Keeping the evil out
Before the onset of the monsoons, it is better to get your house waterproofed. Following a few simple guidelines will ensure that your house is leak proof.
Er. Jagvir Goyal - The writer is an Author of many technical and general books and leading technical columnist for many periodicals and newspapers.
Four things that every house builder fears while constructing his house are termite, cracks, leakages and dampness. Though there are remedies available for them, the joy of living in a trouble-free house is lost and the eyes keep looking for re-appearance of any signs of distress signals. The best remedy is to take extra care during construction itself and eliminate all chances of occurrence of these evils.
A systematic approach towards handling these problems can lead to their elimination. Water-proofing of a house can lead to elimination of leakages and dampness. Termite and cracks too get contained to a significant extent. The battle against the four evils is almost won if we succeed in water proofing the house well.
To water proof a house, following six fronts need to be handled:
- Basement Construction.
- Damp Proof Course.
- Sunken Floors.
- Water Supply Piping.
- Sanitary and rainwater Piping.
- Leak Proof roofing.
Here are a few guidelines for having a leak proof and damp proof basement.
Use RCC Structure for basements: To overcome the problem of leakage, always use RCC walls and RCC raft for the basement. Avoid stone or masonry walls. Use designed concrete. Avoid nominal mixes. M20 is the designed concrete having a strength of 200 kg per sq. cm., while the nominal mix of 1: 1 ½ : 3 concrete is also considered to have same strength.
Difference between the two is that in the former, quality of concrete is ensured while in the latter, it is not. Interestingly, M20 concrete consumes less cement than 1 : 1 ½ : 3 concrete, but gives better results.
Mix Designs for basements: For external walls of basements, prefer to use M25 concrete. For the base slab, top slab and internal walls however, M20 concrete can be used. Provide a base of M10 or 1 : 3 : 6 concrete below the base slab.
Though expansion joints are unavoidable for concrete, try to avoid these as far as possible by restricting the dimensions. Add water proofing agent to all the RCC work. Consult a good water-proofing agent or ask your engineer to specify a good brand as there is a boom in water proofing industry and countless agencies have come up. Fosroc, Pidilite and Roff are some good and reliable names.
Right method of blending: If you are using a water proofing compound in dry form, the right method to use it is to blend it with cement in dry form. Keep the quantity of water proofing compound as 2 percent to 3 percent of cement. Thus, 1.0 to 1.5 kg of water proofing compound should be added to each bag of cement.
In case water proofing compound in liquid form is to be used, calculate the required quantity of water, measure it in a separate drum and add liquid water proofing compound to it. General tendency of adding water proofing compound to mixed concrete or mortar should be avoided.
Prime requirements for basements: Good ventilation and freedom from dampness are prime requirements of a basement. If dampness is not tackled effectively, unhygienic conditions prevail in the basements. Always construct a basement when the underground water level is at its lowest.
Note that basements can be made leak proof during construction only. Post-construction treatment is very difficult as only inner and leaking face is available for repair work while the outer face where the problem lies can’t be accessed. Moreover, underground water level may rise at any time, causing leakage in basement, which becomes difficult to repair. Thus, keep ventilation and lighting points in view during their planning, and water table position in view for choosing construction time.
Design aspects for basements: For basements, get the walls and floors designed to withstand external earth and water pressures without cracking. For this, it has to undergo special checks. Take into consideration the maximum level of water table, likely level during the rainy season and the rate of change of water table. Provide fillets at the junctions of RCC walls and base slab. Provide inclined steel along the fillets. Always apply a coal tar epoxy resin coating to all outer surfaces of RCC walls. This will keep the dampness away.
Effective water proofing: Provide well compacted stone soling below the PCC layer laid below the base slab. Apply two layers of ‘One part water proofing acrylic polymer and Two parts Cement’ with brush over the Plain Cement Concrete (PCC) laid on the stone soling before laying RCC raft on it. This will arrest the rise of any dampness from the ground into the basement.
