Waterproofing is the formation of an impervious barrier, which is designed to prevent water entering or escaping from various sections of building structures. In this regard, hydrostatic pressure is pressure exerted or existing within a liquid at rest with adjacent bodies.
Hydrostatic pressure rises as the water table rises in the monsoon. While, for structures located in the vicinity of a water body, the hydrostatic pressure may be permanently present. The deeper the structure is set into the earth, greater the hydrostatic pressure will be, which will try to force water into the pores of concrete and assist in a rapid deterioration.
Internal areas that are waterproofed include bathrooms, shower recesses, laundries and toilets. While, external areas waterproofed extends to roofs, planter boxes, podiums, balconies, terraces, retaining walls and swimming pools.
In this paper, we shall restrict us to ‘Waterproofing in basements’, which shall cover the evolution, importance, role, types of waterproofing treatments, brief procedures, pros and cons of each of this type, ‘Box type waterproofing treatment’ which is the most popular treatment in India, drainage in basements and the future of waterproofing.
The first real need for waterproofing dates back to the days of Noahs Ark. The 40 days of incessant rain inspired people to take some course of action to prevent water from entering their habitat. In the early days people relied upon thatch, such as straw, reed, leaves and other dried vegetable matter as a barrier against water entering their home.
Over time more sophisticated waterproofing materials were adopted. These included: animal skins, timber shingles, and natural stones like slate. The architectural designs of the day such as high pitched roofs helped overcome some of the shortfalls and limitations of the materials that were used. Over the centuries other waterproofing materials were used such as metals eg. copper, lead, zinc, and tin.
Waterproofing has come a long way since Noah’s day. The discovery of oil, coupled with the advances of chemistry saw the arrival of numerous petroleum derived waterproofing products such as bituminous, butyl rubber, neoprene rubber, hypalon etc.
Technological improvements and breakthroughs are occurring on a daily basis. Over time today’s waterproofing membranes such as polyurethanes, acrylics and polyesters will become as antiquated as leaves and animal skins are today.
THE IMPORTANCE OF WATERPROOFING
If we refer back to the definition of waterproofing as an impervious barrier designed to prevent water entering or escaping from building structures, then the importance of waterproofing is reflected in the consequences of not waterproofing.
Water which enters or escapes from buildings can have immediate and long term undesired effects. Apart from damage to the buildings contents, structural damage is unavoidable if the problem persists.
Water damage is second only to fire as a cause of building decay and deterioration. Furthermore, majority of building materials have a considerable shorter life span when subjected to moisture or emersion over a prolonged period of time.
The casualties of water damage include:
The importance of waterproofing can not be overstated. The damage caused to the building’s structure, coupled with the high cost of rectification warrants the careful design and application of waterproofing.
The role of waterproofing is to protect a building’s visual and structural integrity. It achieves this by forming an impervious membrane that prevents water entering or escaping from wet areas to dry areas.
In order to effectively fulfil this role a membrane must possess the following qualities:
TYPES OF WATERPROOFING
There are generally two types of waterproofing membranes – sheet membranes and liquid membranes. The nature of the problem to be addressed determines which type of membrane to be used.
The purpose of sheeting membrane is to completely cover any imperfections in the substrate or background. They are numerous and include:
The sheeting membranes can be applied as fully bonded to the substrate or unbonded. The most commonly specified sheet materials are self-adhering rubberized asphalt membranes. These 60-mil-thick membranes are composed of rubberized asphalt laminated to a waterproof polyethylene film. The asphalt side is incredibly sticky but is covered by a release paper, which you remove during application. In both cases sheets must be overlapped about 100mm wide and bonded to each other by adhesive or by heat welding. The seams are the weakest point in the system. It takes two people, one on top to smooth it out and stick it down, the other on the bottom to pull off the paper. The work output of this treatment is tremendous. Once a piece is down, you won’t get it back up again at least not in reusable condition.
However, the system allows easy repairs of holes, fishmouths, puckers, and wrinkles. You’ll patch holes or damaged areas with a piece of membrane placed right over the first layer. With a fish-mouth or wrinkle, all you do is slit the raised area, press it down flat, and cover it with a patch.There are many details about surface preparation, priming, patching, joint treatment, terminations, lap joints, penetrations, and corners.
The advantages of sheeting membranes provide highly trafficable surfaces and have insulating properties.
A chief advantage of sheet membranes is their consistent thickness. Because they’re manufactured to exacting tolerances, you can be sure of the 60-mil coverage. These membranes also have good elongation.
Sheeting membranes in general suffer from poor exposure resistance, temperature stability and little recovery from deformation.
All sheet membranes require venting if the substrate is water logged, or severe bubbling will occur developing stresses onto the adhesive leading to eventual adhesion fracture.
