The composition may vary between places, though the basic considerations may include cement as the binding material.
The first material early humans discovered for their construction purposes must have been mud under their feet and strangely it continues to be valid even today.
To deepen this exciting thought, just imagine a case where we dig out mud and put it back as the foundation! Yes, it was proven as a simple and fast system in many villages of Karnataka for small houses.
Excavated mud is added with broken tiles, stones or pottery with jaggery, lime and water. The mix is well trampled for two days while keeping wet, so it gains the required strength to be placed back.
Despite being a time-tested method, mainstream-size stone approach replaced it, and now sadly, the concrete column foundation is side-lining even the stone one, though RCC is mostly unwanted, costing more and damaging nature even more.
Concrete is like hard rock, but is a human product with cement, sand and coarse aggregate. If cement content can be reduced, the mix can last longer, but the prescribed mix strength cannot be compromised with. This is where mudcrete can step in.
One safe area to replace concrete by mudcrete is in the foundation where the soil is hard with good bearing capacity. With both wall sides, the trench will never give way.
A normal 1:4:8 concrete mix at the trench bottom may act as a levelling and anti-termite course. Subsequently, mudcrete may be placed in layers of 9 inch each, compacted to about 6 inch thickness. At maximum two courses a day, a 3-ft.-deep foundation can be raised in 3 days, very safely.
The composition of mudcrete may vary between places, though the basic considerations may include cement as the binding material; sand to reduce shrinking and cracking; lime to resist termite attacks; mud as the base inert material; and brick bats, aggregates from rubble, broken stone pebbles or construction waste as the coarse material.
Proportions also change based on specific characteristics of mud and size of brick bats.
If the mud has more than half as gravel, about one-fourth silt and minimal clay, around 10% , it suits the purpose. Likewise, brick bats could be 20 to 40 mm in size, more of it in the lower sizes.
Given this, cement, sand, mud and the coarse material can be around 1:2:7:10 for a stronger foundation, and can increase mud to 10 and brick bats up to 20, based on site studies. Of course, all this needs expert supervision and engineering calculations.
A major step towards reviving it happened recently near Bengaluru for the house of Timmaiah along with students of architecture from KSSA, hoping to train the next generation. Mudcrete concept is diluted today for varied reasons, mainly lack of applied knowledge among the younger generation, hence failures. The ideal soil composition and availability of coarse aggregates could also be the causes.
However, there is no real reason why this should not be revived, at least for small and safe applications. May be it’s a matter of mind and time.
Though laying the foundation is the first task at site, it should be the last decision to be taken.
The most invisible, but critically important part of any building is the foundation. Incidentally, though it is the first task at site, it should be the last decision to be taken, after all the ideas about the superstructure of walls, voids, roofs and such others are finalised.
Traditionally, foundation meant only one option – dig into the ground, run a thicker and widening wall down under all along the wall. Even if the building were to have intermittent wooden pillars, arches or any other design feature, full-length wall foundation was mandatory. Possibly, the failure of earlier structures would have made people wiser, to evolve the load-bearing wall system.
The idea of isolated column foundations connected by beams at ground level was introduced when the RCC frame construction became popular, where we could save time and money by not digging into the earth all along the wall.
Locations with loose soil composition, water-logged sites, constructing along sloping grounds and such other contexts hugely benefited by the RCC column footings. The discovery of this frame construction system with plinth beam is gaining popularity even in rural areas today.
On the flip side, this system meant the total building be built with concrete columns and beams resulting in budget escalation, higher embodied energy consumption and the need for a technically better supervised project. On most occasions, for simple G+1 houses, RCC frame is simply unwanted, but adopted to hike project costs to financially benefit all in the team. RCC is also short lived, unsustainable and difficult to dispose upon demolition some day in the future.
Imagine a case where the conventional load-bearing wall foundation would have worked out costlier due to soil condition, which gets realised only after the earthwork excavation. Is there a way out to economise without compromising on the load bearing capacity of the foundation?
Structural engineer Ravindranath Bontadka came up with a curious solution for a house in Erode by merging the plinth beam concept with load-bearing wall.
Load points were located, masonry piers as if the house would have masonry columns was introduced and the top of these piers connected by plinth beam. Now, the house plinth is ready for its nominal one or two floor construction without any RCC columns, but has equivalent to column footings underneath built with conventional size stones.
Surplus mud dug out from foundation trench was used for making interlocking stabilised mud blocks, leading to a win-win situation. Of course, we need to seek expert advice before venturing into such hybrid concepts.
Eco-friendly and cost-effective architecture is not a one-stop solution to be applied all over the country, like the RCC frame and slab system. Everywhere we see the one and only type of building with columns and slabs cast, later covered with walls, be it on a hill slope or the seaside. It’s time to localise our actions.
With earth below, the arch would be even more stable and hence can take greater load, supporting the building walls.
It is interesting to note how we tend to forget what we learn. Just leaf through an old book of medicine, construction, cooking or stitching, documenting certain ideas. Only after proving itself, that idea would have been codified, written about and became part of the book. As such we may assume the written idea is a proven idea.
Let us check how many of the ideas explained in the texts are followed now. Maybe a handful or little more, not because the rest of the ideas have failed, they have been either replaced by newer ideas or have simply been forgotten.
The art of constructing a building foundation using arches is one among such ideas – simply forgotten. We continue making arches above ground but why not below ground? With earth below, the arch would be even more stable hence can take the greater load, supporting the building walls.
There are two methods to do an arch foundation – if the full foundation would be underground, the foundation trench is dug directly with arch profiles with adequate spacing between them to build foundation piers to spring the arches. This space where arches start would need a normal footing with enough width to take on two arches. The unexcavated earth stays underneath the arch as if that’s the centring support.
If the site is lower than the road, we dig only to erect the foundation piers, taking them deep enough to reach hard soil. From the top of piers which is at the site level, we can start the arches, which should be within 5 to 8 feet span for general safety. In case of uneven sites, the rise of arches can also be varied to suit the context. Arch centring is generated by filling in mud in the required profile, where using an M.S. template ensures the curved profile is perfectly suited to take the arch action.
The curved mud profile is topped with water mud mix and manually consolidated. If the top mud layer appears very brittle, a thin cement or cement-stabilised mud mortar can be applied, ensure there is a level base layer below the arch.
Now, stone or brick arches are built just like we do in any wall and cured well. Plinth beam is placed above the arches and backfilling the earth up to plinth level completes the foundation work of the building.
Architect Rajesh Jain from R-LEEF has been reviving this forgotten technology for many years now, improving it from its textbook days. Of course, it needs an engineer’s supervision, masons with arch construction skills and contractors with inclinations to explore. If the team is not interested in exploring, the idea may fail due to a badly done job.
Imagine a small plot with a dozen RCC columns and next to it a dozen arches – both take the load. To live a green future, we need to revive older ideas