Causes of dampness and preventive measures

When the materials consume water, dampness in any building happens. Dampness is harmful for the residents of the building.

Damp Proof Course(DPC): The purpose of a course is to resist the penetration of the damp into the building and it is called as damp proof course(DPC). DPC should be provided when the construction of the building is started.

Reasons for Dampness: The dampness happens for the following reasons -

1. Ground Water Table: When the groundwater table is high, it significantly impact the foundation since the building material utilized for foundation consumes the water from the ground through capillary action.

2. Rain: When there is no proper protection for the external walls, then rainwater may harm the building.

3. When the building is situated in such an area that the water can’t be easily discharged, dampness will occur.

4. There is also possibility for dampness due to bad workmanship in construction.

5. When the walls are constructed afresh, dampness may occur for a short period.

6. If the slope of a roof remains very flat, the rainwater may enter and water is temporarily stockpiled on the roof.

7. There should be proper damp proofing course on the uncovered tops of the parapet walls and compound walls so that the damp can’t penetrate through these exposed tops.

Impacts of Dampness - The dampness may provide the following harmful effects:

1. The plaster will be soothed and may crumble. 2. Electric fitting will be affected. 3. Distempers or paints will be damaged. 4. Unhygienic conditions will be created for dwellers. 5. Growth of termites. 6. Steel utilized in building construction will be eroded.

7. Unattractive patches will develop on the wall surface and ceiling. 8. The material utilized as floor covering will be damaged. 9. Due to continuous existence of moisture in the walls, efflorescence will occur and it results in detaching of stone, bricks, tiles etc.

Methods of Damp Proofing - To get rid of dampness, the following techniques should be applied:

1. Application of Damp Proof Course: Damp proof course stands for the layer of materials like bituminous, cement, stones etc.

They are arranged in the building at all suitable positions from where water may penetrate the building. Normally, it is arranged in the building at plinth level for walls, over the concrete bed for flooring.

2. Surface Treatment: Under this method, a thin film of water repellent material is arranged over the surface which fills the holes of the materials of the building which are uncovered to the moisture.

3. Integral Damp Proofing Treatment: Under this method, water repelled compounds are blended to the concrete or mortar throughout the mixing process of concrete. These compounds function as barriers and resist the entry of moisture to the building.

4. Cavity Wall or Hollow Wall: It comprises of cavity or air drains into the wall to resist the rising of moisture from the ground to the wall.

5. Pressure Grouting or Cementation: Under this method, holes are drilled at the various sections of the building at selected points. Then thin cement paste is plunged into the holes by pressure to make the structure water-resistant.

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Published By
Rajib Dey
www.constructioncost.co
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Method of silt content test

Sand is considered as one of the vital construction materials for concrete, plastering, brickwork and flooring. Therefore, it is always recommended to use standard quality sand in the construction works.

To check the quality of sand, silt content test should be conducted. Silt content stands for a fine material that is lower than 150 micron. It becomes unstable in the existence of water.

When silty sand is applied for bonding, the strength will be decreased and rework should be required. It is mostly found when the plastering is going on for roof where the plaster continuously peels off at the time of being plastered with the mortar.

Extreme quantity of silt decreases the bonding of cement and fine aggregates as well as hampers the strength and stability of work.

In the job site, it is required to carry out silt test for each 20 Cum of sand although it may differ.

Silt Content Test for Sand

Purpose: Determine the silt content in sand (fine aggregate).

Necessary Tools:

• 250 ml measuring cylinder
• Water
• Sand & Tray

Test Method:

• Initially, the measuring cylinder should be filled with 1% solution of salt and water up to 50 ml.
• Include sand to it unless the level goes to 100 ml. Then fill the solution up to 150 ml level.
• Cover the cylinder and shake it properly.
• Once 3 hours are completed, the silt content settled down over the sand layer.
• Now record the individual volume of silt layer as V1 ml (settled over the sand).

• Then record the sand volume (underneath the silt) as V2 ml.
• Apply the method twice to obtain the average value.
• Silt Content = V1 / V2 x 100

The allowable silt content in sand percentage should be only 6%.

