Whenever given a waterproofing strategy or proposal to review, there are few details that are required in order to provide a functional design. These are:
• The topography and type of the ground
• The type of structure
• The internal use
• Drainage of ground water (if required)
Once these elements have been obtained you will be able to create a design.
Knowing how the structure interfaces with the topography of the land is key. This will help identify if the property is going to be subjected to a rising bed of water.
On sloping sites, a cavity drain membrane system can be used in conjunction with a beam and block floor. This can drain to a sub-floor void if, the sub floor void will remain free draining. This can be achieved either by its ground type, or, connect to drain that will remain free flowing and to point lower than the internal slab level.
Conversely, if there are no points of drainage that can be guaranteed to remain free flowing, then a cavity drain membrane system would require mechanical extraction.
Presently, the only method of utilizing the wastewater from the cavity drain membrane system, is to dilute and mechanically extract water from condensers, dishwashers and washing machines. However, the pump often requires an upgrade from the standard cavity drain membrane pump used.
Throughout the UK a common method of constructing basements is using a re-enforced concrete frame due to its strength, durability, versatility. To achieve a better-quality concrete that is denser and then by design, better able to resist the passage of moisture, the following methods may be considered by the engineer:
• Lower water/cement ratio
• Use of plasticizers, not water to maintain flow
• Increase re-bar to reduce crack width
Some manufacturers can offer systems which incorporate injectable crack inducers. This prevents sporadic cracking and will allow for injection with a waterproof acrylic resin, post-installation of concrete.
Although more common on sloping sites, another method of building basements is the use of pre-cast concrete infill blocks. The structure that holds 2 leaves of formwork, that creates the block, can prevent proper vibration of the concrete. Therefore, creates a more cavernous structure, which will allow water to pass through to the internal environment.
This doesn’t prevent the structure from being sealed from water, but it may put more strain on the internal protection system. As recommended in the BS8102:2009 (also dependant on the grade required by the client), 2 forms of protection should be used i.e. an externally applied membrane and internal cavity drain membrane system. The BS8102:2009 provides guidance to specifiers of what grade would be required. Please see below.
Grade 1 – Some water tolerable e.g. Car park
Grade 2 – Some damp tolerable e.g. Plant suitable for a humid environment
Grade 3 – Dry – Incorporate ventilation. Habitable.
Each system relies on a, or a combination of, waterproofing systems classified below;
Type A – Barrier protection (Cementitious slurry)
Type B – Integral Protection (Waterbars and injection)
Type C – Drainage protection system (Cavity drain membrane)
Most A & B systems in isolation will offer a grade 1 or 2 environment, other than a few exceptions on the market i.e. injectable crack-controlled concrete.
The most common and risk adverse system to use for a Grade 3 environment, is a cavity drain membrane system and if possible, in combination with another waterproofing system.
This cavity drain membrane system can be used on most substrates and requires little preparation, compared to liquid applied systems. The membrane creates a cavity which acts as a depressurization layer. The water trickles down to a channel void former which sits at the wall floor junction. Holes within the channel allow the water to drain out an open elevation, or into a sump and pump system.
The system can be installed with a battery back-up system to allow for continual pumping, even during a power outage. Manufacturers offer different systems for different levels of monitoring and back up protection.
Sovereign would be more than happy to assist you with your design to ensure the correct grade is achieved.