Stone house - foundation too high

[Toshak]

Hi,

Have just removed sand cement plastering from inside walls of my rubble stone cottage which I am renovating.
All walls bar one seem very dry and sound.
I have a problem on one gable wall however, where the gable seems to be built on a solid seam of shale type rock. This seam of rock is approximately 8 inches above current finish floor level. and is quite wet indeed.
The ground outside the gable is a little high, and I am in the process of going down as much as I can, but I suspect I will still have a fair amount of water ingress on the inside.
Could anyone propose a solution?

Thanks in advance for your help.

 

[Penners]

If the gable wall is built on shale rock that projects out of the ground, I really can't see any way that you can dry it out, as it is currently configured. Presumably the dampness is rising osmotically from below ground through the seams in the shale, so you have little or no chance of (a) cutting off the source of water, or (b) drying out the rock.

The only solution that I can think of is pretty radical:- support the wall, dig the shale out down to foundation level, then build a masonry foundation incorporating a DPC.

Maybe someone else will come up with a less expensive plan.

 

[Toshak]

Penners,

Thanks for your comments. I am actually thinking as follows as the most reasonable solution.
The wall is almost 30 inches thick. I plan to chip away at the shale projection to a depth into the wall of say 6 inches or so, and going down circa 18 inches below finish floor level.
I then plan to lay a concrete strip on heavy guage polythene ubderneath the overhanging wall. Then I plan to build a 4 inch block on edge on the concrete strip foundation to up to meet the overhanging stone wall. The ploythene strip will be wide enough to come up inside the new blockwork and form a damp proof barrier.
Obviously as I remove the strip of shale inderneath the stonework, some stones will probably tend to drop down, but I do not expect that this would be too much of a problem, given that on average the size of stone used on the inside wall leaf should be big enough to stay put with a 6 inch channel excavated underneath.

Am I crazy?

Thanks

 

[Penners]

If I have clearly understood your plan, Toshak (and I'm not entirely confident about that) it seems to be based on the presumption that there is an unbridged air gap between the inner and outer leaves of your stone wall.

My experience of stone walls is quite limited, but such as it is, I doubt whether the above assumption is the case. I believe that double-skin stone walls usually have the gap between the leaves filled with loose rubble (called "dross"). This would form a bridge across to the inner leaf above your half-DPC, providing a route for damp, so I have my doubts as to whether the idea would work.

But maybe I'm wrong about the construction of the wall...?

 

[Toshak]

Penners,

You seem to understand my plan OK, and yes the inner section of wall is rubble infill.
However in my situation, the actual stone wall is only very slightly damp.
My problem, boils down to the shale seam which projects 12 / 14 inches above floor level. This is very damp. The stone wall sitting on top to my surprise is not very damp at all.

My thinking is to cut away a section of shale and replace with a 4 inch solid block wall which I would protect from direct contact with the shale by use of a dpc membrane.
Not ideal I know, but maybe it's a case of horses for courses.

As I write this, I wonder if use of a chemical injection method in the shale section would be of any use. Do you think it might seal the shale and prevent ingress of water???

Toshak.

 

[Penners]

Chemical injection DPC's are a topic of some controversy on this forum. The concensus seems to be that they are far from reliably effective. I can only say that I don't think I would attempt that idea. Even if the injected chemical was able to resist the hydraulic pressure of the water, I have severe doubts whether it would be able to soak far enough into natural rock to create a continuous, effective barrier.

As to your idea about lowering the rock outcrop below interior floor level, I'm afraid I have a few concerns about that, too (sorry - I seem to be very pessimistic don't I?). Damp has an infuriating way of behaving like bubbles on the surface of a balloon. Eliminate it in one place and it pops up in another. For example, this forum has heard endless tales from people who have incorporated new damp-proof membranes in their floors, only to find that the relocated damp suddenly becomes a major problem in the walls.

So I'm concerned that stopping the damp coming up through part of your shale outcrop will only force it to find another route to the surface - logically this will be through the shale under the outer leaf of the wall, which then provides it with a route back through to the inside again.

This is all total theory. It's never possible to predict what damp will do. Your idea might work like a charm, or it might not. The only way you'll find out for sure is to do it and see.

As it's only the actual shale outcrop that you find worryingly damp, would it be possible simply to box this in (ensuring that there's a good flow of air through your boxing-in) and provide some sort of drainage from the inside of this boxing-in to the outside of the house?. Most people advocate taking a step-by-step approach to damp management, starting simply and ramping up the complexity if the simple approach fails. This boxing in idea might be a good place to start, if it's aesthetically acceptable.

 

[Gervase]

I'm one of the loudest critics of chemical DPCs on this forum and yet...
I do think in this particular case a chemical DPC might be the answer (but please don't burn me at the stake!).
Not injected into the rock, though - that wouldn't work. What you need is to put a layer of mortar between your shale outcrop and your wall stones (by drilling a bit at a time and grouting), and put the DPC in there.
I'd recommend getting an RICS surveyor with knowledge of old buildings to have a look (you can find one through the links on this site, or ask you local SPAB person), and if an injected DPC is recommended, to go for one that's gravity-fed rather than pressurised.
To compound the heresy, this could be a situation where you use concrete - as Penners suggests, boxing in the shale outcrop. If it's continuous and massive, it's unlikely to move or segment, so an impermeable concrete cap may be the answer.
But it really needs to have someone who knows and understands stone buildings to take a close look.

