by Refresh PSC »
Thu Apr 26, 2012 8:18 pm
I realise this is a reply to an old post but I thought it might come in handy for anyone thinking about waterproofing/tanking your basement/cellar either now or in the future.
Before I continue, please note that the majority of below ground areas will require some kind of drainage services to move any ingressing water out of the area. I will not go into drainage in this post as each area is different and certain calculations have to be met with regards to water pressures, available local services, local drainage regulations etc etc etc. I would recommend in every instance you request the assistance of your waterproofing material supplier to help you in these matters before you even attempt to waterproof your own cellar or basement. You only need to make one mistake and you can potentially allow your basement to flood causing damage. It IS possible to waterproof your own basement with this system but please please please make sure you know what you are doing first and you have everything you need. Do NOT cut corners. This is only a very brief introduction to CDM's
Cavity drain membranes (CDM) are usually polypropylene sheets that are dimpled a but like an egg box. They are used to line walls and floors of basements to provide a dry internal space.
unlike other systems such as waterproof renders and waterproof slurries which are designed to prevent water coming in, CDM's are designed to allow the natural ingress of water through the walls and floors and divert it away from the internal living space and into a drainage point such as a local gulley or specially designed sump pit housing a pump.
CDM's are becoming the preferred method of waterproofing below ground due to a number of reasons, they are a physical barrier as opposed to a chemical barrier, they are relatively quick to install and they are longer lasting due to the fact they are not resisting water pressure and made from an inert plastic.
Speak to either Delta Membranes or Safeguard Europe. They are 2 of the UK's biggest suppliers of CDM's, they will provide you with everything you need to complete your basement waterproofing project with not only the supply of materials needed but advice on what you'll need and how to do it.
Firstly, to measure up how much you'll need you need to know the quantities available. Standard size cavity drain membrane rolls for walls are 2m x 20m x 10mm so you get 40m2 per roll and 2m x 15m x 20mm for floor membrane = 30m2.
Work out the height of your wall x length, so a standard headheight of a room is around 2.4m, multiply that by the length of each wall and you will get the square meterage per wall. Add those amounts together and hey presto, you've got your total square meterage.
For example, a room measuring 5m x 8m x 2.4m will require 62m2 of CDM. It's a good idea to add around 10% for your overlaps and offcuts so lets call it 70m2 needed for walls.
@ 40m2 per roll, you'll need 2 rolls of standard 10mm, to do the floor with the 20mm membrane, you'll need 40m2 + 10% = 2 rolls.
To go with that, you'll need sealing joint tape, overseal tape and fixing plugs.
Dependant on how you apply your membrane (either in vertical strips or running the roll horizontally around the perimeter) will dictate how much tape and the amount of plugs you use. Speak to the supplier and they will be able to advise.
Sealing tape is used to join to layers of CDM that are overlapping (sandwiched inbetween the two sheets)
Overseal tape is used to seal over a join of where two sheets meet. Overseal tape can also be used to wrap around any penetrations through the CDM such as pipework and/or cabling.
With the fixing plugs, there are different types, but the main one used is dual purpose, not only does it hold the membrane onto the wall but provides a fixing point for future battening. These plugs have a rubber/foam gasket just under the head of the plug which when hammered home, provides a waterproof seal. You would drill through the membrane with a 10mm drill bit and then hammer in a fixing plug.
I normally install these plugs in vertical lines at 600mm spacings in order to facilitate subsequent battening and plasterboarding (each vertical line would have an average of 4 plugs on a standard height wall)
I am not going to go into depth about overlaps, how to lay the membrane, how to seal junctions and joins as this information can be found freely on numerous supplier sites.
When the CDM has been installed to the walls and floors, I always insulate and screed the floors before installing battens and plasterboard in order to get the right heights.
You can then batten directly onto the fixing plugs using a 2" 12 screw and some 25mmx50mm timber battens. I usually space my battens at 600mm centres as standard 2400mm x 1200mm plasterboard fits nicely with those measurements but you can choose your own spacings to suit.
When this is all done, plasterboard and skim finish.
If done correctly with adequate drainage and ventilation, you should have a completely waterproof space.
I realise that this is a very rough and brief introduction and explanation but hope it helps someone.
