Monthly Archives: August 2013
Often we get to see a many-decades-old tiled house being replaced by a new RCC-roofed house. The chances that the old house roof was supported by bamboo rafters is very high. Repeatedly coated with cashewnut oil in coastal areas, hence surface protected, these rafters would have hidden their actual age. The north-eastern States virtually live with bamboo – pile foundation, support pillars, floor sections, wall mats, roof supports, window frames, objects to live with and such others. Despite all this, we feel bamboo is a mere local temporary material.
Possibly, the myths about bamboo have come to stay due to the wrong way of using them. Any bamboo, however mature it is, if left to the vagaries of rain and sun untreated, will not last beyond a few years due to the high starch content. Local methods like cashew oil coating cannot be replicated everywhere and not everyone keen on using bamboo is aware of other treatments. People tend to think bamboo is cheap, which is not a fact always; hence discard the idea without looking at the value for money. Bambusa Arundenesia and Dendrocalamus Strictus are better suited for construction, yet we tend to use whatever is locally available and then blame the idea of building with bamboo itself. No wonder, though India is the second largest producer of bamboo in the world, most of the production goes to the paper industry, daily use objects, screens or temporary supports for construction.
The common comments against bamboo revolve around it being a fire hazard, which is partly true. However, the high silica contents of the surface wards off fire for longer time than timber and fire-proof chemical coatings can improve the performance comparable to any other material. The wall panels of bamboo are rather thin, just 2 to 3 inches only; hence do not assure sound-proof qualities.
Bamboo mats can be enmeshed within cement mortar, a simple method that improves both its fire retarding and sound-proofing qualities, but this has to be done carefully. Incidentally, all bamboo buildings require skilled workmanship and good working knowledge of the material. The joints can be very tricky, cut sections demand careful handling, while grooves, ropes and knots need to be complimenting the overall structure.
It is easy to justify why bamboo should be used. We can list reasons like economical in regions where it grows, lighter weight for the dead load calculations, faster in construction, faster re-growth of cut bamboos, hence regeneration of the material and such others.
However, the criteria to assess bamboo structures cannot be the same as those for timber, masonry or modern buildings. If we apply different yardsticks, case by case, then bamboo buildings will also get as accepted as are other mainstream buildings. To that end, we will have to follow the proper methods of building with bamboo.
In all fields there are great potentials, unfortunately lying hidden waiting for their day. There are solutions that go unnoticed and unsung. Leave alone mainstreaming them, even recognising them to ensure larger public acceptance becomes a challenge. In construction, such ideas could be region specific and not universal, material specific and not for every kind of material, and knowledge specific and not for casual application.
Bamboo fits into the above background note more than any other construction material around. Hailed as wonder grass by the experts, it is a plant material that matures for construction purposes approximately in six years, possibly the shortest time span of its kind. Though bamboo has proven its potential across many regions in the world, it does not grow everywhere; hence it is not known as an option outside its habitat. Even if known, majority of people believe that bamboo can be used only for structures of minor importance and temporary in nature, which actually is a myth. Widespread usage of all types of bamboo, especially in untreated conditions, has led to this judgment.
Across Indian regions, there are hundreds of varieties of bamboos; Kerala alone has more than 130 types. Not all of them are best suited for building construction, with less than 10 varieties satisfying the checklist of criteria. Choosing the right type of bamboo is of utmost importance in ensuring the right kind of building. This requires studied knowledge and skill, for in the market all of the stock may look alike. The best method of course is to check out bamboo grove supplying the material and ensure the particular grove has the shortlisted bamboo type. The cut bamboo should not have flowered and should not be aged, when it would have had reduced strength. What if we end up using some bamboo not knowing if it is the best or not? There would be no disaster, but the durability, maintenance, load-bearing capacity and such others may not be very satisfactory.
Bamboo has more tensile strength than mild steel, in given specific conditions!.While living and standing tall, bamboo may swing in the wind violently, but takes the wind load very well, suggesting its hidden load-bearing capacity. Its fibrous structure ensures a shear-proof material that can transfer vertical load efficiently and diagonal loads fairly well. Without cutting equipment, it does not get cut into parts by hands, rain and wind. The unique structure of bamboo ensures material integrity, minimum water penetration across the skin, longer life than timber even if left exposed to weather, light weight for its given volume, and ease of working with, thanks to the manageable sizes.
With no options for metal fabrications and holdfast hinges that are common today, houses either had no gates at all or were provided with an animal barrier with thin tree trunks and thorny branches.
House site demarcations in cities led to the emergence of newer concepts of security, fear of encroachments, need to barricade the self and such other practices, a combined challenge answered by the idea of lockable gates. Gated communities found in large cities today have taken this phenomena to the epitome, where the collective community, individual property and the family house – everything can be secured and locked up!
Eliminating the idea of gates is easier said than done; hence looking for judicious gates makes greater sense. Majority of mild steel gates are found to rust after a few years, due to water penetration at the welding points and lack of periodic painting. They also tend to be heavy due to the weight of the metal, hence reducing the efficiency of the hinges. Where possible, replacing heavy metal by wood and such other alternatives helps.