Construction joints in basements: Avoid construction joints in basements or keep their number as minimum. Whenever a construction joint is given, treat it well before laying further concrete. For treatment, chip off old concrete if it is older than a day. Roughen it with wire brush if it is only a few hours old and still looks green. Clean the surface off all loose particles. Now apply the same ‘One part acrylic polymer and Two part cement slurry’ over old concrete and only then lay fresh concrete over it. Always fix nozzles in the walls, preferably at construction joints for grouting the walls with non-shrink injection grout at a later stage if leakage or dampness is noted.
Grout well: Enter all conduits for electricity and other services into the basement from a level above the ground level. See that no open space is left around the conduits. If there is an open space, seal it well.
Remember that construction joints are vulnerable points for leakage into the basements. Fully prepare and treat their locations carefully to avoid any leakage from there. Wherever required, do the grouting work through nozzles after 28 days of laying concrete and not earlier. During this period, concrete will gain its final strength and shape and grout will have its way into the voids. Choose one inch diameter nozzles. Remove nozzles on completion of grouting work and seal the surface with cement mortar.
Ground treatment: Ensure that the ground around the basement area does not slope towards the basement. Ensure that the back filling in foundations has been compacted very well. As we take limited measures to compact the backfill in the foundations of the houses, it settles in the first rainy season directing the rainwater towards the foundations. Place earth around the house in such a way that it slopes away from the house for a width of about six feet at least. Provide a slope of one inch per foot in this six foot length.
Damp Proof Course
Provision of a sound damp proof course at plinth level of a building saves its walls from ‘rising dampness’ through capillary action as the bricks used in foundations are porous in nature. Here are a few guidelines on providing an effective damp proof course in a house.
Specification of DPC: In case you are not using RCC framed structure and providing brick foundations for your house, Damp Proof Course (DPC) must be laid well to stop rise of dampness by capillary action. DPC should be kept 1.5 inch thick. The concrete used for it should be 1:2:4 or 1:1.5:3. It is preferable to add water proofing compound to it. Use 10 mm size coarse aggregate in it.; don’t use 20 mm size.
You must see to it that the sand used in concrete is coarse with a good fineness modulus. It should have a minimum Fineness Modulus of 2.5 or more. Keep the water content of DPC concrete as low. This will help in avoiding flowing out of cement slurry. Let the volume of water be 31 to 32 litres per bag of cement. This will help in keeping the slump below three inches.
Provide strong supports: Generally, the side supports required to confine DPC are provided haphazardly leaving wide gaps between the supports and the walls. This allows the cement slurry to flow out. Allow no gap between the supports and the walls. Provide sufficient supports behind the side supports so that when the concrete is compacted, the side supports don’t give way.
Save the doorways: Never lay DPC in doorways. Door sizes should be marked accurately on the brickwork. If laid in the doorways, DPC interferes with the flooring and has to be dismantled. Connect the DPC of internal walls and external walls through steps. Lay DPC on these steps also. It should be a complete and closed band. Only then it will prevent dampness from rising up.
Provide vertical DPC: All the external walls should be provided with vertical DPC on their inner side. Vertical DPC is in cement mortar, not in concrete. The cement mortar ratio should be 1 : 3. The thickness should be between 12 mm to 20 mm.
The purpose of vertical DPC is to prevent the entry of moisture through that portion of external walls which falls above external DPC but is below the plinth level and, thus, comes in contact with the filling done inside the rooms below the flooring. Though it is very important to provide vertical DPC, yet it is often found missing.
Extend the vertical DPC from each external wall to both the internal walls meeting it, up to a length of 50 cm along the internal walls. This is a safety precaution against rise of moisture.
