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  • #729555
    chris-le-bricoleur
    chris-le-bricoleur
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    Joined: 03 Dec 2010
    Location: NL and 52
    Total posts: 1381

    In this forum I’ve read several statements about damp problems and how others attacked these. Here’s a short collection of quotes:
    – Cement render can be very dense and not allow water vapour to pass and can be the reason for interstitial condensation and water vapour retention, incorrectly diagnosed as rising damp.
    – Stone walls inside houses often have been rendered in cement and then hidden by plasterboard. The original stone wall underneath is bone dry. The cement is trapping humdity.
    – The only thing to use is lime render, the walls have to breathe, water has to escape; block it all up and your walls will sooner or later collapse, or you store water and get damp.
    – We had serious damp problems when we moved in but we lime rendered inside and out, never a bit of damp since. Too many non-French builders cement render the outside and cover the inside with plasterboards.
    – I would never buy a renovated property unless photos show me what was behind the plasterboard.

    This made me think about our renovation and the damp problems we’ve met. Let me tell you the story.

    When we bought our house it was all damp. It had not been used for some years. Several exterior and interior walls on the ground floor were damp up to 1m high, and the outside of some walls showed traces of water that had run down on them.
    Picture [1]

    It’s a terraced house in a hamlet built along the scheme barn+house then house+barn and so on. We own two adjoining houses. So we have a double house with a barn/stable at each end. Since our double house has only one house number the two must have been combined before house numbers were issued, and that was in the thirties of the last century.
    Picture [2]

    When we experienced the first heavy rainfall we noticed that the front gutter was overflowing. The gutter was new, about six month old, it had been replaced together with the front field of the roof, which had suffered severe damage in a heavy hailstorm. You can still see that the neighbour’s roof is temporarily covered by an awning (une bache). I removed one of the down pipes (it was full of water) and discovered that it was connected to a clogged drain.
    Pic [3]

    When a contractor dug up the drains we found a number of strange connections; things had simply been done the wrong way when the drains of the house were connected to the public sewer, which was installed in our village in the nineties. So we decided to replace all drains on the front side of the house by new ones (3 domestic outlets and 2 for rainwater drainage), complete with the proper inspection chambers.
    Pic [4]

    pic [5]

    Some years later I also disconnected the old fosse septique the outlet of which had just been piped to the new sewer (outlet simply diverted from the leach field to the public sewer), the fosse was thus still used as a sort of collecting chamber for several waste water drains. Then I filled the fosse with rubbish and sand and covered it by a concrete slab.
    It took a year for the front wall to dry, and later we planted ivy to cover it.
    Pic [6]

    Our house is built directly on the ground, without a basement or vide sanitaire. Only one room of the ground level has a floor about 1.20m lower than the surrounding ground, I would call it a semi-cellar. The outside wall of this storage room was extremely humid, water running down the wall. Since the ground water level in our village is very low (a nearby farmer had to drill down 18m to reach water for a new well, and our old well, 6m deep, was completely dry) this must have had another reason than ground water percolating through the wall. I suspected a downpipe of the gutter which was close to the wet wall to be the culprit, but found that it was all right. This downpipe, however, ended in a custom-made gully: three walls of this gully were in masonry, and the fourth was just the outside wall of the house! Exactly the way window wells for basements are made. I replaced this gully by a prefab one of 50x50cm in concrete (regard en elements) with several elements, and I also connected the terrace drain to it.

    pic [7]

    pic [8]

    Pic [9]

    Another wet place of the rear outside wall was where the two former houses met each other; you remember, our house had originally been two houses which were combined about one hundred years ago. The gutters of the two houses had been connected in a clumsy way. You’ll see that the render under this gutter joint is in very poor state and had partly disappeared. This was corrected in 2003 when we had the rear roof replaced and when I repointed that wall.

