Gas membrane installation in Staffordshire

Mine gas, marl holes and made ground

The North Staffordshire coalfield underlies Stoke-on-Trent, Newcastle-under-Lyme and Kidsgrove, and the Cannock Chase coalfield runs from Cannock towards Rugeley. Methane and carbon dioxide can seep from old shafts and workings in either. In the Potteries, many of the clay pits dug for the pot banks were later filled with waste, and the steel, pottery and mining industries left made ground over large areas.

When that land is redeveloped, the ground investigation commonly ends in a gas risk assessment to BS 8485, and the building is given a protection level. Hydrocarbon barriers come in where former depots, garages and works have contaminated the ground.

Installed to the specification

We work from the consultant's risk assessment and the membrane schedule; the design isn't ours. The slab or blinding is checked first, because a gas membrane needs a surface that won't puncture it. Laps are then made as the product's maker requires, welded or sealed, and not hurried through in rain or cold.

On coalfield sites the protection level may also call for a venting layer or void beneath the slab. Where that is part of the design, we lay the membrane to suit it and coordinate with whoever installs the venting.

Penetrations, one at a time

Brownfield buildings in the Potteries are often piled, and every pile cap is a hole in the barrier. We collar and seal each one individually, along with every service entry, stack and column, because those details are where gas protection is won or lost.

• Pile caps collared and sealed individually
• Service ducts and drainage stacks detailed
• Laps made to the maker's instructions
• Integrity testing where required
• Independent third-party validation available
• Installation records for warranty and building control

Close to most of the county

With our base at Tamworth, Cannock, Lichfield and Burton are a short run, and the Potteries are reachable up the A38 or M6. That helps when the slab programme moves and we need to be back for a late service entry before the concrete goes in.

Estates on former coalfield land tend to rise a few houses at a time, which means the barrier is laid in small batches across many months. We keep a separate record for each plot, with photographs of its pile and service details, which is what the warranty provider asks for at completion.