9 Building materials used in Building construction

The other day I   found myself poring over the Kenya building code for 1997. I   was  consulting it     because it’s  the law  that  ensures order ,sound  building practice and  a level  playing  field  is this niche.  One  drawback  about  the  document  however ,is that its  written in 1963 convoluted legal language which  I  suppose render the  document barely accessible to   contractors  and Masons, not to mention  many Kenyan  with an interest  in the built environment. After  a lot of   behind  the scene  heavy  lifting that  demanded the patience of Job , I gleaned  some insights that   clarified  a few  issues.

According to this building code   foundations and  walls  for   the built  environment  may  be  constructed  using fired clay  bricks, building  stones   and  concrete  blocks.  In addition to these materials, Masons   are also required   to use good quality building sand, Gravel, Ballast, Hard-core rocks and Murrum. In the next ten minutes, I  shine a beam of light on these materials that are important in Mason’s work.

Bricks

Bricks   are manufactured by molding   moist clay according to specifications in moulds. These are then allowed to dry slowly-in sheltered conditions. When they ready, the green bricks   undergo a firing process in a Kiln at a temperature of between 940 degrees Celsius to 1200 degrees Celsius .The oxygen content in the Kiln has an effect on the color of   the finished bricks. High temperature and low oxygen produces blue bricks while on the other hand, higher oxygen level will produce red bricks. The red coloration is due to the chemical reaction between the higher amounts of oxygen and iron oxide in clay.

It worth noting that bricks can and are produced with other coloration such grey, yellow, and black. These colorations depend on type of clay used, firing conditions and type of pigments added to the clay

Large producers use a highly automated and controlled manufacturing process. After the  firing  process, bricks  absorb  moisture  from the  atmosphere  irreversibly   up to a maximum of  0.1%.Its therefore  recommended that bricks  should not be  used  for at least two  weeks  after  firing.

The standard bricks sizes are (a) 6 inches by 6 inches by 12 inches, (b) 5 inches by 6 inches by 12 inches   and (c) 4 inches by 6 inches by 12 inches. These  brick  sizes   weighs   between 2 and 4 kg, can easily held by hand and sell at between Kshs 6/ and Kshs 12/.

Three types of bricks

There are variety of brick types to choose from depending   on the soil condition of the construction site, the depth of your pockets, and type of building and architectural design preference. That said, the four brick types that are commonly used by contractors and Masons in Kenya are:

  • Common bricks –These bricks have no visual finish and are used for general building work.
  • Facing bricks-These bricks have a surface rendered with a designed texture, sand faced or made smooth.
  • Engineering bricks-they are  dense and  vitreous(look  like  glass)  with  high  load  bearing  and low  water absorption capacities. They  are   more expensive  because  they require  high  firing  temperatures.
  • Standard specials—these bricks have special shapes to enhance the architectural quality of the brick work. For instance we have bullnose   and radial  bricks.

Bricks are known to absorb water. It’s therefore advisable to use building stones or concrete blocks for the foundation in damp grounds, and then switch to bricks for the wall above the ground or damp -proof course.

Building stones

The building stones, in Kenya are sourced from Juja quarry in Kiambu County. Other sources include but not  limited to  Narok, Kisumu and Eldoret. The stones can come in any size so long they are easy for the mason to handle and the resulting wall width can withstand the building load. Having said that I will add that in Kenya the standard building stones come in three sizes: 4 by 9, 6 by 9 and 9 by 9 (measurement in inches). Price start from Kshs 25 per piece exclusive of transportation.

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9 by 6,,9 by 9 and 9 by 4 building stones at a quarry

Concrete Blocks

Concrete blocks are prepared by mixing water, cement, sand   with or without gravel and molded into three dimensions rectangular shapes. Concrete mixer machines    can hired to mix the ingredient to make the process run like clockwork.  The mixture forms a hard rock like material when it dries up. Mortar is a mixture of cement, sand and water, which can be used to make concrete blocks or bond courses of say bricks when constructing a wall.

Standard solid concrete block   size in Kenya is 16 inches by 8 inches by 8 inches .These blocks are more expensive than building stones, selling as they do at between Kshs 80 and Kshs 90. However since most of them may be manufactured on site, there may be zero transport cost from the supplier to the construction site.

Gravel

This is what is commonly called Kokoto and many people confuse it with ballast. Gravel may be   machine cut and manual cut.  Building gravel is produced by quarrying and crushing very hard rocks such sandstone, limestone or basalt. In Kenya gravel is in produced by crushing basalt rocks.

Gravel is expensive, selling at between Kshs 1500 and Kshs 1450 per ton. The total cost is even higher when you add up the transport cost of the gravel to the construction site. Tipper trucks are preferred mode of transport for gravel. Gravel is used to make concrete for foundation and slabs, concrete blocks and mortar.

Natural  occurring  gravel  that  accumulate  in large  deposit in river beds  or mountain side  can also be used in construction in place  of  commercially  produced  gravel.

Building Sand

Sand is readily available material and cheaper than gravel. A  common source of sand in  Nairobi  is Makueni County and Naivasha.In others  areas,  a lot of  high quality sand  is  harvested from rivers beds  and  even streams. Developers usually Transport sand using Tractors, or Canter Isuzu Trucks. In Naivasha, sand    is sold at   Kshs 35,000 per 25 ton tipper (price inclusive of transport cost to Nairobi).

There are three type of building sands

  1. Grey black sand-fine to medium grained   and with  a shade of   greyish black  color
  2. Coarse sand- Its  coarse grained  and brown in color
  3. Fine sand- Its fine grained and brown in color .This sand is the best.

Sand is used to make Mortar and concrete.

Ballast

Ballast is composite building material. It   is a mixture of sand and gravel and is used to make high density concrete. Concrete is manufactured by mixing sand, Gravel, and cement plus water. In other words concrete is mixture of Ballast, cement and water. Concrete will dries up within a few hours after mixing the ingredients together. The amount of cement, sand and gravel used will determine the strength   of the concrete. Ballast is more often than not, used to make mixing concrete for foundation and slabs.

Hard-core rocks

This are required for filling the base of a foundation   in order to raise the floor above certain desired level. Hardcore stones are granite rocks   , readily available and cheap. However raising the foundation to given height can consume a lot of these hardcore stones.

Murrum

Murrum is made up of disintegrating sandstone or other rock types .It is used to spread on hardcore stones in the base of   foundation   to create an even surface.  Concrete slab is   then poured and spread over Murrum surface of the   foundation.A  vibrator  is usually  used  to  in spread the  concrete slab more thoroughly and  systematically  over the foundation base  before  it  hardens up  within a  short  time. Murrum is cheap and readily available building material.

Copyright© 2017 East Africa Little Hardware Ltd

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