Houses of the past had walls built with mud and exposed to sun and rain for many decades with no sign of damage or decay.
What could be an effective solution towards eco, green and sustainable? If we select two – being local and being frugal – it may surprise most people. Haven’t we heard these words too often, which do not belong to our modern times anymore? It is too late to live local now in our hyper-urbanised contexts and frugal living is an unfortunate curse on the poor, to be eradicated at all costs.
Given such thoughts, can we relook at the local and frugal, not as a curse but as a studied choice? Something common that we see across India while travelling is housed with mud walls. How many of us observe them, without taking them for granted?
If we go searching for the local and frugal, every other region has much to offer, especially in natural materials like mud and stone. In an old house in the historic village of Manne near Bengaluru, one can still see the old walls built with a specific technique called “kudali ittige”. Typically owner-built houses, we can still meet the septuagenarian seniors who claim to have built the walls with their own hands.
Mud for construction was dug out from their own land, also to get irrigation ponds; so it’s a double benefit! After careful sieving to remove unwanted dry leaves, debris, hardened mud particles and such others, it is mixed with grass shreds and small stone pebbles. Depending upon the actual soil characteristic, they may add sand, silt or gravel, for mud with too much clay cannot be built with. After two to three days of preparing the mix with water and foot trampling, it is spread flat on the ground to about 3 to 4-inch thickness.
Just before it gets set and very dry, the mat-like spread is cut into blocks using an axe to the size required. Since no individual brick is made upfront, this method allows for making bricks with different sizes as may be required by the construction of external walls, pillars, niches, thin inner walls or so. Primarily it is a variation in doing sun-dried adobe bricks.
Using the same mud composition, slurry-like mud paste is made to be used as mortar.
The wall observed at the site has been partly exposed to sun and rain for many decades with no decaying. Mud consolidated has become like a stone!
The soil varies from place to place, some good for cultivation, construction, pottery or even for toys. Soil for tubers is not good for rice – amazing to see the worldwide local variation within the same global material, without which early human civilisations would not have evolved up to our generation.
If we are, to begin with soil and end with soil and if mud has sustained humans all these 200,000 years, it is not fair that we forget it.
Cob walls can take any shape, including curves, sculptural forms and furniture profiles.
Anyone who explored how our past generations built is bound to have discovered mud walls, be it of Didi Contractor up north at Dharamshala or Laurie Baker in deep-south Kerala. We owe much to such pioneers who re-created our confidence in eco-friendly approaches. However, the introduction of newer ideas has eroded societal belief in traditional systems, including the cob wall, which is among the greenest material with not even cement as an additive.
Soil mix with approximately 20% clay, 20% silt and rest sand, a proportion that can vary slightly, is ideal for cob. Chopped straw, rice husk or such non-decomposing fibrous binders are added to control cracking, and lime is added to make it termite proof. Once this smooth mix with no lumps is added with water, it shapes well as a ball or elongated egg. Testing it is important, checking for consistency by how it cracks while dropping, breaks while being pulled or feeling its stickiness to hand.
These handmade lumps are placed side by side, gaps filled with soil, pebbles, or burnt brick pieces. The surface can be leveled by hand and compacted by hammering. Each layer is checked for consistency in width, say 2’ or at least 1’ 6”, and allowed to dry before next layer is placed. The side of the wall needs to be smoothened before it dries too much using wooden leveling bar with the sharpened edge or even hacksaw blade.
Exposed cob is not advisable anywhere, especially the lower part of wall vulnerable to erosion by rain, where we may use stone. Since the soil mix is unstabilised, walls facing lashing rain would also need protection. Besides, the wall surface tends to crack, more initially and slowly later on through one full cycle of all seasons, i.e. up to a year.
Given these reasons, cob walls need crack filling with the same mix, later plastering with mud stabilised with cement and quarry dust. The final coat can be with lime or left as mud wash with oxides for colour effect.
