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Peter Cox is renowned for its work on historical and heritage buildings and our Uxbridge branch recently worked to waterproof a Second World War air raid shelter situated in a period detached property in Bedford.
Bedford offers numerous areas of outstanding natural beauty and attractions, from stately homes and gardens to woodland walks and nature reserves. It also enjoys excellent transport links to London, the north and beyond, making it a popular place to live work and visit.
A starring role for Peter Cox
The large property in question had been converted into modern flats and the client in one was adapting a basement into a home cinema. In the original plans for the cinema, the door opening onto an emergency tunnel which leads to the shelter was to be blocked and the basement room tanked and refurbished.
However, the client then decided to make the tunnel and shelter an integral part of the project which would have a WWII theme. The problem however, was water in the shelter. It was so bad that at one time, a couple of canoes stored there were actually floating!
Surveyor John Tuddenham said: “The plan was to include a ground water sump to control water ingress into the areas and we advised the main contractor Stuart Barr to carry out various preparatory works before we could commence our part. Once this was carried out a temporary sump and pump was put in place to remove any existing water from the working area and our experts set out to resolve the problem.”
First, Peter Cox had to create a triangular fillet at all wall floor junctions which ran for the entire length of the junction. The fillet was then left to cure for several hours before applying a generous coating of a thin fluid product which is based on a polymer and silicate combination.
John said: “Köster Polysil TG500 is a unique liquid which is applied with a hand pump sprayer and has the effect of hardening mineral surfaces, blocking salts within the structure and at the same time providing a good surface for the following layers to adhere to.”
Once the liquid is dried, a mineral coating containing crystallising and capillaryplugging agents was mixed with clean water to form a slurry consistency which was then applied with a thick masonry brush in an even layer. After leaving overnight a second coat was mixed with clean water to form a slurry. After application the surface is sprayed with with Polysil TG500 which hardens the NB1 Grey slurry.
Next it’s time to fit the all-important membrane. We fixed Delta Profile strips to the base of walls to allow any water to run down into the sump chamber and then provided and fixed Delta PT membrane to all walls. The membrane is placed dimple-side to the surface, and this allows any moisture to drain by gravity to a channel in the floor, which then runs to the sump and pump device which evacuates the water outside.
“This membrane is resistant to water and water vapour, and to salt transfer, as well as puncture, impact and loading,” said John. “The membrane is not damaged by normal foot traffic during installation, or while laying concrete or screed finish.”
A happy ending
The Delta PT meshed membrane was fixed to wall surfaces using standard fixings which were sealed and all joints near flanged sections were located and sealed with tape. Where studded sections meet, sealing rope was used.
The meshed membrane was rendered with sand and cement applied in two coats to a thickness of 15mm and then followed by a coat of finishing plaster. Once completed, Peter Cox checked the system to ensure that the pump and drainage system were functioning correctly.
“Our experts and those of Stuart Barr were able to ensure that this Bedford basement cinema was ready for action,” said John. “As always it was always fascinating to experience working within a slice of our history and should the cinema show any war films they will no doubt have an extra special meaning.”
