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Damp Proof Course (DPC) – Methods of DPC application in Construction

What is DPC?

Concept of Damp proofing: The most important factor to make the building long life is to maintain it to be dry or free from moisture traveling through walls roofs, or floors. Dampness is the presence of hygroscopic or gravitational moisture. Dampness not only reduces the strength of the structural components but also gives rise to unhygienic conditions. So, in the building design, damp prevention is one of the important factors to be considered, and every building Should be damp proof. So, “damp-proofing” or “damp proof courses (DPC)” is a prevention method applied in buildings walls and floors to the entry of moisture in the building, it should be a perfect design.

Related article: What is Shoring? Types and Uses

Causes of Dampness in buildings

Followings are the main causes of dampness in building:

  1. Moisture rising from the ground to the walls
  2. Rain travel from wall tops
  3. Rain beating against external walls
  4. Condensation
  5. Miscellaneous causes

1.  Moisture rising from the ground to the walls

If the foundation soil on which substructure is is embedded is previous, moisture slowly and constantly travels through the structures founded on the soil. There is also a lot of moisture present in the impervious soils. By the capillary action, this moisture may rise into the floor through the wall. This process of rising groundwater I will also so slowly result in moisture entry into the building. 

2.  Rain travel from wall tops

If the top of the wall is not protected from water penetration, rainwater enters the wall and will travel down. If the roofs of the building is is not a leakage-proof, that may cause water to enter. 

3.  Rain beating against external walls

The external faces of the world are not treated properly, moisture main enters the wall, causing dampness in the anterior. Sometimes water may accumulate on balconies and chhajja because of the not proper outward slope, enter the walls through their junction. This type of moisture travel can deteriorate paintings and interior decoration of the wall.

4. Condensation

Due to much decrease in atmospheric temperature, there is a condensation of atmospheric moisture that causes deposition of water on the walls, floors,  and ceilings. This moisture may cause dampness.

5.   Miscellaneous causes

Following are the other causes of moisture enter:

  • Poor drainage at the building site.
  • In the perfect orientation of building; less entry of sunlight, heavy showers may remain damp.
  • Imperfect roof slope: flat slope may cause more water accumulation.
  • Defective construction: in perfect wall jointings, joints in roofs, defective throating, etc.
  • Absorption of water from defective rainwater pipes.

Effects of dampness in Buildings

The followings are the effects of dampness in the building:

a) Travel of Moisture through walls and ceilings couches unsightly patches, shortening and crumbling of plaster and paints.

b) Breeding of mosquitoes and the growth of termites are common due to dampness in buildings.

c)      warping buckling and dry rotting of timber fittings such as door window almirah and wardrobes are caused due to contact with damp walls and damp floors.

d) the continuous presence of moisture in walls houses in efflorescence resulting in this integration of bricks stone tiles and consequent strength reduction.

e)      electrical fittings get deteriorated giving rise to leakage of electricity e and danger of short circuits.

f)        rusting and corrosion of metal fittings attached to walls, floors, and ceilings are due to moisture.

g)     Softening and crumbling of plaster takes place due to moisture travel through it, especially in lime plaster.

h)      A very serious and difficult disintegration of wall decoration (i.e. painting, putting, etc.) occurs which is very difficult and costly to repair.

i)        The flooring system in the building becomes loose, and crack because of loss of adhesion when moisture is in continuous contact with theme.

j)        Contact of moisture can damage the floor coverings.

k)      Termites can easily grow and survive in damp are.

l)        There is a possibility of growth of germs, bacterias in damp and dark areas, which may cause serious diseases like tuberculosis, neuralgia, rheumatism, etc. and asthma problems may also take place.

Methods of damp proofing

Commonly used methods for making building damp proof are:

1.     Use of damp proofing course (D.P.C.): membrane damp proofing.

2.     Integral damp proofing.

3.     Surface treatment.

4.     Cavity wall construction.

5.     Guniting.

6.     Pressure grouting.

1.     Membrane damp proofing:

In membrane damp proofing, a  water repellent membrane is inserted between the source of dampness and the part of the building adjacent to it. Damp proofing material may be like bitumen, mastic asphalt, polythene sheets, bituminous felt, metal sheets, cement concrete, etc. damp proofing course may be provided either horizontally or vertically in floors and walls.

