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Tuesday, 10 June 2014

Concrete floors - hate them!

Typical suggestion for a replacement concrete floor

My house is a very typical Victorian Welsh terrace. Solid walls made from a mix of local and imported stone, bricks around the windows, doors and chimney etc. It has also had the typical 'improvements' over time:

Replacement windows
Replacement stairs
Replacement tiles
Toilet moved inside
Rendered with a water proof concrete
Chimneys blocked and replaced with gas boiler and radiators 
etc etc

One of major changes was the replacement of the old suspended floor with a new concrete one. This is proving to be a real pain.

What happens when people replace a suspended floor is that they line the new floor with a Damp Proof Membrane (DPM) underneath and fold it up around the edges of each room. This is meant to tie in with a damp proof course (DPC) in the walls. Unfortunately this is a real weak point as injected DPCs are not very reliable (due to poor installation and not really being the ideal solution in the first place - but it is quick and cheap!) So what happens is that the damp (that was under the floor and previously being wicked away by a healthy draught under the floor boards) now has to find another way out. It does this be focusing on the internal (and external walls) through the foundations of the building. It is carried up by capillary action into the walls (this should be stopped in theory by the DPC, but often is not). If the old plaster was left there then it would travel through this and out into the internal environment (this is why internal ventilation in an old building is really important), however what happens is that the old plaster is removed and replaced with a water proof plaster. This effectively seals any water into the wall and hides it from view. Hooray!?!?

In my house what has happened is that this water has appeared above the new plaster and also crossed through it - water is a persistent beast. So it is my internal walls that are now giving me hassle. The external ones I have largely dealt with by removing the cement render and also creating a drainage channel around the house, but the internal ones!! I recently did a quick damp meter check on the walls and where the external walls are now giving me a figure of 7 - 10% damp but I am getting 30% on the internals. Needless to say the dehumidifier is running on our free PV electric during the day now to try and dry the walls out during the summer months. I will have to re-inject as well to try to slow the next batch of damp that will no doubt be keen to get into the walls. I might even bite the bullet and get a physical DPC installed. The dust, the dust!!

So as a word of advice don't install a concrete floor in an old house, refurbish the old suspended floor, insulate it, ensure that the vents are clear and working etc as it will save you a lot of headaches in the future. If you are really keen on removing the wooden floor then look at using a limecrete floor solution, anything but DPMs, DPCs and concrete!