Rising damp on very old walls

[joddle]

We live in a very old building - some parts around well over 200 years old. The original walls are solid and well over 2 feet thick part is made of irregular stones and bricks held together with a very loose mortar.

There are no foundations under the walls and of course no damp course - nor is there any real way of putting one in! That part of the building has no visible foundations.

Most of the wall of the oldest part of the house are now contained within the house and due to many extensions over the last few hundred years have become internal walls nevertheless they are subject to a very gradual rising damp which makes any modern paint or plaster fail very quickly. quickly turning to powder and flaking off. This only happens for the bottom few feet on the wall. The damp is really slight and the walls feel actually dry but you can sometimes smell the dampness when you peel the plaster off

Having had portions of the wall repaired but only to fail again we realise its not going to be an easy thing to overcome. We avoid using plasticised paints now but really need to have a mode of action to repair some rather unsightly areas where the plaster underneath has failed.

In part of the house I have had some success using Dryzone cream but not all the walls are suitable for this as many of the lower mortar joints are irregular and soft and wide. Where I have been able to apply the Dryzone cream it seems to have cured the problem in those areas.

My thinking is to remove all the failing plaster and build in to the lower wall some vents to allow the wall to breath a little. then re-plaster the rest with lime mixed with dog hair (we have a log haired German Shepherd and could amass enough material quite quickly!) then use no paint - white is good for us and would suit an old building anyway.

Anyway - before I start this has anyone any other suggestions/experience bearing in mind:

a) the thickness of the walls
b) the age of the building
c) the impossibility of putting any form of damp course in.

Thanks

 

[KenGMac]

joddle, good evening.

As an alternative, OK off the wall,

Try Googling.

Electro-Osmosis ?

Lots of conflicting advice on the Web?

Suggest you have a look? no paint, no plastering Etc.

OK an archaic system but ?

Ken

 

[^woody^]

Electro osmosis, even if it did work as a system, would not work on old walls of the OP's description due to the number of voids and material differences.

Dry lining may be the only answer

 

[joddle]

Well thanks for the link Ken - very interesting and at first I thought maybe the answer - but on looking further it seems that the system is thought by some authorities to be just about useless (see here) so I won't be going down that route. In fact it confirms what I was thinking and that is ventilation appears to be the best solution so will be looking more at that unless there are other solutions.

Woody also thanks but dry lining is not going to be an option for many reasons. I had even though of stripping the walls back to the base material and leaving it at that - with modern lighting it could look quite good and it would be able to breath naturally. A huge job though as the room is over 12 feet high and the walls almost 30 feet long!

 

[IWalkLikeHimaMartian]

Remove all internal cement or gypsum based pointing/render and replaster with lime plaster.

But, I have had excellent results with a waterproof cement based render on the lower 1 meter of wall, with the whole wall then plastered in lime plaster.
The waterproof render needs to have a very fine sharp sand, and a good quality waterproofer added. It is the spaces in between the particles that make the plaster/render breathable, which in this case you are trying to avoid, on this lower part of the wall..

In addition, leave about 25mm at the bottom of the wall unrendered/unplastered to avoid any damp bridge between wall and floor. Cover this gap with a plastic or ceramic 'skirting'.

 

[joddle]

Thanks wannabe - sounds a good idea - I particularly think leaving the gap at the bottom is something I need to do - instead of skirting I think I will cover with a grill so air can circulate to the wall and evaporate any damp before it rises higher. I have never used lime plaster before but think it worth having a go - and its a good excuse to use all the excess dog hair!! ! Cement based covering may be a bit too brittle as I suspect these walls may move a little over time.

 

[IWalkLikeHimaMartian]

You might find that dog hair is too fine.
I suppose depending on which part of the coat it came from, the top thicker, oily layer or the fine, soft under-layer.

At £2.50 for 100 gram of horse hair (for about 6 m² of lime plaster), is it worth bothering?
http://www.limestuff.co.uk/additives-primers-sealers/horse-hair-100g-bundle/

Your 12ft by 30ft wall (30M²) would need just five bundles of horse hair @ approx £12.50

Despite the brittleness of cement render, the lime plaster over the whole of the wall prevents seeing any 'join'.