Day 83
July 13th, 2012

This post will cover on 2 topics - 1) Plinth beam casting and 2) Retrospective of Foundation

Plinth Beam Casting
Plinth beam is the horizontal cement beam across the house perphery laid on top of foundation.

This picture shows how the finished plinth beam looks.            

Purpose of the plinth beam is to:

1. Prevent leaking of water into foundation - To prevent a house from settling it is critical that no water be leaked into foundation. Being made of cement, plinth beam is impervious and therefore prevents water from rain, flooding, etc. from leaking into foundation. 
2. Provides support for walls - For load bearing houses, walls carry the weight of the house. Plinth beam provides solid footing to raise those walls.
3. Holds house together - Since plinth beam sits across the periphery of the house, it provides binding force across rooms. For example, without plinth beam it is possible for one of the rooms to settle thus creating uneven floor level. Plinth beam prevents that from happening. 

Basic process to construct plinth beam is as follows: 

1. Mark-up width - Usually width of plinth is half that of the foundation. In this case, foundation is about 18" wide and so plinth is 9" aligning with the outer edge of the foundation. Inner 9" of foundation meshes into the floor level of the house. 
2. Lay down the steel beam - As the adjacent picture shows beams are the core of the plinth beam.  Beams have a loop every 6" that holds it together. 
3. Setup re-inforcement - Before concrete is poured, re-inforcement has to be established to provide rectangular shape to the beam. This takes majority of effort as planks have to be nailed properly in place and once concrete is poured they need to be removed. 
4. Pour the concrete - Next step is to pour the concrete. As concrete is poured, mason ensures that it is evenly spread and smoothens out any edges. He also needs to ensure the height of the beam is consistent throughout the periphery. 
5. Remove re-inforcement - Concrete turns solid within 24-hour and final step is to remove the planks leaving the beam intact. 

This short video explains this process in action. 

Foundation Redone:

To give background context, ground level at living room area is 1' higher than that at the guest bedroom level. Typical height of plinth level is 2.5' that includes 1' of plinth beam and 1.5' of foundation masonry. Turns out though that foundation masonry was 2.5' at living room and 3.5' at guest bedroom. What this meant was plinth height would be 3.5' from natural ground level. This was realized only when plinth beam casting was about to start. To add to misery, by then Rainwater tank was already done to align with 3.5' of plinth !

My architect was clear that plinth level can be no taller than 2.5' or else house would look place oddly high. What followed was no fun - We ended-up undoing a few days of work. Specifically

• Reduce Rainwater tank height by 1' by chipping away at just-finished concrete tank
• Remove 1-layer of foundation stone masonry from across the house periphery to reduce the foundation height by 1'. 

Here is the clip of work being undone. It could have been worse had plinth beam been built. Good news was we caught it at a time that cost us about a week and some cost in material and labor. Having said that, there were key lessons learnt -

1. Trust your gut instinct - Even though as homeowners we may not be in construction business, you have a feel for what's going on. I certainly did feel that foundation was looking tall. While "plinth" was a new term and I didn't know that it was 1' in height I concluded I knew no better. That was the critical mistake. No question is a dumb question especially when you are new to the domain. Had I had surfaced my instinct more strongly or did some research things could have been different. 
2. Working drawing consultation - I independently found my architect and contractor. So they had no prior relationship between them. When architect released drawings there was no consultation that occurred between the two. So, architect didn't get a chance to explain the nitty-gritty and contractor felt drawings were clear-enough. A big no-no ! It is critical that drawings are released to contractor only after architect has had a chance to explain them to the contractor. It is best to have such meetings at the site to relate paper drawings to the actual mapping onsite. Often times, what looks right on paper doesn't feel right to the eye. If that's not possible, have them meet at architect's office. 
3. Inspection schedule - Identify stages at which architect would come and inspect the site to validate it is built according to the specifications. In this case, architect mentioned a couple of times need to schedule inspection. However, given that this was first or second inspection we were not as diligent as needed. 

Again, in retrospect, it was not a terrible setback.. Like many other things in life, none of the lessons were new; rather they were re-inforcement of what you would learn at many other times. Lessons learnt were critical and have since been put in practice. There is now tighter collaboration between me or my wife, architect and the contractor and crisper conversation about respective point of view. So, in the end it definitely had a silver lining !

July 2nd
Day 72

RainWater (RWH) Tank:

Last blog talked about center-marking pillars.. You would notice in this video a number of such pillars are now set up to mark various edges. Also, various rooms are now filled with sand (aka earth material). Once foundation masonry layers are completed they will start consolidating earth material in each of the rooms. This process is equivalent to making dough. The volume of dough shrinks as it absorbs water.. Similarly, they alternate process of adding earth material and water so that rooms themselves are flush with dense earth material. The idea behind this is - more dense the earth material, less chances of air bubbles within that and therefore less chances of house settling in ground. 

