Concrete waterproofing: a two-fold protecting process we often forget

The service life of structures depends on a variety of factors, such as their purpose, the materials of construction, the surrounding environment and – mostly – the degree of maintenance. The definition of expected service life has varied over time. Whereas BS 7543 (1992), defined the ‘normal’ life of a building as 60 years, the new Eurocodes, e.g. BS EN 1992-1-1 (2008), assume this period to be a lower one, of 50 years. The factors affecting service life can vary, not only from building to building, but even within a given building. For example, the quality of the substructure, superstructure and even the roof structure in a building may vary, especially if different subcontractors were responsible for them. Also, the environment a building is subjected to, will vary from external elements to internal elements and even from seaward side to landward side.

Carbonization and chloride ingress are the two main mechanisms that lead to the deterioration of concrete structures and affect service life. Although we may not be able to control the amount of CO2 in the atmosphere around a structure, we can certainly control the amount of salts-carrying water entering the concrete. Keep in mind that the service life of a concrete construction, is all about the time it takes for chlorides and sulphates to penetrate the matrix, travel all the way to the passive protection film of the steel rebar and disactivate it. From this point onward, the steel-concrete bond is lost, and we are looking into problems. It is important to remember that if a reinforced concrete building has been exposed to a chloride source, major repairs will be required after only just half of its design life.
This is why the repair of old concrete buildings and infrastructure – most often bridges, ports and wharfs – constitutes a substantial percentage of the waterproofers’ work.

For many years, the traditional method of preventing this has been by waterproofing the surface of the concrete, with membranes or brushed coatings, in the hope of preventing salts-carrying water getting to the concrete. No provision however was made for the fact that membranes fall victim to moisture, the very medium they are supposed to be protecting against, as micro-organisms will develop in moisture and are the reason behind membranes’ demise. Let not go forgotten the fact that quite a few such brush-spread waterproofing is helpless against cracks occurring to the concrete, for numerous reasons. Finding a way to seal the capillaries of the matrix, rather than merely covering the concrete surface with a thin sealer coat, is the only effective means of blocking the diffusion of chlorides and sulphates and extend the service life of any construction.

CWS100® is applied on the structure after repairs, to prevent a re-occurrence. A revolutionary waterproofing product, CWS100® is not a surface coating, admixture, crystal growth, or water repellent. It is a biochemically modified sodium silicate, that is spray-applied to cured concrete. Through a three-day watering process, the product penetrates the matrix and reacts with the calcium, forming a sub-surface barrier gel, within the top 20 mm of the concrete, effectively sealing and waterproofing pores, capillaries and large cracks – up to 2.2mm! –  against the ingress of water and corrosive agents. Its self-healing properties protect the concrete against future cracks and keep it watertight. Contrary to membranes and similar brush-applied waterproofing, it will not deteriorate with time and, therefore, provides lifetime waterproofing and structural protection. As it is IN the concrete, rather than ON the concrete, it can neither be torn, delaminated or scratched, like traditional waterproofing, nor is it sensitive to UV radiation or penetrable by plant-roots, making it ideal for special applications, like roof-planters, green roofs etc. The cost of protecting concrete with the product is minimal compared to that of repairing damaged concrete. Now couple this with super-fast application (up to 6,000m2 in one day, with one single person) and you have a no-brainer solution, for protecting your concrete for life.

While even the best of concrete cracks, protecting it with CWS100® can prevent damage to concrete as it will heal future cracks. This view is endorsed by Ivar Ness, former chief engineer of bridges for the Norwegian Rail Administration, who says: “The concrete we are using is of high quality, such as with a cube crushing strength of 45 MPa or higher, which it is waterproof in its own right. However, cracks can never be avoided, not even when adequate measures are taken during the curing period. The application of CWS100® over the whole deck surface, gets the cracks tightened and thus prevent moisture to find its way to the reinforcement.

CWS100® is available to Contractors and Applicators via the international distribution network of Concrete Waterproofing Systems Ltd.

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