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Damp circles on outer wall in ensuite

  • 17-01-2023 1:41pm
    Registered Users Posts: 29

    I'm living in a new build (A rated) for just over 4 years. I'm the first owner. I've noticed for maybe the last year that damp patches have formed on the outer wall in the ensuite. I've circles them below in red. All other rooms are fine.

    The first ones to appear were the two directly above the window, on the top part of the bay. These are exactly symmetrical with each other which is unusual. Maybe this is where the screws are?

    Top left side of bay:

    Top right side of bay:

    Then more recently (some time after the summer) additional ones started appearing on the wall above the window, as well as an additional one right next to the extractor.

    The outer wall has insulated slabs (400mm insulation) on the inside of the block. Then presumably insulation in the cavity between the blocks.

    The damp is worse after I have a shower in there.

    I'm not sure if it's a ventilation issue as the extractor comes on with the light (I always ensure it is on regardless of whether I need the light on or not). Also the extractor itself provides ventilation even when off.

    I usually have the window open during the day, unless it's really cold out.

    This is the outside of the house on the gable end where the ensuite is (photo keeps uploading sideways, not sure why). I can't see any obvious problems on the outside wall.

    Is this issue something the builder should look at? I'm only in the house 4 years. Even though I know he will try to blame me for the lack of ventilation (e.g. not opening window). I'm worried that the insides of the wall might be really damp and I'm only seeing it right now where the screws are.

    Do you know if Homebond do a moisure check on the walls? I recall the guy fitting the kitchen telling me that the walls were moist (he told me this after I asked his advice on mounting a TV bracket on the wall as I've never hung something off a wall with insulation on the outside of the block). He said he thinks maybe the house was built too quickly and possilby required longer time to dry out. I said this to the builder who said Homebond signed off the house so there were no issues.

    Do I have any comeback here with the builder or homebond?

    Any thoughts on the cause of these damp patches, and whether some damage might already be done inside the wall? I don't work in the building trade so don't really have a clue about this.


  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    You need to retain a Construction Professional to carry out a Survey of your property using Surveying Instruments, Moisture Meters, Relative Humidity instruments, Data Logger, etc. in order to diagnose the cause of the stains

    I cannot make any diagnosis with the details you have provided

    The Builder saying that “Homebond signed off on the house and there were no issues” - is a load of unadulterated rubbish. It will be a waste of time asking him anything.

    Homebond provides a Structural Guarantee. I do not see these as structural defect.

    There was a Construction Professional with Professional Indemnity Insurance, who provided a Certificate of Compliance with the Building Regulations and after 6 years you will be Statute Barred from taking any legal action.

    You mentioned screws. Are there screws under every stain.

    The TV guy might be a building expert, but the walls of a house dry out in a few weeks after construction.

    You asked do you have a comeback with the builder??. - This is a legal question, and may depend on what is causing the damp patches.

    Retain a Construction Professional immediately to diagnose the cause of the dampness and the remedial action necessary to eliminate same.

  • Registered Users Posts: 3,371 ✭✭✭chooseusername

    Maybe nothing to do with it, but if that's a soil vent pipe to the right of the vent, it should be a meter above that window.

    If it's insulated plasterboard (400mm?) it may be that the steel mushroom fixings have not been insulated.

    As for Homebond sign off, I thought they just signed off the structural work.

  • Registered Users Posts: 29 millsy

    Yes there are screws under every stain. I ran a magnet over the rest of the wall too and it didn't stick. However around the window bay which also gets damp after a shower there is metal.

    There's another part of the wall on the inside of the ensuite close to the door that is a bit discoloured from damp. The edge on this has metal which is where the damp occurs. More so the top half. Not sure if the bottom gets damp. I'd need to check after my next shower.

    Because this wall which is separate to the outer is getting damp (although not as severe as the outer wall) I'm wondering if it is indeed a ventilation issue. If it is then I'm not sure what more I can do with regards to improving the ventilation.

    Sorry a typo with the insulation thickness. Should be 40mm.

    And yes it's a soil vent (taking waste from ensuite to the sewer below the house).

  • Registered Users Posts: 757 ✭✭✭C. Eastwood


    You said that the wall is drylined with a 40 mm insulated slab on the inside.

    These slabs are probably mechanically fixed in place with Metal Mushroom.

    The diameter of the head is approximately 35 mm.