Best way to describe RWH tank is through pictures that describe various phases. As a reminder, tank has a capacity of about 60,000 litres. For more description on how I arrived at 60,000, refer to <>. Tank area was excavated about 7' below the natural ground level. Further, tank is built-up to be about 2.5' above ground level - in line with the plinth beam.

Next step is to to setup steel re-inforcements to provide structural support. At the base of the tank, they criss-cross steel rods and tie them together with hooks. Then, vertical rods are tied at the edge with the flooring. Finally, similar criss-cross pattern is setup at the walls of the RWH tank. It is important to excavate tank about 1' wider than the required capacity so as to allow workers to perform their work. Although the structure looks a bit daunting actual work didn't take more than 6-7 days.

Once steel structure is established, pouring concrete on the floor is fairly straightforward. Doing the walls is more complicated though. Essentially, they split-up wall into 3-layers, each 2.5' tall. Then, across the boundary of RWH tank, both sides of vertical steel rods are "bound" with wooden planks. As the picture shows, wooden planks themselves are supported with wooden rods. Finally, concrete is poured in to them. All said and done, each layer takes about 4 days, and it took about 12 days to get the tank done.

Final step involves a few minor, but important activities

1. Sloping at the floor pointing towards the manhole. The intent being while cleaning the tank all water should accumulate near the manhole. 
2. Water the concrete to allow it to strengthen. Plaster the walls and floor for nice and consistent finish.
3. Apply chemical treatment on walls to make them water proof. Test for leakages by spraying water and checking for dampness on the outside.
4. Fill the outside of RWH tank with earth material. Allow them to consolidate to form completely immersed structure. 

All said and done, it took about 30 days to complete this tank. Besides cost, this delayed the project a bit.. I am hopeful though this investment will some day prove worth it.

Completed tank:

Next post will cover plinth beam casting.

Foundation Masonry Layers

May 10, 2012
Day 20: Foundation Masonry layers

Last post talked about components that make up foundation of the house. This post focuses mostly on masonry work. First, it may be obvious, but just to be explicit, house construction requires a LOT of water. Till the super-structure is completed, almost every activity, starting from excavation, making cement, watering foundation and walls, compacting earth metal, and many more that I will only realize in due course. On an average, expect to use up 20,000 litres each month i.e. about Rs 2,000 on an average.

Masonry work is done with a set of cement concrete blocks that are "glued" together with cement mortar. You might recall that excavation was about 900mm deep. Each block is about 150-175mm tall and including mortar height of each block would roughly be 200mm. Foundation of a house is typically up till plinth which generally is 450mm above the ground level. This implies several layers of foundation masonry.

In our house, ground at the rear-end of the house is 300mm lower than that at the entrance-end.

Hence, plinth-level will be 900 + 450 + 300 = 1650mm from the excavation level. Considering each layer of masonry is 200mm, total number of masonry layer at rear-end is about 8 and at the entrance-end is about 7.

 

The section view of cement blocks is sketched here. As is evident each layer of cement block works its way towards the center. Space on the outer periphery is filled with earth metal whereas the space between cement blocks is filled with cement mortar. I was surprised at the speed with which this work got done.. It took workers just a little over one week to do about 4 layers across most of the house.

Columns: There are 4 columns to bear the load of the first floor balcony and the family room areas. Excavation for columns is about 1500mm. Base of the column is filled with mortar. Then a steel column of about 3000mm is erected as shown in sketch here. Rings are tied approx 150mm from each other to hold the column together. Finally, they'd pour cement concrete around it to create the actual column structure.

Center-line marking pillars: Towards 4-minute mark in the video is description of center-line marking pillars. Center-line marking is to mark center-line for all the edges. Picture shows marking of center-line for window. Blue squares are center-lines that were already marked for main edges of the room. Those were the basis for excavation to occur.

Additionally, a new center-line is now marked (shown with red rectangle) for where the window edge on ground floor would be established. The center-line is marked with pillars (refer to the video) that will remain placed until ground floor actually comes up. These center-lines are marked throughout the house wherever a nook changes the direction of the primary edge of the room.

Finally, this video shows the actual work to build that column described above. 

May 4, 2012
Day 14: Foundation plan 

Excavation is more or less complete for load bearing walls now. Now that we know quality of the ground, I asked Ravi to explain plan to reach the plinth level. Plinth level is the base level above which ground floor walls come up.

