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An Introduction To Damp & Waterproofing

The lack of damp proofing is the cause of most defects in structures. It is important that architects, contractors, developers, inspectors or any party concerned ensure that damp proofing systems are installed correctly. It is also important that the correct materials are used. Most damp proofing applications are in the form of sheets of PVC or malthoid used in various areas.

Are you building a problem?
You´re investing a lot of money in this project. With damp causing the walls to effloresce, and surface finishes such as carpets, floor tiles and wall cladding to deteriorate and decay. It makes good sense to attend to damp proofing needs at the construction stage, at a fraction of the cost of your building.

To remedy a damp problem at a later stage is costly and labour intensive. And it is wise to insist on recognised manufacturers like Gundle, because Gundle manufactures specially formulated plastic sheeting for each damp proof application. Damproofing systems account for less than 1,2% of the building cost of an average structure. Visit for more info.

Water Containing Structures

Permastop - Concrete Penetrating Waterproofer
A cement-based mixture containing chemicals which combine with the water in the cement and migrate into concrete plaster thereby effectively waterproofing the structure against hydrostatic pressure. For slurry coatings and plugging holes.

Supplied as a dry grey or white powder for mixing with water. Suitable for permanently waterproofing, in all climates, structures such as basements, cellars, reservoirs,dry docks, bridges, tunnels, sewers, hydro-electric stations, retaining walls, lift shafts, machinery pits, grain silos, underground in mines, magazines, subways, underground telephone structures, etc. Can be effectively applied to outside or inside of structures.

Permastop is only effective on cement surfaces such as clean concrete and cement plaster, and will not work on painted or other surfaces. Coverage as a slurry coat: 1:3 square meters/kg/coat.

Flexbond - Portland Cement Admixture
A non-toxic latex-based liquid admixture for Portland cement plasters, screeds or concrete. It's purpose is to replace some or all of the water in cement mixes to improve bond, waterproofing, flexural, tensile and abrasive strengths, adhesion, thin film hardness, weak acid resistance, adhesion to asphalt and drying shrinkage. Avoid use of Flexbond in freezing weather and protect from freezing in storage.

Applications: Waterproofing water containing structures such as reservoirs, water features, fish ponds etc. Used in conjunction with Cemcrete's Polypropylene Membrane for cracks and joints in structures, improving adhesion of slush-coat for re-marbeliting, patching, repairing or re-screeding floors.

Improving adhesion and waterproofing qualities of: Cemcrete's Tile adhesive, Cemcrete's Tile grout, Cemcrete's self-levelling floor screed.

Waterproofing Unpainted Cracked Reservoirs:
Acid-wash the walls and floors of the reservoirs using a solution of 1 volume hydrochloric acid (spirits of salts) and 2 volumes water. Allow the acid to act for about 10 minutes then wire brush and flush with water. Allow to dry. Hack out cracks. Wire brush internal surfaces of cracks.

Fill cracks with a mix of 1 cement 2 plaster sand mixed to a stiff paste with a solution of 1 litre Flexbond and 1 litre water. When filling is hard and dry, mix 1 litre Flexbond 1 litre water and sufficient cement to produce a pourable slurry. Cut polypropylene membrane into convenient widths, dip into slurry, apply over filled cracks and smooth down using gloved hands and finally paint the membrane with the slurry.

Coverage: 1 litre Flexbond, 1 litre water, 4 kg Portland cement will cover 1,2 square metres using Cemcrete's polypropylene membrane. If it is desired to paint the entire internal surfaces of the reservoir after cracks have been repaired this may be done using the same mix of slurry.

Coverage: 1 litre Flexbond, 1 litre water, 4 kg Portland Cement will cover approximately 20 square metres/coat. Allow all work to dry and air cure for 4 days before filling the reservoir.

Polypropylene Membrane
Polypropylene membrane is a geotextile having a random arrangement of fibres ensuring uniform strength and flexibility in all directions. Its alkali resistant properties enable it to be used in conjunction with Portland cement-based slurries in water-containing structures to seal over cracks and joints. Used in conjunction with Permastop or Flexbond/ cement slurries for waterproofing reservoirs, etc. Polypropylene available in bulk or cut in 10m x 100mm strips.

Siliconseal - Solvent Based
A low-viscosity penetrating liquid for application to vertical surfaces of masonry or concrete by brush, roller or spray. It is designed to penetrate the surface up to the depth of 10 mm, making the capillary passages water repellent. This prevents the passage of water but allows the masonry to breathe and dry out. Also useful for preventing rising damp in brickwalls by pumping the fluid into previously drilled holes along the course of bricks immediately above the faulty damp-proof membrane.

Coverage: Face bricks 6 sq. metres/litre

Porous bricks 3 sq. metres/litre

Concrete 4 sq.metres/litre

Water-Repellent Cement
An intimate mixture of cement and Cemcrete's waterproofing compound, to obviate site mixing. Useful for producing water-repellent plaster, mortar and concrete.

An integrally fibre reinforced, waterproof, coloured cement-based concrete mixture supplied in dry powder form for mixing to a stiff mixture with clean water for construction of fish ponds and other small water features.

Coverage: 40 kg/0,7 square metres-30mm thick.

Colours: Sandstone, Granite Pink and Ironstone.