To locate openings, we need to fix temporary shuttering, to be removed once the wall is shaped. Stone or wooden lintels suit the cob most, though thin precast RCC lintels can be inserted above very wide openings, to be finished with mud later. Electrical conduits can be fixed externally on the wall, though they can be embedded by making grooves like in normal construction.
Being a loamy material, cob walls can take any shape, including curves, sculptural forms, and furniture profiles. Feasibility of cob depends much upon space available for wall thickness, local climate, availability of the ideal soil mix, local precedence, the speed of construction expected and of course owner’s acceptance.
In India, we do not document our works adequately and provide knowledge to others. Given this, the documentation at Sacred Groves is really remarkable, besides which workshops by Thannal and website postings by many consulting architects today provide basic information if one desires to revive cob walls.
Re-discovering the virtues of cob construction, a mud wall so thick that it can take all load without getting eroded by rains for a long time.
All of us have heard of mud walls, possibly the wall material for the majority of standing structures in India today including all rural buildings. Of course, the increasing presence of burnt bricks and cement blocks are a threat to the popularity of mud, yet traditional mud walls are around us. But how many of us have heard of the term ‘cob walls’?
Dictionary definitions apart, cob walls are the original approach humans used to construct walls with, even before learning how to make mud bricks to specific sizes to sun dry or kiln-burn them. For many thousands of years, cob walls dominated the early human settlements, including those in Babylonian or Gangetic plains.
Have they lost their relevance today? Partly yes, but not entirely. In many rural areas, people continue to build with cob, but in cities, it has almost vanished. Curiously, now there are increasing attempts to revive this technology by groups such as Thannal and Marudam in Thiruvannamalai, Sacred Grove at Auroville, Made in Earth, Mudhands and Biome in Bengaluru and few others in different parts of India.
We are rediscovering the virtues of cob construction. Simply stated, it is a mud wall built so thick that it can take all load without getting eroded by rains for a long time. Some surface moisture, peeling and erosion may occur, which can be repaired periodically. The volume of the wall acts as thermal mass, keeping the building cool in summer and warm in winter. With high compressive strength due to the thickness, cob walls are also earthquake resistant.
Having said this, haven’t we heard, seen or been to such structures like shrines, choultries, monuments, heritage homes or even palaces? Of course, many of us have been there to wonder about the thick walls, not realising their possible potential today. Often these walls were thicker at base, tapering as they reach the top at least in one side, often on both sides.
Cob walls do not need much structural calculations, great construction skills or big budgets. A lump of clay is called cob, so building with them must have been an easy discovery during early civilizations. The fact that even after construction became regular and formalised, cob continued widely, seen even now from lower Himalayas to coastal south India, proves its time-tested qualities.
Cob walls make minimal demands of clean sub-soil with less clay and more silt, space to accommodate thick walls, some local additives to reduce cracking and material options for final finish. Typically, cob walls are plastered with mud mixed with straw, though in poorer homes they were left un-plastered, with mud slurry and lime wash as crack fillers. If we walk into an old house with plastering peeled off, we can see the original clay lumps revealing the origins of wall construction.
While cob uses local soil to build, it is not the same as the other mud architecture techniques. Building with double hand size mud balls dipped into additively mixed mud slurry as the joint binder is seen some rural areas, which is very close to cob practices. Rammed earth walls could be mistaken as a cob. But they are much thinner at 9 inches only, while cob could be 18 to 24 inches thick. The other differences being the smoother surface of rammed earth, very few surface cracks, no need for plastering and such others.
The Adobe system depends upon mud bricks made to size, sun-dried at the site itself and used to build with. Stabilised mud blocks are also sized blocks, with cement and quarry dust added to gain different properties like strength, thinner walls, durability and better surface density. Cob walls are much simpler than all these.