A higher in-place cost is one of the main disadvantages of sheets. The cost of the material itself is likely to be greater on a square-foot basis than the liquid membranes. Labor cost is also higher, because of all the cutting, handling, reinforcing, and detailing you have to go through during installation.
Not everyone agrees, however, that sheet membranes lessen the quality-control risk. A rubberized liquid forms a continuous, seamless coating, whereas a sheet membrane results in many seams, with the potential for a poor seal. It has to be made sure that the lap joints are tight and properly detailed and the correct use of the manufacturers mastic or other accessories are made. For example, one manufacturer requires you to apply a bead of mastic to every lap joint within 12 inches of a corner when using its product.
The liquid applied membrane provides a fully bonded, continuous seam-free, homogenous layer with no laps or joins which is a major advantage over sheeting membranes.
Some of the liquid membranes available are:
A liquid membrane is applied by spray, roller, or trowel. The liquid cures into a rubbery coating on the wall. One manufacturer has a spray-applied liquid membrane composed of polymer-modified asphalt. Polyurethane liquid membranes in separate grades for trowel, roller, or spray are also available from various manufacturers.
The manufacturer probably has a special procedure for treating voids, form-tie holes, and joints. At the wall-footing joint, you may be required to use cement or other trowel-grade material to form a “fillet” (radius or cove) before applying the overall coating.
Liquid coatings have the advantages of quick application, low in-place cost, and excellent elongation.
In general liquid applied membranes are easy to apply, seamless, semi-flexible or elastrometric, ease of detailing, ease of maintenance and repair, UV resistant and economical. One of the important characteristics of liquid membranes is it’s ability to breathe.
One of the chief disadvantages is the possible inconsistency in coverage. The typical application thickness is 60 mils, but it takes a careful applicator to be sure of always achieving that minimum coverage.
Regardless of which class of membrane is used, waterproofing membranes are only as good as the applicator. Manufacturers and distributors expect their product to be applied as specified. Failure to adhere to their recommendations can retard the performance of the membranes.
Cementitious products are probably the easiest waterproofing materials to use. They’re readily available, and they’re easy to mix and apply. You’ll get better bonding and a more solid, durable coating.
The chief disadvantage cementitious products have is that cement just doesn’t stretch to any degree. They will stand up fine to a head of water, but will tolerate almost no joint or crack movement.
Sodium bentonite, a clay material, has enjoyed a steady upsurge in popularity over the past several years. In panel form, bentonite has become the choice of a growing number of architects and builders. Bentonite works because it can absorb a tremendous amount of water. As it takes in water, the clay swells to 15 times its original volume and pushes itself into cracks and voids. When it reaches its maximum volume, it stays in these areas permanently to seal against water. One firms panels are 4×4-foot corrugated cardboard with clay particles held within the flutes of the cardboard. The panels can be nailed, fastened with a powder-actuated tool, or simply laid in place for horizontal applications.
Bentonite has its advantages, however: It’s safe to work with, non-polluting, easy and quick to apply, and can go on even at low temperatures. One company makes a sheet membrane that uses a compound of bentonite and butyl rubber.
With other products, you can inspect the finished waterproofing application and confirm the integrity of the seal before backfilling. With bentonite panels, the seal doesn’t form until the foundation is backfilled and water reaches the panel.
BOX TYPE WATER-PROOFING
For basements, Swimming Pools and under-ground ducts such as lift-pits, the waterproofing has to withstand the water pressure in addition to it’s basic stress. Shahabad Box Type treatment method of waterproofing is very commonly used in India.
Bhati Mohiuddin, the founder of the New Construction Waterproofing Company, born in 1919 in Sikar, Rajasthan, started his career with the India Waterproofing Company, the pioneers of the cement based structural waterproofing in then united India. His progress there was phenomenal, and he became the head of his division in no time.
He had an inquisitive mind since his childhood and he felt a sense of wonder in everything. This sensitivity increased and got enhanced with the years and pervaded in his sphere of vocation that is waterproofing. He was always introspecting in methods, means and techniques to better and develop further the structural waterproofing which resulted in the invention of Box Type waterproofing with Shahabad tiles which was tried in the Churchgate Subway for the first time. It was so successful that it became one of the classical treatments of waterproofing.
His experimentation in his field of endeavour led him to adopt various techniques which resulted in greater durability, lesser time consumption and saving of costs in waterproofing treatments. He had empathy with structures and method of work. He took structures as living things and treated leakages, seepages, leaching, thawing effloresence, etc. as a physician will treat the injuries and infections of his patients. And of course, he had patience, which allowed him to meticulously workout, plan, detail out, execute and accomplish his feats.
