Vitrified Clay Pipe Work

The most common form of drainage in the UK found usually in sizes from 100-225mm on domestic systems and typically in lengths of around 700mm, they traditionally have a collar at one end and a spigot at the other, the spigot is pushed  into the collar of the next pipe in a downstream position and then jointed.You can`t really fault those Victorians can you, a lot of these systems are still in use today, and if there had only been some sort of specification when it came to pipe bedding and back fill a lot more would have survived.

Vitrified Clay is an earthen ware and because of this it is brittle, the jointing methods made the systems rigid and any movement on the system or the surrounding sub-soil will lead to stress fractures, while a half brick carelessly tossed in the trench during back fill could undo a lot of good work.

The sand and cement joints offer little resistance to persistent and hungry tree roots and the resulting weeping and leaking joints erode the very sub-soil that  the pipes relied on for structural support.

Clay Drain Pipe Joints

If you you have a posh system tarred rope or a gaskin will have been used to space and seal the joint before the sand and cement was applied to the collar, more often than not the pipes were set out on bricks or laid out in the base of the trench and the collars filled with just sand and cement and its not unusual to find systems jointed with clay, but don`t tell your loss adjuster that when the system is full or roots.

Numerous variations of these joints were used around the UK including the use of caulking, hemp, canvas and bituminous composites, ingenious methods of pouring mortar in a slurry condition into the joint were developed and pipes were manufactured with self aligning joints.

The systems were jointed, sealed and a test of some type would often be carried out, this could be a pressure test using water or simply a wooden ball being rolled through the system to ensure it had fall and that there were no lumps of mortar left inside the pipe. However a lot of the early systems would not have been inspected or tested and due to the lack of supervision corners would obviously be cut on the jointing or the system would be backfilled to early and the joints would be disturbed.

Ring Seal Pipe Joints

Rubber sealing rings were then introduced to help seal and align the joints with the rubber ring sitting inside a rebate in the collar or on the spigot end of the pipe, single or multiple rings were used however they were not adhered to the pipes and it was down to the guy laying the pipe work to ensure that firstly they were used and secondly that they remained in position when the pipes were pushed together.

The new joints and longer lengths of clay pipe work speeded up the installation process and also offered some flexibility to the system with the joints maintaining a seal even after slight movement. Pipe bedding was also specified with granular materials being used to ensure the system remained stable, the improved joint were however prone to tree root ingress

Concrete seemed to be the order of the day back in the 1960/70s with many of these supposed flexible systems being surrounded in or partially covered over in the hard stuff, we often find stress fractures or dipped sections of pipe work to be the result of excessive or carelessly poured concrete.

Modern Clay Pipe Couplings

The majority of modern clay pipes are plain ended and plastic collars with rubber seals in them are used to connect the lengths together, pipe lengths have increased meaning less joints in a system. This along with specification for bedding pipes on a granular fill means that the systems are less prone to stress fractures and they are designed to be flexible but still remain water-tight.

A lubricant should be used when joining the pipe work with great care being taken to ensure that the rubber seals do not pop out and hang in the pipe work causing solids to snag until the system blocks.

A slight bevel should be applied to the end of the pipe and it is vital that the pipes are square and aligned when pressure is evenly applied. If the rubber seals are displaced the system will fail any kind of pressure test

Surrounding joints or flooding the pipe work with concrete is frowned upon as it obviously makes the system rigid so in order to prevent root ingress through the joints a root barrier system should be used.

Clay Pipe Diameter & Shape

Domestic pipes are normally circular in shape ranging from 100mm (4") to 225mm (9") in size, larger pipe work was also  available but this was usually reserved for sewer systems.

The wall thickness on pipes can vary from manufacturer to manufacturer which is not a problem these days because we use the flexible adapters with the large jubilee clips.to make a connection, but way back when these new fangled adaptors cost more than your van we would spend many a happy hour sat in a muddy trench chipping away at a pipe so that the rigid pipe adaptor at hand would fit.

Egg shaped clay pipe work was also used in certain areas of the country for a time, it has an advantage over circular pipe work in that it has greater velocity and therefore to a degree is a self cleaning system. However this only applies with a steady and continues flow usually found in larger sewer systems and for this reason and probably cost we seldom find house drainage systems in this shape.

Common Defects On Clay Drainage Systems

Displaced Or Misaligned Joints

As already mentioned pipe bedding was seldom a concern on older systems with the excavated soil being used for back filling purposes, there were some guidelines with regard to using the more suitable material at hand such as any dry or finer ground type, and the removal of bricks and masonry from the fill until there was a safe covering over the pipe work,  we do however find cases where bricks and rocks have clearly damaged the system during the backfill.

Even the slightest water loss from a joint can be detrimental to the system given the correct ground conditions as the water erodes and washes away the sub-soil that it relies on for structural support. The water loss undermines the next pipe which then moves and causes another defective joint, which then leaks, loses water and so on................

Joints that are stepped against the flow of the system also present snagging points for solids and paper to build up on until the system blocks, when the system is blocked water is pressured out of joints with even the slightest defect which continues the deterioration process through the system.

The above process continues and the system starts to occasionally block, on occasions there are no warning signs until the system totally collapses or there may be other issues such as subsidence to your property the result of years of water loss adjacent to the house foundations.

Fractured & Broken Clay Drains

As mentioned above water loss from defective joints can lead to the erosion of the sub-soil supporting the pipe work, this leads to movement and stress fractures within the pipe wall, and you guessed it the fractures then leak and so the process goes on.

Clay drainage systems also fracture and break for several other reasons such as a carelessly placed brick during the back filling process or impact damage from the installation of a fence post or a utility company installing a new gas or water main. 

Constant vehicle movement on the road or a driveway can affect drainage systems and the simple process of rodding a drain can damage sharp bends or drop shafts.

The defects on the pipe work can lead to eventual collapse, they allow root ingress into the system and the sharp and jagged pipe work will lead to the build up of solids and paper until the system eventually blocks

Tree Root Ingress In Clay Pipes

One of the main causes of blockages to clay drainage systems in this green and pleasant land is tree root ingress, tree roots will penetrate mortar joints particularly if there has been shrinkage in the curing process, they will access the system through fractures and breaks in the pipe wall and even modern systems will be prone to ingress if a suitable root barrier system is not used.

Disturbed ground such as back filled drainage trenches make easy traveling for roots and it is generally thought that condensation that naturally occurs on the outer wall of the pipe, or moisture from leaking joints attract roots looking for a good nutritious feed, though i still prefer to tell customers that the tree`s find the drains because they can here the running water inside.

Very fine roots initially access the system through a defective joint or break and once inside the system the roots fan out reducing the internal bore of the pipe work and causing solids to snag until the system blocks. Water loss from the system is accelerated as is the movement to further joints and the ingress increases.

Well established tree root ingress will completely fill the internal bore of a system and the fine roots that initially accessed the system grow into tap roots that break and fracture clay pipe collars.

Methods Of Repair On Clay Drainage Systems

Modern Cipp lining processes are particularly useful when dealing with root ingress, patch lining allows the repair of specific defects like a leaking or fractured joint, pipe bursting is useful when there has been extensive movement to the system or you wish to increase the pipe size and of course there is the traditional excavation methods.