Victorian House with Concrete Floor

dickieh1

Hi,

 I have just bought a Victorian semi detached house which is little more than a shell, although it does have radiators!  There is a concrete floor throughout the whole of the downstairs and no visible airbricks, although I am told by the neighbour that there was, at one time, a suspended floor.

 The bottom 4 inches of several internal walls are wet to touch and you can clearly see a 'damp' line, although the house has been empty with no heating or ventilation for several months.  Also at some point a few inches of plaster have been hacked off just above the skirting board on several internal walls, I assume to inject some chemical DPC (which was clearly a waste of time) and then re-plastered with gypsum plaster as have some entire walls. 

 I totally get period houses need to breathe for moisture to evaporate but am worried that the level of moisture/damp is above what is normal.  Ideally I would like to install 'wet' under-floor heating throughout the whole of the downstairs, though this could involve digging up the existing floor or if I can get away with it installing on top of the bare concrete  (I realise this will add several inches to the floor height)..... so....I would welcome any views on:

 i) installing under-floor heating in this case and any effect it might have on the 'damp'?

ii) if I should remove all of the gypsum plaster and replace with lime plaster?

iii) how to deal with the 'damp' walls.

 Thanks

grumbler

dickieh1 said:

Ideally I would like to install 'wet' under-floor heating throughout the whole of the downstairs, though this could involve digging up the existing floor or if I can get away with it installing on top of the bare concrete  (I realise this will add several inches to the floor height).....

Unless you want to heat a huge amount of concrete, a heated floor is a thin layer of screed with pipes lying on a thick (typically 10cm) layer of hard insulation. Without breaking the existing floor you are looking at adding about 6 inches.

Mickey666

Sounds like the house has already been ruined by people who have no understanding of older properties and their need to breath.  If only they had used limecrete for the floor and lime plaster for the walls it would still look the same but would not be having these problem.  Such a shame.  To answer your questions:

i) to install UFH will require digging up the concrete slab (which is a good idea).  Just be sure to replace it with a breathable limecrete insulated floor using something like foamed glass instead of cell tea.  Lots of info online - check out the Mike Wye website.
iI). Ideally yes, though you could try one thing at a time.  Maybe the UFH first?
iii) the two above actions might well be enough to sort the wall out.  Just give things time to settle down to their new equilibrium after making significant changes. It can take a long time for walls to fully dry out.  A rule of thumb is 1 month per inch of thickness, but there are lots of variables.  Basically it will need more than couple of days!

Meanwhile, do lots of reading (if you’re interested that is).  Lots of info at the SPAB and Heritage England websites.

frayedknot

Floors don't breathe though do they. There's an unlimited amount of damp under them and they just pump this into the atmosphere. Fine when we had coal fires and windows and doors that would let gales in. Not so good in today's hermetically sealed houses.

They didn't invent dpcs for nothing. Limecrete lets the moisture up.You can choose between wet floors or wet walls.  And good luck getting a builder to use it  , as soon as the word is out of your mouth he'll be running to his Transit.

tacpot12

My experience is more in line with frayeknot's comment - I had a Victorian terraced house where the original floor was quarry tile laid on bare earth. I hacked off a meter of plaster from the ground floor walls, installed a chemical DPC into the walls myself, and had a builder dig out the floor and install 4 inches of EPS foam, a polythene DPC and six inches of concrete. The walls were replastered with waterproof concrete, with a 4 inch air gap to the concrete floor that was covered by 5 inch tall skirting boards. Both the floor and walls were dry as a bone for the next 25 years. The house has just been sold, although the energy surveyor who did the EPC never believed me when I told him the depth of the insulation under the floor! Following a flooding event due to poor sewers, Severn-Trent tanked the cellar with a waterproof concrete, and that also remained dry as a bone.

I now live in another Victorian terraced house in a different part of England that has had a chemical DPC installed, but still has the original suspended floors. Again the walls are bone dry, and we have no other problems. The cellar is damp because is below the level of the DPC, but we keep a good airflow through it to prevent problems.

