What Is Tanking In Civil Engineering
Tanking is a term used to describe the provision of an impervious layer in the floors and walls of basements. Tanking generally consists of three layers of mastic asphalt forming a continuous membrane up to 30mm thick on floors and 20mm thick on walls. Alternatively, two or three layers of bitumen sheeting bonded with hot bitumen may be used. Although, three layers generally being used for sheeting, weighing 3.5kgm^-2 and two layers for sheeting weighing 5kgm^-2.
Unless protected, both types of membrane are liable to be damaged. E.g., if laid externally, they may be punctured by backfill material. Consequently, they are always protected by sandwiching them between the structural floor or wall and a protective coat which may be concrete, brickwork, blockwork or a mortar screed. Where membranes are not fully contained, they may be extruded under pressure and in such circumstances, pressures should be limited to 600N/m^2 and 1000N/m^2 for asphalt and bitumen sheeting respectively.
The condition of the surfaces to which the membranes are applied is also important. If the surfaces are very rough, they may puncture bitumen sheeting, and if they are very smooth, particularly on vertical surfaces, asphalt may not adhere. Soft, flaky or friable surfaces will be carefully detailed and generally reinforced by asphalt fillets in the case of asphalt membranes and for bitumen sheeting, by internal and external angles constructed for bitumen sheeting.