    Pic [10]
    Pic [11]
    Pic [12]

    But then there was the big living room, le séjour. Its walls were rendered in cement, and the floor consisted of ceramic tiles, grouted with cement, and apparently with a concrete floor under these. From the uncle of the last owner we heard that the floor was originally laid with tomettes, and these were laid the traditional way, on sand and with open joints. With this floor the earth underneath could breathe (get rid of its moisture). The walls, built from natural stones, were finished with loam, the stuff we normally address as mud, and partly lime render. With these techniques floor and walls could ‘breathe’. Yes, I know, floors and walls do not breathe, but in the builders’ world this term is used to indicate that there is an exchange of water vapour. Now, with the tiled floor all the moisture rising from the underground had to go up into the walls to evaporate from these – but there was the cement render. Should we remove the tile floor and make the floor breathing again? But the tile floor was in such a good condition that we wanted to keep it. We thus decided to do something about the walls.
    This picture shows the floor during the high pressure cleaning (Kärcher) of the outside wall.
    Pic [13]

    A damp proof course in these walls was no option. First of all, retrofitting a chemical damp proof courses in stone walls is almost impossible; this may be possible in brick walls, and even there the result is difficult to predict. And, secondly, what would happen to the rising damp if it couldn’t rise into the wall and evaporate from there?
    Therefore our first action was to take the cement render from the walls. This wasn’t a big job since its adhesion to the underground was very very poor. It came off the walls in big flakes. Under the cement we found a layer of partly mud and partly lime, but at some places this also had no more cohesion to the stones and fell down together with the cement.
    Pic [14]

    The result was a wall which was partly bare, partly covered with mud, and partly with lime render from which chips had been cut to provide adhesion for the cement render. The wall also had a certain curvature and felt wet up to a height varying from 0,8 to 1,5m.
    Pic [15]

    The limit up to which the moisture could be detected was particularly high on one part of the wall which had been covered by a wooden sheathing, 105cm high. This sheathing consisted of a framework and plywood panels with aluminium foil on the backside! This prevented any moisture from evaporating into the room, the moisture was therefore forced to climb up even higher!
    I must admit that the whole situation in this séjour (our future living room) was not ideal: no vented space under the floor (pas de vide sanitaire) and walls which were partly humid since they had to deal with the rising damp. Our house in the Netherlands, in a place where the groundwater level is 60 to 80cm below the ground, is also built without a basement under a big portion of the ground floor, but there’s a well ventilated air space of 80cm under the wooden floor.
    Pic [16]

    On this old drawing (dated 1915) you can see one of the air admittance wells at the rear side (right), and at the street side there is a number of grates, similar to the register shown here, but much bigger.
    Pic [17]

    All damp rising by capillary action from the ground into the foundations can evaporate on its way from the ground to the living floor and be taken away by the air current – this works; I’ve inspected the underside and beams of our wooden floor at several occasions, the last time when I placed countersunk convectors. The floor of this vented space is sometimes covered with water, but the upper part of the foundations is always dry.
    Pic [18]

    Since we had decided not to create a vide sanitaire under our French house we had to rely on water evaporation through the walls. We waited, and after three months of intense ventilation we considered that the damp level in the walls was lowered by about 20cm. This made us hope, and after a year the walls, now freed from the cement coat, were practically dry.
    In order to keep the walls dry we placed plasterboard on metal studs behind which they can still ‘breathe’. For this purpose I placed openings in the plasterboard and the plinth which I decorated with plastic vent opening covers.
    Pic [19]
    Pic [20]
    Pic [21]

    At the upper end the gap between wall and plasterboard was left open, it continues behind the plasterboard of the first floor and ends in the loft. The plasterboard is, after nine years, still in good condition. My conclusion is that the walls are now permanently dry, or that there is an equilibrium between rising damp and damp evaporation.

    Another point of concern was the terrace behind the house. This was a concrete slab of 3,5 by 8m which was not properly drained.
    Pic [22]

    Since it had a slight inclination towards the house I thought that an open drain between house and terrace, one of the typical caniveaux with gratings on them, would solve this problem.
    Pic [23]

    But then my wife suggested that a bigger terrace would be nice; thus we had the whole concrete slab removed.
    Pic [24]

    We excavated the ground 30cm deep, filled it with 20cm of rubble (10 to 50mm), covered this with woven géotextile, and put a finishing layer of gravel (3 to 16mm) on it.
    Pic [25]
    Our son-in-law helping me with the transport of rubble, wife and daughters waiting for the work to be completed.