The re-discovered cob walls are not merely repeating the rural practices, but have attempted technical improvements. There also has been deeper studies about the causes behind surface cracking with solutions; possibility of avoiding thicker base where the whole wall width could be same; different options for additives for the mud; scientific modes of quantifying the components of mud into clay, silt, sand and such others to accordingly decide the right kind of proportion ideal for the cob wall.
These methods of improvisation re-validate the use of cob walls again to claim a position in sustainable architecture. It is time we look into it.
This wisdom comes from observing how the rural buildings in many parts of India have lasted for decades and centuries, with stone or brick exposed. The material does not deteriorate by itself, unless faced with heavy rain, sun and wind, which were in those days protected by deep overhangs and verandahs. Water, the commonly suspected culprit in letting a building decay, does not seep through the masonry itself, but primarily through the joints. Traditional structures built with thick walls minimised this possibility, the thickness itself being a deterrent to the movement of water. Also, the more commonly used lime mortar would get stronger against water permeability over age, ensuring buildings lasted long without much maintenance.
Today, with thinner walls, we need to solve these challenges differently. In case of heavy rainfall areas, the mortar used to build the wall could be completely mixed with water-proof admixtures, such that the joint beds resist water penetration throughout their depth.
Even if the wall is only 8” thick, such an integrated water-proof mortar does the magic. Alternatively, the mortar could be the normal one, with the mixed mortar batch used only for finishing the joints.
A rich mix of 1:2 mortar with the water-proof powder mixed as specified by the manufacturer, is pressed into the joint with a special narrow ‘karni’ with good pressure from the hands to form an impervious high density surface on the face of the joint. This procedure is termed as pointing, done primarily to water proof the joint and also of course to make the joints appear neat.
Accordingly, pointing could be done with few optional finish – finish only the groove; touch upon the broken edges of the masonry; surface finish the face of the masonry along with the joints and such others.
Groove pointing suits exposed walls the best; however the expert team may decide the type of pointing based on case by case.
All kinds of pointing for the joints demand skilled workmanship, as such cannot be left to some team at site casually. In heavy rainfall areas, water-proof coating like shylax or other chemicals have been applied, to protect the wall and joints together. Such full wall application should be minimised, for they tend to show off by creating different kinds of surface shine.
There have been long standing sentiments against exposed walls, mainly rooted around the dampness seen in such walls.
The solution to the said problems are simple. It is only a matter of following the proper code of practice, the workers being sincere to their job and not compromising on the material quality.
Between bamboo and structural steel, which one has more strength? Which one will perform better in case of deep soil pile foundation? If left open without any protective coat, which one will last longer without rusting or withering? Which one has more options of application and is versatile enough for wall, column, beam and floors?
The surprise answer for all the above is bamboo. At an average tensile strength of 12,500 kg/sq. in., it is 2,000 kg units more than that of steel. The stems of bamboo, popularly called poles and technically as culms, have been traditionally used for pile foundation in water-logged and loose top soil sites. Bamboo mats can be laid as foundation bed in case of soils with low load-bearing capacity. As a versatile material, it is good for both temporary and medium term usages, besides for long term, if designed and built properly.
While bamboo can be used as a single pole, it works equally well in groups and as a composite material. For transferring heavy loads, multiple numbers of culms, say 3 or 4, can be joined by nuts and bolts to act like a single column. Likewise, it is possible to form beam trusses in groups or in lattice formation. Of course, all the bamboo poles in such composite forms need to belong to the same species, of similar girth and be of comparable maturity of age.
In Kerala, lime concrete bamboo reinforced beams have been attempted since the late 1990s and in regular use since then at the Laurie Baker Centre. While stand alone use is feasible, bamboo gains more potential as part of a composite structure and reinforcement material.