Matcrete and Flexbond used with Cemlam and Cemforce (Polypropylene matting) for repairing or construction of water containing structures.

Application: Building fish ponds, lining of channels, lining of soil dams, relining of pipes, repair of cracked reservoirs.

Cemforce is an open textured reinforcing (4mm x 4mm) mesh fabric, made of polypropylene strands and fibres. It was designed for use with cement matrices. It is totally inert to the alkalinity of cement and has an extended fibrous interface area with which cement matrix can interact and mechanically bond. The Cemcrete mixes are specially formulated to form part of the Cemforce, similar to fibreglass and resin.

Available in 1m & 2,6m widths up to 500m lengths.

Cemlam is tightly woven polypropylene tape with a 4mm x 4mm mesh fabric made of polypropylene strands and fibres laminated by hot extrusion forming a tough waterproof substrate. It is totally resistant to the alkalinity of cement and offers extended fibrous interface on the strands with which the cement matrix can mechanically bond. The cement matrix is specially formulated to form part of the Cemlam to act like fibreglass and resin. Available in 2m widths up to 250m lengths.

Flat Roof Waterproofing

In South Africa there is enormous variance in climatic conditions - from desert conditions to a Mediterranean climate. Temperatures can range from below zero to the mid-thirties. Whilst this, in itself, is not unusual, what does make it a factor in structural waterproofing is the fact that these variations occur all in the space of 24 hours. Rain, driven by gale force winds, hits some of the coastal regions and other regions go from drought conditions to floods. All these dramatic climatic conditions affect our building in one way or another and accordingly climate must be taken in consideration when designing structures. When drawing up specifications for flat roof merely to state Waterproofing strictly to manufacturer's specification can be dangerous philosophy to follow, as it will not always provide the required job. Poor specifying details are one of the major failures of waterproofing, and hence leak. Also, locating all the plant equipment on flat roofs must be planned carefully to prevent any problems with the flow of water and easy access to the waterproofing.

There are many waterproofing materials on the market, most of them good, but every material has its performance limitations. Unique emphasis is often placed on a material's guarantee, merely a warranty on their materials, ie. that it will be free of defects for a specified period. They certainly do not guarantee that their materials will work, regardless of the circumstances.

It also appears to be easy to operate today as a waterproofing contractor. There are many companies from which to choose, with more and more springing up all the time. Clearly the reason for this is that it is not a capital-intensive industry. These days, with the varied selection of available materials, however, coupled to the complexity of modern building design, many buildings are in fact neither straightforward nor simple to waterproof. A depth of experience and knowledge of the trade is essential to provide a waterproof building.

Designers, it seems, are constantly trying to create the most complicated structures, in order to test the ingenuity of engineers and the abilities of contractors to execute design work. It seems also as though designers expect the material to perform miracles in extreme situations. Not to mention, of course, the ludicrous time scales the clients set, time scales that barely allow the concrete to cure… and all for a suicidal price as well!

No wonder some buildings leak.

The design of the waterproofing to flat roofs is the first important stage, which takes place on the drawing board. It is not just a question of plotting dotted lines on a drawing: careful consideration and thought needs to go into the detailing but also the construction sequence. Can the principle be put to practice? It is always advisable to ask the advice of experienced waterproofing contractors who not only have the practical knowledge of fixing waterproofing systems but who also can demonstrate a long successful track record. Once the detailing is correct a suitable waterproofing system can be selected. The same details are relevant to all waterproofing systems, but specific requirements may call for certain specific systems ie. gussets at internal and external angles, or fillets formed in the material. An important factor which should be pointed out at this stage is that, in designing a watertight roof, the DPCs in walls, relevant to the roof, must be considered at all times. The waterproofing details must be correct, after which the right materials for the situation can be selected. Then the first stage to produce a leak-free building has been achieved. Correct detailing is possibly far more important than material selection, as there are a number of materials that will perform in the same situation.

Many of the waterproofing material manufacturers and suppliers offer warranties on their material and possibly sells their systems on guarantee. The old saying that ' A guarantee is not worth the paper it is written on" must seriously be taken into account when deciding on a waterproofing system. A history of the material should be obtained in the credentials of the manufacture checked.

Of course, the same also applies to the waterproofing contractor. In selecting the waterproofing contractor care should be taken to ensure that the company has the expertise and knowledge, the financial ability and the qualified manpower to carry out the work and to produce a first class job. Ideally, the company should be a member of the Waterproofing Federation of Southern Africa. It is important that the professional team, the building contractor, waterproofing material manufacturer/supplier and the waterproofing contractor work together as a team, and not against each other.

Supervision of all aspects of the work and frequent checks on site to ensure that the detailing is being done without any compromises is vital; especially in the case of major projects where many trades are involved. The main contractor and especially the other trades (such as plumbers, electricians, bricklayers and tiler), must all be made aware of the importance and principles of waterproofing. It is not always easy and on occasions impossible, to repair the waterproofing after it has been damaged.

In conclusion, the success of a "leak-free" roof lies in the initial design, selection of the correct material for the job and careful, uncompromised application by a reputable and experienced waterproofing contractor. There are no "wonder" materials. Prices and guarantees should not necessarily be the only, or main criteria applied when selecting and specifying waterproofing - and neither should it determine the choice of the waterproofing contractor.
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