rising damp?

Discussion in 'Builders' Talk' started by Blue Girl, Sep 14, 2009.

  1. Blue Girl

    Blue Girl New Member

    I've recently moved into a new house (new to me - built around late 40s) and seem to be having what I think is rising damp in two areas.
    The first is on an outside wall, just above the skirting. Although the skirting itself shows only slight signs of damp when i've tested it, the wall itself is very wet and causing the paint work (and plaster it seems) to crumble away. Also on the outside of the house i've noticed that about 3 rows up all around the house, the face of several bricks has blown.
    The other problem is on an inside wall. It's only on one side of the wall (ie in the living room but not the hallway). I've cut away the plaster here but the brick work doesn't seem to dry out at all and it's started to grow white furry mould on it.
    I've had a quick look under the floor (it's pretty damp under there, which i'm guessing is normal?) but I can't see anything obviously wrong with these two areas in comparison to the rest of the walls.
    Anyone got any suggestions as to the best way to remedy this?
    I was wondering if the cavity wall insulation might be blocking the air vents on the outside walls (it's kind of yellow fibre stuff)? Would this cause the problem or at least make it worse?
    I've no idea on the internal wall.
    Any advice would be much appreciated!
    Blue Girl
  2. Blue Girl

    Blue Girl New Member

    Aw c'mon fellas surely one of you can help me out here!
    Blue Girl.
  3. devil's advocate

    devil's advocate New Member

    Hi B-G. Jeepers, give the 'fellas' a chance to answer...

    Until they do, you can have my t'uppence worth.

    It is not uncommon for the underfloor area of a suspended wood floor house to be damp - often what's at the bottom is just 'earth' with no membrane.

    This shouldn't be a problem provided (a) the underfloor area is vented adequately - there should be free-flowing air vents peppered around the house circumference just below DPC level, and (b) the DPC (damp proof course) layer is still intact and working. This layer blocks the path of rising damp up the walls before it gets to 'house' height.

    First thing to check is that the vents have not been covered - sometimes peeps do this to cut down on draughts coming through the floor boards.

    Next thing to check is whether the DPC has been bridged or has failed where the internal wall goes through the floor - the DPC is usually immediately below the floor joists, sometimes with the joists actually sitting on it or sometimes with an additional layer of bricks/block/cement between it and the joists. The DPC should be easy enough to identify. If the wall is damp above it, you have problems.

    Possibly the damp will be caused by lack of ventilation under there - with no air flow all the surfaces can become damp, but such localised - and serious - damp is more likely to be due to a failed DPC - I think.

    The white furry mould is either due to 'salts' being extruded out through the brickwork by the rising damp and drying in the air causing this furry stuff, or it is actually white furry mould. If it's dry rot, you need to get proper help in eradicating it - all affected timbers cut away with a few extra feet for good measure, and the whole area - wood and brick - treated.

    As for the exterior wall, I don't know. I think some types of early cavity wall insulation were accused of causing damp bridging, but I don't know if yours is one. Blown bricks are likely to allow more water to penetrate - as you suspect - and this could be carried across the cavity. Or, since the DPC on the other internal wall has failed, this could have happened here too. Lifting the floor to have a looksee would help.

    You need professional help...

    Get at least three reputable companies out. Lift the floor in affected areas to help them check it properly and not leave them guessing.
  4. Mr GrimNasty

    Mr GrimNasty Active Member

    So many possibilities with condensation/damp it's difficult to comment - especially without any history of attempted remedial work. You don't even say if it is a cavity or solid wall, although probably the former. Is there a visible damp proof course - is it sound?

    Start with the obvious, anything that will wet/breach the outside wall near/above the damp area inside - spilling gutters, lack of sealing around windows/doors/pipes/wires through wall.

    Also the trouble with blown bricks is that they become like sponges and draw rain into the cavity. It is also likely that over the years all the mortar snots and work to put pipes etc. through the walls will have bridged the cavity with rubble so the wet will be getting through to the inside.

    It may also just be condensation on a cold spot.

    Your other wall certainly sounds more like condensation as the damp is on the presumably warm side against the colder hall? It is unlikely only one side would have rising damp but one side may have had remedial work or any damp proof membrane/bitumen may have been damaged or degraded on just one side so who knows! Also check for the obvious leaks from any buried pipes/other water fittings.

    In both cases remove an area of plaster and immediately test the underlying brickwork for damp - if that is a lot dryer than the plaster surface, it is most likely condensation rather than damp.

    Did you have a survey? These things should have been spotted and you may well be able to claim against them (depending on the supposed scope of the survey obviously).
  5. Blue Girl

    Blue Girl New Member

    Sorry for may impatience! Thanks very much for your replies.
    I've taken the plaster off the walls around the damp areas and in both areas the bricks are very wet. I'm gonna have a look under the floor and check out the damp course and vents. There's definitely no pipework in the wall. As for condensation, the house has been empty for about a year, but i've been working there over the last six months. There's no heating installed at the mo, but it's not especially cold, and i've not noticed any signs of condensation at all - not even along the bottom of the windows so i don't think it's that.
    If it is an area of damp course that is damaged, is it easy to repair?
    Also, what is the best course of action for repairing the walls. Do I just let them dry and re-plaster or should i use some sort of damp protection or anything?
    One final question, is the damp likely to have caused the damage to the bricks outside, or are the blown bricks likely to be causing the damp?
    Thanks again for your help.
    Blue Girl
  6. devil's advocate

    devil's advocate New Member

    Hi B-G.