If your house had suspended floors, but now has concrete, the depth of the concrete might be substantial. As the thickness goes beyond 6 inches, the difficulty of removing the existing floor increases. You shouldn't drill through the floor to check it's thickness as you'll puncture the polythene DPC if there is one. However, if you look around the periphery of the floor, you should be able to see evidence of the polythene DPC if it is there - the edges should not have been cut off neatly level with the floor. If the floor has a DPC, I would leave it down and redo the chemical DPC and possibly the replastering. 

You have described the walls as having been replastered in part or completely with new gypsum plaster. It sounds like the chemical DPC could have been bridged by the plaster, but you would need to hack off some of the existing plaster or do a test drilling into the wall at a height of about 400mm to check whether there was concrete under the skim coat of plaster. If it is concrete, then it is very likely to be waterproof and there should be no issue if it bridges the DPC, and no need to remove it. If it is gypsum plaster throughout, you have found the source of the problem, and just been to replaster with waterproof concrete. 

Clearly I do not subscribe to the view that the floors of Victorian buildings need to breath, but then my experience of a water and vapour proof floor was entirely positive.

justwhat

How deep are your pockets? ....dig the floor out and use physical dpc , avoid  chemical if you can. Insulate the property well.
Trying to cure penetrating or rising damp in walls by using heat is a losing battle. 
Alternatively live in the house like the Victorian's did lol Well ventilated drafty with coal fires in many rooms.

FreeBear

frayedknot said: They didn't invent dpcs for nothing. Limecrete lets the moisture up.You can choose between wet floors or wet walls.  And good luck getting a builder to use it  , as soon as the word is out of your mouth he'll be running to his Transit.

A few of the members of the Period Property forum have installed limecrete floors over foamed glass - From the comments I've seen, the foamed glass provides a pretty good barrier to moisture in the ground, and the floors remain perfectly dry. Whilst there are a lot of builders that just don't "get it" with lime, a growing number are prepared to use the stuff. Attitudes are changing.

Mickey666

frayedknot said:

Floors don't breathe though do they. There's an unlimited amount of damp under them and they just pump this into the atmosphere. Fine when we had coal fires and windows and doors that would let gales in. Not so good in today's hermetically sealed houses.

They didn't invent dpcs for nothing. Limecrete lets the moisture up.You can choose between wet floors or wet walls.  And good luck getting a builder to use it  , as soon as the word is out of your mouth he'll be running to his Transit.

Ah, but you’re missing the point.  Today’s ‘hermetically sealed houses’ do indeed have effective DPCs to provide a moisture barrier to the entire house.  Older houses were not built this way and and moisture moving into the building is dissipated through ventilation.  A well ventilated suspended floor will dissipate and ground moisture well before it causes any actual damp problems.  However, in this case the house has been ‘improved’ by the addition of an impervious concrete floor that will prevent the dissipation of ground moisture and cause it to migrate to the walls where the increased concentration will cause a damp problem.  Probably the same cowboys that did this also tried to add an injected DPC in to the walls to get around that problem, despite the fact that injected DPCs are well know to be pointless at best and destructive at worst.  Basically, the house has been ruined by the injudicious use of modern materials/techniques on an older house.  There are plenty of houses with no DPCs that have no damp problems.

You’re dead right that most builders would ‘be running to his transit’ as soon as the ‘lime’ word is mentioned, but frankly running away is the best thing they could do when it comes to older properties

Also, moisture and damp are two very different things and the former need not lead to the latter.  You can demonstrate this very easily for yourself.  First, feel how dry your hands are.  Now put on a rubber glove, or maybe a small plastic bag sealed around the wrist with an elastic band.  After 20-30 minutes your hand will be soaking wet from the trapped moisture that normally would simple evaporate from your skin.  That’s pretty much what happens to an old house when it’s covered with impervious modern materials such as cement-based mortars and plastic paints.