PVC: today's standard
Since the 1960s and 1970s PVC has been the most widely used material for household drainage, inside and out. The pipes are light, smooth inside and are joined with a solvent weld socket or a push-fit socket with a rubber ring. A lighter grade is common indoors, while underground pipes have a higher ring stiffness to cope better with soil pressure. House connections are usually 110 or 125 mm. Indoors PVC is often grey, but you cannot always tell the grade from the colour alone.
A well laid PVC pipe lasts many decades. Defects arise mainly from installation: a socket that was not pushed in fully, a pipe resting on a stone and deforming, or a section that sags because the ground beneath was not properly compacted. Water stays standing in such a sag and dirt settles, which over time leads to blockages. Roots can also find a way in at a socket that does not seal well.
Vitrified clay: fired clay in older neighbourhoods
Vitrified clay is fired and glazed clay and was widely used until around the 1970s for house connections and street sewers. The material is highly resistant to chemical attack, so the pipe itself is often still in good shape. The weak spot is the joints: clay pipes were laid in short lengths with many sockets, which in older systems were filled with mortar or a simple seal.
During a CCTV survey of clay pipes the engineer therefore often sees displaced joints, root intrusion through open joints and cracking or fracturing caused by settling ground or heavy loads. Vitrified clay is brittle: a hard knock or subsidence can break a pipe. When cleaning clay pipes, an experienced engineer therefore chooses the pressure and nozzle with care, so old joints are not damaged further.
Concrete: for larger diameters
Concrete is mainly used for larger diameters, such as main sewers under the street, business parks and sometimes the collector pipes of larger buildings. Concrete pipes are strong and heavy and can take a lot of soil pressure. Concrete is less common in household drainage, although in some older neighbourhoods it is also found in the house connection. Concrete pipes are joined with a spigot and socket joint and a rubber ring.
The best known ageing effect in concrete is corrosion of the inner wall. Gases such as hydrogen sulphide form in the sewer and above the waterline can be converted into acid. The concrete then becomes rough and soft and the aggregate is exposed. Joints can also start to leak and the pipe can crack when the ground settles.
Cast iron: internal drainage in older buildings
Cast iron was used well into the twentieth century for soil stacks and internal drainage, especially in walk-up flats, apartment blocks and larger town houses. The material is heavy and dampens sound well, which was an advantage in apartment buildings. Cast iron is still sometimes chosen in modern buildings for that reason, for example in hotels and offices where quiet matters. Modern cast iron pipes have a protective inner coating.
Old cast iron rusts from the inside. A rough crust of rust and scale forms on which grease and dirt get caught, reducing the flow. Eventually leaking joints, cracks or rusted-through spots can appear, often in the horizontal sections and bends. Careful cutting and cleaning followed by relining is then a common approach.
Other materials: PP, PE and asbestos cement
Other plastics also appear in new builds and renovations. PP is used indoors in low-noise systems, while PE is welded and popular in commercial premises and commercial kitchens. Both are smooth and resist hot water and chemicals well. PE is also widely used for the rising mains of pressure sewers, because welded joints have no sockets that can start to leak.
Some homes from the 1950s to the 1980s still have asbestos cement, for example as a vent pipe or in the external drainage. As long as such a pipe is intact and is not worked on, it can stay in place. Leave sawing, breaking or drilling to a certified asbestos removal company. Relining can be a way to renew such a pipe from the inside without removing it.
How Bosmans determines the material and condition
Which material lies in the ground, and in what condition, is best shown by a CCTV drain survey. The engineers of Bosmans Rioolservice assess the footage using the coding from NEN-EN 13508-2, so cracking, sagging, root intrusion and displaced joints are recorded unambiguously in the report. Based on that they advise cleaning, a patch repair or relining, with a 10-year guarantee on relining. With a patch repair only the damaged section is restored from the inside with a short liner; with relining the whole pipe gets a new inner wall. In most cases this means no garden, driveway or floor has to be opened up.