Mould 11 days after tanking membrane

Discussion in 'Builders' Talk' started by 1978kg, Oct 2, 2018.

  1. 1978kg

    1978kg New Member

    2D3D3953-C0F4-4FB0-BF1A-8E34F697CEAA.jpeg 9245DC1C-84AD-47FE-A74E-F671E16B63D7.jpeg ok, so this is all new to me - I’m looking for the opinion / comments from people in the know.

    Apologies for the long post but you’ll have the full run down.

    In short - Newly tanked basement is mouldy within a 11 days.

    Not long moved into 1890/1900 stone terrace.

    The basement was damp, long story short - years of water coming from a leak outside (managed and hidden by the seller). Anyway- Yorkshire fixed it all, we hired an industrial scale Dehumidifier for almost 2 weeks until bone dry. More test by YW, and a few weeks later it was officially dry.

    We had some builders in to tank it (the room is around 3.5m square (only small but wasn’t useable).

    The job they did:

    1. Dig up 2 x old concrete floors out (makes it just over 6ft 6” in height).
    2. Remove original/damage lath ceiling.
    3. Remove old (redundant) lead pipe from middle of the wall all way around.
    4. Move mains water pipe from middle of the wall to ceiling height.
    5. Reroute some radiator pipes.
    6. Made good stone walls - Always been bare stone - with patches of mortar missing / uneven, etc.
    7. Dig a hole in a corner for sump and sump.
    8. Lay a bed of sand followed by visqueen, then concrete to floor (leaving 3 to 4” gap around the edge for the drainage channel - no sand/concrete around the edge).
    The area where the sump is only has concrete and visqueen up to one edge. It is in an alcove so they dug the hole there - they submerged a plastic tub and concreted around the other 3 edges. The channel runs into to tub from the edge where the visqueen is.
    9. Fasten membrane to the wall, using membrane plugs (and membrane tape on vertical joins).
    10. They laid the drainage pipes around (most of the wall). They laid it around the square - not in the two alcoves (one of which has the sump/pump. The channel was laid on to bare ground, the visqueen overlap pulled over the top and a thin layer of concrete over the top of the pipes. I’ve noticed there is no membrane seal between the floor and wall - not sure if this is an issue.
    11. Lag and box in mains water pipe.
    12. Fixed acoustic insulation and acoustic plasterboard to ceiling.
    13. Plumb for radiator.
    14. Dot & dab ordinary plasterboard to walls. Because the walls were uneven they used pieces of board to pack it out in places - they also used pieces of board to keep boards off the floor - keeping a small air gap around the bottom.
    In the middle of this - the mains pipe needed moving a bit more - this spilled some water behind the plasterboard - with nowhere to go.
    15. Thin coat of plaster to walls and ceiling - done over 2 days. 1 wall and ceiling one day - followed by 3 walls and odd bits a week later.

    The first plaster job took about 5 days to get about 85% dry.

    The second job was 50% dry after 5 days.

    I was told to let it dry naturally - get a small heater and fan if necessary but natural is better.

    I left the basement door (at the top of the stairs) open most of the time - it is the only ventilation to the basement - not great as only leads into the dining room.

    As I say, after 5 days it was still wet - told the builders who said to ventilate and wait it out. I noticed a mold smell and mold appearing on the plaster (one the bare board and fresh plaster).

    I got a small heater and fan, also got a dehumidifier.

    I haven’t really used the heater/ fan - it got very humid very quick when I put it on. The dehumidifier has worked well - over 20 litres in 3 days. It’s been on most of the time since.

    The board felt damp at the bottom. The edges of concrete - on top of the channel is damp to touch. Cutting a small hole out the plasterboard (without damaging the membrane) - I see the inside of the membrane is wet at the bottom of the wall where the concrete floor meets the membrane. The back of plasterboard is damp to touch and moldy (smells).

    It’s only been 11 days - the dehumidifier is on all day. The builder says leave it another week.

    The radiator is going in and I have someone coming around to look at feeding a positive input ventilation system into the basement - which I think should keep it dry but I am concerned the mold smell won’t got anywhere and might even get worse.
     
    Last edited: Oct 2, 2018
  2. Mr Rusty

    Mr Rusty Screwfix Select

    Think about how much water is used to mix the various concretes, board fixing, skim. In a basement this is going to take a long time to dry, and with high humidity and cool walls you are inevitably going to get condensation and mould.

    Keep that dehumidifier running, get some heat and ventilation in if you can.

    When laying wooden floor over concrete slabs they reckon a minimum 8 weeks/ 5-6cm slab + 4 weeks for every cm over that otherwise trapped water can warp the floor - it might seem dry, but there is still trapped moisture to come out. Add in skim/ D&D needing to dry out and I reckon it will be several months before it is totally dry, assuming no more water is coming in.

    Doesn't sound like you really have a problem other than it is going to take a bit longer. Don't seal/paint anything for a bit, or it will take even longer to dry out.
     
  3. masterdiy

    masterdiy Screwfix Select

    1978kg, You could post up a couple more pictures so we can see better. (use thumbnails)

    New concrete floor 3.5 mts squ, how thick?
    Plus the plaster work, I would say, lack of ventilation plus lots more of drying out to do.
    Get your radiator working, & ventilate.
    Why have you got drainage pipes around ???
     
  4. Richard_

    Richard_ Screwfix Select

    Also an oscillating fan, moisture evaporates from a surface much more quickly with moving air.
     
