What Is DPC In Construction?
DPC means Damp Proof Course which is applied at basement levels, which restricts the movement of moisture through the walls and floors of a building.
Mostly DPC courses are required in new build properties which are most sensitive to moisture in order to prevent rising dampness subsequently.
The role of DPC In Construction is to prevent dampness from the ground rising up the walls which might cause damage to property.
Excess moisture results in damage to plaster, and decoration and could also result in wet rot, or dry rot affecting unprotected timbers of a structure.
Every building is required to have a damp-proof course that is situated at least 150 mm above ground level.
A DPC material maintains its effectiveness until the building movements further result in cracking or bridging.
What Is a Damp Proof Course?
A Damp Proof Course is an essential element of a property that is required to protect the property against any moisture rising from the ground.
In this, we will be provided with a deeper understanding of what is a damp proof course and its types.
This knowledge of Damp Proofing is greatly helpful for all property owners to ensure that their property is protected with an effective damp proof course.
The occurrence of different damp issues causing damage to property arises from excess moisture gained by property. Hence it is necessary to make sure that your building is equipped with an effective damp-proof course to repel water from the ground.
Types of DPC And Its Thickness
Currently, various remedial damp-proof courses are available which can be installed. However, it is important to select the appropriate damp proof course which will be well suited to the construction of the property.
The following are different types of DPC and their thickness used in construction,
1. Damp Proof Course Injection
This system of the Damp Proof Course involves fluid or liquid being injected into the wall to stop the dampness from the ground from rising above the damp proof course acting as a water-repelling layer. This is generally also known as a chemical damp proof course injection.
The fluid used for injecting involved in the system is injected in holes that are drilled into the wall at least 150mm above the external ground level.
2. Mortar Injection Damp Proof Course
This method of damp proofing is similar to the Damp Proof Course Injection but instead of fluid, cream, or liquid being used a chemical-enhanced here mortar is used for damp proofing material and caulked into the holes drilled in the wall.
It is applicable where the construction of the wall may be of random rubble and the structure is very prone to having voids within the structure.
Here mortar acts as filler which fills the hole in the masonry, from which chemical is drawn into the wall structure in order to block the rising damp. It has a minimum thickness of 3 mm.
3. Electro Osmotic Damp Proof Course
Electro Osmotic Damp Proof Course is used where chemicals are not appropriate or the client requests a non-chemical damp proof course alternative.
In this method, copper and titanium wiring are used to install a small electric charge into the wall which results in reversing the polarity of the capillary in the wall hence pulling the rising damp way below the level of the new damp course.
4. Damp Proof Membrane Course
In this method of Damp Proofing specially designed damp proof membranes are used to efficiently form part of a damp proof course which is thoroughly positioned under a pre-designed concrete slab with the intention of protecting the concrete from any moisture and hence obtaining a damp proof layer.
It is one of the simplest and most flexible methods of damp proofing used to protect properties from penetrating damp problems in the case of the home, having earth retaining walls.
DPC Level In Construction
Capillary Action in the brickwork causes the moisture to rise up in the building hence the foundation of a building is always intact with the moisture present in the soil.
Hence to tackle such a phenomenon DPC (Damp Proof Course) is provided at the plinth level of the construction.
In timber suspended floor DPC is provided below floor level, however in the case of solidly constructed floors the DPC is always situated above-finished floor level.
The building embeds a type of physical bitumen damp proof course within the outer and inner leaf walls in various elements.
Plinth protection is provided to prevent water implication into the soil and reaching the equal of the plinth wall and floor by capillary action resulting in moisture, acting as a barrier, and water in the ground near the plinth wall blocking direct access.
Plinth protection is supported by offering an additional thickness/peak under the beam or under the foundation. In short, the plinth is the base of the structure that carries the weight of the structure to the soil.
Many times, the plinth has to deal with outside actions such as water, tree roots, and termites as it affects the life of the plinth and fails it, so it is necessary to protect the plinth from such activities.
Methods of Damp Proof Course Installation in Construction
The general procedure to be followed while laying a damp proof course is,
- The DPC should be installed in a manner so that it covers the full thickness of the walls where rendering is exceptional.
- Before laying DPC the mortar bed upon which the DPC is to be laid should be made level, even, and free from projections because an uneven base is likely to cause damage to DPC.
- For the circumstances where a DPC in a vertical direction is continued up to a vertical face, a fillet made of cement concrete with a 75mm radius has to be provided before initiating treatment at the junction.
- DPCs should form a correct combination with each other such that they can develop complete and continuous resistance to the passage of water from walls, floors, or roofs.
What Is Damp Proofing?
Dampproofing is a method used to prevent dampness to enter through walls or floors into the interior property of the building.
Dampness can be seen in many properties, especially older properties which may have been constructed without a damp-proof membrane.
But some of the new properties also experience this problem because of water leakage, heavy rainfall, change in temperature, etc.
Causes of Dampness In Buildings
- Heavy rain smashing
- Low level of site
- Drainability of soil
- Atmospheric condition
- The defective orientation of the building
- Moisture entrapped during construction
- Defective construction e.g. joints
- Use of poor quality bricks which ultimately absorb a lot of water.
