Go ahead and Proof it!

The effects of increasing pollution, seismic variations and changing climatic conditions are more pronounced today with changing construction technologies and the introduction of advanced methods of designing and construction of large complexes. And, it has become all the more important to use the right waterproofing solution to ensure the longevity of the structure.

Waterproofing in civil engineering generally refers to waterproofing of reinforced concrete, plain concrete or plastered masonry structures. It is a complex subject. The main ingredients of these structures: cement, sand, aggregates, steel, need to combine in a definite proportion to act as a single member and perform in a desired manner. Waterproofing of structures made of other building materials is fairly simple.
Construction technology has been changing with the changing requirements in utility of buildings and infrastructure. Requirement of Large Span bridges, high rise residential structures and very large commercial structures and auditoriums have introduced advanced methods of designing, construction, instrumentation and maintenance techniques. On such large structures, the effects of increasing pollution, seismic variations and changing climatic conditions are more pronounced.

Waterproofing methods have also been advancing with new products, technologies and application methods being introduced in this sector. The purpose of waterproofing now is not only to prevent leakages in a residential building but also to prevent corrosion of steel in the structure and enhance its life and safety.
In the earlier days, waterproofing used to remain an insignificant aspect of building construction and was only taken up if a building leaked. Now, however, with huge budgets and critical safety factors involved, waterproofing aspects are often taken up at the designing stage itself.

Selection of Waterproofing Treatments
Before selecting a waterproofing treatment, it is important to know some basic characteristics of the area to be treated with respect to material of which it is composed of, and its functionality for which it is designed.
There are two types of waterproofing materials employed. One is integral waterproofing material, which is added to the concrete itself during mixing, and the other is surface applied.

Integral Waterproofing Compounds
The integral waterproofing compound is expected to take care of any deficiencies in the mix itself and is treated as a precautionary measure. It carries the same importance that proper mixing, proper laying of concrete, good compaction, and efficient curing carries. These materials are generally air entraining type and the dosage is prescribed such that the material imparts about 3.0 per cent air entrainment.
The entrained air, which is of the size of approximately 20 micron bubbles, spread in the concrete, and block the progression of capillaries in the concrete. One percent entrainment of air results in six percent reduction in compressive strength. To restore the compressive strength, a strong plasticizer is added so that it reduces the water cement ratio and helps in gaining higher strength so that the lost strength due to air entrainment is restored.
There are integral waterproofing compounds which work by imparting water repellent property to the concrete, and there are some which work on crystallization technique (this system is explained in detail below).

Surface Applied Waterproofing Systems
Surface Applied Waterproofing systems are the main waterproofing systems. The materials employed in this are liquid applied membranes, pre-formed membranes, chemical compounds which work on water repellence and crystallization techniques.
Selection of waterproofing system with respect to its utility and suitability on a structure is a complex mechanism. This calls for detailed understanding of the structure and the waterproofing system and a good specification.

Material Composition
Now that we are mostly referring to waterproofing of concrete surfaces, some basic facts about the concrete surfaces are:
After mixing and placing of concrete, it continues to gain strength. Some believe that this process goes on for up to 90 days, while some believe it gains strength for up to one year. Others are of the opinion that it goes on developing strength for much longer, provided conditions are favourable.
References are drawn from the historic mortars with which centuries old monuments are standing even today without a blemish. International committees are working and meeting regularly towards understanding and evolving such materials and conditions for future buildings.
Those mortars have been based on lime or calcium oxide, which again is the main functional material in today’s ordinary Portland Cement. Mortar or concrete – whether cement-based or lime-based – are highly alkaline.
Acid breaks and dissolves mortars and concrete. Polluted atmosphere, which in combination with atmospheric moisture, reduces the alkalinity of concrete surface, thereby reducing its strength.
Another property of concrete is that it absorbs water from rain – or moisture from atmosphere – and releases water vapour when the temperatures rise. This is called the breathing property of concrete.
Maintaining alkaline atmosphere around the concrete and allowing the breathing property of concrete to continue unhindered is referred to as creating favourable conditions. While selecting a waterproofing system, it is important to know whether the product selected is alkali compatible or not, and also whether it allows the concrete to breathe or not.