  5. 1978kg

    1978kg New Member

    BBE63046-AFCC-4D2B-BAAC-904483ABC51C.jpeg 1D10286F-9DD4-46A9-AC37-2020F96F03E4.jpeg BBE63046-AFCC-4D2B-BAAC-904483ABC51C.jpeg 3B953B2F-520C-47B0-8B92-91F3B09C6136.jpeg 153AB7B5-42EB-4AFF-A531-4CC2C2E14281.jpeg CA6CE009-DE8F-4A8B-A093-8EF594D0F34F.jpeg 20C1B165-C5EC-4B0C-AC47-BF491494D82F.jpeg 95ABF9AF-2E1F-4FDF-B4EB-28BF8B4702E9.jpeg
    Masterdiy, thank you for the reply.

    Here are a few thumbnails.

    If I remember right, the floor is 160mm thick.

    Radiator is being plumbed in the next few days. The PIV - possibly in the next 2 weeks.

    They have still to fit the wooden stairs - using a ladder at the min. They’ll be fitting them in the next few days.

    I’ve had the small heater and oscillating fan to start - didn’t seem to make a huge difference. Adding the dehumidifier made a difference (of course).

    No natural ventilation in there - so think the PIV is needed.

    The pipes are because the house isn’t far from the river and occasionally the water table can get high - not very often but we want the room be useable. One of the neighbors did there’s over 25 years ago and still going strong - apparently the pump has only ever kicked in twice in 25 years though (he didn’t have an issue - the rest of the street did).
     
  6. Isitreally

    Isitreally Super Member

    Im not seeing any tanking in those pics. ??
     
  7. 1978kg

    1978kg New Member

    FE6642E3-55F2-43D0-B7BA-EC097A1198FA.jpeg
    It’s behind the plastered board - it’s a membrane. Here is pic with a little still exposed.

    At the gap at the bottom the membrane is a little wet in places - only where the concrete meets the membrane or visqueen.
     
  8. masterdiy

    masterdiy Screwfix Select

    Quote " floor is 160mm thick." What? Over 6" thick.
    That is going to take some serious time to fully dry out.
    As mentioned, plaster + concrete will take weeks.
    Mr Rusty mentioned 8 weeks plus.

    I would not be surprised if it takes 3 months.
    So keep the dehumidifier going.
     
  9. Richard_

    Richard_ Screwfix Select

    It's the combined fan, heater and dehumidifier that will dry it out. The heater warms the air to increase the amount of moisture that the air can hold. It might warm the walls a bit but you haven't mentioned insulation so the wall and floor will be constant at a few degrees above ground temp.

    The fan makes a big difference in getting the wall moisture from the surface into the warm air.

    The dehumidifier grabs the water out of the air, but only because the fan and heater got it there in the first place.
     
  10. 1978kg

    1978kg New Member


    That was a typo - it’s 100mm thick. Still, sounds like it will take a while to dry out.
     
  11. Martint86

    Martint86 Member

    The spots on the membrane let air flow behind it, water in between the wall and plastic runs down to the floor, so the floor joint shouldn't be taped up, there should be a drainage channel all the way round, they did use fixing plugs with seals on the heads didn't they?
     
  12. 1978kg

    1978kg New Member

    Ah, I see - so the visqueen shouldn’t be taped to the membrane (with the channel running all the way around).

    Yes, they used the plugs with a seal on the head. They also used membrane sealing tape on overlaps followed by a thick permaseal strip. They applied the same to any areas of potential weakness.
     
  13. Martint86

    Martint86 Member

    Yep if its taped to the membrane that's good, sounds like you've got nothing to worry about and it's just residual moisture from work carried out
     
  14. 1978kg

    1978kg New Member

    Just to clarify, the wall membrane is not taped to the visqueen. The concrete has trapped the two together - the channel is underneath.
     
  15. Beeero

    Beeero Active Member

    I think you are over reacting a bit! it’s only been a week and a half you need to warm the room and get maximum airflow, that’s going to take weeks to dry out properly
     
  16. 1978kg

    1978kg New Member

    I’m not saying there is an issue per se - just looking for opinions / comments from people in the know as haven’t had this kind of work done before - knowing what mold smells and looks like I wanted to check it out on this forum rather than take the ‘wait and see’ approach.

    Taking the advice on here (which is not what the builders said - they actually said they would not get a dehumidifier and fan), it is getting a better - it’s a lot drier, the smell seems to be going and there doesn’t seem to be any new mold appearing.

    I’m forking our for a positive air system to bring fresh air in so that should help.
     
  17. Beeero

    Beeero Active Member

    Wasn’t a dig mate just being frank. I wouldn’t use a dehumidifier either you want to encourage it to dry not force it. I certainly be giving it 4-6 weeks to dry. Keep it warm and get some airflow
     
  18. Mr Rusty

    Mr Rusty Screwfix Select

    Um, it's a cellar. Exactly where does the water vapour that comes out of the walls and floors go? Using a dehumidifier is exactly the right thing to do because that water ends up in the tank, and you carry it out and dispose of it. Yes, warming it and getting airflow will move the water from the fabric to the air, but then where does it go? you either pump air in and out from outside so you transport the water away with air movement or use a dehumidifier. Just moving water vapour around the room dries nothing.
     
  19. 1978kg

    1978kg New Member

    I get it, wasn’t taken as a dig fella.

    Lots of people have said use the dehumidifier - when the positive air system is in I’ll probably turn it off (that’s in 2 weeks).

    To be honest the damp and mold growth would have spread quick without the dehumidifier - the spores were spreading quickly and the plasterboard was getting damper as the water had nowhere to go.
     
  20. blarblarblarblar

    blarblarblarblar Active Member

    Should it have been boarded and skimmed with so much water about, looking at the skimming at the bottom, I’d be be wary, sounds like and looks like it’s been a little rushed.
     

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