Gary Johns Architects Tanking

The raft mentioned in our last blog is starting to take shape. Being formed in clay soil, the structural engineer has specified 200mm of Cellcore to the middle. This will form a void under the reinforced concrete to allow any heave in the clay to take place without affecting its structure.


We have chosen to use Dual Seal tanking membrane to the floor and walls below ground level. The product consists of a waterproof membrane with a layer of Bentonite attached to one side. The Bentonite is a clay substance which swells when it comes into contact with water, making the product self healing. This product was chosen over RIW Structurseal on the basis that Dual Seal can be used on blockwork walls – Stucturseal can only be used when cast against in-situ concrete.

We have used Dual Seal pre-formed corners to all of the corners of the raft, and a pre-formed top-hat to a drain penetration to ensure watertight junctions.

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Steel reinforcement is intricately formed over the top of the Dual Seal – expertly carried out by DJ Francis! Its a shame its all going to be covered over!

Gary Johns Architects- steel reinforcement

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