The traditional bamboo walls were made with woven bamboo mat with mortar coats on both sides, so that bamboo is not exposed to any adverse weather condition. While lime and mud mortar goes better with the natural material, cement mortar can also be used. Subsequently, protective painting coats can be applied. Being 2 to 3 inch thick, they are light weight, hence save on structures. If split bamboo culms are used, keep them to the outside with inside finished as desired. External silica-based skin of bamboo resists fire for a while, but can be improved by chemical coatings. Bamboo boards with split lengths and panel are very popular as visual barrier in semi-open spaces like verandahs and pavilions.
Roof supports by bamboo rafters are very commonly found even today. Thicker girth culms are used as ridge beams or wall beams, while the smaller diameter ones can go for principal rafters in sloping and cross beams in flat roofs. Their spacing may vary from 1 to 2 metres depending upon context. Floor finish can be achieved by 1:6 ratio lime mud or cement mortar with topping by floor tiles and any other item of choice. There are many valid reasons to use bamboo, which need to be explored further.
The idea of compound walls is a western import into India, especially during the British times.
Can any of us guess the resources spent in building compound walls around us? Statistics can be mind boggling – and here it goes. A typical owner of 30 x 40 ft. plot in Bangalore builds 450 sq. ft of wall, excluding the gate area, which is enough to enclose an additional 10 ft. x 15 ft. room, excluding the openings. So, just by spending for a roof additionally over the compound wall cost, we can get an extra room. On the higher side, a 50 ft. x 80 ft. site demands 850 sq. ft of compound wall that can enclose three adjacent rooms of 10 ft. x 12 ft. size each, virtually a small town row of shops. The comparison is simple: if only we had not built compound walls in modern India, many lakhs of new houses could have been built with the same amount of time, energy and materials.
Statistics can be misleading, but they often reveal facts that we never tend to recognise. The idea of compound walls is a western import into India, especially during the British times. The same British did not wall up all their village homes nor did they promote the idea in the U.S., country of their immigration, where even today it is difficult to find compound walls. The absence of such walls has not hindered living in the U.S. in anyway, instead has created a much better civic sense and urban aesthetics there.
Incidentally, even India in the past did not have any compound walls. All houses and buildings opened directly to the road, path or the space in front. The adjacent buildings had only space around commonly used by both the neighbours. This typology continues to function in our villages, small towns and the older parts of new cities. Absence of the wall does not mean anyone can claim our land, for the papers clearly record the ownership, which need not be demarcated and expressed on site all the time.
Even the side wall comes with its own bag of problems. The narrow setback space gets further fragmented, leaving no option for a shared space there for a kitchen garden or parking of two wheelers that both the neighbours can enjoy. Access to fire tender gets narrowed by these side walls, restricting the movement of firemen with water pipes and nozzles. Instead without a wall there, two neighbours, possibly both with narrow setbacks, can enjoy wider space between them.
We are not discussing the social distancing created by the walls that we build around us; we are not discussing the division of us which the walls bring about, both of which are true. We are simply discussing how unfriendly these compound walls are from an ecological perspective. From all arguments, personal to environmental, compound walls are not a healthy sign of a sustainable society.
When you get rid of the straight lines, you have to use your imagination to deal with all the curvatures.
Know the basics: Rough-textured walls receive less heat
Have we ever tried to go close up to a tree trunk or a hill-side cliff? We notice the seemingly plain surface has a thousand minute folds. How is the surface of a seemingly smooth rock boulder? Close up, it is rugged and not in one smooth plane. What about fruits, vegetables, timber logs or tender coconut shells? It is the same story everywhere — all non-planar, rough textured, micro-folded and gently curving.
If nature never had a smooth, straight and fine finish, where did we humans get all these ideas for our constructions from? Why are we not trying to learn from and emulate nature?
Incidentally, we have followed nature, but mostly during the bygone days. Let us look at any typical Indian village home. This vernacular-style approach used to be rustic and not in perfect plane, being hand- or simple trowel-plastered.
Often there would be natural materials such as stone, timber or bricks left exposed, hence solar passive, also creating a sense of local material and character.