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Published By
Rajib Dey
www.constructioncost.co
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Different grades of Ordinary Portland cement

Ordinary Portland Cement(OPC) is extensively utilized in the construction sectors as primary component for developing concrete, mortar, stucco, and non-specialty grouts. Ordinary Portland Cement is graded on the basis of its strength. The grade specifies the compressive strength of the mortar cube that will be achieved once 28 days of setting is completed.

Grades of Ordinary Portland Cement - The following grades of OPC are available:

1. OPC 33 Grade Cement: This grade of cement is suited for general construction under normal ecological condition.

Compressive Strength of OPC 33 – The average compressive strength of minimum three mortar cubes with a face area of 50 sq.cm is considered at the time of verifying the compressive strength. These mortar cubes comprise of one part of cement and three parts of standard sand.

Compressive Strength of OPC 33:

a) 72 +/- 1 hour = Not under 16 N/mm2
b) 168 +/- 2 hours = Not under 22 N/mm2
c) 672 +/- 4 hours = Not under 33 N/mm2

IS Code – IS 269 : 1989 for Ordinary Portland Cement, 33 Grade.

2. OPC 43 Grade Cement: Now-a-days, this grade of cement is gaining popularity in the construction sectors. OPC 43 is suitable for general RCC construction where the grade of concrete is up to M30. It can also be applied for the construction of various precast items like blocks, tiles, asbestos products like sheets and pipes, and for non-structural works like plastering, flooring etc.

Compressive Strength of OPC 43:

a) 72 +/- 1 hour = Not under 23 N/mm2
b) 168 +/- 2 hours = Not under 33 N/mm2
c) 672 +/- 4 hours = Not under 43 N/mm2

IS Code – IS 8112: 1989 for 43 Grade Ordinary Portland Cement.

3. OPC 53 Grade Cement: OPC 53 is useful while requiring concrete with greater strength at very reasonable cement content. OPC 53 facilitates 8 to 10% saving of cement in concrete mix design, for concrete M20 and over.

This cement grade is very effective for specialized works like pre-stressed concrete components, several precast items like paving blocks, building blocks etc, runways, concrete roads, bridges, and other RCC works where the grade of concrete remains M25 and over.

Compressive Strength of OPC 53:

a) 72 +/- 1 hour = Not under 27 N/mm2
b) 168 +/- 2 hours = Not under 37 N/mm2
c) 672 +/- 4 hours = Not under 53 N/mm2

IS Code – IS 12269 : 1987 for Specification for 53 grade ordinary portland cement.

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Published By
Rajib Dey
www.constructioncost.co
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Different components of super structure

Superstructure stands for segments of the structure that is situated over the surface of the ground. The superstructure is built with different sections of walls, roof, doors, and windows, flooring. The sections of the structure situated on the grounds and underneath the ground floor level are known as the plinth.

The objective of superstructure is to bear different types of loads operating on the structure which range from dead load, live, load, wind load etc. These loads are then transferred to the underlying soil through the substructure.

Each element of superstructure is applied as a specific purpose, but the prime function is to arrange privacy, safety to the inhabitants. Wall and roof safeguards from the surrounding, doors permit entry and give safety, windows arrange requisite sunlight and fresh air and floor provides a leveled surface to live and protection from beneath.

Building superstructure

Column: A column in structural engineering stands for a vertical structural component that disperses the weight of the structure over to other structural components underneath , through compression.

Floor: A floor normally comprises of a support structure known as a sub-floor on top on which a floor cover is placed to arrange a walking surface.

Roof wall :

Flat – Should contain a slight slope for drainage

Shed – A single slope

Gable – Two slopes intersect at a ridge. Two walls expand up to the ridge.

Hip – Two gables, a pyramid is treated as a hip roof.

Gambrel – Four slopes in one direction, the usual barn roof.

Mansard – A four-sided gambrel-style hip roof formed with two slopes on each of its sides with the lower slope, perforated by dormer windows, at a steeper angle than the upper.

Beam: Beam stands for an inflexible structural member formed to bear and transmit transverse loads across space to supporting components.



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Published By
Rajib Dey
www.constructioncost.co
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