Check the quality of building materials yourself
Given the wide variety of building materials needed for constructing a house, you may be in a dilemma, when it comes to making a choice and deciding on the criteria for it.Here are some tips on how to go about selecting some of these materials - sand, bricks, steel rods, gravel and so on. But first let us look at some basic descriptions:
Concrete - a mixture of cement, sand, coarse aggregates and water in specified proportions.
Mortar - mixture of cement, sand and water.
RCC - Reinforced Cement Concrete or concrete combined with steel bars to provide strength.
Sand
The selection of good and clean sand is very important. Sand is used as a fine aggregate to fill voids while concrete is made.
What should not be present in sand?
Clay, dirt, mica and seashells not at all!
Sand should not contain water or be damp and wet. If you must use wet sand while making concrete or mortar, you will need to add a little more quantity of sand.
Example: If sand contains 5 per cent water, you will need to use 25 per cent additional quantity of the wet sand.
How do you check sand?
By touching and feeling: Take a handful of sand and press it in your palm. If there is mud, dirt or other contamination, it will stick to your palm. Examine it carefully, if there are lumps of clay, grit, pebbles, dust or pieces then do not use it; mud bits are harmful and need to be separated using a screen of wire mesh.
By testing: There is another method. Fill half a glass tumbler with sand and add water to it. Stir with a spoon. If there is contamination in the sand the water will turn muddy. If the thickness of the layer of mud is more than 4 per cent of the layer of sand, then the sand should be washed clean before use. If despite this you find that the sand you have purchased is not very good; do not despair. There are ways in which the sand can be cleaned. The sand could be sieved through a wire mesh so that mud pieces and shells are properly separated.
Wet sand can cause problems. Labourers often tend to add a lot of water to most mixtures. If the sand being used is already wet, then more water will weaken the mix. Therefore, if you find that the sand being used is already wet, instruct your contractor to use less water.
Bricks
Bricks are like the skeleton or bones of your dream house. To build a strong house, good quality bricks need to be used. Always buy bricks straight from a brick kiln that will give you the best in terms of price and quality.
Check the quality of bricks:
- By seeing: Its shape should be proper and corners sharp, not broken.
- Its colour must be uniform.
- When broken it should not scatter into small pieces.
By testing: Strike two bricks with each other. Good quality bricks will produce a clear ringing sound on hitting.
Drop a brick vertically from a height of 1 m. A good quality brick will not break.
Moisten a brick in a water tank for 24 hours till completely wet. Check its weight after 24 hours. If there is more than 15 per cent difference between the dry and wet weights of the brick, it is not fit for use.
Example: If the weight of dry bricks is 2 kg. After soaking in water for 24 hours if the weight of the bricks turn out to be 2.3 kg or more the bricks are not fit for use.
Steel rods
Although concrete has good compressive strength, it does not withstand tensile or bending stresses and forces, by itself. To take care of this deficiency, steel rods and bars are placed inside concrete to provide with the necessary strength in this respect. This is called Reinforced Cement Concrete or RCC. For purposes of RCC construction always use IS certified steel bars. It is good to check that there is no rusting on the surface of the bars. The steel is fixed at the appropriate places, fitted properly with cover blocks and binding wires. While fixing steel bars, care must be taken to provide for adequate development length (50 x diameter of steel rod) wherever two bars are being joined or the bar in one member goes into another member such as beam bars in a column.
Cover block
Cover blocks should be made using mortar of 1:3 cement: sand ratio and its thickness can be made into 2 inch for footing, 1.5 inch for columns and half-inch to three-fourth inch for slab and beam structures.
Stone gravel/coarse aggregates
These are small pieces of stone gravel (also called gitti or metal in some regions), which give strength to the concrete. Generally, they come in two sizes for use in construction work - three-fourth inch or 20 mm and half-inch or 12 mm, or a mixture of both together (normally in the ratio of 60:40 to 70:30).
Selection
These pieces should be solid, cubical and free from dirt. See that they do not contain clay, mud or dirt particles. These should be in differing sizes with a right mix of big and small sized pieces.
The space between big pieces of stone/coarse aggregates should be filled up by small pieces and the vacant space between small pieces of stone/coarse aggregates also needs to be filled up using sand. This makes a dense concrete.
Do not procure stone/ coarse aggregates of uniform size, as such uniformly sized aggregates tend to leave voids in between, which reduces the total weight.
Water
As far as possible, use potable water for preparing the mortar. The water must be free of all contaminations. Never use salty or seawater in making Reinforced Cement Concrete (RCC which comprises steel bars/rods used to strengthen concrete). Use the same quality of water for curing as well. Water reacts with cement to give concrete or mortar a solid form. Besides this it facilitates proper mixing together of other ingredients making them suitable for casting. Add only as much water as is recommended to make the concrete mix suitable for casting. Do not add excess water. A low water, cement ratio makes the construction strong and durable while excess water weakens concrete.
Quality control
How can you help control the quantity of water?
Always remember that water should be used minimally. Workers sometimes tend to be careless and liberal while adding water and do not measure it correctly. You can help to ensure that water is correctly measured and used. Just get hold of an empty tin of cooking oil of 5 litres volume for use as a measuring device.
Get it from your own kitchen or neighbourhood store. If you cannot find one, use a bucket that holds 10 litres of water. Give it to your workers or contractor and insist they use only this to measure water. To make a concrete mix with one bag of cement you will need about 25 litres of water. So it would be useful to keep handy containers of 5 litres and 10 litres.
Quantity test
You can test the quantity of water yourself very easily. Seeing is believing. And you will feel reassured to see the result in front of you. As soon as the concrete mixture is ready, take a small amount of it into your palm and roll it into a small ball. Now, throw this ball up into the air to about one metre height.
If the ball breaks or crumbles before returning to your palm, it is likely to have excess water in it. If so, have the quantity of water reduced immediately or the strength of the mixture will be weak.
posted by Gaurav Malik @ 9:16 pm
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