At a high-level there are four main areas:

1. Foundation masonry - Cement building blocks that are about 38cm tall, 15cm wide and 15cm deep are the foundation of the building. They are "stuck" together with cement concrete masonry. It is recommended that anti-termite treatment be done twice - once before placing any cement blocks and next after placing all layers of cement blocks. As Ravi says, they make this mixture with 1 part of cement, 4 part of sand, and 8 part of aggregate. They do a number of "layers" of such building blocks which together provide load bearing support. In our case, ground level at living room side is about 6 to 12 inches higher than that on the guest bedroom side. Hence, they'd do more layers at latter so plinth beam will be at even level. 
2. Rain water tank - Bangalore outskirts have water shortages.. As you see from our plan we have decent size garden and we didn't want to feel guilty of over-burdening already acute supply of water. Hence, we decided to go with what seems like a good size rainwater (RWH) tank - 60,000 litres. My calculation for 60,000 was as follows:
• Our monthly usage for a family of four is about 25,000 litres each month (~200 litres per person per day). Out of this, my guess is about 10,000 litres is used for gardening and 5,000 for bathroom usage. Those are the obvious low-hanging applications for RWH water. 
• Bangalore gets about 1000mm rainfall each year with raingods showering in for all except four months (December to April) within a year. I wanted to have sufficient water to live through that period. Hence, we got the tank size to be about 60,000. For those interested, amount of rain that'd be accumulated is roughly calculated as - Accumulation area x Amount of rain. Our roof area is 180 square meter and September rainfall is 200mm. So, accumulation in September would be 180x200 = 36,000 litres. Chances are with this size RWH tank it may not overflow. But, in case, it does, there would be a recharge well to let overflown water seep back into the ground.
3. Columns - Four columns need a bit of special work to get set up. They would essentially setup iron columns in those areas and put concrete around them. Once columns come up to the plinth level, they would be connected to the rest of the house via plinth beam. 
4. Plinth beam - Foundation around load bearing walls will be done first followed by columns and finally by RWH tank structure. Once each component is built they will be joined together through plinth beam. Our expectation is plinth beam will be about 2.5 feet above the natural ground level. This so as to keep house safe from flooding as well as provide appropriate elevation. 

General expectation is foundation level will be reached within 6-8 weeks from start. However, this doesn't consider construction of RWH tank. With that, we should expect 10-12 weeks, first fortnight of July, to complete plinth level and start the ground floor construction. 

April 21, 2012

After such a long wait to get plan approved, finally, we start! Both Krishna and I are bubbling with excitement. We can finally start to shape our imagination!

Ravi, our contractor, says it will be 18-months to finish. That would mean December 2013 finish. It is going to be an intense, but fun, next 18-months. We have very high-level idea of what all is involved, and I am hopeful to capture as many details as possible through this blog. 

Day 1: Puja

All auspicious work must begin with puja. Here is our humble offerings to seek blessings of the land and support of people to realize our dream home. 

Day 3: Site markings

Site has been center-line marked now. Using working drawings from architect, outer-edge of site is marked. Those are designated by white threads. Then, based on setbacks, exterior edge of each room is marked, designated by neon green threads. It is critical not just to ensure measurements, but also perpendicular edges as these markings will be the basis for all further excavation and cement work. Those neon green threads guide sand-markings about 9-inch on either side for them to excavate. Finally, at the either end of those green threads, cement pillars are placed such that the green thread intersects through the center of the block. That's why it is called center-line markings. Eventually, green threads and sand-marks would go away and those cement pillars provide guidance while constructing walls.

April 30, 2012

Day 10: Watchman's Shed and Excavation start

Usually, first thing is to create Watchman's shed and restroom. Usually, layouts allow a watchman's family to stay at site overnight to look after site and stocked materials. So, this is the first thing that usually gets constructed. Ravi, our contractor, decided to setup shed near kitchen area. They got a bunch of rectangular cement blocks and essentially stuck them together through concrete masonry. To figure restroom they had to dig at a couple of edges of the site to identify sewage line and do hook-ups. 

Workers used site markings, specifically 9-inch sand markings on either side of neon threads to start excavation. As far as I know, building structures are of two types - load bearing walls and columns. As the name suggests, load bearing walls bear the weight of the house and are usually suitable for smaller buildings such as this. Column structures tend to require much deeper excavation to setup foundation. Additionally, columns structures are setup with iron pillars that hold the weight the building. These are usually suitable to carry load of large beams, or load of multi-story buildings. Our house has four columns, 2 on each side of the first floor verandah as that would be about 26-feet wide beam. 

Excavating ground reveals critical knowledge about the soil and therefore dictates the design of foundation. For example, for reclaimed land (i.e. ones that originally hosted lake and were filled with sand), soil tends to be soft and therefore chances of further strengthening the foundation to avoid it from setting-in. In some cases, ground may be full of rocks and therefore can take longer to excavate. Fortunately, none of that is needed here. As you'd see in video, soil texture is quite soft and colour is nice orange. Thankfully, we don't need any special treatment. Trick they use with excavation is to excavate about 6-inch and then thoroughly soak ground with water. This makes excavation extremely easy. For all load bearing areas excavation is done for 4-feet and column area are excavated for 6-feet. This building is small-enough that all excavation is done manually itself. Having said that, this is real work. Amazing to see these guys sweat it out the whole day !