Requirements of Good DPC
- Totally impervious and should not allow travel of dampness.
- Durable and keep the building damp proof permanently.
- Economical and easy in laying.
- Able to resist load to which it is subject.
- Accommodate some structural movement without fracture.
Prevention of Dampness: Use of DPC
Prevention dampness in a building is done by various methods. The most common method is the use of a damp proof course (DPC). The other methods are damp-proof surface treatment, integral damp-proofing treatments, cavity or hollow walls, shot concrete, and pressure grouting or cementation.
A sectional view of building wall and floor is shown above figure. In this figure. A layer of damp proof course (DPC) of 2.5 cm applied to the wall and floor is shown.
This layer of DPC consists of water repellent materials such as cement concrete, or mortar mixed waterproofing compound in powder form, bituminous felts, mastic asphalt, plastic sheets, metal sheets of copper and lead, PVC sheets, slates, stones, bricks, etc.
The rigid materials like stones, bricks, slates are painted with bitumen. This layer or membrane is interposed in the building structures, as shown above, figure. Basically, this DPC is provided to prevent the water from rising from sub-soil or ground and getting into the different parts of the building.
This damp proof course may be provided horizontally or vertically in floor and wall. The choice of effective DPC materials for a building requires a judicious selection. It depends on the climatic and atmospheric conditions of the area and site, nature of the structure.
General Principles of Damp-Proofing
The general principles observed in the case of all the damp-proofing methods are as follows:
- The damp-proof course may be horizontal or vertical.
- The horizontal damp-proofing course should cover the full thickness of the wall.
- At junctions and corners of a wall, the horizontal damp-proofing course should be laid continuous.
- The damp-proof course should be laid continuous, so as to make proper protection from dampness.
Methods of Damp-proofing
The following methods are generally adopted to prevent dampness in a structure.
- Membrane Damp-proofing
- Integral Damp-proofing
- Surface Treatment
- Guniting
- Cavity Wall Construction.
#1. Membrane Damp-proofing:
This consists of providing layer or membrane of water-repellent material between the source of dampness and the part of the structure adjacent to it. This type of layer is commonly known as a damp proof course (or D.P.C.), and it may comprise of materials like bituminous felt, mastic asphalt, silicone, epoxy, polymers, plastics, cement concrete, etc.
Depending upon the source of dampness, D.P.C. may be provided horizontally or vertically in floors, walls, etc.
#2. Integral Damp-proofing:
This consists of adding certain water-proofing compounds with a concrete mix to increase its impermeability. Such compounds are available in powdered as well as in liquid form. The compounds made from clay, sand, or lime help to fill the voids in concrete and make it waterproof.
Another form of a compound like alkaline silicates, aluminum sulfates, calcium chlorides, etc. Reacts chemically when mixed in concrete to produce waterproof concrete. Pudlo, promo, Imperio, etc. are some of the commercially made preparations of waterproofing compounds commonly used. In general, one kg of waterproofing compound is added with one beg of cement to make the mortar or concrete waterproof.
#3. Surface Treatment:
It has been observed that the moisture finds its way through the pores of materials used in finishing. These pores must be filled up in order to check the entry of moisture.
Surface treatment consists in filling up the pores of the surface subjected to dampness. The bituminous solution, cement coating, paints, and varnishes, etc. are used for surface treatment. The walls plastered with lime cement plaster of proportion 1 : 1: 6 is found effective to prevent dampness in the wall due to rain.
#4. Guniting:
This consists of depositing an impervious layer of rich cement mortar over the surface to be waterproofed. The operation is carried out by a machine known as a cement gun.
The surface to be treated is first thoroughly cleaned and wetted properly. Cement and sand have usually taken in the proportion of 1 : 3 to 1: 4 are then fed into the machine. The mixture is finally shot on the prepared surface under a pressure of 2 to 3 kg/cm2 by holding the nozzle of 75 to 90 cm from the working face.
The quantity of water in the mix can be controlled by means of regulating the valve. Since the material is applied under pressure, it ensures dense compaction and better adhesion of the rich cement mortar, and hence the treated surface becomes waterproof.
#5. Cavity Wall Construction:
This consists of shielding the main wall of the building by an outer wall leaving a cavity in between the two. The cavity prevents the movement of moisture from the outer to the inner wall. The outer skin wall is termed as a cavity wall.
Frequently Asked Questions (FAQs) About Damp-Proof Courses (DPC) and Dampness Prevention in Buildings
What Is a Damp-Proof Course (Dpc)?
A Damp-Proof Course (DPC) is a barrier integrated into building structures to prevent moisture from rising through walls and floors from the ground or other sources.
Why Is Dpc Necessary in Buildings?
DPC is essential to prevent dampness, which can lead to structural damage, mold growth, and health hazards for occupants.
What Materials Are Commonly Used for Dpc?
Materials include bituminous felt, mastic asphalt, silicone, epoxy, polymers, plastics, cement concrete, and more, depending on specific building requirements and environmental conditions.
How Does Horizontal Dpc Differ from Vertical Dpc?
Horizontal DPC spans across the thickness of walls or floors, while vertical DPC runs along the length of walls. Both serve to block moisture ingress but are applied differently depending on structural needs.
What Are Integral Damp-Proofing and Surface Treatment Methods?
Integral damp-proofing involves adding waterproofing compounds to concrete mixes, enhancing their impermeability. Surface treatment fills pores in finishing materials to prevent moisture penetration, using coatings like bituminous solutions or cement.
What Is Guniting in Damp-Proofing?
Guniting refers to applying a dense cement mortar layer under pressure onto surfaces to waterproof them effectively. This method ensures tight adhesion and prevents water ingress.
How Does Cavity Wall Construction Prevent Dampness?
Cavity wall construction involves creating a gap or cavity between inner and outer walls, preventing moisture from passing through to the interior wall surfaces, thus safeguarding against dampness.
How Should Dpc Be Installed for Maximum Effectiveness?
DPC should be installed continuously without interruptions at junctions and corners, ensuring complete coverage across vulnerable areas of the building to effectively block dampness.
What Considerations Influence the Choice of Dpc Materials?
Factors such as climate, site conditions, and structural requirements dictate the selection of DPC materials to ensure long-term durability and effectiveness against dampness.
How Can Maintenance of Dpc Be Managed Over Time?
Regular inspections and timely repairs or replacements of DPC materials are crucial to maintain their effectiveness in preventing dampness and preserving building integrity.
