---
title: "5 Warning Signs of Pitch Fibre Pipe Failure"
description: "Pitch fibre pipes installed between 1945 and 1975 are failing across the UK. These 5 signs tell you whether your drains have a problem that won't fix itself."
author: "Drains Cleared Engineering Team"
published_at: 2026-05-12
canonical: "https://drainscleared.co.uk/help-and-advice/pitch-fibre-warning-signs"
tags: ["pitch fibre pipes","drain failure","drain survey","CIPP relining"]
---Pitch fibre pipes were installed in millions of UK homes between approximately 1945 and 1975. They were made from layers of cellulose fibre impregnated with coal tar pitch. After 50–80 years of use, ground movement, and biological degradation, most are now failing. The problem is that the symptoms are easy to attribute to other causes — until the situation becomes serious.

If your property was built between 1945 and 1975 and has never had a [CCTV drain survey](/drains/cctv-drain-survey), the chances of having pitch fibre underground are high. Here are the five signs that should prompt urgent investigation.

## 1. Recurring blockages in the same drain

However, a drain that clears and then reblocks within a few weeks is not responding to treatment. Pitch fibre pipes deform over time into an oval cross-section — a process called "bowing" or "ovality." The reduced internal diameter restricts flow and catches debris. Each blockage clears the immediate obstruction but does not fix the pipe shape. Jetting helps temporarily, but [CIPP relining](/help-and-advice/drain-relining-cipp-guide) or replacement is the only lasting solution.

## 2. Progressively slower drainage across multiple outlets

Additionally, if drainage throughout the property has been getting slower over months or years — not suddenly, but gradually — the underground drain may be partially collapsed or severely deformed. Pitch fibre does not fail suddenly in most cases. Instead, it deteriorates progressively, reducing the effective bore of the pipe year by year.

## 3. A CCTV survey report showing delamination or ovality

Specifically, if you have had a survey and the report uses terms such as "delamination," "blistering," "ovality," or "pipe deformation," these are pitch fibre failure modes. Delamination means the internal layers are peeling away, restricting flow and creating ledges where blockages catch. A survey graded [D3 or higher](/help-and-advice/cctv-drain-survey-what-to-expect) for these defects means repair is required within 6 months.

## 4. The property was built between 1945 and 1975

For example, this is not a symptom — it is a risk factor that should be treated as near-certainty of pitch fibre presence. Local authority planning records can confirm drainage materials in some cases. However, the most reliable way to establish what is there is a CCTV survey. Properties in this age range that have already had drainage work (often visible as newer white or grey PVC pipe in accessible inspection chambers) may have had some sections replaced, but rarely all of them.

## 5. Subsidence or ground movement near drain runs

As a result of the coal tar content in pitch fibre, the pipes can absorb ground moisture and soften further when drainage from a failing section wets the surrounding soil. Unexplained settlement, cracking in paving near drain runs, or damp patches along pipe routes may indicate structural failure. Ground movement then makes the pitch fibre problem worse — a self-reinforcing cycle that requires prompt investigation.

---

## What to do next

Consequently, if any of these signs are present, a [CCTV drain survey](/drains/cctv-drain-survey) is the correct first step. The survey maps exactly what is in the ground, identifies the extent and severity of any deformation, and provides the information needed to specify [CIPP relining](/help-and-advice/drain-relining-cipp-guide) (the no-dig repair method) or targeted excavation. Acting on a D3 finding typically costs a fraction of emergency repairs after collapse.

Call **0333 772 0123** or [book online](/book-online) to arrange a survey.