eBusiness Weekly
Engineering and Construction Matters
With Innocent Chatikobo
Waterproofing is a process designed to prevent liquids from entering a structure. Some measures of moisture control are provided during construction while some waterproofing materials are applied after the structure is built to eliminate any problems that may be encountered.
During repairs of walls, before repainting the walls must be waterproofed. Moisture penetration into a building causes the structure to deteriorate, causing discomfort as it changes the microenvironment.
Structure deterioration is also a health hazard. Measures should, however, be taken to prevent moisture penetration. The Model Building By-laws define the following modes of moisture penetration prevention.
Damp proof: having the ability to prevent the passage of moisture in the absence of hydrostatic pressure
Water proof: having the ability to prevent the passage of water under hydrostatic head
Weather proof: having the ability to prevent the entry of water into a building under unobstructed conditions of runoff.
This article will simplify the information as contained in the Model Building By-laws Chapter 6 Part 1(Section 1-9)
Waterproofing methods
Waterproofing systems can be installed indoors or outdoors, depending on the level of water damage or the owner’s preference. There are different methods of waterproofing. The most popular methods are:
Cementitious waterproofing method – application of a cement based coating or slurry to the surface to provide a waterproof barrier. This also includes additives like the one popularly referred to as impermo
Liquid waterproofing membrane – application of a liquid coating or membrane to the surface to prevent water from penetrating eg rubber or plastic applied using roller or brush.
Bituminous membrane waterproofing method – use of a sheet or membrane made of bitumen and a reinforcement layer such as fibreglass or polyester
Polyurethane liquid membrane waterproofing method – used for flat roof areas exposed to weather eg balconies, terraces, water tanks, roofs, damp walls, parking decks/bridges
Rubberised asphalt – use of a mixture of asphalt and rubber to create a flexible, durable waterproofing membrane.
General requirements for damp proofing and waterproofing
Water proofing and damp proofing should be provided in the erection of every building
Water and moisture must be prevented from entering the interior of every building unless where it is allowed to enter through weep holes to sump / collecting point where it should then be pumped out
In some cases, the local authority may permit the omission of damp proofing or waterproofing in any building in which there are no habitable rooms.
It can also be permitted provided it has been proved beyond doubt that no danger to the health of persons or to the stability of the building will be caused by the entry of moisture or water into the building.
Damp proofing and waterproofing materials should comply with standards or be of material approved by the local authority.
Mastic asphalt damp proof courses should be applied in at least two layers.
Every horizontal damp proof course (dpc) shall be constructed to the full width of the wall resting upon it , and should also extend the full width of any wall plate which may rest upon the doc
Vertical dpc — in some walls a vertical dpc is required which is positioned between walls from the horizontal dpc upwards
Importance of waterproofing
Increases durability, longevity and sustainability of buildings
Protects from water damage and infiltration
Increases the value of your home and improves structural integrity
Prevents cracking which may happen due to free thaw cycles or water pressure built up behind walls
Protects occupants from potential health hazards caused by mildew(fungi) and bacteria build-up in damp areas
Protects underlaid reinforcement steel from moisture and damage
Reduces energy costs by preventing moisture from entering the building and reducing the load on heating and cooling systems
Improves indoor air quality by reducing moisture content, which can reduce the risk of respiratory issues and other health problems
Positions of dpc on the walls
Damp proof course is positioned on all points that are potential entry points for the water into the walls.
These points include:
150mm above the highest ground level
Below a window chill
Immediately below the chimney cap
Immediately below the coping of a parapet wall or any exposed wall
Below the lowest member of a suspended / timber floor
Below the wall on underground structures
Below oversite concrete
Before casting of concrete slabs and underneath gravel pack for pavements, black plastic sheeting is also used for prevention of moisture rising up from the ground and this sheeting is known as damp proof membrane.
Qualities of a dpc
It should be flexible
It should be durable
It should be easy to apply
It should be strong enough to withstand loads
It should be impervious to moisture
We shall continue the topic next week as we look into types of dpc, applications of water proofing systems, flashings in buildings, etc
Innocent Chatikobo is an Engineer by profession with AtroServe Engineering Zimbabwe. He has extensive knowledge and experience in Structural Engineering and Construction. For your comments, views, questions and feedback he can be contacted on the following platforms. Cell: +263 777 950 224; +263 712 376 037; +263 782 502 732. Email: [email protected] <mailto:[email protected]>
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