Fixing damp in cob walls

[bondge]

We have a mid terrace 18th cen cob walled house with brick and flint exterior. There is a quite bad damp in the ground floor hall and lounge. As part of the renovations we have had several suggestions as to how to fix this but are unsure what to do. Key facts are:
The floor has original quarry tiles that have been set into a screed (probably concrete)
A damp proof injection has been made at least once into the cob walls
Vinyl paints on the walls
Flint on exterior have been cemented in using modern cement
The property has double glazing with no trickle vents
The loft has been well insulated
The house has been closed up for nine months
Will be used as weekend cottage
Electric radiators and occasional multi-fuel burner
We want the house to be warm when we come down and paint/plaster to stay on the walls

Choices:
Dig up floor, lay an impermeable sheet and concrete slab and insulate
Dig up floor, lay clay marbles, limecrete replacement quarry tiles
Strip back plaster and tank
Remove cement around flints and internally
Remove vinyl paint replace with clay based paint
Add trickle vents to windows
Put in pressurised ventilation system
Dig up part of floor and lay new quarry tiles on limecrete to allow floor to breathe
Leave floor repair lime plaster and improve ventilation - hope.

Any ideas?

 

[MatthewC]

We have a mid terrace 18th cen cob walled house with brick and flint exterior. ... A damp proof injection has been made at least once into the cob walls

Oh noooooooo!

Having picked myself up after seeing that one, if it has been shut up for a while, do you think that has made the dampness worse? Before doing anything, I would be inclined to live in it and leave it to see if things improve with "normal" heating and ventilation - which is probaly what you mean by your last option

Leave floor repair lime plaster and improve ventilation - hope

I would say that if you do dig up the floor then you really should lay a limecrete floor, not concrete. Why go to the trouble of digging it up and then lay the wrong stuff? The contact thing on the right has a link to my blog where I have described (April 2011) the limecrete floor I laid.

Matthew

 

[88v8]

Hello and welcome.

As I'm sure you realise, injection is quite useless. So is tanking. As there is no dpc, the walls will always suck a certain amount of water, depending on groundwater levels, and the consequent damp must be allowed to dissipate by breathing. Trying to shut out the damp is pointless. Indeed, if the walls are permanently damp they could collapse, they're basically mud after all.

At the moment, the floor is not breathing because of the cement, so any damp under the floor is being pushed into the walls.
Then the walls cannot breathe because of the vinyl paint and the cement render.

Being in a terrace, the house(s) next door may have similar ignorant anti-damp treatment, which could exacerbate the problems in your party wall.

As to the floor, I would go for your limecrete on leca option. No dpm. Quarries or stone bedded and pointed in lime. Not cement. Anyone who brings a bag of cement to the house is a menace and should be banished.
The finished floor will be a foot deep, so some investigation of the foundations would be advisable.

The vinyl paint needs taking off the walls, they can be painted with clay paint or limewash.

Externally, the outside of cob must have what is sometimes known as 'dry feet'. It has to be protected from damp. So there should be a good roof overhang and the gutters need to work, and the outside ground must not be high nor impermeable, ie tarmac, concrete. Cement render is a no-no as it does not breathe. Lime render is correct.

If you have lived in a period house before, you may know that the house may always feel slightly 'damp' compared to a modern house, and leaving it shut up for weeks will in no way help, especially without ventilation.

All this is going to run into some money. Or many weeks of your own labours. The people who can do such work - where are you? - are hard to find, often booked up and not cheap. If you are not living there they will be working unsupervised, all the more reason to seek the right people. Not cheap.
Don't wish to rain on your parade, but for a weekend cottage, you might want to harden your heart, sell it and move on.

Ivor

 

[formerly known as]

brick and flint external skin?

you must be in the east.

is the walling not clay lump / shuttered clay - as opposed to 'cob' ?

 

[Flyfisher]

Don't wish to rain on your parade, but for a weekend cottage, you might want to harden your heart, sell it and move on.

That was my first thought when I read 'weekend cottage', though I imagine it's not the sort of advice being sought.

As well described above, breathability and ventilation will be the key to success but having the house closed up most of the time will compromise both. There will be solutions but they will be expensive and time consuming.

 

[bondge]

Thanks for the responses. Fortunately I was ready for pain when we bought the place. I thought you might enjoy the range of solutions offered by the various people who have looked at the damp.
It seems the forum consensus is get it properly venitlated to see if it really does have a damp problem. We will be putting a kitchen and bathroom in an extension this autumn which, if we are going to do it, will be when we would dig up the floor (and yes lay quarry tiles on limecrete if we do this). We would love to keep the current original quarry tiles that someone has lifted then relaid in concrete so do you feel that digging the floor up and relaying is imperative? I doubt we will be able to salvage the tiles if we dig them up.
Selling on is not an option - we need to get the house back to where it deserves to be.

 

[JanieB]

I had a surveyor round a few years ago for advice as to how to go about making my house into something more liveable. It had been "modernised" in 1981 and the owners at the time did some diabolical things to it. Some things I would love to undo but am constrained by finances so I have to put up with the concrete floors and tanking 18" up the walls.

I made the mistake of putting vinyl paint on the walls. It didn't stay on so I've used a paint that breathes. The surveyor pointed out that two of the internal walls had been external in the past and were cob with no foundations and they needed to breathe. He advised reopening the inglenook fireplace and putting in a woodburner. I've had no heating or hot water for two winters now but the house has survived it marvellously with open fires and the draughts that come through the old doors and windows.

I'm not going through another winter like that but will take the construction of the house into consideration.

OP, your house was built to deal with open fires and draughts. You can't shut it up for weeks and expect it not to be damp.

 

[MatthewC]

We would love to keep the current original quarry tiles that someone has lifted then relaid in concrete so do you feel that digging the floor up and relaying is imperative? I doubt we will be able to salvage the tiles if we dig them up.

The issue with a concrete floor is that any moisture underneath is driven to the walls, and so the base of the walls may get damp. If this is happening in your cottage (and still happens after some decent ventilation, and after checking obvious things like external ground levels and condition of rainwater goods) then you need to consider sorting it. One solution that some people here have tried is to lay a limecrete channel around the concrete, say about 18" wide, which then allows evaporation and prevents water reaching the walls. If that works it is a far cheaper and less intrusive solution. However, I have no personal experience of doing it as we dug the entire kitchen floor up as it was truly awful.

You are right about concrete and tiles - it would be very difficult to salvage them, I suspect, but you can buy them at reclamation yards. Sadly, I sold ours off, more to get some space than for financial gain!

Matthew

 

[noj]

One thought - if you lay new floors then you'll be introducing a huge amount of water as part of the process - this could actually cause more grief if you're then not there enough to ventilate sufficiently during the long drying period...

 

[bondge]

After further investigation the walls seem to be mixture of decent size chunks of chalk and what I guess was mud/clay. The house is in N Dorset and there is a reasonable amount of chalk in the area. Does anyone know a good builder and surveyor around here who has experience with old propoerties. Digging a channel around the walls seems to make sense rather than dig the whole lot up. I suspect the cement the tiles are set in is pretty shallow so we would not need to go too deep.
Is there a senstive way to remove the vinyl paint it is quite well adhered to the lime plater? We could try try a wall paper stripper but I am loathe to introduce more moisture to the wall.

 

[formerly known as]

is it cob, clay lump or shuttered clay??

 

[bondge]

The parts of the wall that you can see are chalk and mud (probably not the technical name for it). I think I will get a couple of tiles up and see what lies beneath. We could then dig down and see how deep the footings are.