Hockey's Heirarchy of Waterproofing: Design > Installation > Product

Recently, I've had a couple of informal conversations with contractors and specifiers in relation to waterproofing products, where we discussed the role of third party product accreditation such as BBA, and in one case I was asked for an opinion on a particular product, more specifically an adhesive bitumen sheet tanking membrane produced by a particular manufacturer, (which I expect they had used on a previous scheme).

My answer (in summary): 'same as any other adhesive bitumen sheet membrane'.  Yes, a bit blasé, but I explained why I feel this way and thought that it might make for an interesting blog post.

My point was that while 'product' is important, it is just one part of the equation, with design and installation if anything being more critical, in the following order:

Oops, poor design (but awesome efflorescence).

Oops, poor design (but awesome efflorescence).

Design > installation > product.

Why? Well, if your design is incorrect then perfect installation and perfect product may not result in a dry basement.

Case in point, we've just started remedial work on a waterproof concrete basement (using an admixture in the concrete), good product and I expect that the concrete pours would have been checked and/or supervised as quality control; however, to provide a means of escape, there is a window opening through the (waterproof) concrete structure, with reveals part lined in (not waterproof) masonry, with the glazing unit fitted into the masonry recess.

The design of the external stairwell leading down to the window is such that water is able to pressure upon the masonry elements and find its way into the basement. 

Probably a simple design oversight, but enough to cause penetration and problems for the homeowner.  Nothing to do with product or the installation of it.

A classic example is the use of external adhesive bitumen sheet (or other) membrane tanking systems, which rely on effective land drain systems to prevent pressure from coming to bear, because while a BBA/other certification might imply that they are capable of totally excluding water, the reality on site is that they will not realistically be 100% free of defects, and as a result rely on the correct design of external land drain systems, to prevent pressure from coming to bear, thus negating any potential defects present.

Following Phil Hewitt's work on the Outwing Vs. Weatherald case it is more common knowledge, but you still see land drains shown too high, with failure often occurring as a result. 

Thankfully the British Standard now advises that a waterproofing specialist should be involved on the design team at an early stage.  We've been promoting such an approach at Trace for many years, because we know that good design is the first stage in achieving a sucessful outcome.  Product is important, but it is only one part of the equation.

My money would be that in the next iteration of the British Standard (8102), installation by specialists is also recommended, but that's another blog post!


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