A base-coat in cement mortar 1:4 mixed with waterproofing compound is laid over the Raft PCC and above this rough Shahabad tiles of size 2’-0” X 2’-0” or 2’-0” X 3’-0” are fixed with minimum thickness of joints. Joints are staggered. Thickness of the Shahabad tile should be between 32mm to 40mm (1.25”-1.5”). After fixing the tiles, the joints are sealed with C.M. 1:3 and 15mm metal is pressed in the joints for enhanced strength and less shrinkage. Over this, a jointless layer of C.M. 1:3 with waterproofing compound approx. 25mm thick is applied and cured for 7 days. This layer provides a smooth layer for the raft and also protects the Shahabad tiles from getting damaged by steel bars laying and labour movement. Over this plastered base, raft is cast and RCC retaining walls are erected. Shahabad tiles are fixed to the vertical retaining walls from outside. Cement paste is applied on all four corners of a Shahabad tile and it is pressed firmly on the RCC wall in line and level. At a time only a height of 1m is fixed. Total height above the ground level is taken as 1’-6”. Joints are then sealed in C.M. 1:2 (Pointing). The Shahabad dado is then grouted using cement slurry with waterproofing compound and cured for 7 days. After curing, a jointless waterproofing plaster coat is applied and cured. Thickness of this treatment is around 65mm to 75mm. This entire process forms a box around the structure and does not allow any water to seep through or leak from the basement.
DRAINAGE IN BASEMENT WATERPROOFING:
The ground water table in the area where the basement is located, rises considerably above the basement level in the rainy season. The water flows are also found at various depths below the ground level.
Due to the rise in the water table and the up thrust of the water pressure from below, the waterproofing measures for the basement may sometimes fail and damage the basement. Additional measures to protect the basement are carried out for large projects or commercial complexes as details below.
Drainage in basements
Pathway of size 0.6m to 0.9m width is proposed, with compacted impervious material with specified flooring on the top. The area beyond this pathway is excavated to form a trench throughout the periphery of the basement. The highest level of the trench is kept at least 0.15m below the bottom of the basement. The perforated pipes, of about 0.45m diameter are laid in gradual slopes. Joints of these pipes are kept open. The collecting chambers are not plastered from inside and outside, to receive water from the surroundings. The perforated pipes are then covered with loose material like chips and metal, to form a filter media. The size o the filing material goes on decreasing towards the ground level.
The underground water finds the way of least resistance through the filter media. The water is collected in the perforated pipes through the filter media. Due to the slopes provided, this water is further collected in the chambers in between. All the water, thus carried away, is finally collected in the deepest chamber or sump. The water collected in this sump is either pumped out or laid into the public storm water drain.
TREATMENT OF FOUNDATIONS ON BAD SOILS:
Where the sub-soil water is not properly drained (in clay or peat soil) the structure should be disconnected from the face of the ground excavation and a trench made all around for a width of 600 mm taken down to a point at least as low as the underside of the concrete footings. The bed of the trench should be provided with a good slope at each end and the trench filled with coke, gravel or stone, graded with fines to fill the voids. An open-jointed land drain may be laid at the bottom to collect and drain out the sub-soil water. A waterproof coat should be given outside the structure foundations (on the external face of the walls) and continued through the thickness of the walls (under the walls over the foundation concrete) and under the floor. A 75 mm layer of waterproof cement concrete can be laid all around. Dampness can also be sometimes be reduced by leaving out an air gap around the external wall of the foundation.
Where sub-soil drainage has been ignored and necessary precautions have not been taken, water will stand about in the foundations, and the warmth of the interior of the building acting through porous concrete floors will set up suction of moisture which will eventually give rise to dampness in the floors and walls. Where the sub-soil water is near the ground surface and can be lowered by underground drainage owing to the flatness of the ground or any other reasons, the level of the floors of the buildings should be kept sufficiently high. It is considered that the height of the plinth should be kept at least 1.8-2.4m minus the level difference between the ground level and the sub-soil water table.
WATERPROOFING IN THE FUTURE
Many people in the waterproofing industry are genuinely excited about the Industry’s future, the advent of new products, wider fields of application, and a growing recognition of it’s importance augurs some encouraging signs for the future.
The awareness and understanding of waterproofing has grown significantly over the last decade. More and more people are recognising the important role that waterproofing plays in today’s building industry. Few years back, there were no industry associations. Today, industry bodies such as Waterproofing Industry Council Of Australia (W.I.C.A.) have emerged as waterproofing grows in prominence as a building material.
Waterproofing is a critical component of any building structure. The four keys to successful waterproofing are:
The ramifications of failing to waterproof, or waterproofing inadequately can be horrendous.