Knapped Flint Boundary Wall, Blandford Forum

The wall

A conservation area boundary wall, around 40 metres of it, in flint with brick lacing courses – the classic north Dorset detail. Roughly 14 metres had bulged badly and was shedding flints onto the pavement.

What had gone wrong

The same thing that has gone wrong with most failing flint and rubble walls in this county. At some point the wall had been repointed in hard cement. Flint is impermeable, so a flint wall relies entirely on its lime joints to let moisture out of the core. Seal those joints with cement and the water stays in the core, freezes, and pushes the faces off from the inside.

By the time we saw it, the core of the failed section was effectively wet rubble with no cohesion left.

Rebuilding it

Flint is slow and there is no honest shortcut. The failed section came down carefully, with every usable flint salvaged and sorted by size and face. A new foundation went in. Then the wall was rebuilt in low lifts – no more than about 450mm a day – because lime takes time to set and building high pushes the fresh work out of line.

Faces were selected and set by hand, the brick lacing courses run true across the panel, and the whole thing finished with a brick-on-edge capping to match what survived.

The undamaged sections were raked out and repointed in lime so the entire wall can breathe again.

The result

Seven weeks for 14 metres rebuilt and 26 metres repointed. It is slow, quiet, expensive work and it is some of the most satisfying we do.