Application of bitumen: Mostly, bitumen is applied on all DPC, may be horizontal, over the walls, or vertical. It should be applied only when curing of DPC has been done for at least seven days and, thereafter, two days are allowed for DPC to dry off. Bitumen should never be applied over wet or damp concrete. As Bitumen is available in many grades, use 85/25 grade bitumen for applying over DPC. Don’t use 80/100 grade that is generally available with road making gangs.
Numerator (85) is the softening temperature of bitumen. Denominator (25) is the penetration of bitumen. Bitumen should be applied well in a way that about 4kg of it gets consumed over three square meter area of DPC. Immediately after applying bitumen, sand should be applied over it. This way, two coats of bitumen should be applied.
Prefer Polymer Coating: Prefer to use Polymer Modified Cement coating instead of bitumen to water proof the concrete layer of DPC. This is a two part compound that can be mixed at site before its application to concrete.
It is greyish in colour and has excellent adhesion to concrete. It is flexible and breathable and covers eight to nine sq. ft. area with One kg per coat. Prefer to apply two coats of it. It can be applied on wet surface with a brush and proves better than bitumen.
Plinth beams: If you plan to provide plinth beams instead of Damp Proof Course, match top level of these beams with the floor level. See that the beams over all the walls together make a band as it will help during earthquakes and will avert some effect of differential settlement of foundations on the building. Keep the concrete mix for plinth beams as M20 or 1:1.5:3.
Provide a minimum of two steel bars each at the top and bottom faces with diameter of steel as 10mm or more. Provide 6mm to 8mm diameter steel stirrups with their spacing not greater than 300mm. Keep width of beams equal to width of walls. Keep a depth of minimum six inches.
In many of the houses and buildings, sunken floors are provided in the bathrooms or toilets to accommodate the depth of Indian type water-closets and floor traps. These sunken floors are often a cause of leakage and dampness in houses if proper water-proofing treatment is not given to them. Here are a few guidelines on making these floors water proof.
Fill the cracks: To provide water-proofing treatment, first, check the slab surface for any cracks. If cracks are present, cut them into small ‘V’s and fill them with a polymer compound. Use a compound like ‘crack fill’.
Water proofing application: Mix ‘One part of acrylic emulsion (liquid) with Two parts of polymer modified cement (powder)’ by weight to form a cream like paste. Apply two coats of it with brush on the slab surface. It can be applied even on wet slab.
Apply it on the walls also and up to a height of six inches above the bathroom floor level. On drying, it will form a flexible water proofing film and that is exactly what we need. One litre of this paste covers 7.0 sq. ft. to 8.0 sq. ft. area in one coat. Pidifin 2K, Fosroc Hydroproof and Roff Hyguard ex are good products for using here.
There are ready synthetic membranes also available in the market which can be used instead of this application. These membranes need to be notched into the walls. Lay the membrane on the slab in the manner prescribed by the supplier. Apply a ½ inch thick 1 : 3 cement sand plaster layer over the membrane. Now, fill the sunken area with clinker or foam concrete fill till you get the screed level. Now, lay the floor like other floors.
Water supply piping
Leakage of joints in water supply pipes is often a cause of dampness and leakages in buildings. Simple precautions taken at the time of plumbing can avoid these problems. Here are a few guidelines:
Basic points: Care must be taken during the laying of water supply lines to keep the joints cent percent leak proof and to pressure- test the pipe network so that no pipe bursts under pressure. To avoid this most troublesome problem of leakage from concealed pipes, some builders are again resorting to unconcealed pipe system these days. Unconcealed pipes look ugly.
Prefer to have concealed pipes and to keep the concealed system trouble proof, take four precautions—one, choose the pipe material carefully; two, take extra care in making pipe joints leak proof; three, allow a minimum, rather no pipe, to run below the floorings; and four, frame and keep an exact layout drawing of laid water supply lines.
See that all pipes are concealed in the walls only and the pipe layout is so designed that no pipe is carried below any flooring. Know that lesser are the number of joints in water supply network, lesser are the chances of leakages.
