Modern techniques in waterproofing

Modern waterproofing technique aims to understand the functional behaviour of the structure, understand the properties of the available materials arrive at a system, which is best suited for the structure and incorporate the system at the design stage only. A single product or technique is not usually enough, involvement of various bodies and techniques in coordination is essential for making structures waterproof. For success of any system the building structure should have sufficient and efficient control joints if the slabs dimensions are more than twenty meter in any direction. Control joints are structural engineering design features. These joints are supposed to be designed and their configuration marked on the drawings and their detailing needs to be given with respect to waterproofing system proposed in large buildings. Different types of control joints are construction joints or day joint, crack inducer joint, contraction joint and expansion joint. Coefficient of thermal expansion of concrete is between 6 to 10 X 10-6 mm/mm/oC. If proper control joints are not provided in large slabs, no waterproofing system works. Modern technique relies basically on two main waterproofing systems, which are fool proof and simple. They are crystalline waterproofing system, and flexible membrane water proofing system. Flexible membrane waterproofing system The main product used in this system comprises of two components one liquid and the other is a powder packed roughly in the proportion of 1:4 by weight. The liquid component is an acrylic emulsion and the powder component is a polymer-modified cement with film forming chemicals and fillers, and some manufacturers add reinforcing fibres to make the product extra effective.

When these two ingredients namely the pre-weighed powder and the liquid are mixed together an uniform slurry results. This slurry is brush applied on the roof surface, which upon drying forms a flexible film. Since there is cement in this product its compatibility with concrete is excellent. The film further allows the breathing of the concrete without any hindrance hence there is no problems of its de-lamination from the concrete surface.

This film being flexible takes care of the deflections in the slab and the movements caused because of primary or secondary settlements, movements due to wind loads and temperature stresses developed in the concrete. This system can be used on surfaces, which had bituminous treatment earlier. In European countries, this type of product is used as coating on pre-stressed concrete bridge girders to protect them from aggressive chemical atmosphere. A typical waterproofing specification using flexible membrane system will be as follows:

• Clean the surface to remove all loose particles, grease shuttering oil and such deleterious materials to get a sound concrete surface.

• Cracks if any should be cut into ‘V’ shaped grooves one inch wide and one inch in depth. Cut honey combed areas back to sound concrete.

• Repair these areas with a stiff paste of fibre reinforced polymer repair mortar generally sold in the name of crack fill.

• Mix the powder and the liquid components of the product to form an uniform slurry and brush apply this slurry on the surface to be waterproofed.

• When the waterproofing coating is still tacky apply 1:4 cement sand screed and cure normally.