Functional behaviour of selected material
The waterproofing material selected should have a comparable behaviour and compatibility with the structure which is being waterproofed. In a structure, we have columns, beams, slabs, shells, etc., which are designed for and undergo different strain conditions. The waterproofing material selected for these structures should compliment these functions. Otherwise, the system will fail, as a rigid pavement over a long span bridge fails.
Some waterproofing treatments recommend protective mortar or screed over it for its protection from weathering. Structural engineers should be consulted before selecting such a system, especially on shell roofs, to know whether such a load can be superimposed on the shell or not.

Membrane Waterproofing system
There are a number waterproofing membranes available in the market. These could be single component or two components. These membranes are called ‘Liquid Applied Membranes’. There are also preformed membranes based on Bitumin, HDPE, Poly olefin, etc.
Membranes, whether Preformed or not based on epoxies, poly urethanes, poly urea, bitumins, HDPE, Olefines, etc., are suitable for metal roofs and unsuitable for RCC roofs, as they do not allow the concrete to breathe normally. Liquid applied membranes based on low Tg acrylics and vinyl acetates have been found to be more durable and successful in temperate climatic conditions as we have in India. These membranes are alkaline in characteristic, UV resistant, highly flexible/stretchable and allow the concrete to breathe.

Crystalline Waterproofing system
The main material for waterproofing in this is a powder which is composed of ordinary Portland cement, natural fine sand, and activating chemicals. This powder, when mixed with water in the recommended proportion (generally one volume of water to two-and-a-half volumes of powder) yields hot slurry. This slurry is applied on the water saturated concrete surface to be waterproofed.
The active chemicals in this slurry penetrate into the water bearing capillaries and react with the free lime available in the concrete to form insoluble crystals. These crystals effectively block the capillaries. Further, these chemicals remain active in the body of concrete and restart the crystallization process as and when a new capillary is formed and water enters it.
Some companies are marketing integral waterproofing compounds based on crystallization process. These are invariably used in deep basements and concreting of water-retaining structures. Integral waterproofers are used only as precautionary measures over and above primary and secondary waterproofing systems.

Main areas that need waterproofing in a structure are Roofs, Podium, Bathrooms and Toilets, Water Tanks, Foundations, Basements, and the walls. If the structure to be waterproofed seems to be having lot of voids, honeycombs, porosity, etc., it is advisable to injection grout the area first to stabilize it before commencing waterproofing treatment.
Injection grouting is done by pouring cement slurry admixed with some expansive chemical and quick setting ingredient under gravity, or with a pump under pressure, through the nipples fixed at regular intervals. This process is repeated several times as hardening of each grouting cycle creates some smaller hollow annular space upon the grout slurry drying or when water escapes the concrete. Surface cracks, if any, need to be repaired with suitable durable material before commencement of waterproofing job.
In new structures, the remains of mould releasing agents or curing compounds cause hindrance to the adhesion of waterproofing material. These need to be carefully removed.
Before commencement of waterproofing treatment, all other ancillary activities in that area, such as sanitary fittings, pipe laying, conduit fixing, etc., should be completed and the area handed over for waterproofing without any hindrance. Before commencing a waterproofing job, it is advisable to flood test or pond test the area for 48 hours to assess the severity of leakages and to demarcate the areas that need special precaution or treatment. Also, it is a good idea to flood test or pond test the area once the waterproofing treatment is over, to see if any area is left out.