    Pic [26]

    Pic [27]

    The place is now completely dry, rainwater soaks away, and the rear wall of our house is slowly getting dry. You’ll notice, that the roof tiles which had a bright red colour when placed in 2003 (see picture 10), now have a warmer brownish colour .
    Pic [28]

    The only moisture problem we had since was due to condensation. One year we arrived late in April in France. Our house had been closed till then and still had its winter temperature, about 12°C, but the outside temperature was almost 20°C. When we arrived we did not notice anything special, but when we opened windows and doors, the warm moisture-leaden air cooled down on the tiled floor and created a film of condensed water. This was only over after the floor (and the walls) had taken up some warmth and their temperature had somewhat risen.
    You see, it’s not only rising damp which makes a house wet. In our case it was a combination of rising damp hampered by cement render, and a number of minor leakages. Installation of a French drain wouldn’t have helped, we had to tackle the causes of the dampness – and wait. Somewhere I’ve read that drying a wet wall takes about 12 days per cm, thus 720 days or two years for the 60cm thick walls of French heritage houses. I can confirm this, so better wait two years rather than one after you’ve done something against dampness.


    Christian - bricoleur par passion, pas par necessité http://www.klussen-in-frankrijk.eu/

    #790113
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    mrsh
    Participant
    Joined: 02 May 2011
    Location: Kent and Mayenne (53)
    Total posts: 285

    Thank you for a very informative and helpful post.


    #790114
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    Clover
    Participant
    Joined: 31 Jul 2003
    Location: N/A
    Total posts: 8226

    We covered our driveway with the cloth geotex type material two years ago before putting ten tons of gravel down and not one weed has come through.Over the years the original gravel we laid has disappeared with grass returning and mud working its way up again but no material was laid first back then. You can buy it very cheaply at bdepot and its worth doing but make sure you overlap the pieces well.


    #790112
    chris-le-bricoleur
    chris-le-bricoleur
    Participant
    Joined: 03 Dec 2010
    Location: NL and 52
    Total posts: 1381

    @clover wrote:

    We covered our driveway with the cloth geotex type material two years ago …
    You can buy it very cheaply at bdepot and its worth doing but make sure you overlap the pieces well.

    … and nail the cloth down to earth. I used scrap pieces of plywood (ca. 60x60mm) and nails of 6x150mm, see my pic.[27] and this one:

    … and char: thanks for making this contribution stick.


    Christian - bricoleur par passion, pas par necessité http://www.klussen-in-frankrijk.eu/

    #790111
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    Clover
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    Joined: 31 Jul 2003
    Location: N/A
    Total posts: 8226

    We have not nailed anything down, too risky where tyres are concerned but if you lay the sheeting down andhold in place with enough large rocks and then cover gradually with the gravel it works very well as enough weight will keep it secure providing you put plenty of gravel down and not just a thin coating, you then just go round the edges and trim it off with scissors and having it overlapping keep the gravel off the rockery, the paths and front patio area until it was all tidy.


    #790110
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    teapot
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    Joined: 10 Jul 2008
    Location: Tours
    Total posts: 2372

    @chris-le-bricoleur wrote:

    Too many non-French builders cement render the outside and cover the inside with plasterboards.

    ahem, a fair number of French builders too. My Nephew did his apprenticeship with a French mason of many years experience and they are still guilty of said act.

    Other than that, another great blog showing how good it is to do the job properly.


    Raising the standards of swimming pool knowledge and technology.

    #790109
    chris-le-bricoleur
    chris-le-bricoleur
    Participant
    Joined: 03 Dec 2010
    Location: NL and 52
    Total posts: 1381

    I’ve just come across a very comprehensive document about damp and mold problems, published by a manufacturer of hygrometers.
    On page 21 of this document the problems in transitional periods of the year are dealt with – exactly what I described in the last alinea of my original posting.
    What’s interesting: the company offers a special hygrometer (DampGuard) which measures the humidity on the surface of the wall, not in the air somewhere in the room. They also give an indication of the accuracy: not very high, but better at critical moisture levels (>80%).