The followings process and precautions should be followed while providing DPC.

·        The mortar bed supporting

  • The surface on which DPC is Don should be free from harmful ingredients and be labeled and also free from projections so that the DPC is not damaged
  •  At junction and corners of the walls, the DPC course should be is in as an integral part in the horizontal direction and should be laid continuous.
  • When a horizontal DPC (i.e.,  that of a floor ) is continued to a vertical face, a cement concrete fillet of a 7.5-centimeter radius should be provided at the junction.
  • The DPC course should not be exposed to the other side on the wall surface otherwise it will get damaged during finishing work and inspection work.
  • The full thickness of the wall should be covered by a damp proofing course, excluding rendering.

2. Integral damp proofing

It consists of the addition of water roofing compounds to the concrete mix so that it becomes impermeable. The principle of these compounds could be mechanical in which they feel up the words of concrete, a chemical in which they react chemically with the concrete two bodies waterproof concrete or water repulsive principle in which the added compound makes the concrete water repellent.

The waterproofing compounds used in integral damp proofing will be in three forms:

(I) to feel the voids of concrete by applying the mechanical action principle are compounds made from chalk, talc, fullers earth, which make feel the words of concrete.

(ii) certain compounds are used to produce waterproof concrete-like alkaline silicates, Aluminium sulphate, calcium chloride, etc.

(iii) sorting water repellent compounds are mixed with concrete that are soap, petroleum, oils, fatty acid compounds, etc.

(iv) commercially available compounds like publo, permo,  silica, etc.

Related article: Properties of Fiber Reinforced Concrete (FRC) – Types, Uses, and Advantage

3. Surface treatment

It consists of the application of a layer of water repellent substances or compounds on the surface to be protected so that it disallows the entering of moisture. The use of water repellent metallic soaps success calcium and Aluminium plates and stearates are most effective against rail water preparation. However overall this method is effective only when the mixture is superficial and not under pressure.

Painting and plastering of the exposed surfaces must be done carefully, using waterproof agents like sodium or potassium silicates, aluminum or zinc sulfates, barium hydroxide and magnesium sulphate, etc. The surface treatment gives better results only when the mixture is superficial and not under pressure. Sometimes walls of stone and brick exposed surface is is sprayed with water repellent solutions.

4. Cavity wall construction

The cavity wall prevents the protection of water inside the building by shielding the main wall by an outer skin wall living a cavity between the two. It is an effective damp proofing technique.

5. Guniting

Guniting consists of depositing under pressure, and impervious layer of reach cement mortar persists of 1:3 cement sand mix which is shot on the clean surface at a distance of 75 to 90 cm with the help of a cement gun under the pressure of 2 to 3 kg/cm2. For the perfect pressure the distance between the surface to be gunited and nozzle of the machine should be kept about 75 to 90 cm from the surface. And the motor mixture of desired consistency and thickness can be deposited to get an imperious layer. This motor mix layer should be perfectly cured at least for two weeks.

6. Pressure grouting

Pressure grouting is a process of forcing cement grout, under pressure, into cracks, voids, fissures, etc. Present in the structural components of the building the consolidating them and enhancing there water penetration resistance.

This method is very sensitive and useful for checking the seepage of rising groundwater through the foundation structure of a building.

Properties of material for damp proofing course (DPC)

The materials use for DPC should have flowing characteristics: 

●       The material should be impervious so that it blocks moisture preparation.

●       It should be strong, capable of resisting the superimposed loads.

●       The material should be flexible to accommodate the structural movement through the fracture.

●       It should fall leak-proof joints.

●       It should be cheap and readily available in the market.

●       It should be durable and should have the same life as that of the building.

●       The material should be e available at cheap price.

●       The material should be placed in study rigid condition so that it cannot change its position and no movement in itself.