Waterproofing of superstructures and roofs
Superstructures of buildings, whether residential or commercial, and the superstructures of bridges, etc., are rather more dynamic than static. They undergo deflection under varying loading conditions and movement under primary, secondary, and tertiary settlement conditions.
They expand and contract under varying daily and seasonal temperature conditions. Movements and sway are experienced due to wind and the seismic conditions as well. These concrete surfaces breathe in, by absorbing moisture either from atmosphere or rain, and breathe out water vapour during hot weather.
Substances used for waterproofing such structures should have strong alkali compatibility, UV resistance, and the final treatment should have flexibility, movement accommodation ability, and allow the breathability of concrete to continue without any hindrance. Membranes and coatings, however strong they might be, which do not allow the breathability of concrete to continue have failed, cracked and delaminated from many superstructures.
Membranes based on emulsions of low Tg polymers of acrylics and vinyl have proven to be flexible, durable, alkali compatible and allow the breathing property of concrete to continue. These have been successfully used on many structures and are now being used to coat pre-stressed post tensioned concrete bridge girders.
Epoxies, Poly Urethanes and Bitumin felts have been tried for waterproofing of RCC roofs. They have all failed because of de-lamination due to their impervious nature, which does not allow the concrete to breath and does not withstand the pore pressure exerted by the water vapour.
If, with the help of strong primers, a strong bond is established between the non-breathable coating and the concrete surface, then the cover concrete weakens in withstanding this vapour pressure and the reinforcement corrodes in the presence of moisture or water vapour under pressure in the cover concrete region.

Waterproofing of Walls
Walls, whether RCC or brick/block work, show wetness or dampness on inner surface. This dampness spoils the paint and aesthetics are affected. This dampness is due to absorption of rain water and its seepage through porous plasters, bricks/blocks or concrete. This is treated by application of water repellents.
Water repellents are silicon compounds based on silanes and siloxanes. There are two types: one is water dispersible, and the other is solvent-based.
Water dispersible ones are economical and last for two to three years. Solvent-based ones are expensive and are effective over a period of 20 years. These compounds are spray applied on to the bone dry surface for best results.

Waterproofing of water retaining structures
Water tanks – overhead or underground – and swimming pools come under water retaining structures in urban areas. In case of an under-ground water tank, leakage of water from the water tank is a loss of water and it will reduce the life of the structure by corroding the reinforcing steel in the structure.
If the ground water seeps and leaks into the water tank, then besides reducing the life of the structure, it also brings with it all the contaminants into the water tank, thus making the clean water unhealthy for any domestic use. It is, therefore, necessary that utmost care and caution is exercised in construction of water retaining structures right from the concreting stage itself.
There has been a practice of applying bituminous membranes over bitumen primer around all under-ground structures, such as underground water tanks, RCC manholes in sewage disposal systems, which not only waterproofs the structures from entry of ground water but also protects the structures from termites and other insects boring holes into them. Crystalline waterproofing systems applied as a secondary treatment internally are preferred in waterproofing such water retaining structures because of their strong activity in the presence of water.

Basement Waterproofing
The primary waterproofing treatment employed in basements is modified Bitumen felt. There are two types of modified bitumen felts available – APP (atactic poly propylene) Modified Bitumen Felt, and SBS (styrene butadiene styrene) Modified Bitumen Felt.

These membranes are reinforced with various materials, such as fibre glass, HM-HDPE, polyester, etc., and are supplied in standard width of 1.0 meter and length of 10 meters. These felts are available in thicknesses ranging from 1mm to 10mm.

APP modified bitumen felts perform well in elevated temperatures or in temperate zones, whereas SBS modified felts perform better in low temperatures or in cold regions. Hence, in India, mostly APP modified membranes are utilized. These membranes are laid with a lap joint of 200mm and are welded by torch. Waterproofing with bitumen felt is done in the following steps.

PCC is made smooth by applying cement, sand, mortar screed, and upon this surface, the felt is laid and welded. Over the felt, again, a protective screed is laid and cured. On this surface, the RCC raft and the retaining walls are casted.
The bitumen felt is raised along the retaining wall up to plinth level. This forms the primary waterproofing treatment for the basement.

Secondary treatment is carried out from inside the basement itself, post-construction. The thickness of the APP modified membranes employed in the basement waterproofing shall not be less than 4mm for their successful performance. For deeper basements, one needs membranes of 6mm and above.

Article contributed by Perma Construction Aids Pvt. Ltd.

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