For concealed pipes, ducts or recesses may be provided in the walls instead of chase-cutting of walls. Such ducts or recesses can be suitably covered with removable covers. In such a case, a leaking pipe will not ask for any dismantling of plaster and brickwork.
Joint material: Use best quality cotton yarn thread in the joints. Never allow use of jute or hemp instead of cotton yarn. Use of yarn should be kept as minimum. Unnecessary winding of yarn over pipe threads will result in loosening of joints after sometime. Use best quality white lead available at about `50 per kg for smearing over the thread.
The plumber should make a paste of dry red lead mixed with moist white lead and boiled linseed oil. This mixture settles the yarn well into the pipe threads. Otherwise, yarn has a tendency to rise and loosen itself.
Testing: Final water supply network should always be tested under pressure to check any leakages. This testing should be done before filling the chases in masonry walls and finishing them with plaster. Once the water supply lines have been erected in position and all pipe grids have been completed, ask the plumbing contractor to test the system under pressure and show it to be leak proof.
Don’t allow concealing of pipes unless pressure testing has been done. Sometimes, plaster work is taken up in parallel in the bathrooms or kitchen and wall chases cut to lay the pipes are filled and finished after erection of pipes. Ensure that this is not to be done unless the water supply network has been tested and made leak proof.
Method of testing: For pressure testing of water supply lines, a pump is used to pump-in water at a pressure of 200 feet of water or more. A gauge erected on the pump gives the water pressure reading. Check this gauge to have zero error or its initial reading should be noted. If possible, see that it has been calibrated by a good test house.
The pressure testing should be done with gauge showing a reading of 6 kg per sq.cm. Ask the plumber to fill up the pipe network slowly. This allows expelling out of air and a phenomenon called water hammer doesn’t occur. Ask to maintain water pressure in the pipes for one hour at least. Thereafter, with the pressure maintained, check that no pipe or joint should have even the slightest leakage.
Sanitary and rainwater piping
In addition to taking care of water supply pipes, take care of soil pipes, waste pipes of sanitary system and rain water pipes of roof drainage system. Joint leakage of these pipes should be avoided at all costs. Here are a few guidelines:
Leak proof fixing of PVC pipes: The pipes used for sanitary work may be of PVC or CI. While installing PVC pipes with sockets, keep the sockets against the direction of the flow. Always store solvent cement in well shaded area. Never store it in the open.
For solvent cement joints, don’t leave solvent cement in open tins for long durations. Use small-sized tins for it. For seal ring joints, see that the ring is seated well in the groove of socket. Don’t rest the spigot of next pipe inside the socket of lower pipe but leave a little gap of 8mm to 10mm between the two to allow space for pipe expansion.
Leak proof fixing of CI pipes: If you are using CI pipes, the joints in CI sanitary pipes should be filled with lead. Joint filling needs to be done very carefully to avoid any leakage. At a later stage, it becomes most cumbersome to repair joint leakages and the plaster/finishing work gets damaged. Repaired finishing never attains the same look that it was having originally.
It is better to ensure leak proof and airtight joints at the outset. For this, centrally place the spigot of the upper pipe in the socket of lower pipe or fitting. Now, fill one third of the socket space around the pipe with hemp yarn and press it well with caulking tool available with the plumber. Next, fill the balance two-third of space with molten lead.
Filling the CI pipe joints: Ensure that pouring of molten lead in the socket is done immediately after the pressing of caulking yarn. In short, a joint is to be completed in a single operation. After pouring of lead, it should be caulked well with caulking tool and finished at 45 degrees to the pipe. Lead in excess should be removed.
Leak proof fixing of Rainwater pipe joints: While jointing CI pipes used as Rain Water pipes with cement mortar, fill one third of space in the socket around upper pipe with spun yarn soaked in blown bitumen of 85/25 grade and press it well with caulking tool. Fill remaining space with 1:2 cement mortar. Don’t add more than 30 percent water for making cement mortar. Caulk it well with caulking tool. You must finish it at 45 degree slope. Well cure this cement mortar for seven days by putting gunny bag pieces around each joint and keeping them moist.
