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Damp - To strip off the walls and inject chemicals, or not?

Discussion in 'Plastering and Rendering' started by MrHfromBath, 2 Sep 2009.

  1. MrHfromBath

    MrHfromBath

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    I have bought a house built in 1900 and am due to complete shortly. I had a survey done and the surveyor noted that there was some low level damp which i should have investigated. he also mentioned that there was insufficient sub floor ventilation which could be the root cause and installation of air bricks may resolve the issue. Additionally the house has been empty for 8 months with no heating, furniture against the walls, etc.

    Some of the walls appear very slightly damp, but it has paper on so it's hard to tell. Also the paper is very old and the house is very cold as it went through winter with no heating. There is a very small amount of damp in the flooring, which I have been advised by two people could relatively easily be repaired by a carpenter cutting out and fixing the joist.

    My dilemma is whether to believe the two damp proof companies who have bee out who have advised that I have 1 m of plaster removed, chemicals injected and then 3 layers of sand and cement/plaster with additives. Now if I go down this route I will remove the plaster myself (is it best to hire a bit of kit from a tool hire place to help with this?) and will have my own plasterer do the repairs, employing the damp proof company to just do the injections. Their prices for plastering were outrageous.

    However I have spent hours reading about rising damp and have also had advice from a friend who assesses houses for the council (not a surveyor or damp expert) and he believes that the only damp is caused by condensation and the lack of sub floor ventilation. If I went with this assumption and got the minor repairs to the flooring and installed air bricks then I would save myself a huge amount of work, inconvenience and money. However I want to live in this house for the rest of my life, so want to get it right. I want to get it right, but not do work I don't need to do.

    Based on my description what are your initial thoughts. Secondly where can I find the details of independent experts who do not work for damp proofing companies? I live 25 mins north of Bath, just into Wiltshire.

    Many thanks for any assistance.
     
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  3. JohnD

    JohnD

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    you have not said where on the walls the damp.

    Start by improving ventilation.

    http://www.diynot.com/wiki/building:condensation_in_houses

    See how many subfloor airbricks you have, and clear them all of dust, rubble and cobwebs. Observe if any have been obstructed by extensions or steps. Ask around for a reliable small builder who can neatly install new airbricks for you. One every two metres all round the house is not too many. Look at recent samples of his work and ask the householders for their opinion.

    inspect your walls for signs of a damp course and see how far above ground level it is, and that earth or paths have not been put over it since the house was built.

    lift a floorboard, sniff and look with a torch for signs of damp, and see how far down it is to the subfloor, and if it is bare earth, rubble or concrete. Does it seem wet? Can you feel air movement under there? Is there any sign of leaking pipes or drains?

    Look at all gutters and downpipes for leaks. Look round the base of downpipes, gullies or drains by the house in case they are fractured where they go into the ground, or just below (there may be signs of damp or sunken patches where the soil has been washed away, or concrete repairs to cover them up)

    the age and method of construction of your house may be relevant. Does it have cavity walls?

    Ask your neighbours with similar houses if they have had damp problems.

    Be aware that damp-proofing companies do not make their money by diagnosing damp problems, they make their money out of installing their fix.
     
  4. MrHfromBath

    MrHfromBath

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    Thanks a lot for the useful advise John. The slight damp is low in the walls. The two front rooms (4m x 4m) have just 1 airbrick at the front of the bay windows. They are partially covered by vegetation outside, although I don't know about inside as I am not in the house yet. I don't believe that the rear rooms have ventilation, but I could be wrong.

    I do not know if the house has cavity walls, although I would guess not. How would I know? When I move in next Friday I will conduct the other checks you mentioned, although where exactly do I look for the DPC and how will I recognise it? Apologies for the lack of knowledge.

    I need to get electrics, central heating, plastering, etc, done, but need to decide about the damp proofing first. As I know that the sub floor ventilation is an issue (max 1 possibly blocked brick per room) would you suggest getting this work done and not having the chemical injection? I am really loathe to spend money and time unnecessarily, but also fear that I could end up having to do the work after putting carpets in and completing all work. I have done hours of research and there does seem to be a lot of informed opinion and research suggesting that ventilation and heating does more than an injection of chemicals. I just don't know......

    All advice and opinion from anyone very welcome and thanks again Dave, I appreciate it.
     
  5. JohnD

    JohnD

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    a house that old would not normally have cavity walls. A wall 9" thick is solid, a wall 13" thick may be cavity. Measure it at a window or door.

    the DPC is likely to be a double row of slates embedded in the mortar, running horizontally all round the house about two bricks above the ground level at the time the house was built. It may look like a black line in an unusally thick mortar bed. Very often paths or flower beds have been put against the side of a house allowing damp to get past the DPC protection. You have to dig this away and restore the original ground level.

    Sort out the ventilation and the air bricks before you spend money on damp treatments. More often than not they are a waste of money.

