Water Proofing Solutions
Terrace is the most crucial segment of a building, and it is exposed to direct climatic variations, extremes of rainfall and structural movements caused thereby. So every effort should be taken at the design stage itself to ensure that a proper protection system has been incorporated. It has often been found that the economic solution is not always the best solution. So, the system, which assures maximum protection, should be selected even though it may cost little more.
IMPORTANCE OF WATER PROOFING FOR ROOFS
A building or structure needs waterproofing as concrete itself will not be watertight on its own. All the flat roofs in the modern age are generally constructed of reinforced cement concrete. This material removes all the problems of flat roofs except that the roof should be made water proof by employing any of the various methods available for moisture proofing.
- USUAL PRACTICE
The R.C.C. Slab of the terrace is generally done with ordinary concrete without using any admixture to take care of the extra workability required to proper placement and compaction of the concrete through the congested reinforcement.
Sometimes integral waterproofing compounds are used in the concrete. But often they are not used properly or sufficiently. Lime terracing, i.e., Brickbat coba with lime, is done on the R.C.C. slab to serve dual purpose. First is weatherproofing of the slab by providing heat insulation for the area below it. The second purpose is waterproofing. This layer also provides the slope required for easy drainage of rainwater. The parapet is of brick masonry and plastered with ordinary cement mortar.
- In due course numerous cracks are developed in the lime terracing. Water penetrates through these cracks to the R.C.C. slab below it. Due to shrinkage of cement mortar, lots of cracks are formed on the plaster of the parapet walls. Rainwater seeps through these cracks into the bricks and slowly comes down to the R.C.C. slab.
- Because of improper compaction, often the concrete of the R.C.C. slab is full of voids and honeycombs. Once the water reaches the R.C.C. slab, it easily seeps inside and corrodes the reinforcement, thus weakening the structure itself.
- Water, after seeping through the R.C.C. slab, makes the ceiling and walls damp. In severe cases water starts dripping from the ceiling. All these leave ugly patches of dampness on the ceiling and walls and paints peel off.
- To avoid leakage of water through terrace, often tar felting is done on the terrace. But due to weathering, the tar felt gets cracked within a couple of years and water penetrates through the cracks to come down to the ceiling.
To protect the terrace it should be made properly waterproof. There are numerous terrace waterproofing systems available in the market; the choice of products will depend upon the requirements of the client under given considerations.
- The environment conditions (dirunal and seasonal temperature variations) a building is subject to expansion/contraction caused as the consequence.
- If the entire structure is weak for the reason of poor quality of construction, sub-soil being weak, vibrations from surrounding pattern of land use too vigorous etc., then terraces are likely to be affected. A waterproofing system should allow such movements. However, if the movement is too significant and the structure is not designed to overcome the same, then none of the waterproofing systems will last unless adequate structural strengthening is done prior to waterproofing.
- Insulation properly desired - some structures are designed to retard excessive heat penetration through the terraces to the areas underneath. At times lightweight concrete is used. In such cases a strong waterproofing layer becomes most essential, because the surface has an element of porosity.
- Terrace garden - Continuous presence of water and contact of organic matter would require additional treatment of waterproofing than normal ones.
- Cost factor - Quality and durability of a system is directly proportional to cost. If the budget available permits an option for a cheaper system only, then we could recommend such treatment.
- TYPES OF SYSTEM
Terrace-waterproofing is possible with varying permutations and combinations within a wide product range, to suit the 'tailor-made' requirements of the clients.
- Whilst any water proofing system is decided, it is imperative to have a basic substrate, which is structurally sound. If the base on which a waterproofing application is done, happens to be weak, then the system chosen will also weaken. In order to have the base concrete strong enough, the concrete should be admixed with an integral waterproofing compound which would give a homogeneous, workable mix at lower water/cement ratio and reduce the permeability. It should be ensured that the terrace is given a proper slope. Any standing water shall not be permitted. Many waterproofing systems have been found to fail because of standing water remaining on the surface consistently for longer duration.
