because the top of the plinth undulates along the wall, that line sits anywhere from about 400 to 700mm above the soil.
At the tap corner there was a concrete upstand against the wall, so the line had to step up above it there.
What happens to the stone
The plinth sits below the new damp course, so it stays wet and will keep slowly fretting. On this wall that is an acceptable loss. The stone is thick and sacrificial, and protecting the brickwork above it is what matters. Before committing, I check the tooling marks on the stone to confirm what it is and how it was built, because that decides whether the standard approach applies.
The specification:
- Inject the first continuous brick bed above the stone
- Step the injection line up and down with the plinth
- Step up above the concrete upstand at the tap corner
- Inject both leaves if the wall is double brick
- Leave the stone plinth as a sacrificial zone below the line
The lesson
There is no single correct injection height. The line follows the construction of each wall. More on older walls on the heritage rising damp page.