Common damp proofing materials:

The commonly used damp proofing materials are listed below:

(1)   Hot bitumen

(2)   Bituminous felt or asphaltic felts

(3)   Metal sheets

(4)   Combination of sheets and bituminous felts

(5)   Bricks

(6)    Stones

(7)   Mortars

(8)   Cement concrete

(9)     Plastic sheets

  1. Hot bitumen: Highly flexible hot bitumen is placed on the bedding of concrete or mortars with a minimum thickness of 3 mm.
  2. Mastic Asphalt: Mastic Asphalt is obtained by heating Asphalt with sand and mineral fillers up to standard temperature. It is semi-rigid material of good property of impervious and durable. Which is also able to withstand very hot climate heavy pressure.
  1. Bituminous or asphaltic felts for Damp proofing

This type of material is available in rolls of various wall thicknesses. It is a flexible material. At the time of laying of it, the cement concrete motor circuit should be flat layered. It is layed carefully by providing full overlap at angles, junction, and crossings with the overlap of 10 cm (4 inches)  at joints. And vidmate seal will be provided at laps. Bituminous felt is only used for lightweight load.

  1. Combination of sheets and Bituminous felts

When lead foil sheets are sandwiched between asphaltic or bituminous felts this is a perfect material for the DPC course. This combined by-product is called the lead core, it has a good property of easily laying, reliability, efficiency, economy, and resistance to cracking.

  1. Bricks

When there is not excessive damp then the special character of bricks can be used as D.P.C. The using bricks should have water absorption not less than 4.5 % of their weight. These bricks are laid in two to four courses in cement sand mortar and the joints are kept open.

  1. Stones

For DPC course dense and sound stones can use on the full width of the walls. Such types of stones are: granite, trap, slats, etc. The mortar used in this course is 1: 3 ratio.

  1. Mortar

Other DPC materials can be covered by cement mortar (1:3). For this course, the water used for mixing is mixed with 75 gm of soft soap by per liter of water and a small quantity of lime maybe e added to increase the workability of cement mortar.

  1. Cement concrete

It is a common method used for DPC, in which 4 cm to 15 cm thickness DPC can be provided at the plinth level with cement concrete of 1:2:4 mix or 2:1.5:3 mix. Such a layer can effectively check the water rises due to capillary action. Water repellent compounds like two coarse of hot bitumen may be applied to it if dampness is more.

  1. Plastic sheets

Plastic sheets new type of DPC material in which of black polythene of 0.5 to 1 mm thickness is provided on walling with And roll length of 30 m ( 90ft). New research developed a new type of DPC course in which 400 gauge thick alkathene is lead offer 12 mm thick 1:4 cement mortar. This is a cheaper method but not permanent.

  1.  Metal sheets

Sometimes for the DPC course, many flexible metal sheets like lead, copper, aluminum are used. Among these Lead sheets are so flexible. The thickness of these sheets are maintained in such a way that it’s weight is not less than 20 kg/m2. These sheets are laid similar to bituminous felts. 

Advantages of lead sheets: 

  • Complete impervious to moisture.
  • Resistant to ordinary atmospheric corrosion.
  • The capability of taking complex shapes without fracture,
  • Resistance to sliding action, etc.

One of its advantages is it may be corroded when in contact with lime or cement, bitumen coating is applied on it to protect from corrosion.

In many cases, Copper sheets are also used for DPC and is embedded in to lie or cement mortar. Copper sheets have good properties on durability, resistance to dampness, resistance to ordinary pressure, and resistance to sliding.

Another metal for DPC course is Aluminium sheets, it is not advantageous as lead and copper sheets. It should be protected with a layer of bitumen for durability.

DPC treatment in buildings

1. D.P.C. Treatment to foundations against gravitational water.

Moisture may be a rise in the wall from the basement foundation damp soil by receiving water from the adjacent ground. Thought to overcome this problem air drain is provided parallel to an external wall that makes checked the receiving moisture.

As shown in the figure below the width of the air drain may be about 20 to 30 CM. Surface water is checked by making the outer wall of the drain above the ground level. RCC roof slab is provided on-air drain the provision of opening with greetings at regular intervals for passes of air. For the better check of moisture, DPC is also provided horizontally and vertically in both directions.

Air drain provision as DPC
Fig.3. Air drain provision as DPC
2. DPC Treatment to basements

When the foundation soil is in damp condition then basements are structures on the three methods:

a)     Provision of foundation drains and DPC

b)     Provision of RCC raft and wall slab

c)     Asphalt tanking

(a) .  Provision of foundation drains and DPC:

It is better to provide trench all around the basement, up to foundation level, and fill it with gravel, coke, and other previous material when the foundation soil is not properly drained. In such type of soil ( eg.peat soil) due to less drainage, great hydrostatic pressure is exhausted and the fluid as well as receives water continuously. 

