Basement waterproofing to BS8102 – getting it right on site.

18th January 2013

basement waterproofing, waterproofing below ground structures, bs8102, tanking

.....There are sound reason for this.

The CSSW (Certificated Surveyor in structural waterproofing) is one way of identifying these individuals. Is this just a way for the waterproofing contractor to make more money or, does it have any real benefit to the customer and the project?

Let’s use an example from a recent site:

We were asked to install a Waterproofing system for this 350M2 basement area, of a new, large domestic property. We chose a Type C Cavity drain membrane, with interlinked pumping stations. However, as the basement extended out into the garden, additional Type A waterproofing, in this case the cementitious based Vandex concrete waterproofing system was specified, to seal the top of the deck, as well as create a sound link with the internal Type C system (Safeguard Europe's proven Oldroyd membranes with three Sentry sump and pumping stations)..

It’s well known that the first line of defense in the Type C waterproofing system is the structure itself. So it’s good practice to  ensure that the structure is waterproof. However, sealing the structure is not always successful or even possible, and due to additional ingress points appearing in the future, due to changing ground conditions or structural movement, a Type C system is often specified. This way, any future ingress of ground water will not impact on the client’s basement, being merely diverted into the drainage system.

Having carried out a full appraisal of the drawings, we designed the combined Type C and Type A system to ensure a 20 year guaranteed lifespan. However, as anyone who’s worked on a building site, with bad weather and planning changes interfering will know, drawings are not always exactly the way a building works out. 

In this case the building became a dynamic ‘work in progress’ with Architect, Client, other sub-contractors and the general contractor making changes and pushing to complete their aspect of the work.

These changes could impact negatively of the integrity of both the Type C and type A system with potentially catastrophic results:

Examples include:

…. the general contractor wishing to push ahead with an external slab detail over the green roof and deck, which would have covered vulnerable joints prior to waterproofing – we stepped in and stopped this.

….. The quantity surveyor wished to dispense with a fall to drainage in the deck detail, moving the drainage to a more ‘convenient place’, which was the last place it should be, from a waterproofing perspective – we were able to step in and modify this detail, so the potential error was avoided and the client still got a detail the surveyor could live with.

….. during installation of a concrete Jacuzzi a sub-contractor buried essential drainage and drain washing inlets in fresh concrete.  This was spotted by us and the problem sorted, before a flood risk could happen.

The fact is that the above, were all situation where the contractor was unaware of the potential damage to the waterproofing system. Had the client not insisted on a competent waterproofing design specialist on site, not just designing the system, but supervising the delivery of it, the system would have been seriously compromised.

A frantic affair

Construction can be a frantic affair on-site. Things get buried, removed, damaged - forgotten even.  Most of the time these are the little things and are either caught in ‘snagging’ or come to light as minor defects later.

Waterproofing is not like this at all. Defects arise, which can bite the contractor, Architect and client, very hard, as water finds it way in to areas it’s not welcome in.  If this happens and damage or unapproved changes have taken place, which cause the leak, the best guarantee in the world will not save the situation.

This is why BS8102 requires a design specialist to be involved; to get the waterproofing right.  I’d go further and say that the waterproofing should be carried out by a specialist, who is familiar with these on-site tribulations, so that everyone knows what is acceptable. The designer, whether contractor based or independent, should also be engaged as a supervisor and he must have sufficient authority to stand up for the waterproofing, when inevitable pressure for change, compromise or omission comes to bear.

These things will happen and they MUST be caught and rectified….. Before it’s too late.

Waterproofing structures over the years has come under all sorts of criticism due to the lack of regulation and high rate of failure. No doubt the scenarios we experience play a big part in this. 

There are  lots of competent project managers, site agents and foreman out there, with vast  knowledge and experience of the construction industry; there is also however a lot of empirical evidence to show; waterproofing  structures is not everyone’s strong point…..  

Sean Tristram-Jones CSSW CSRT
Specialist Basement waterproofing Surveyor.

For further advice or information call me on 0800 591541 or use our basement waterproofing contact page

If you are unfamiliar with type A and C waterproofing here's of our site videos, featuring a contract where both methods were employed to waterproof a new 1500M2 commercial basement in Richmonshire.

Our MD Bryan Hindle CSRT CSSW has also written about Vandex type A waterproofing on his blog, here's a post which fill out the details of this remarkable concrete waterproofing method

Filed under: Surveying, Waterproofing,

Tagged as: basement waterproofing, Cellar waterproofing, BS8102, Type C cavity drain membrane, type a waterproofing,

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