Several hundred years of heritage
Our London team were called to investigate and resolve an issue for a market shop in the heart of London’s historic Leadenhall Market.
Leadenhall Market dates back to the 14th century and is situated in what was the centre of Roman London. In the early 1300s the Manor of Leadenhall became renowned as a place for poulterers and cheesemongers to meet. In the 1440s the marketing is bigger and also sells grain, eggs, butter, herbs and other foodstuffs and continues to be a centre of commerce for the next 200 years.
After suffering some damage in the Great Fire of London, the market was rebuilt to become a covered structure and is divided into a Beef Market, the Green Yard and the Herb Market. Eventually in 1881 the market is redesigned with wrought iron and glass and as a result now enjoys grade II listed heritage status.
Today the market is used for general retailing and leisure and is one of the City’s five principal shopping centres thanks to its beautiful Victorian buildings.
Giving the basement a new lease of life
Surveyor Simon Johns said: “The client wanted the basement to be a dry and usable space and upon examination we found moisture meter readings which suggested dampness to the wall areas.”
“We found the problem to be caused by the lack of an effective damp proof course, hygroscopic plaster absorbing atmospheric moisture and lateral penetration of damp due to high abutting external ground levels and structural abutments.”
Peter Cox adheres to the strict requirements of the British Standards 8102: 1990 “Protection of structures against water from the ground”. This meant that our team had to assume that even when current conditions and recent history suggest that hydrostatic pressure is not the source of ingress this can still occur due to changing water tables, drains becoming blocked and heavy rain causing localised saturation.
In order to resolve the problem of damp walls we recommended the installation of a Cavity Drained Membrane System to the areas affected. This is by far the safest method available for any client seeking maximum assurance against system failure.
Simon said: “The ground water is controlled, diverted and harmlessly removed rather than being ‟blocked” at the point of entry which considerably reduces the risk of increased hydrostatic pressure and provides the client with complete peace of mind.”
Our experts recommended utilising the existing drainage outlets in specific areas and the fitting of the correct Back Water Anti Flood Valve protection device prior to Peter Cox undertaking the waterproofing works.
“The effectiveness of any waterproofing system is totally reliant on the drainage system,” added Simon, “and we liaised with the client to ensure the correct system was fitted. Water can penetrate a basement through capillary suction when a wall is earth retaining and/or it can rise up from the ground through floors or free standing walls appearing internally as rising damp.”
“Where hydrostatic pressure occurs water will be pushed through the capillaries of the ground structure where the water comes to the surface and the pressure behind it will be forced into the property in the form of liquid water and flooding will occur.”
In order to achieve a dry basement there are several options available. Firstly penetration of water from the ground had to be stopped, which is usually done by applying a water proof membrane or by fitting a draining membrane. Or the basement cab be heated to a specific temperature and adequate ventilation installed.
In this case Simon and his team formed perimeter drainage channels / sumps to the required areas and installed a drainage channel leading to the sump / pump prior to making good of the disturbed floor slab as necessary.
“We carried out a flood test to ensure that the water is fleeting to the proposed collection and exit points,” said Simon. “When we were satisfied, an 8mm DryRoom membrane system was fixed to the wall / ceiling surfaces with standard fixing plugs which were sealed.”
This plug has a dual purpose – it fixes the membrane system to the wall surface and allows studding/battens to be secured without piercing the installed system.
Making damp history
All joints where flanged sections were located were sealed with tape and where studded sections met, sealing rope was used. The team fixed pre-treated battens to the wall membrane using self-taping screws into the dual purpose plugs. Next 12.5 mm plasterboard was battened to specific areas before applying two coats of skim plaster to a trowel finish and then fixed cavity drained membrane to the floor area and installed an 18mm chipboard floor.
“The solutions we carried out have produced a usable, dry basement that the client requested,” said Simon. “Working on historic structures like Leadenhall Market means we never know if our modern day team also has to factor in resolutions to challenges presented by our historical counterparts. However, in this instance there were no hidden, historical surprises.”
