External membranes, also known as Type A solutions, are
located on the outside of the building. They are installed under the floors and
on the outside faces of walls. The key design principle is that they form a
continuous barrier around the building to stop the ingress of water.

The products are commonly sheet materials, paint on products or trowel applied products. Often a design will be a combination of several materials.

It is essential they are fitted correctly and joined together in line with the manufacturer’s guidelines. It is also essential that they are protected from site damage after installation. Protection is usually given by a sheet materials which will also allow water to drain into external land-drains.

A good design will take account of pipe penetrations, changes in levels, changes in direction and elements such as lightwells. It is essential that the system complies with BS8102:2009 and that the system is correctly designed to hold back water.

Octopus Waterproofing fit a wide variety of Type A membranes, from Cetco Voltex to Visqueen Presapplied, Newton Hydrobond 403 and SikaProof A.  We are experts in the various jointing methods typically using Leister welders, tapes and self-edges.

In most basement waterproofing solutions, external Type A membranes form one line of defence against water ingress. It is common to include a second line of defence in the form of Type C protection (typically an internal cavity drain or paint on membrane), or a Type B protection (typically a structurally integral solution).