After constructing the sump, the next step is digging/excavating for the foundation of the building. This is an important stage as  the dimensions of the foundation have to be perfectly right because otherwise, the future spaces will be affected. The foundation depth depends on the soil quality and the design of the foundation is decided by the site conditions. The excavation drawing and foundation details are prepared by the structural designer and approved by the Architect. 








MARKING THE EXCAVATION:

 Marking: The Contractor has to follow the excavation drawing prepared by the structural designer and approved by the Architect. The excavation plan is marked at site and the dimensions are cross-checked by the Architect. It is advisable that you also check the dimensions as any mistake can be brought to the Architect's and Contractor's notice so that it can be rectified before it is late.

DECIDING THE EXCAVATION DEPTH:

 Excavation: Once the marking has been approved, the excavation can begin.

Depth of excavation: The excavation depth depends on the soil condition. Digging is done till hard soil is reached. For a fair idea, you can check with the neighbouring buildings, the depth of their excavations.

Filled up soil:  If your site/Layout is formed on lakes or low-lying areas, it may have a lot of filled up soil. In such areas excavation must be done till firm ground is reached. Usually the depth of the foundation will be more and consequently the cost of the foundation will be very high. But do not compromise. Make sure the building is resting on solid ground even if it means you have to go 15 feet down, because otherwise it will affect the stability and strength of the house.

Excavation trenches/pits:  The excavation details depends on the construction method that you have decided to adopt, the load-bearing-wall system or the column-beam-frame structure system. If it is a load bearing system, then trenches along the walls of the house have to be excavated. If it is a column-beam structure, then footings for columns have to be excavated. In either case, the architect approved, structural engineer's foundation drawings and details must be followed. 

Anti-termite treatment:  Before laying the foundation, make sure that the trenches and excavated areas have been given the anti-termite treatment by the Contractor. This will ensure protection against termites and other pests from underground, in the future.



BUILDING THE FOUNDATION:

Once the excavations are done, the next step is to build the foundation.

Load bearing structure foundation: A bed of concrete (PCC) is laid at the base of the trenches  and the foundation masonry is built using size-stones in accordance with the foundation details provided by the structural designer.

Column-beam frame structure system: In this case,  a mat of steel bars tied together according to the structural engineer's specifications is placed at the bottom of the footing pit. The steel bars for the column are also tied in place with the help of binding wire. Column boxes are erected around it for pouring concrete. 

Pouring concrete: After the architect and structural engineer have approved the steel details and the quality of work, the concrete can be poured. Concrete can be prepared at site or the contractor may opt  for ready mix concrete (RMC) if there are very large footings and large requirement of concrete.

Plinth Beam: After the concrete columns have been raised to the Plinth beam level, the plinth beam is erected for the walls of the house to rest on.



CURING OF FOUNDATION:

Curing is very important during the construction period. If not done properly, cracks can appear and even the strength and life of the building components can be affected. Curing ensures that certain chemical reactions take place which strengthen the structure.

Chemical reaction during curing: There are two types of chemical reactions, one that releases heat during the process (Exothermic) and another that absorbs heat (Endothermic). The mixing of cement with water is an exothermic reaction due to the presence of lime stone. Because of this heat generation, the water in the mortar or concrete mix evaporates even before the compound gains strength. But for the structure to gain maximum strength, chemical reactions in a cement compound must go on and this can happen only in the presence of water and at an ambient temperature. Hence there is a need to preserve the water content and the ambient temperature and this is achieved by regular curing.


Starting the Curing process: Curing should start from the very next day after the concrete has been poured. Initially more water will be absorbed by the concrete elements, but after a week, the water required will be much less. If there is water runoff when water is poured on a new construction, curing should be stopped. The hotter the outside temperatures more amount of curing is required.

Curing schedule: Curing should be done at least twice a day though three times is better. Ensure that your Contractor entrusts this job on one person, so that it is not forgotten.

Curing of Columns: For columns, the preferred method is to wrap the pillar with wet gunny bags and then wetting them regularly. This is done because, while pouring water, the column does not absorb much water as it flows away. So to ensure that the column gets cured evenly, the gunny bag method is used. Sometimes a plastic bottle or polythene bag with a small hole is placed on the column so that the water drips steadily and the gunny bags are wet all the time.


VASTU SHASTRA PRINCIPLES FOR EXCAVATION AND FOUNDATION:

Auspicious day: The Excavation work for the foundation of the Building should start on an auspicious day, from the North-East corner of the building and end in the South-West corner. Therefore, the direction of excavation should be from N-E to S-E, then S-E to S-W corner. Simultaneously, the excavation should be from N-E to N-W, then N-W to S-W corner. 

Shilaanyaasa: It is the foundation laying ceremony. After the excavation for the foundation has been completed, the stone which is consecrated at the time of the Vastu Pooja, is laid first in the South-West corner of the excavated trenches.

Construction work: The construction work like laying of the bed concrete, stone foundation or column footing, etc. should be started from the South-West corner to the North-East corner.

Filling: The filling of earth within the foundation should be done from the South-West to the North-East for the same reason as above.