Smooth-plastered walls receive more heat compared to rough-textured ones, since the latter cast micro shades within the wall, thanks to their roughness. If used in the natural state without plastering, brick and stone exhibit such a textured surface that they absorb much lesser heat.
Beauty of curved walls
Gentle curves are part of most objects found in nature, which could be blended with our regular walls to get multiple benefits. We rarely make full use of all the four corners of the room, as such converting one corner into a curved edge does not reduce functionality. Critical areas where storage, furniture, shelves, platforms and such others happen could be left straight, while the movement areas and passages can flow along a curve.
There could be issues like fixing windows, casting curved lintel beams, workmanship, perfect plaster levels and difficulty in using tools. However, if we are able to retain the sense of curve, the job is well done.
In our context, building materials such as stone or brick are rectilinear, hence making the curve using such geometrical blocks needs an expert mason.
Among the much less used variety is the folded wall typology. It was Laurie Baker who discovered that thinner walls with half-brick thickness save money, but need to be folded to gain strength. Incidentally, from an ecological perspective, these folded walls have add-on values!
They create so many external deep-set alcoves that most wall surface is under shade. Not all rooms of a house could be comfortable with folded walls.
In non-residential building types like those at Hosa Jeevan Daari at Melukote, such a wall plan internally creates storage niches, with an overall elevation that looks different and attractive.
Windows now set within the alcoves are well sheltered from rain, with no additional chajja protection needed. One approach can reap many benefits.
We can attempt to merge the curved lines gifted by nature and straight lines discovered by human beings in our building plans
Try them out: Curved walls receive less heat from the sun’s rays and hence offer a great advantage for home designers
The first time one hears that nature has no straight lines, the very statement appears unbelievable. However, the fact is, it is impossible to get even one case of straight line in a natural setting, including the sun rays, which actually are curved across a path in the universe. Contrastingly, most of what we humans do today is in straight lines!
The earliest shelters discovered by humans were curvilinear, normally round in plan, as seen in igloos, Buddhist stupas or African huts. Earliest mud pots, with no exception, were always round in form.
Even our traditional village homes are never in perfect wall planes, mostly being hand plastered.
With the advantageous principles of round shapes discovered, they found application not only in large water tanks and grain storages, but also in tea cups and kitchen utensils.
Have we noticed how the shape of radios, stereos and cars have changed over the decades, from rectilinear boxes to curvilinear forms?
Curved walls stronger
In architecture, straight walls are susceptible to side bulging and buckling, hence require stiffening as per case. Whereas, curved walls cannot easily bulge in one direction, hence are stronger.
If we need to enclose a specific floor area inside either a circle or a rectangle, it’s the circle which does it with least circumference of wall length, hence works out more judicious on the budget front.
A typical linear wall, lit by direct sunlight, receives the full impact of sun rays on the complete area of the wall, gaining heat in the process. Comparatively curved walls receive direct sunlight only for a part of the wall, rest of the wall receiving rays from an oblique angle.
Since heat gain is directly proportional to the direct solar radiation, curved walls receive lesser solar heat. Incidentally, even the roof too can be curved to get the passive cooling benefits.
Architects across continents, from Buckminster Fuller to Laurie Baker, have tried building with non-linear ideas. As a follow-up, we can attempt to merge the curved lines gifted by nature and straight lines discovered by human beings.
Designing with curves
Besides the eco-advantages, there also are visual benefits of curved walls. From no two points the curved wall will appear same, while the straight wall is all visible as a flat surface; as such the curved wall creates greater visual appeal. Routinely, in every room we see two adjacent straight walls with a sharp corner.
Now, let us imagine the sharp corner made into a curved profile. The two walls appear like one long wall making the room appear longer and larger, though the measured dimensions are same.
Alternately, instead of a full-fledged curve, only the sharp corner could be gently curved by your home designer to get a soft corner. Imagine a soft-cornered building, just like a soft cornered person!