DPC teatment for basement on Undrained soil
Fig. 3. DPC teatment for basement on Undrained soil

Detail about drain layout is shown in the figure below., In which open joined drains collect the underground water, and jeans pants embedded in the gravel bed may also be provided. In the walls and in foundation concrete horizontal and vertical DPC are provided. Drainage water is fed into catch drain by the suitable longitudinal slope in the main drain.

Layout od Drain - Plan
Fig. 4. Layout of Drain – Plan view
(b) . Provision of R.C.C. raft and wall slab

In this system, floor slab, as well as walls, are constructed in a rigid RCC structure. As shown in fig. no.5. at least 3 layers of bitumen felts are used as DPC. Horizontal and vertical DPC treatment is also provided there. The outer surface of the RCC wall slab is protected by a half brick thick outer wall. This type of system is better from the above systems because it can solve the problem effectively when the underground water pressure is severed, and it can also so less expensive because of not pumping water continuously.

DPC treatment in damp soil for basement level
Fig. 5. DPC treatment in damp soil for basement level
(c). DPC as Asphaltic tanking

When the subsoil water table is not very high Asphalt ranking is adopted for DPC course. In the figure below we can see all detail about the section in which horizontal DPC in the form of an asphaltic layer of 30mm thick coats over the entire area of the basement floor and then extending it in the form of vertical DPC on the external faces of the basement walls. 

Asphalt tanking as DPC for Basement
Fig. 7. Asphalt tanking as DPC for Basement

The vertical faces make the same function as a waterproofing tank in which the sequence of the vertical asphaltic layer maybe 20 mm that layer keep all the system dry. Generally, vertical DPC is Laid on at least 15 cm above the ground with one half (1 and ½) brick thick outer protection wall. For the purpose of safety during the construction of the floor slab, on the foundation concrete (1:3:6) oppo attractive flooring of flat bricks is also provided.

3. DPC Treatment to floors

For the floor construction in building in the place of dry foundation soil area software release welcome compacted and for 7.5 to 10 cm thick layer of sand is spread over the entire area under the flooring. Sometimes another method of construction is on the compact it’s of soil all layer of stone soling is provided with the proper compaction then a lean mix of concrete (1:3:6 to 1:4:8) is provided with the flat surface on which flooring could be laid.

Watch in dam software condition where the water table is near the ground surface there is a serious problem with dampness on the floor. So so in this case a membrane DPC is provided over the entire area as shown in the figure below. And the construction process is slow

DPC for flooring
Fig. 8. DPC for flooring

●       First of all area of flat bricks soling is provided over a fine send course

●       Din lean concrete floor is preferred.

●       Then on the foundation concrete off primer quotes @ 1.5 kg per meter square is applied.

●       After that, a layer of bituminous felt, a coat of hot bitumen ( in the form of mastic Asphalt or fibrous Asphalt felts) is provided.

●       After leaving bituminous held over it of finishing coat of hotel vitamin is applied at the rate of 1.5 kg/meter square over the felt.

4. DPC Treatment to walls

For the basement walls, a vertical DPC is laid over the external face of the wall, as shown in figure no. 9. This vertical layer of DPC is laid over the base of the water-cement plaster grounded on the external face of the walls. This vertical DPC is protected by the external protective wall of half brick thickness. The vertical DPC should be carried at least up to level 15  cm above ground level. Related article: Brick Masonry Construction, Lab Tests , Classes of brick, defects in brick

Horizontal DPC is also provided at least 15 cm above the ground level extending from the floor. As shown in the figure in the internal walls DPC is provided in level with the upper surface of the concrete floor. Figure b also shows the DPC system on two floors at different levels and connected by an internal wall. The DPC system in the cavity wall is explained in my other post here.

DPC system for internal wall
Fig. 9. DPC system for internal wall

5. DPC Treatment of roofs

In the case of roofs, the DPC providing methods are given in another chapter separately all about fault roofs, parapets, copings, and pitch troops as shown in fig there.

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