Leak proof roofing
Here comes the last but most important part to handle. It has been noted that leakage from the roof slab has a negative effect on the health and psychology of inhabitants of a building. It gives rise to a sinking feeling besides damaging the health and longevity of a house. Thus, all precautions must be taken to guard against dampness and leakage during the laying of roof slab. As mostly RCC roof slab is used in houses, we will discuss a few very important steps here:
Provide proper slope: Always provide proper slope to the roof towards the rain water pipes. Keep this slope as One in 60. If there are a number of rain water pipes, divide the roof area into pockets and slope each pocket towards the nearest rain water pipe.
Keep the rain water pipes covered with iron gratings so that no debris or stone pieces etc., fall inside them and block them. If you are able to keep the rain water pipes choke-free and allow no rainwater to stand over the roof by providing proper slope to it, you have almost clinched the issue.
Pre-monsoon check: Before the onset of monsoons, get the roof of your house cleaned of all the debris, tree leaves, etc. See if there are any visible cracks on it. Get them repaired with water proofing material or cement grout. This is important, as in addition to drain off the rain water, you are not to allow its entry below the topping. This water is entrapped in between the slab and the roofing material and later surfaces on the underside of the ceiling. Check all rain water pipes. All the pipes should be free of debris and choking material. You are now ready to welcome the monsoons.
Provide bearing plaster and joint: Always provide bearing plaster on top of brick walls before laying of RCC slab and giving bearing to it on the walls. Cure this bearing plaster well, allow it to dry and then apply bitumen coats on it before laying the slab on it.
Leave a gap of, say, 10mm between the edge of slab and end course of bricks while resting slab over the wall. This gap will take care of expansion of slab during summers, will allow the slab to expand and no cracks shall appear in the slab. Fill this gap with sand or a compressible material so that nothing else undesirable is filled in it. Don’t use thermocol to fill the gap. Shaltex, like compressible board, is a good choice.
Roof slab coating: In general, roof slab is well cured after its laying, allowed to dry and then covered with two coats of 85/25 grade bitumen laid hot at a consumption of 1.65 kg per sq. meter per coat and then sanded. This technique has a number of flaws. Slabs are not allowed to be fully dry, bitumen used is not of good grade and its density is not maintained. The end result is that its application doesn’t bring desirable results.
It is preferable to apply two coats of waterproofing compound. Don’t use any non-flexible compounds. Use breathable, flexible, cement-based compounds, such as Conpro WP 2. Apply two coats of it, and then lay the topping materials.
Roof topping: A variety of materials is used by people as roof topping. Some people prefer Kota stone. Some go for marble, some prefer brick tiles and others prefer ceramic porcelain tiles. Brick tiles don’t look that good but remain the cheap and best material if well grouted and finished with flush pointing. Otherwise, ceramic porcelain tiles of tough type and Group V, laid and grouted well is a good choice as these serve the aesthetic purpose also. Prefer not to use Kota stone or marble as roof topping. These are porous materials and entrap water, causing trouble for the house owner.
Seal well the parapet joint: Often, the parapet joint is a source of leakage. So seal it well. To do that, leave the cement plaster on the inner surface of parapet above the level of roof topping. Lay the topping on the slab.
Generally, mud plaster is provided over the slab followed by a three inch layer of earth as these act as good insulators and also keep the house warm during winter and cool during summers. Over these two layers, tiles are laid and grouted. After doing this, make a water proofing course all along the junction of parapet with the roofing top. This course should consist of cement concrete mixed with water proofing compound and its size should be around one inch diameter. Now, finish the inside plaster of the parapet over the water proofing course.
These guidelines can help in completely water proofing the house and may succeed in keeping the evils i.e. cracks, termite, dampness and leakages at bay.