Water tank repairs

How to repair a cement water tank. This page describes the repairs to one of the cement-lined Victorian cisterns at Winsford Walled Garden. Concrete tank repairs became essential when a leak was discovered all around a newly discovered cistern.

The cause of the problem was due to an extension that had been previously built on top of the original subterranean water tank so that it could be accessed at the surface. The tank was used to store rainwater off the adjacent original Peach Greenhouse, the outline of which is just visible on the right hand wall.

The picture left shows the tank before clearance, and many months before concrete pond repairs were actually begun. We did not know it at the time the photo was taken, but the dark ‘Plimsoll line’ running around the upper wall marks the ‘leak line’ or where concrete crack repairs were needed

The author during the chasing out of the walls.

The leak had to be repaired if the tank was ever going to hold its full capacity. A search was made for a suitable tank or pond sealer at the usual aquatic locations. On the carton of each new ‘find’ the instructions were not particularly helpful for our particular situation and I quote: “Ensure all surfaces are clean, dry and free from dust”. Which, for pond repairs seems to me to be somewhat ridiculous! Even during the summer (2000), there seemed little enough time between any shower to enable the wall to dry out to the extent required of such products.

Until I found the same cement used for reservoir repairs.

After a return trip of about 180 miles I bought a bag of cement that cost about £125 including transport!

A 2″ chase was cut along the leak line to discover the true extent of the problem and to provide a key for the cement.

The actual water tank repair work is a two-part process using a first coat water proofer followed by the waterproof cement used for the actual plugging.

The picture left shows both stages clearly. On the left the pale grey water proofer has already been added and on the right the water proof cement is being added.

Care needed
After measuring the volume of the chase I reckoned that if used one bag it might do the job – just. Otherwise it was a repeat trip and another £125. The packaging says it can be used “for plugging active water leaks”. You’d better believe it! I mixed up an initial test batch on the timber deck by adding ¼ kg of cement to a litre of water and it ‘set’ before it arrived at the bottom of the ladder to do the job!! From then on, the water tank repair cement was always mixed right alongside the job.

Completed cement pond repairs. The next time I mixed cement it was inside the tank. Even today I can still recall my hands shaking while stirring the water into the powder for fear it would set solid before I could use it. I really did not want to buy a second bag of cement at that price! Fortunately, there was cement left over and this was used to smear the existing walls as additional insurance.

Filling the cement pond following completed repairs.

Following the primary repairs to the chases, any surplus cement material was spread over those areas which might otherwise provide a source of any secondary leaks. Near the base of the wall as in the photograph. Better safe than sorry.

Bottom: The newly-completed cement-lined Victorian water tank used as part of the irrigation system at Winsford Walled Garden.