Concrete Engineering International – Volume 8, No. 1 – Spring 2004
Chemical waterproofing has been used in Europe and North America for more than 50 years, despite this, it is still met with considerable scepticism. In fact many people have never even heard of this method of waterproofing concrete. Repeated and consistent success of chemical waterporofing applications over many years has led to its acceptance around the world.
The basic idea behind chemical waterproofing is to prevent the ingress of water through the concrete by plugging or blocking the natural pores and capillaries found in all concrete. Other, more conventional, methods usually involve the application of some sort of coating or membrane to the concrete surface. In the last 30 years, advancements in chemical technology by Canadian manufacturers such as Kryton International Inc. have resulted in the use of Integral Crystalline Waterproofing. This can be installed using various methods, and results in improved constructability, performance and savings in time and costs.
Capillary action and diffusion
Chemical waterproofing products are generally supplied as a dry powder comprising Portland cement, silica sand and special chemicals. The powder is mixed with water to form a thick slurry. The slurry is brushed on to a prepared concrete surface and the chemicals contained in the waterproofing compound combine with water to create a chemical reaction. This reaction causes long, narrow crystals to form, which grow in and through the pores, capillaries, and hairline cracks of the concrete mass. The crystals block these passages, thus preventing the movement of water. The chemicals themselves are carried in to the concrete by capillary action and diffusion. Capillary action is the natural wicking movement of liquids in a porous structure. Diffusion is the natural movement of chemical molecules. These processes cause the crystals to penetrate deeply into the concrete.
As long as there is moisture present, the crystals will grow through the concrete over a period of days, weeks and months. When moisture is removed, the chemicals will sit dormant, waiting for the next dose of water to begin the reaction again. This ability of the chemicals to sit dormant and then become active again in the presence of water, gives the treated concrete a ‘self-sealing’ ability. Occasionally, new cracks form in the concrete due to settling or some other cause. Water entering these cracks will come into contact with the dormant chemicals of the chemical waterproofing and cause them to become active again. New crystals form and grow to shut off the water.