Tanking in Barrow

The Problem

This Victorian terrace in Barrow-in-Furness has a full-depth basement that had been flooding regularly for years. The original stone walls had no damp-proofing, and the high water table in this low-lying area of Barrow meant groundwater was actively pushing through the walls and floor during wet seasons. Standing water reached 150mm depth in the worst events, ruining stored possessions and creating a persistent damp smell throughout the house. Previous attempts to solve the problem with waterproof paint and sealant had failed repeatedly — the hydrostatic pressure simply pushed the coatings off the walls from behind. The homeowner wanted to convert the basement into a home office and needed a guaranteed, permanent waterproofing solution.

Our Solution

We implemented a dual-approach tanking system. First, the stone walls were cleaned back to solid substrate and two coats of cementitious tanking slurry were applied — this is a rigid waterproof coating that bonds to masonry and resists hydrostatic pressure from the outside. Second, a cavity drain membrane (CDM) system was installed over the tanked walls and across the floor. The studded membrane creates a controlled drainage cavity that intercepts any water that does penetrate and channels it to a new sump chamber in the corner of the basement. A dual-pump sump system was installed with mains power and a battery backup, automatically activating when water reaches the sump to discharge it to the external drainage system. The CDM was then covered with a sand-and-cement screed floor and the walls were battened and plasterboarded, creating a dry, insulated space ready for the home office conversion.

The Result

The basement has remained completely dry since completion, through multiple periods of heavy rainfall and high water table conditions. The dual-system approach means the tanking slurry prevents the majority of water ingress, while the cavity drain membrane provides a failsafe backup that manages any residual moisture. The sump pump activates occasionally during prolonged wet weather but operates quietly and efficiently. The homeowner has successfully converted the space into a fully functioning home office with electrical installations, carpet, and furniture — all completely protected by the waterproofing system. We provided a 10-year guarantee on all tanking work.

Cementitious Tanking Slurry

The two-coat tanking slurry is a polymer-modified cementitious coating that bonds permanently to masonry substrates and resists hydrostatic pressure up to 7 bar — equivalent to 70 metres head of water. Applied at 2mm thickness per coat, it penetrates the masonry pores and crystallises within them, creating a waterproof barrier that becomes part of the wall structure itself. This active waterproofing mechanism continues to work even if the coating is subsequently damaged.

Cavity Drain Membrane (CDM)

The 8mm studded HDPE membrane creates a controlled air gap between the tanked wall and the finished surface. Any water that penetrates the primary tanking is intercepted by this cavity and channelled by gravity to the sump chamber. The CDM system provides a failsafe secondary waterproofing layer that operates entirely by gravity — no power, no maintenance, no moving parts.

Dual Sump Pump System

The sump chamber houses two submersible pumps — one mains-powered and one battery-backed. The mains pump handles normal operation, while the battery unit activates automatically during power cuts. The dual configuration ensures continuous basement protection even during storms that combine heavy rainfall with power outages.

Insulation and Dry Lining

The battened plasterboard finish incorporates 50mm PIR insulation between the battens, providing thermal comfort in the converted basement space. The insulation and plasterboard are fixed to the battens rather than the membrane, allowing the cavity drain system to function independently.