- The concrete, after casting, should be cured by ponding or sprinkling water or with a suitable curing compound spread over the entire surface. Initial curing is critical and should start immediately after the initial setting of the concrete, say after 4 to 6 hours of placing concrete. Lack of initial curing is the main cause of drying shrinkage cracks.
- For construction of the parapet wall, a suitable mortar plasticizer should be used with the bricklaying and plastering mortar to improve the quality of the mortar.
- Before starting any treatment for waterproofing of the slab, all the visible cracks, undulations, joints etc. should be taken care of with a suitable waterproof repair mortar.
- On the cured and repaired concrete surface, there are 3 alternatives, which can be considered for waterproofing.
After taking care of all the vertical and horizontal joints with the waterproofing mortar, the concrete surface may be treated with a surface applied cement based, crystalline action, hygroscopic waterproofing chemical and then covered with layer of cement mortar (25 to 75 mm) admixed with a mortar plasticizer (commonly known as IRS finish.) Expansion joints and Dynamic cracks shall be filled with flexible and waterproof sealing compound.
After taking care of all the horizontal and vertical joints with the waterproofing mortar, the concrete surface may be treated with a polymer based, flexible waterproofing chemical, which would take care of thermal movements. Then the terrace may be finished as in alternative 1.
Where the terrace is likely to come in contact with water and organic matters regularly, as in roof gardens the terrace should be treated with epoxy resin based surface waterproofer.
- The plaster of the parapet wall should be treated with a resin based water repellant chemical to avoid any chance of water seeping through the wall down ward to the concrete slab just below the wall.
- If the brickbat coba or surki is to be done on the terrace for weatherproofing, that should be done only after the waterproofing treatment is done. An admixture should be used with the surki mix to make it watertight itself.
PRINCIPLES OF WATER PROOFING FLAT ROOFS
The functions of any dwelling unit are broadly three in number:
- Protection from rain
- Shelter from extreme cold or heat
- Privacy and safe storage of possessions
The evolutions of modern dwelling units- call them flats, houses or bungalows- can be traced to natural caves, which must have been the earliest form of shelter. Traditional house types have developed in response to the needs- when agriculture was the predominant occupation or business, over a hundred years or so, the building materials were provided by the neighboring country. Everybody was a house-builder as he was a herdsman or an agriculturist. Today we are living in a world of specialists and specialization. We have masons who can do wonders in stone but not brick and vice-versa. In the same way we are looking at a particular aspect of construction technology and methods and maintenance; that of water proofing and that too terraces.
Architecturally, terraces would imply a flat-roof or an open platform. The other meaning is a colonnaded porch or a promenade or a porch. In the mountainous region in our country, especially in north and north-east, where flat land is minimal, hill slopes are flattened at different levels and look like steps. An ingenious system of channel provides water to each flat piece of land and rice is grown. This is known as terrace cultivation.
Today our terraces in construction provide a very useful space, practically for anything, drying, storage, parties, and functions and so on. The terrace performs the same functions as the courtyard, which once formed an integral part of the vernacular architecture of Indian houses.
On one hand, we need terraces functionally, while on the other we perceive it as a problem area, as it often is the source of unwanted water, in form of damp, or water seepage or as rain sometimes, even as rain has stopped outside.
Not so long ago, flat roofs or terraces were a byword for trouble and there was a common saying was that the only way in which the problems of a flat roof could be avoided was only through building a pitched roof over it. But in the recent years, there have been advancement in materials and design choices and the record of terraces has improved tremendously.
Historically also, terraces did have problem of leakage and some solutions must be found. Perhaps the degradation of material does cause permeability or cracks or both, volume changes, shrinkages, expansion, entrapment of water- all these caused by the characteristics f the materials cause us problems. Many new materials provide us with novel solutions also.