    Christian - bricoleur par passion, pas par necessité http://www.klussen-in-frankrijk.eu/

    #790108
    chris-le-bricoleur
    chris-le-bricoleur
    Participant
    Joined: 03 Dec 2010
    Location: NL and 52
    Total posts: 1381

    This is a rather complete literature survey about damp problems:
    http://www.ukdamp.co.uk/damp_decay.php
    The experts from UK Damp & Decay Control deal with almost any aspect of moisture diagnosis and damp control. They also deal with all the discussions about ‘rising damp which does not exist’ – it exists, but not all damp problems are due to rising damp!
    Forget what they write about Victorian Bricks and loft tanks, these are British and do not exist in France.
    And once again I came across the Sunday Telegraph advisor Jeff Howell.


    Christian - bricoleur par passion, pas par necessité http://www.klussen-in-frankrijk.eu/

    #790107
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    mikej
    Participant
    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    UK Damp & Decay Control are just another company selling their expertise, they have a vested interest in perpetuating the existence of rising damp, they are not a government body as their tittle would suggest. It would be interesting to find out if Paul Taylor, the head of that company is a member of the RICS, because his hypothesis is against their instructions to building surveyors with regard to rising damp.

    Mike


    WFIPFLL

    #790106
    chris-le-bricoleur
    chris-le-bricoleur
    Participant
    Joined: 03 Dec 2010
    Location: NL and 52
    Total posts: 1381

    Mike,
    surely they are a group which sells expertise.
    But in contrast to the damp proof course lobby their information is in equilibrium; they inform about almost all sources of damp problems.
    You’re not obliged to believe them, but their literature is a good input for one’s own thinking.
    Their approach reminds me of mine:
    1. Look at all possible sources of humidity before you do something.
    2. Don’t expect immediate results; wait, be patient.


    Christian - bricoleur par passion, pas par necessité http://www.klussen-in-frankrijk.eu/

    #790105
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    mikej
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    Joined: 21 Jun 2011
    Location: Dordogne sometimes and Kent the rest
    Total posts: 5287

    Chris

    They are a company, not a group, that sells expertise and will take the cost of that expertise off the bill for any remedial work, so just another company with a vested interest in what they write about, look here: http://www.construction.co.uk/company_513080.htm your original link is a very well put together web page that can easily be mistaken for an official web site, but the link above gives a truer picture.

    Mike


    WFIPFLL

    #790103
    chris-le-bricoleur
    chris-le-bricoleur
    Participant
    Joined: 03 Dec 2010
    Location: NL and 52
    Total posts: 1381

    In my first posting on this subject I had written under pic.[27]:
    You’ll notice, that the roof tiles which had a bright red colour when placed in 2003 (see picture 10), now have a warmer brownish colour. Pic [28]
    This should have read pic [12], and the promised pic [28] has disappeared (or was it never there?).
    Therefore here the three pictures concerned:
    pic [10], the old roof, 2002
    pic [12], roof new, 2003
    pic [28], roof in 2012


    Christian - bricoleur par passion, pas par necessité http://www.klussen-in-frankrijk.eu/

    #790104
    chris-le-bricoleur
    chris-le-bricoleur
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    Joined: 03 Dec 2010
    Location: NL and 52
    Total posts: 1381

    @mikej wrote:

    Chris, They are a company, not a group, that sells expertise and will take the cost of that expertise off the bill for any remedial work … Mike

    Mike, I agree.
    But I do like their information more than others I’ve seen.


    Christian - bricoleur par passion, pas par necessité http://www.klussen-in-frankrijk.eu/

    #790102
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    jak
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    Joined: 14 Mar 2006
    Location: N/A
    Total posts: 41

    Clover wrote:
    We covered our driveway with the cloth geotex type material two years ago …
    You can buy it very cheaply at bdepot and its worth doing but make sure you overlap the pieces well.

    Could you please advise which geotex type material you bought from bdepot. We have been today and they had two completely different types so we didn’t know which to buy. Both said geotex but one was black plastic and the other one was a white cloth type. Thanks for any help.


    #790101
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    thomas16
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    Joined: 15 Jul 2003
    Location: 16/87 border
    Total posts: 6176

    The thin white cloth type, if that’s what they sell is useless after a couple of years. I’ve just been and sprayed the driveway around a large local house for friends that they had dug out, white membrane layed and tons of local sand and scalpings compacted down a couple of summers ago. Weeds are now coming through.

    There is a thicker green porous geotextile available at better bricos; more expensive, but it works… Plastic isn’t a good idea as it will get boggy..


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