    Unoccupied houses can tend to have a damp musty smell because they've been left unvented (windows tightly shut) so air inside is stale. However, actual condensation to the extent you are experiencing needs a source of moisture - often things like showers, tumble driers, etc - and this is very unlikely to be the case here since none of these things have been used and the actual ambient temp has been reasonable high the last few months.

    So, I suspect very strongly you have rising damp on your internal wall, and possible rising and penetrating damp on the external one.

    A fix is quite straight forward - lift the floorboards, locate where the DPC has failed, jack up the floor joists (er, good chance they'll need replacing - likely to have some rot), and insert new DPC making sure it overlaps the ok original stuff a fair bit. If the timbers look to be ok, at least spray them with timber rot treatment. This is not really a big job even if you have to have someone else do it. Make sure the 'fluffy' stuff is identified - as I said before, if it's DRY rot, it'll need eradicating from the timber AND walls.

    The damp on the external wall could be from a similar cause. The fact some external bricks have blown can certainly allow more moisture to penetrate, but that's what a cavity is for - to prevent it getting through to the internal skin. Pure guesswork whether your cavity insulation material is acting as a bridge.

    You certainly want the blown bricks replaced - this shouldn't be expensive; a well known co in London was doing them for £10 each - unless there's lots top do! Does the actual pointing need redoing? That can also allow water to penetrate.

    Anyways, you need to life floorboards around all the damp areas and get some peeps in for a look-see.

    Keep us posted on the outcome.
  7. Removed 4

    Removed 4 New Member

    Does the actual pointing need redoing? That can also allow water to penetrate.

    I was wondering earlier why no one had asked about the condition of the pointing to this 1940's house.

    I wouldn't be at all surprised if that cavity were to be found <u>full</u> of muck droppings at low level (as touched on by Mr Grimsby, earlier).

    I would remove a few outer bricks just above damp just to see if the cavity needed a darn good D and C......

  8. lightning bolt

    lightning bolt New Member

    i own a 40s house doing it up to rent out this had a bad damp problem ,i replaced row of bricks with blue bricks and a damp course sorted :)
  9. devil's advocate

    devil's advocate New Member

    B-G, it's the colour of your bricks, love - you need 'em as per your username.
  10. fitero

    fitero New Member

    Dont do the pointingdontdothepointingdontdothepointing.
  11. sooperman

    sooperman New Member

    Check that you have a dpc course around the parameter of the house. If you do not you can inject one. Also make sure that you have air vents if you have suspended floors and that they are not blocked as ive been on many a job where people have blocked them to stop drafts coming in. Another thing you sound like you might need to replace he pointing as that will cause penetration. If you live in the london area email me and il give you a quote or tell you the best way and what plasters to use. Pics would help. Good luck.
  12. Big Jumbo

    Big Jumbo New Member

    Just to add to the excellent responses, is it possible that a pathway has been laid /soil allowed to build up and bridged the dpc. Check first that there is at least one brick showing below the dpc all the way round the house.

    Sorry if this is already covered and I missed it...siesta time calls :)
  13. Mr GrimNasty

    Mr GrimNasty Active Member

    And thank you for your most excellent suggestion too.
    Party on dudes.
  14. Blue Girl

    Blue Girl New Member

    Thanks for all your replies folks.
    Pointing looks fine. Other than that, i'm going to need to do some digging around - probably won't get a chance 'til weekend, at the earliest, so probably won't be an update till next week, but i'll keep you erm....posted.
    Blue Girl
  15. devil's advocate

    devil's advocate New Member

    Hi B-G.

    By digging around, do you literally mean 'digging' around?

    Can you tell where the DPC is on the outside - it should be fairly obvious. If not, take a level out from the inside floor of the house and it should be around, ooh, 10" below thatish.

    If you can see where the DPC layer is, and the surrounding ground outside is a fair bit below that, then don't bother digging - it's unlikely to be the problem.

  16. paddyodoors

    paddyodoors New Member

    rising damp is a myth
  17. Ooh - the enigma.

    Explain, oh wise one.
  18. Blue Girl

    Blue Girl New Member

    Hi Devil's Advocate
    No, should have been a bit clearer there.
    What I actually meant was crawling around under the floor boards. It is a fairly deep gap, so easy enough to do. Not checked the vents properly yet. Been dark when I've got in from work every night this week, so can't face it! Will look this weekend and report back!
  19. Fairy Nuff

    Fairy Nuff New Member

    Looking forward to the next instalment.

    D A.
  20. Blue Girl

    Blue Girl New Member

    Sorry it's been a while since i updated this, I've been dead busy.
    Anyway, had a look under the floor - vents all clear, damp course bridged where damp is on inner wall, so sorted that, but couldn't see any obvious problems with wall under the front window.
    So, what i've done is, removed all the wet plaster and put in a piece of foil backed plaster board i had knocking around, then skimmed over it. That was about 2 weeks ago. The inner wall where I fixed the damp course, now seems fine. The window wall still has a problem though:
    The new plaster has dried out, all except a thin line around the edge which is still pretty wet. The old plaster immediately next to it is completely dry, as is the rest of the new.
    There's no heating in the house at the moment, but it isn't particularly cold in there and i've had a fan heater on it when i've been there. Could it just be that it's too cold for it to dry out? Or is it drawing moisture from the wet brick around it? If this is the case, can't figure out why none of the old plaster near it is wet also?
    So, anyone got any ideas what to do next? Once i get heating on in there, do you reckon it'll just dry itself out? If the reason the bricks are wet in the first place, is that the old window was badly fitted (the only thing i can think of now!) should they have dried out by now - 6 months on?
    Do any of these products that you paint over damp patches to stop them showing through paintwork etc actually work?
    Any help'd be much appreciated - it's driving me mad at the mo!

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