    If I were you I would get the roof and plumbing sorted first of all as they may be letting water in. I once bought a house with a leaking watermain embedded in the concrete kitchen floor, and broken downpipes and soilpipes under the concrete yard. I became aware that my neighbour also had a broken drain when I was standing in a hole I had dug to repair mine, and he pulled out his bathplug, filling my excavation with warm water.
     
  6. NickB_99

    NickB_99

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    Did you go back to the vendor with the results from the survey?
    I thought it was normal practice if the survey showed anything untoward.

    It gave you some leverage for either negotiating a small reduction in the price or they should at least contribute to sorting the problem?
     
  7. MrHfromBath

    MrHfromBath

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    DIYNewbee, it was an auction purchase, so no such opportunity. However the surveyor was clear that there is no major issue, just some minor damp in an old house and it needed to be checked out to see if ventilation could resolve. It's not a big deal, but quotes from damp proof companies are outrageous because of their expensive replastering. I could save £5k not doing it.

    I'll have a good look at the house next Friday John. Luckily the roof is new, so no issues there. I'm having a whole new central heating put in and all pipes replaced. I might have a better idea when I remove the carpets, skirting boards and wallpaper. Hopefully a builder can put the bricks in for me fairly cheaply and that will be enough.
     
  8. Micilin

    Micilin

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    Try this in the meantime, while you are getting sorted

    Wipe an area of the affected wall dry and dust free.

    Tape a square of tin foil (say 250mm sq) to the area, sealing the edges with tape so that it is airtight.

    Wait for a few days, or as long as you like, a week or two.
    Remove the tinfoil.

    If the water droplets are on the outside of the foil, it's likely to be condensation caused by poor ventilation .

    If it is on the inside then it's damp .
     
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  9. trowelmonkey1

    trowelmonkey1

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    oh i like that micilin! :cool:
     
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  11. JohnD

    JohnD

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    and if you use clear polythene instead of foil, you can see if water droplets are forming on the underside without taking it off!

    In your case if the house has been unoccupied, the walls might have got damp with condensation and will dry out with ventilation.
     
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  12. NickB_99

    NickB_99

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    ok, thanks for the update.



    The polythene trick sounds good too:cool:
     
  13. MrHfromBath

    MrHfromBath

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    Thanks guys, I think I will gut the place, then tape the polythene/foil to the walls. I'll also took under the floorboards and will arrange to get the joists repaired and get some new airbricks installed - I assume that's a simple job? I'll also look for the DPC.

    I have had two damp proof companies out who tutted a lot and gave me a big quote, so I'll give them the swerve until I have done all of the suggestions made above. I need to move fast, but I guess the foil/polythene trick will be revealing quite quickly.

    I know that there's huge debate about injecting chemicals into bricks (it's stone at the front) and I just want to rule out all alternatives before parting with big money and causing a lot of disruption.

    Thanks for the advice everyone and if anyone has any more then bring it on. I would be prepared to find an independent damp expert to take a look, but don't know where to find them as most surveyors I have spoken to seem to be more 'general' and don't have specialist knowledge in this area. They have just said get it injected.
     
  14. Micilin

    Micilin

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    Polythene is a good idea, but perhaps we were told to use foil because of it's insulating properties ie the warm /cool interface will speed up the condensation effect.

    Any thoughts on this theory anyone? Because my memory is shot and maybe tin foil was a new invention when I was told !!
     
  15. noseall

    noseall

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    What is untoward about a C 1900 property having damp issues, be them condensation or otherwise?
     
  16. NickB_99

    NickB_99

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    'Untoward' just in the sense that immediately after purchase the new owner has to spend some cash resolving it.

    I would agree with you that C1900 having some damp is not unusual.
     
  17. PerryOne

    PerryOne

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    The height and the position of the damp will be some indication of the cause.
    For damp that is under four feet from the ground out side, then you have two possibilities, rising damp due a fault in the damp proof course or bridging of the damp proof course by something outside like piles of earth.
    Higher up the wall it may be due to a leaking gutter, down pipe or hole in the roof even rain blowing through the wall.
    It will not be condensation as condensation only happens when warm damp air meets a cold surface and as the place has been empty for some time its been cold all the time.
    Damp in the floor is interesting, again in the normal way of things, a damp joist will be down to warm moist air being pulled under the house by the suction of the passing air, or the warm air inside the home rising up through windows, doors and holes and dragging air from the sub floor, and this air cooling suddenly as it moves past a colder object, like a joist and depositing the water vapour. Adding more air bricks will only make this a more frequent occurrence.
    The influx of warm air outside happens about 200 times a year, you can tell when, as there will be frost or a heavy dew outside.
    However, once you are living in the place and heating the inside then heat from the rooms will heat the joists by conduction and radiation and the deposit of future water vapour will be avoided.
    Indeed once you are living there and have the heating on then what little damp there may be will be encouraged by the warmth to move through the walls to the outside and evaporate.
    If on checking out the damp situation, you discover that there is rising damp in a specific location where a slate in the damp proof course is cracked, then taking it out and replacing it with a piece of plastic dpc is cheap and easy.
    If there is no dpc then inserting your own using a cream from e-bay is simple and will cost little in comparison to the figures you quote.
     
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