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How can I Cure this Damp Problem in 19th Century House in France?

Postby toulouselechat » Mon Jan 19, 2015 12:49 pm

We have a holiday home in Western France which consists of two 19th century stone properties. It’s left standing empty for most of the year, and is used mainly in the summer months. The main house doesn’t have any problems really, it smells a little musty and we get the occasional bit of damp coming through one of the walls by the window but nothing that you wouldn’t expect from an old property that is unoccupied for most of the year. The problem lies with the guest cottage/gite. When we initially got the keys to the house, we immediately noticed a very strong damp smell in there as well as an absolute bitter cold. At the time, we put this down to the fact that there hadn’t been anyone in it for a month, and thought it just needed a good airing. But the smell didn’t go. Last October we had to take up the floor in the kitchen area (it’s open-plan) as they had used these lino-type floor ‘tiles’ that were laid on chipboard. It was so damp that the lino had started to lift up and all the chip board underneath was damp and mouldy. When we lifted the floor we noticed that the soil underneath was stacked against the joists, meaning there was no airflow. The soil was bone dry though, much to our surprise. We thought we’d found the route of the problem, we levelled out the floor creating a space between the joists and the ground, so that it could breathe. We purchased a dehumidifier which was left on constantly for around 2 weeks, and warmed the property using the log burner. At the end of the two weeks, you could tell that the air was much drier, and the damp smell had disappeared. We then came back to the UK, so the gite has been left standing for approx. 3 months.

Our caretakers went in this week to open up for renters, and the property was very very damp, worse than it’s ever been. The linen upstairs was wet, there was mould growing on the wooden utensils in the kicthen, along the wooden pannelling, mould had also attached itself to some decorative boxes I have upstairs, hanging off mirrors in big strings, it was bitterly cold in there, you could see your breath in the air….you get the picture. So we are now perplexed as to what is causing this. The floor underneath has been checked again and it’s totally dry, so it’s like the damp is there in the air not rising from the floor. When we had the floor up, we checked everything for leaks, but there was nothing. After doing a bit of research I’ve read that chemical injections as a damp proof on old stone properties are not practical and can do more bad than good. So we don’t know how to deal with this problem. Obviously when we go over in March, I can dry it out with the dehumidifier again, but it’s not going to solve the problem when we shut it up again. Like I already mentioned the main house is made of stone too but it doesn’t get this problem. The only difference between the two houses is that the gite has double glazing, whereas the main house has the original windows. Is there a chance that the double glazing could be causing the cottage to ‘sweat’? Again, I ‘ve read that double glazing is not always practical for old buildings as it doesn’t allow them to breathe. Any suggestions or guidance would be greatly appreciated.
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Postby welsh brickie » Mon Jan 19, 2015 5:49 pm

you will need to install more airbricks in the floor, and cover the soil with concrete, This will stop moisture and spores from growing. Any rotten joists need replacing as it could be dry rot causing the damage
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Postby Ryan@Renovate » Tue Feb 03, 2015 8:25 pm

There is 3 types of damp and to cure a problem we first have to find out which it is that is causing the issue. There is Rising damp, penetrating damp and the easiest to cure and most common, condensation.
Rising damp
Rising damp is caused by ground water moving up through a wall. Most walls allow some water in, but it’s usually stopped from causing damage by a barrier called a damp-proof course. This is usually a horizontal plastic or slate strip in the wall.

If this is missing or ineffectual, your wall may suffer from rising damp. This type of damp can also happen when the level of the ground outside your home is higher than your damp-proof course, allowing water to get above it.

Symptoms of rising damp
If you have rising damp you may notice damaged skirting boards and floorboards, crumbling or salt stained plaster and peeling paint and wallpaper. There may also be a tide mark along the wall.

Penetrating damp
Penetrating damp is caused by water leaking through walls. This type of damp may move around within a building, but this is through horizontal movement rather than by travelling up walls (as is the case with rising damp). Penetrating damp is usually caused by structural problems in a building, such as faulty guttering or roofing.

Symptoms of penetrating damp
Penetrating damp often shows up through damp patches on walls, ceilings or floors, which may darken when it rains. You’re more likely to get penetrating damp if you live in an older building with solid walls, as cavity walls provide some protection.

Condensation is the most common kind of damp and is caused by moist air condensing on walls. It's mainly a winter problem, as at this time of year walls are much colder than the air inside. Condensation can be exacerbated by poor ventilation, and heating that comes on and off, as this allows warm, damp air to condense. The removal of existing chimneys and fitting air-tight double glazing can reduce ventilation. There are systems available to help improve ventilation, such as the Drimaster Heat positive input ventilation system.

Symptoms of condensation
You may notice water droplets on windows or walls, see dark mould appearing and/or notice an unpleasant smell. If left untreated, condensation can damage paint and plaster and cause window frames to decay.
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