Why drains fail in London
Clay, in two senses. The pipes in most pre war London streets are vitrified clay in short lengths with mortar or rubber joints, and the ground they sit in is London clay, which shrinks in dry summers and swells again in wet winters. That movement works the joints apart over decades. Once a joint has opened, roots arrive within a season or two, and from then on the pipe collects everything that passes.
The other recurring cause is a connection made badly: an extension waste cut into an existing run at the wrong angle, or a rainwater downpipe put into the foul system, which overloads it in every storm.







