[Fleecewife]

We have had the outside of our stone-built cottage renovated, including having all the old mortar removed and replaced with Lime Mortar.  At the same time we had double glazing installed.

Obviously the weather has been excessively wet since the builders finished, but I don't think that can be the cause of our problem.
We are finding that the wall under the new windows, on the inside, is covered with mildew, expanding all the time.  It's mostly where the bit under the window is not the full thickness of the main walls - these are of a double stone construction with rubble filling in the space between, except under certain windows where it's just the outside wall.  We had no problem with mildew, except in the bathroom, before the lime mortaring was done.

Is it possible that as the mortar dries, which I believe is a slow process, some of the moisture is heading into the house, as the atmosphere outside is too wet for it to go that way?  Or could it be to do with the windows themselves?

What can I do apart from use anti-mould paint, which just disguises the problem?

[Jukes Mum]

we have been in this house for 3 years now, but this is the first winter we have had a serious mould problem. We can pnly think that it is due to the excessively damp weather. The part of the wall under the window where it is only a single thickness, will be colder that the rest of the wall where it is double later with rubble fill.
Anywhere that you have a cooler surface will cause moisture in the air to condense, hence the mildew on the colder surface.
Our bathroom is a brick built add on. Last summer we refit the bathroom and insulated two of the external walls. Obviously the insulted wall now has a lovely mildew coating :-(
We solved the problem by fitting a polystyrene backed wallpaper. This gets rid of the cold surface on which the moisture was condensing.
We have also acquired a dehumidifier which is, shockingly, collecting 2 litres of water from the house every day!

[ramon]

I would doubt it is anything to do with the lime mortar. I had real difficulty finding anyone with the skill to carry out lime mortar pointing. (Competent people seem to be in high demand and few willing to trek out to remote places).  The new windows will stop moisture escaping which has to condense somewhere.

[Marches Farmer]

Is there a damp proof course and, if so, has it been compromised?

[Fleecewife]

Is there a damp proof course and, if so, has it been compromised?

We had a chemical damp proofing put in when we came here 20 years ago, where they drilled lots of holes into the stone at the bottom of the walls.  I don't think it will have been compromised because the holes are into the stone not the mortar.  I don't know if chemical damp courses need to be redone at intervals?  Until we had that done, the house had always been damp and cold, but it wasn't too bad once we were living here with heating and fires.  Since the renovation was done, with roof, porches as air locks and the windows, it is wonderfully cosy - so clearly I need to ventilate more.

Interesting about the polystyrene backed wallpaper - I'll investigate that.  I'm a great one for having doors and windows open so a dehumidifier struggles, but I'll persevere with that.

[ramon]

Is a damp proof course needed? When I bought my home I really looked into this and ignored sales pitches to fit one. My home is stone built and about 150 years old,  It does not have a damp proof course and it does not need one.

I have placed polystyrene backed wall paper on the wall of one porch (brick built addition) where there is a cold spot and it seems to have solved the problem.

[Clarebelle]

I have recently been researching lime mortar etc. as we are planning to convert an old stone byre into living accommodation and so far it sounds like, to get the benefit of of the lime mortar you need to also use breathable insulation (wool etc) and breathable paint/wallpaper (chalk based?). Is it possible that an impervious layer has been used on the lime mortar wall meaning it can't 'breathe' as its meant to?

[goosepimple]

Hi FW, yes I would say you just need to ventilate more - your new windows should have sliding vents in them.  The lime mortar does take longer to dry out and it will need ventilation - the cosy interior of your house will act like a poultice drawing the moisture in to the warmth.  It will continue to happen unless you find a permanent ventilation solution.  A cauld blast would help - I usually open the windows in our bedrooms and bathrooms every morning for an hour or so while I'm out breakfasting the livestock, then shut them when I come in.  Sounds daft but our house is an old stone built too - unless you build new you just have to put up with things like that happening and learn to control it, but you won't get rid of it completely.  You'll get mould starting too, might be worth looking for a propeller type fan on gumtree or the like to stir the air up a bit.  Or stop breathing and sweating, cooking and bathing, boiling the kettle etc....

[ladyK]

Fascinating thread, thanks for asking the question FW!
We have the same problem in our old (but renovated) cottage on a serious scale, only around windows/doors facing the weather. It's fine in 'normal' rain conditions, but in stormy weather the wind seems to be driving the rain in to the wall around the windows with big damp/mouldy patches growing every winter. We had everything repointed/resealed around the windows in our second winter but it made little difference. Luckily we have lime paint inside so it only sweats rather than peels off, and it takes very well to brushing the mould off (spraying with white vinegar after scrubbing slows down the mould regrowth considerably but it does come back eventually.)

It never occurred to me that the problem might be due to condensation rather than rain seeping in, I will now investigate this angle too when looking for a solution.

[waterbuffalofarmer]

This is indeed a very interesting thread. I live in a farmhouse built in the late 1800's, the walls are very thick and it gets quite cold and damp in the winter, we have had a lot of trouble with mould growth on the walls and have had to treat them many times since living here. Could this be the cause do you think?

[goosepimple]

Buildings need to breathe.  The Building Regs these days prevent this from happening but even in the 80s there was what was known as 'sick building syndrome' which was found could make the inhabitants therein ill.

Be a fresh air fiend. Even keeping your furniture a couple of centimetres off the walls helps air circulate behind them.  Often you can find mould growing on the backs of wardrobes and the like.  And you're breathing it in of course. 

Our routine of opening windows and doors in the morning (we turn down the bedding, open bathroom doors etc) is good as we don't then forget to shut the windows when we go out, just part of the routine.

[Fleecewife]

It's been so endlessly wet that I suppose I have had the windows and doors open less frequently than usual since the builders left.  It's also a bit of a battle with Mr F who hates having doors open, and goes round shutting windows behind me  .  This week it's sunny and dry, so even he's letting me have the windows open, and I hope that will help the situation.  One of the new windows (in our bedroom) is sticking, so we are waiting for the installers to come back and sort it (the weights are catching somewhere inside) then I can have the window open at night, which certainly should help in there.
Yes, breathing in mould spores has to be bad for us 

[Foobar]

Opening windows first thing in the morning is best as a lot of water vapour will accumulate in the evening and overnight.  Also, most old houses are usually cold in the morning anyway so opening the windows doesn't make it much worse than it is already .  (unless of course you splash out and have the heating come on timer in the morning)

Dry air warms up faster than damp air - so open the windows for half an hour to an hour and then close them and only then put the heating on.

Also, think about which windows to open - if you can get an air flow going through the house then that will work the best.


I've lived in an poorly insulated house for the past 10 years so I know what cold is ... just about to move to a 400 year old stone cottage which has a slight damp problem so looking forward to being able to fix that .

[Marches Farmer]

The damp proof course in our stone holiday cottage is in the mortar. 

[ramon]

Yes but I am not convinced this type of damp proof course does anything. Having one fitted sometimes keeps the mortgage company happy but not sure it does anything for the building. Wonder if the surveyors who recommend them are linked to the damp proof companies.