Fabricators tend to charge the total cost on the material consumed, hence lesser the material, cheaper the gate. Today fancy-looking gates are being suggested and made, at huge expenditure, as if the gate itself is a status symbol.
Besides wasting material and costing more, they also affect the beauty of the building. If they can lie low and merge with the compound wall, gates can actually compliment the building design.
The load factor
The gate posts should be strong enough to take the load, often achieved by a metal pillar visible or embedded within the brick pillar. Even concrete pillar can be used, though in extreme cases only.
Making the gate totally solid to stop street animals from straying in or for privacy into the property sounds logical, but leaving a few openings within the gate makes it lighter in weight, attractive in design and does not always lets in animals as we may be fearing.
Raising the compound wall height, hence the gate height is a recent tendency among some buildings. It feels funny to walk along a street with such high walls around, that cut off the beautifully worked-out elevations of the buildings.
Options for gates have grown many folds, to include cast iron gates, sliding shutters, remote controlled and such others. In all the cases, facilities such as milk box and letter box can be embedded within the supporting pillars. Latches and lock bars can be made operable from both sides.
By restricting the height to less than 5 ft., they can create better sense of space. However, we need to remember that a good gate is the one which is functionally efficient, budget-wise economical and simple to see.
Ask any engineer contractor to list areas of concern and we are almost sure to find water seepage and terrace water-proofing to be among the top. From the very local solutions like mud layer poured with lime slurry, a traditional cost-effective solution, to the latest research on chemical-based methods have all been explored, yet no one idea stands out as ‘the’ solution. Possibly, we cannot list varied eco-friendly options here, but some cost-effective ideas exist and are in practice.
By far, the most cost-effective method appears to be treating the concrete roof on the same evening of concreting, when it is still not hard set. Thin slurry with one part cement, two part fine grain river sand and ample water to create the flow condition is poured on the top of the freshly cast roof. Then, starting at one end, the masons will work backwards, gently levelling and pressing the slurry into the concrete, filling its micro pores; wiping out the step marks and such other undulations using a square, flat, handled trowel. This slurry should become an integral part of the roof while the concrete is still being soft and ensure that the top layer becomes impervious. Water-proofing admixtures in liquid form can be added to the slurry to get better quality. Normally, the top surface gets finished with thread lines to stop any possible crack from developing across the surface.
While this top surface would survive most climatic conditions, topping the terrace with weather proof course (WPC) tiles has many advantages, despite the additional costs. The terrace is cleaned, applied with slurry mix of 1:2 and surface made rough by sweeping it with broom stick. A mortar mix of 1:4 is applied on top, as if we are plastering the surface, and the thin WPC tiles are fixed with 2 to 3 mm gap in between. The WPC tiles are made of burnt clay with two surfaces and small holes in between. Normally, these tiles are broken into two parts, and laid with the smooth surface on top. Water-proofing compounds are not required at this stage, though there are contractors who prefer using them with the mortar. The WPC layer protects the concrete surface from sun, rain and wind, giving it a longer life. The terrace becomes more usable due to the good flooring.
Many companies have been promoting methods and corresponding products of their own towards effective terrace finish. Most of them rely upon chemicals, polyurethane coatings and admixtures, hence tend to have a limited life span, though they guarantee the surface until then.
Every terrace solution comes with its own advantages and disadvantages. The practice of terrace tiles may not go well with heavy rainfall areas, unless quality of workmanship is achieved. In such cases, the simple method of plaster on the same day works better. In hot, dry climatic zones, this method may heat up the interiors more, the top being just a dense concrete layer. As such, it is important to seek local solutions to the terrace.
During the recent decades, reinforced concrete roof, popularly known as RCC, has possibly evolved as the most common roofing solution in India, relegating traditional solutions like clay tiles, stone slabs, wood planks, brick domes and such others to the back seat in the competition. While increased availability of raw materials, flexibilityof construction and possibility of covering larger spaces has elevated RCC to the top position, whether it is really the best option is still debatable.
RCC performs best during the early years with minimal maintenance cost, but as decades pass by, the roof can be a burden, often with irreparable problems. Being cast as a homogeneous element, spot-specific repairs are not possible or even if possible, they may not work effectively. Preventive maintenance strategy can mitigate the problems to some extent, but people believe that RCC roof needs no attention, hence ignore it only to face problems later on! In case the top surface finish is inadequate, the roof itself gets affected over the decades, with reduced life span. Rehabilitation of concrete structures has emerged today as a major profession, suggesting that all is not well with this wonder material..
Unlike the simple local roofing solutions, the concrete solutions come loaded with many structural theories, methods of preparation and prescribed procedures at site, which are not known to majority of concrete workers. Coupled with inadequate technical instruction and expert supervision, vast majority of concrete roofs being done in India tend to suffer from poor quality and integrity. No wonder, numerous problems surface over RCC roofs, despite the idea itself being an advanced technology.