- Use of Poor quality concrete (permeable concrete)
Effect of Dampness
- It causes a Musty smell & Damp and
- Mildew or mold forming on walls
- It causes Peeling wallpaper, Staining of wall coverings, & blistering paint
- Damp walls & dark patches
- Fragmenting plaster & Discoloration
- It leads to the Decay of timber by wood-rotting fungi or the presence of wood-boring weevils
- Dampness symptoms are visible on skirting boards, where nails or screws show signs of rust
- It develops rusting on angle beads within damp plasterwork
- It causes the appearance of salt stains on outside walls
- Cement plaster mortar on the outside of the property begins to crumble away
Methods of Damp Proofing
The following are the various Internal damp proofing methods,
1. Membrane Damp Proofing
In this method, a water resistance membrane or damp proof course (D.P.C.) is introduced in between the source of dampness and the part of the building adjacent to it.
DPC may consist of flexible materials such as bitumen, mastic asphalt, bituminous felts, plastic or polythene sheets, metal sheets, and cement concrete.
The DPC can be introduced or placed either horizontally or vertically on floors, walls, etc. Damp Proofing Course provided basement is normally termed as ‘Tanking’.
The following point should be kept in mind while providing a waterproof course,
- The DPC should cover the full thickness of walls, excluding rendering.
- The mortar used for DPC should be leveled and even, and should be free from projections so that the damp proof course is not damaged.
- DPC should be laid in such a way that a continuous projection is provided.
- While providing DPC at junctions and corners of walls, the horizontal damp proof course should be laid continuously.
- When horizontal DPC is continued to a vertical face, a cement concrete fillet of a 7.5 cm radius should be provided at the junction.
- Continuous correct relation should be maintained between two damp proof courses, to ensure a complete and continuous barrier to the passage of water from floors, walls, or roofs.
- Care taken that no damp proof course is left out of wall surface; otherwise, it can get damaged during wall finishing.
Damp Proof Membrane Cost: Rs. 80 / Kilogram
2. Internal Damp Proofing
In this method of damp proofing, some waterproofing compounds are added to the concrete mix, so that it becomes impermeable. Following are some waterproofing compounds that may be used for internal dampproofing.
Compounds made from chalk, talc, and fuller earth, may fill the voids of concrete under the mechanical action principle.
Compounds like alkaline silicates, aluminum sulfate, calcium chlorides, etc. This compound chemically reacts with the concrete to produce waterproof concrete.
Compounds like soap, petroleum, oils, and fatty acid compounds such as stearates of calcium, sodium, ammonia, etc. work on the water repulsion principle. When this compound is mixed with a mix, concrete becomes water-resistant.
Commercially available compounds like Pueblo, Permo, Silka, etc. The amount of chemical compound added to cement depends upon the manufacturer’s recommendations.
For general waterproofing work 1 kg of chemical compound per one bag of cement to render the mortar or concrete waterproof.
3. Surface Treatment
In the internal finish, dampness finds its way through the pores of the material used in finishing. To prevent the entry of moisture into the pores, they must be filled up.
To limit the entry of moisture into the surface finish a layer of water repellent substances or compounds is applied on these surfaces through which moisture enters.
The use of waterproof metallic soaps such as calcium and aluminum stearates (Stearates are the salts and esters of stearic acid)are much more effective against rainwater penetration.
The finishing of outer work such as Pointing and plastering surfaces must be done carefully, using waterproofing agents like sodium or potassium silicates, aluminum or zinc sulfates, barium hydroxide and magnesium sulfates, etc.
This method of treatment is effective only when moisture occurs on the surface and is not under pressure. For exposed stone or brick wall face may be treated by spraying with water repellent solutions.
For external wall plastering use of the mixed proportion of cement, lime, and sand mixed in 1:1:6 is found to serve the purpose of preventing dampness in the wall due to rain effectively.
4. Cavity Wall Construction
The method of Cavity wall construction is an effective method of damp prevention. In this the main external wall is shielded by an outer skin wall, leaving a cavity between the two.
The cavity leaves a gap between walls which prevents the moisture from traveling from the outer to the inner wall.
In Guniting, the exposed damp surface is covered with an impervious layer of rich cement mortar deposited under pressure over the exposed surfaces for waterproofing or over pipes, cisterns, etc. for resisting the water pressure.
The Guniting of mix or spraying of mix operation is carried out by use of a machine known as a cement gun. This cement gun machine has arrangements for mixing materials and a compressor for forcing the mixture under pressure through a 50 mm dia flexible hose pipe.
A nozzle is fixed to the hose at its free end to which water is supplied under pressure through a separate connection.
In this method, before Guniting is done the surface to be treated is first thoroughly cleaned of dirt, dust, grease, or loose particles and wetted properly.
As the surface is sufficiently wet a cement mortar consisting of 1: 3 cement sand mix, is shot on the cleaned surface with the help of a cement gun, under a pressure of 2 to 3 kg/cm2.
The distance between the nozzle of the machine and the surface to be gunite is kept at a distance of about 75 to 90 cm.
The mortar used for uniting treatment should be desired consistency and thickness can be deposited to get an impervious layer. The surface should be properly cured at least for 10 days.
In this method, to ensure dense compaction and better adhesion of the rich cement mortar is applied under pressure with the help of a Guniting gun and hence the treated surface becomes waterproof.
Watch Video: What is DPC (Damp Proof Course) & Material Used For DPC
What do you mean by Damp Proof Course?
The DPC treatment is mostly applied at basement levels, which restricts the movement of moisture through walls and floors.
Why is DPC used in building construction?
The role of DPC is to prevent dampness from the ground from rising up the walls which might cause damage to property. Similarly, it is required to protect the property against any moisture rising from the ground.
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