Pitch-fibre drain inspection in Great Sankey

Pitch-fibre drain inspection — how it works here

Pitch-fibre is a pipe made from wood cellulose bound with coal tar pitch, laid across Britain from the mid-1950s until the late 1970s because it was light and quick to install. It fails differently from clay: instead of cracking it slowly ovalises under ground load until the bore is a slot rather than a circle, then blisters and delaminates from the inside. In west Warrington the window that matters is Old Hall and the older part of Great Sankey, where the tail end of pitch-fibre meets the start of plastic — frequently on the same run, joined with whatever fitting was to hand. That junction is where we find most of the trouble, because the pitch-fibre section deforms and the plastic one does not, so the connection between them pulls open. The camera identifies the material on sight and measures how far the deformation has gone, which is the number that decides whether it can be reformed and lined or has to come out.

• Identified immediately by the fibrous wall texture and oval bore
• Degree of deformation measured — that decides lining versus excavation
• Particular attention to pitch-fibre-to-plastic junctions, the usual failure point
• Houses built roughly 1955 to 1978 are the candidates
• Catching it before collapse is the difference between hundreds and thousands