 

[Penners]

What you need is to put a layer of mortar between your shale outcrop and your wall stones (by drilling a bit at a time and grouting), and put the DPC in there.

Gervase - reading back, I don't think Toshak is too concerned about damp rising from the outcrop into the stone wall. Currently, that doesn't seem to be happening to any great extent. It's actually the damp in the outcrop itself that seems to be the main problem.

However, I do agree that a concrete "jacket" around the outcrop is worth considering, perhaps using a tanking mix. And if that technique were used, then perhaps your injected DPC idea between the outcrop and the wall could become necessary, to prevent the "stifled" moisture from deciding to go up the wall.

 

[biffvernon]

This might be useful It's from the Sept/Oct Green Futures, the magazine from Forum for the Future. Read the rest from here http://www.greenfutures.org.uk/

Old houses can be green, too

Energy efficiency showcase supports “refurb not replacement”

A report by Oxford University has stirred up a royal reaction – propelling Prince Charles back into the fight to save Britain’s Victorian housing heritage. He’s supporting a new scheme to show how energy efficient such older buildings can be. The BRE Victorian House of the Future project will be the first concrete manifestation of this bid to counter the claims in Oxford University’s 40% House report [see ‘Exchange of Fire: Bring on the bulldozer?’ GF57] that more than a million such homes should be demolished by 2050, replaced with new energy-efficient ones to meet climate targets.

Prince Charles is not alone. In Liverpool, residents have gone to court to halt the proposed demolition of hundreds of Victorian homes in the city, destined to make way for a dual carriageway and new housing. It’s part of a wider drive to remove thousands of old terraced houses across the north of England. The government and English Partnerships argue that the Liverpool development will offer improved retail and community facilities. But local MP Jane Kennedy has invoked the emotive term “social cleansing”, amid fears that it marks a return to the old days of the 1960s ‘clearances’, when tower blocks replaced much traditional neighbourhood housing.

The BRE project is the first fruit of a collaboration with the Prince’s Foundation for the Built Environment, along with the East of England Development Agency and the University of Hertfordshire, to show the environmental benefits of retrofitting old housing stock with modern green technology. Its first project is the refurbishment of a Victorian stable block at BRE’s Watford HQ. The aim: to demonstrate and analyse how older buildings with solid walls, poor insulation, draughty windows, inadequate heating and in a state of general disrepair can be transformed to provide flexible and energy efficient accommodation that’s attractive, too.

BRE Environment’s managing director, David Strong, says it will show how we can “upgrade existing stock whilst avoiding the waste associated with demolition – and of course preserving the mix of architecture that makes our urban landscape a more humane and interesting place to live and work”. The project’s based at BRE’s Innovation Park, which is open to the public, and showcases modern methods of construction and the latest building technologies. – Charlie Jacoby

BRE Environment, 01923 664133
Prince’s Foundation, 020 7613 8500,
http://www.princes-foundation.org

 

[Moo]

Good old Charlie!

 

[biffvernon]

Charlie Jacoby or Charlie Windsor?

 

[thiambal]

The BRE Victorian House of the Future project will be the first concrete manifestation of this bid

Not concrete surely :wink:

Can you have a limecrete example of something?

 

[Penners]

I wonder whether the Prince's Foundation is concrete.

 

[Toshak]

Hi all,

Well I got working on the problem foundation. Managed to eke out a groove under the bottom layer of stones to a depth of 8 inches average into the wall and down to a depth of 30 inches below bottom layer of stones (circa 14 inches below finished floor level).
My next move is to line the new cavity with a continuous strip pf damp proof membrane and fill with concrete. I will not need to make the concrete infill, proud of the gable wall. I plan to have it flush, as space in this room is really at premium.
The way I see it the concrete will not be in contact with any source of water or damp and will quickly dry out, leaving me with a new dry bottom wall section on the gable wall.
I will then replaster with lime based mortar.

Aftewards, I will probably, repeat the process on the outside gable wall.

At the end of the day I know there will still be the section of rubble in the centre of the wall still sitting directly on the shale outcrop, but hopefully the amount of moisture travelling up the wall through this section will not be too great, and will in any case breath out through the lime plastered wall above the new concrete section.

Please do not tell Charlie, unless of course he proposes to come over and get his hands dirty in helping me out.

Thanks for all the advice over the past few days.

Toshak.

 

[Penners]

I will then replaster with lime based mortar.

Nothing wrong with using lime plaster, Toshak, but immediately above a layer of DPC and concrete, I don't know that it's actually going to contribute anything to the situation.

 

[Gervase]

Given the upheaval the poor old stonework's going to have to go through, lime plaster is probably the best stuff as it's far more forgiving of movement. Any water that hits the wall will be able to transpire naturally - so all in all, lime is still the best bet.