Technical -Reinforced Concrete
Habitable / Grade 3
What are my options?
This page will set out your options for combining systems. At the bottom of the page you will find links to a BS8102 overview, NHBC, Premier and third Party warranties and the types of waterproofing.
The British Standard BS8102 says you have to consider 2 forms of waterproofing if the risk of a leak is high, or the consequences of a leak are unacceptable. Insurance companies will insist that you employ 2 forms of waterproofing and that the system is designed by a CSSW qualified designer.
MacLennan do not use or recommend concrete additives because concrete is watertight. Water can only come through a concrete structure where there are cracks or defects.
If you have a crack or a defect they will not have any benefit from additives as the additives do not fill the defects and are not present in the defects.
You cannot rely on external membranes on there own, It is proven in law ( Outwing case 1990 ) and accepted in the industry that type A external waterproofing cannot be installed defect free.
All codes of practice and insurance
companies require designers to consider the form and feasibility of repair in the event of a leak.
This is why MacLennan will always install a cavity drain system, and either Type A if gas mitigation is required
or an applied Crystal Coat to provide a Type B structure.
If you are building a basement for accommodation or recreation, you are required to achieve a Grade 3 Habitable basement to comply with BS8102 the British Standard for earth retaining structures.
If there is a high-risk of a leak, such as in a high water table, or if building a basement where the consequence of a leak is unacceptable, then you should have 2 forms of waterproofing. External waterproofing is difficult and sometimes impossible in piled construction.
External waterproofing cannot be installed in inclement weather and can effect programmes for weeks on end in poor weather.
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First / Primary Form of Waterproofing
The concrete box forming the basement should be well constructed with correctly placed hydrophilic strips or, better still, water bars.
We recommend the use of additional joint detailing and crystalline slurries to create a type B watertight structure.
The water bar we recommend is fully serviceable and comes as a hollow hose wrapped with hydrophilic material. In the event of a leak, the hose can be filled with acrylic resin or Polyurethane, or even cement grout to repair defects in the concrete structure such as cracks, shrinkage voids, or honeycombing. All of which are common and sometimes unavoidable in concrete placement in normal site conditions.
A concrete structure without waterproof additives that is well compacted, isn't honeycombed and has well prepared and detailed joins with water bars, will provide a Type B structure. Crack control can be employed by the engineers to provide additional waterproof properties to the construction if required.
Service entries need to be well designed to ensure that they are watertight but can also be easily remedied in the event of damage externally.
To this end, pipes and cables should be separated by 20mm and come through the entry in a manner where they are supported but can be moved within the duct for remediation with resin filler if required.
Waterproofing Concrete with Crystalline Slurry
Crystal Coat is a concrete waterproofing system applied to the concrete after it is poured and the form-work is struck.
Concrete additives are commonly applied to the concrete mix before it is poured. This means that when concrete cracks or becomes damaged and results in water ingress, the additives are of no benefit. MacLennan use Crystal Coat to waterproof concrete as the system is applied once the concrete has set but is normally still green. Crystal Coat is absorbed into the concrete and reacts with free lime to repair the defects by effectively filling them, providing a once again waterproof structure.
This system is effective, proven and acceptable to all major insurers.
Crystal Coat for waterproofing concrete is less expensive and more effective than additives, and provides the first part of the MacLennan fully insurance backed guaranteed waterproofing system.
Second Form of Waterproofing
From a design point of view Type C is mandatory to comply with BS 8102 2009 for a habitable basement.
Type C waterproofing is a cavity drain, often in the form of a plastic membrane with drainage that is built into the structure behind walls or linings.
It is essential that drainage is reliable or that the system is pumped. The pump design is critical.
It is the most effective form of waterproofing for cobvious reasons. If the waterproofing system leaks for any reason, you have to be able to resolve the problem with minimal disruption to the occupier. You cannot do this with A or B systems.
The cavity drain system is now favoured by all insurers and used by all reputable designers because industry professionals are aware of the issues associated with external membranes and concrete additives.
The system is not designed to allow water in and then manage it. The basement is built as watertight as possible (1st form of waterproofing) , however as the industry knows, it is difficult to guarantee a successful watertight basement construction in normal site conditions. The cavity drain is installed as the serviceable, repairable and guaranteed waterproofing system which then ensures compliance with insurers and British Standard requirements.
Before building a basement, ground gas has to be taken into consideration.
If testing proves thatf Radon, CO2 or Methane are present then the basement has to be designed so that the gas cannot enter the basement structure.
This can be achieved with the waterproofing system.
Deck & Roof Waterproofing
If the basement is not completely covered by the house above, as is often the case, then you will have a deck or roof to waterproof.
The deck waterproofing should always be carried out by the same waterproofing specialists who waterproof the basement, as the detailing between the two is critical and split responsibility should be avoided at all costs.
In the last few years, deck waterproofing has moved away from single ply membranes and felt which have a history of failure due to the numerous laps, joins and seams.
The industry is moving towards, seamless, fully bonded, elastomeric applied systems such as Polyurea and Polyurethane.
Finishes on decks include green roofing and hard landscaping or even driveways and parking areas.
Due to the large number of products with different properties available on the market, the deck/roof waterproofing should be specified by the waterproofing specialist and the work guaranteed and insured for design, supply and installation by the same company.
Reinforced Concrete - Technical Download Area
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What else do you need to think about when waterproofing a basement?