I'm starting to do some renovation work in the living room of my 1820's cottage. The construction is basically a concrete floor slab and double thickness brick walls with no air gap in between. However, I have noticed that in some areas the concrete slab goes all the way to the brickwork, but in other areas the plastering goes below the level of the concrete floor, as if the walls were plastered first and then the concrete slab added. I suspect that the floor has possibly been re topped at some point after the plastering. Which of these methods is correct, and does it actually make any difference.
Concrete floor and brick walls
- Thread starter roofmog
- Start date
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1820's cottages didn't have concrete floors.
Whatever concrete is down there should be a membrane (a DPM) below it - it will show behind your skirtings if its there.
Plaster should finish about 40mm above any concrete floor contact.
Is the FFL higher than the external ground level?
Do you have any existing damp problems or signs of damp or condensation?
Whatever concrete is down there should be a membrane (a DPM) below it - it will show behind your skirtings if its there.
Plaster should finish about 40mm above any concrete floor contact.
Is the FFL higher than the external ground level?
Do you have any existing damp problems or signs of damp or condensation?
I guess that the original floor was tiles and that at some point a concrete slab was added, possibly more than once. There is no sign of a DPM but I assume there must be something, otherwise the whole slab would presumably be damp. The plaster/render is sand based and topped off with a skim of some kind. Again this skim continues below the level of the concrete in places, which leads me to believe that somebody who didn't really know what they were doing added an additional layer to an existing floor.
There is no sign of damp in the render except for one corner where a gap in the concrete had allowed moisture to be sucked up into the render. (Which was how I discovered the anomaly in the first place. - see picture).
What is the thinking behind the 40mm gap between floor and plaster, and would it make sense for me to remove the bottom 40mm of plaster all the way round the room to decouple it from the floor?
It is quite hard to tell if the finished floor level is higher or lower than the external level as the external level is very uneven an so it probably varies. Also the external walls are surround by an 8 inch wide trough that is filled with gravel. Never quite known why.
Condensation is not a problem, nor is damp apart from the previously mentioned corner. This may be because I have a large open fireplace and chimney which helps regulate the atmosphere in the room.
Thanks for your reply
There is no sign of damp in the render except for one corner where a gap in the concrete had allowed moisture to be sucked up into the render. (Which was how I discovered the anomaly in the first place. - see picture).
What is the thinking behind the 40mm gap between floor and plaster, and would it make sense for me to remove the bottom 40mm of plaster all the way round the room to decouple it from the floor?
It is quite hard to tell if the finished floor level is higher or lower than the external level as the external level is very uneven an so it probably varies. Also the external walls are surround by an 8 inch wide trough that is filled with gravel. Never quite known why.
Condensation is not a problem, nor is damp apart from the previously mentioned corner. This may be because I have a large open fireplace and chimney which helps regulate the atmosphere in the room.
Thanks for your reply
There's not much you can do about the no-membrane situation but the regulated room temp will help enormously.
Yes, cut a 40mm gap to break plaster to floor contact. Its to prevent any moisture from the floor creeping up behind the plaster.
The area shown in the photo: hack off to brick about 300mm beyond any damp signs. Render back up with sand and cement or sand and lime. Fill the floor gap with semi-dry sand and cement.
The trough around the house is a French drain - it should carry water away fro the walls but could be old an need investigating.
Best practice with solid floors is for the FFL to be 150mm above the ground level. But its obviously not always possible.
If your structure is rendered then carefully examine every inch of it for hollowness and cracks or ground contact.
Yes, cut a 40mm gap to break plaster to floor contact. Its to prevent any moisture from the floor creeping up behind the plaster.
The area shown in the photo: hack off to brick about 300mm beyond any damp signs. Render back up with sand and cement or sand and lime. Fill the floor gap with semi-dry sand and cement.
The trough around the house is a French drain - it should carry water away fro the walls but could be old an need investigating.
Best practice with solid floors is for the FFL to be 150mm above the ground level. But its obviously not always possible.
If your structure is rendered then carefully examine every inch of it for hollowness and cracks or ground contact.
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The external render is in contact with the gravel in the French drain. Is this wrong?DIYnot Local
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