Tanking

[edit] Introduction

Tanking is a term used for creating a tank-like seal to protect walls against water penetration. The Building Regulations stipulate that tanking must be applied to all new build structures below ground, but tanking can also be applied to existing buildings, to prevent water penetration into basements and cellars, as well as helping to tackle rising damp.

The two main methods of tanking are by using a membrane or a coating. The type of damp and the precise requirements of the building will determine the most appropriate method to use, and sometimes a combination is required to ensure walls remain dry.

[edit] Tanking membranes

Tanking membranes (or cavity drain membranes) consist of a studded or dimpled plastic sheet which is fixed onto the internal face of masonry, block or rendered walls and sealed with tape.

The studs create an air gap cavity between the wall and membrane. Where there is no visible water in the cavity, ventilation may be adequate to prevent the accumulation of moisture. Where water is present, drainage or a or sump and pump may be necessary.

Tanking membranes can have a plain surface which allows battening and insulation boards to be attached to them, or a mesh surface for direct plastering.

[edit] Coating

Tanking coatings include; bitumen, asphalt, resin/tar and tanking slurry.

Liquid bitumen is painted onto cleaned masonry or render but is best for smaller jobs or for coating externally below the damp-proof course. It can prove difficult to apply to masonry in older buildings as it can separate from the wall if applied incorrectly.

Resin/tar coatings are typically epoxy or polyurethane resins extended with tar or bitumen. They are generally able to withstand higher pressures than bitumen coatings.

Asphalt is typically applied in a thick coat with a further wall constructed to prevent it from delaminating under water pressure.

Cement based tanking slurry is typically used for larger areas. It can be applied with a brush, and once dry, overcoated with a breathable render and finished with plasterboard or plaster.

Both floors and walls may require tanking to prevent water ingress.

[edit] Related articles on Designing Buildings Wiki

• Basement waterproofing.
• Bitumen.
• Damp in buildings.
• Damp proofing.
• Defects in brickwork.
• Dry lining.
• Latent defects.
• Penetrating damp.
• Plaster.
• Rising damp.
• Rising damp in walls - diagnosis and treatment (DG 245).
• Sealant.
• Treating brickwork with sealant or water repellent.