Damp/ water problems on old stone wall

Hi all

Looking for some advise please. We bought a converted 19th century farmhouse last year. Moved in just before last xmas. Had no problems until the summer. The gable wall of the house, stone very thick, has damp/wet patches and is leading to mildew on the walls.

Background info - the internal and external walls are plastered. The bedroom above this room (sitting room) seems to have previously had damp problems on the same wall but now has none. The external plaster has been redone from the chimney to ground floor ceiling level so this must have solved that problem. There is a patch of wooden floor in the sitting room which seems to have been replaced at the damp area. The affected wall has a large old fashioned open fireplace where we have installed a new stove and new pipes and sealed the large opening. There is a second chimney at the other end of this room and we have blocked at top and bottom to prevent draughts. This room is extremely large and the windows have no vents. Both sides of the stove are affected. Sometimes the walls are weeping, sometimes they are bone dry for weeks.

On one side there was a downpipe puring into the ground. We replaced this and dug out around this wall and put down new drainage. This did nothing to alleviate the problem inside. The water marks are coming from ground up but are spreading horizontally at particularly bad times to the adjoinging walls and its these walls that develop mildew.

Two lots of builders have advised us that its not rising dampo. One says it is solely a ventilation problem. This doesnt seem to marry with the fact it started at summer when all windows and doors were open. The other first though maybe it was a leaking pipe from well but no pipes were found when we dug out.

Sorry for long post but fed up of trying to solve and have very small baby in house

The following diagram may help diagnose the problem.

[broken link removed]

ColoFio said:

One says it is solely a ventilation problem.

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This would be my first guess too. Condensation and mildew problems usually present themselves more often in the Winter as some people tend to dry clothes on radiators (without adequate ventilation) instead of tumble drying.

Other reasons could be

(a) rising damp caused by having no damp proof membrane in the rising walls

(b) no insulation in the walls which means hot air generated from the heating system is condensing on the cold outer walls.

T

Guns N Roses said:

This would be my first guess too. Condensation and mildew problems usually present themselves more often in the Winter as some people tend to dry clothes on radiators (without adequate ventilation) instead of tumble drying.

Other reasons could be

(a) rising damp caused by having no damp proof membrane in the rising walls

(b) no insulation in the walls which means hot air generated from the heating system is condensing on the cold outer walls.

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thank you. There is no insulation In walls as they are about 3ft thick stone walls. We don't want to dry line inside and hide the problem. It's staring at ground level and goes so high and then spreads horizontally to the adjoining walls. This makes me think it's rising damp?

ColoFio said:

The affected wall has a large old fashioned open fireplace where we have installed a new stove and new pipes and sealed the large opening. There is a second chimney at the other end of this room and we have blocked at top and bottom to prevent draughts. This room is extremely large and the windows have no vents.

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You need to make sure that the room with the stove has adequate ventilation (wall vent or similar) and that you have fitted a Carbon Monoxide Alarm.

As for the damp problem, you should hire an Architect specialised in this area to diagnose the issue which may have one or more causes. It impossible to tell without a proper site investigation.

I imagine it's rising damp. Looks as if it has been going on since the house was built but maybe exacerbated by double glazing and new heating technique etc. Injection won't work due to the nature of the irregular pointing/mortar. But you could hack off the render up to about 3' and proceed to replaster it with waterproof plaster. This will only work if the walls are not retaining and you being able to get at least 1/2" of plaster on the highest point.

Sammy's Daddy said:

I imagine it's rising damp.

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A lot of experts wouldn't agree.

As noted above, you should get an specialist architect to look at this.

You state the wall is plastered. Any idea what they're plastered with? Any idea if the wall has been repointed?

A major problem with old walls is where they have been "repaired" but repaired incorrectly using modern materials. Using cement plaster or pointing exacerbates the damp problem by not letting damp evaporate out through the walls.
Old walls should be lime-plastered.

Be careful what builder you use. Many will not have experience with old properties.

Hi Leo,
Yes I know. In the picture you see that the hacked off plaster breached the DP injection course, as it did with the slate DPC. That would cause moisture to migrate up the wall between the plaster and the brickwork - capillary action. Render should never go below the DPC/DPM
Sometimes when walls are plastered with waterproof render, moisture appears on the surface as the finish is dense and cooking, drying clothes etc condensate on the cooler surface.This is called sweating.
So, if rising damp doesn't exist what causes the tide marks, efflorescence et al to adorn the bottom of plastered brick/stone walls? Taking into account that the height of the ground outside, downpipes and gutters are in order and there are no abutted external walls? How come it doesn't appear up near the ceilings?
A lot of the the architects that are well known for railing against modern building techniques are fossils of a bye-gone era.
How do I come to that conclusion? I've worked with them for over 30 years.

I'm by no means an expert, just someone with a passing interest who has read many a thread here and elsewhere over the years.

I'm certainly not saying it doesn't happen, but am pretty confident it's way over-diagnosed. See post #5 here. There are lots of cases reported online where chemical DPCs have been injected at significant expense into walls demonstrating efflorescence having absolutely no effect whatsoever. In most cases the cause is water penetration due to other faults.

For high-pressure DPC injection, it's reckoned that it needs 20+ minutes per hole to be effective even in porous materials. How many installers take that time?

Sammy's Daddy said:

Hi Leo,
A lot of the the architects that are well known for railing against modern building techniques are fossils of a bye-gone era.
How do I come to that conclusion? I've worked with them for over 30 years.

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As most architects, including myself, are well accustomed to dealing with 'modern building techniques' you obviously haven't been working with them closely enough. I wasn't aware we were dinosaurs already - but ignorance is bliss I suppose....

Anyway, I don't pretend to know it all but I can definitely assure you it's not a rising damp problem if some of the damp is in the bedroom above the sitting room at first floor level!