Tanking a damp wall

Summary: Learn how to tank a wet or damp wall, basement tanking, install a polypropylene membrane and apply an epoxy damp-proof membrane.

Damp patches on an external wall following a period of wet weather could indicate a problem with penetrating damp. Carrying out a technique called Tanking will effectively eliminate the problem. Tanking is a damp-proofing method generally used when it’s not possible to gain access to the outer wall, as with basements and cellars.


There are two methods for tanking walls. The first involves fixing sheets of polypropylene membrane to the wall's surface using membrane clips and joining the sheets together with double-sided tape.

Alternatively, you may choose to apply a two-part epoxy damp-proof membrane or a bitumen-latex emulsion to the floor and walls.


Fitting a polypropylene membrane

This is effective for areas with a severe damp problem. However, if the problem is very severe it may be necessary to install channels to collect the water and a pump to remove it from behind the membrane. So it is advisable to seek professional help on this.

  • Calculate the surface area of the walls you wish to cover with the polypropylene membrane.
  • Taking the measurement from the floor to the ceiling cut the membrane with a sharp knife into lengths.
  • Now you'll need someone to hold the membrane against the wall, while you use a power drill to drill a series of pilot holes 300mm apart through the membrane and into the wall.
  • Hammer the clips into the pilot holes to secure the polypropylene membrane to the wall.
  • With the first sheet in position fix the second sheet to the wall ensuring you have an overlap.
  • Starting at the top of the first sheet stick the double-sided tape to the edge, then remove the backing from the tape and stick the second sheet to the first. All sheets should be joined in this way.
  • You can then plaster over the top of the membrane, using a damp-resistant plaster.

Hammer the clips into the pilot holes to secure the polypropylene membrane to the wall.

Use double-sided tape to join each sheet, ensuring there is an overlap.

Applying an epoxy damp-proof membrane

Follow the safety instructions issued by the manufacturer of the epoxy damp-proof product you are using. These will include wearing protective goggles, a respiratory mask and rubber gloves.

  • Strip away any render or plaster from the wall to expose the masonry or concrete.
  • Brush the dust from the walls and wash away any oil or grease using sugar soap.
  • Following the manufacturer's guidelines mix together the two parts of the epoxy membrane.
  • Paint the wall with a first coat ensuring you achieve total coverage. A paintbrush or roller can be used for this purpose but apply the epoxy membrane using horizontal strokes.
  • When the first coat is dry apply a second coat using vertical strokes, again taking care to cover the entire surface of the wall.
  • You can decorate the wall as soon as the epoxy membrane has dried completely. However, if you plan to render and plaster the walls it is recommended you throw sand onto the wall while the coating is still wet to produce a key for the render.

Author: C J Mills Google+