Technical - Damp Brick Basement
Habitable / Grade 3
What are my options?
The basement is damp but has never flooded. All basements are at risk of flooding unless they have a suitable waterproofing system installed.
You cannot design from the past you have to design for the future.
Waterproofing cannot be patch repaired. If it is damp, it has failed and has to be replaced. If walls are damp, finishes and decoration cannot be installed.
The options for waterproofing are cement renders, coatings or Cavity drain.
Brickwork is soft, and probably laid in Lime mortar. If the walls have been damp for a long period of time it will be contaminated with salts.
All applied mortars and coatings rely on the strength of the substrate which in older buildings is a weak lime mortar joint and soft brick.
This completely rules out any applied cement renders, epoxy, or cement coatings for effective long term waterproofing.
The only suitable system is a cavity drain system. The cavity membrane will not damage the substrate and is de-mountable so more likely to be acceptable to conservation officers.
It does not require much preparation and will accommodate normal movement which renders will not.
It can be finished with any plaster or dry lining system so can be re-decorated as soon as dry. It is quick to install, with less mess and should be less expensive than any properly installed cement tanking system.
It is the only system that can be guaranteed without caveats with regard to movement.
The Existing Basement
To install waterproofing; The walls should be sound with no voids and no loose plaster.
It is critical that all timber is removed from the walls and that timber joists and beams bearing into the wall are dry or isolated.
The floor has to be thick enough to accommodate a 50mm channel, or the ceiling height has to be great enough to accommodate a 50mm insulation and 65mm screed.
Other options can be provided if the heights are limited.
It is critical that a channel is installed at the wall floor junction
It is also possible to retain existing feature or historic floors by removing and replacing over the waterproofing system once installed. see images of a brick floor which had to be retained as part of our design.
Get in touch with our technical team today!
The Membrane System
The Cavity membrane is a modern plaster lathe.
The plaster lathe can be meshed to bond Plaster, lime mortar or cement render too, or it can be unmeshed with very few fixings for dry linings or independent Gypliner frames or even an internal skin of brick or blockwork if space allows.
The system can be installed over nearly any sound substrate including stone, flint and earth walls such as cob.
Water will be managed to a sump and pump system. A 1m x 800mm hole will be required for the installation.
The basement finishes, fixtures etc all need to be removed including stairs and door linings.
An engineer should be instructed to discuss and agree floor slab options.
All electrical and plumbing fixtures should be removed leaving one tap and one socket for use during the work.
All existing and proposed service entries should be discussed and detailed by the waterproofing contractor.
Environmental Controls
It is critical that you consider the internal environment of your new basement. You need a relative humidity of between 45 - 65 rh.
MacLennan will prevent any water penetrating into the basement affecting the internal finishes by installing a well designed cavity drain system.
The design team has to provide suitable heating and ventilation system to prevent condensation and create a comfortable environment for the intended use of the basement area.
A critical element of any basement waterproofing design is the sump, pump and drainage system.
You have active leaks or even flooding MacLennan will calculate flow rates in and flow rates out for suitable pumps.
The pumping system will be designed to cope for an agreed worst case scenario.
Ground Gas
Before building a basement, ground gas has to be taken into consideration.
If testing proves that 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.
What else do you need to think about when waterproofing a basement?