    It appears that these metal fixings are producing a Cold Bridge as they are drilled in to the block wall, and the metal is causing the cold from the block to be conducted in to the head of the mushroom, which in turn is causing surface condensation to form on the 3 mm cold gypsum plaster covering the metal head. Usually with this problem there would be a mild dark olive green mould form on these spots over time.

    However, on one of your photos you refer to a metal angle bead fixed on to the plasterboard slab. There is supposed to be a 12 mm slab and 40 mm of insulation behind this metal bead, and therefore the bead in approximately 50 mm away from the block wall. And you state that there is more insulation in the construction of the wall. Under normal habitable circumstances it would be almost impossible for surface condensation to form on this metal angle bead.

    Condensation is caused as follows:-

    S - (I + V) = C

    S = Steam. ( including moisture )

    I = Insulation

    V = Ventilation

    C = Condensation.

    I cannot understand how a new build, A rated Dwelling has these problems.

  • Registered Users Posts: 29 millsy

    Mould has formed on these spots. I've had to use a spray (Cillit Bang Black Mould Remover) to remove it.

    Is it possible that the extractor fan is inadequate to remove the steam and I might need to install a more powerful one?

    Any idea how to treat these damp patches e.g. dry them somehow (with hairdryer?) and paint over them? Any special paint to provide some kind of damp proofing like an undercoat before painting with normal paint that's already on the walls there? Or is painting over damp a bad idea?

    Any other suggestions?

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  • Registered Users Posts: 6,228 ✭✭✭10-10-20

    "There's another part of the wall on the inside of the ensuite close to the door that is a bit discoloured from damp. The edge on this has metal which is where the damp occurs. More so the top half. Not sure if the bottom gets damp. I'd need to check after my next shower."

    Upper-half of an inner wall...? I'd be inclined to think that it's moisture related too.

    I'd recommend a few temperature and RH meters and monitor the average RH value around the house. In the main living rooms it should be able to drop to just over 50% at ~20 degrees C or thereabouts on an average dry day. The bathroom should also drop to below 60% at 18 C.

  • Registered Users Posts: 3,371 ✭✭✭chooseusername

    As an internal wall it probably has no insulation and connected to the exterior wall, so there would be a cold bridge there.

  • Registered Users Posts: 29 millsy

    I wonder if the builders didn't do something right? Any comeback against them?

  • Registered Users Posts: 11,459 ✭✭✭✭Ush1

    It's a cold bridge from the mushroom fixings as said, very common. Tricky one other than ventilating more I would think.

  • Registered Users Posts: 12,072 ✭✭✭✭Calahonda52

    fan is crap, need to relocate the fan location to inside the shower, so will need a LV one, with a run on timer with a decent flow rate.

    Its also too close to the door, which is where the replacement air will come from so basically its a sh$t fan in the wrong location.

    Also consider putting a 4 " perspex drop down from the ceiling around the shower so as the moisture laden air is kept inside the shower area while the the 5" fan does its work.

    I suspect the bathroom is cold so you might consider having a wall mounted fan heater, also on a timer, fitted which will run in conduction with the fan.

    The fan heater will heat the air and this heated air can carry a higher moisture load.

    As for comeback, forget about it, as Clint says its not structural

    “I can’t pay my staff or mortgage with instagram likes”.

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  • Registered Users Posts: 29 millsy

    Bathroom not typically cold. House is A rated with air to water heating (which is always on) so never too cold.

    In fact I often have the window open while showering to help remove some of the steam. But I wonder should I keep it closed?

    Thinking about your perspex suggestion, before considering that option, would keeping the shower door closed help a bit? It would force the steam to only leave the shower area through the part above the shower door which is a similar height to the fan.

  • Registered Users Posts: 6,118 ✭✭✭screamer

    My thick insulation does the same it’s the cold bridging. Just open the windows after showering and ventilate the room well. Cold bridging will cause condensation no matter the energy rating.

  • Registered Users Posts: 6,228 ✭✭✭10-10-20

    "Also consider putting a 4 " perspex drop down from the ceiling around the shower so as the moisture laden air is kept inside the shower area while the the 5" fan does its work."

    A highly under-rated solution there. Makes a massive difference when there is effective ventilation within the shower enclosure. LV fan essential as also mentioned.

  • Registered Users Posts: 29 millsy

    As a short term and immediate solution I was thinking about applying some kind of damp proof paint. Something that might break that bridge between the mushrooms in the wall and condensation on the wall by reducing the cold spots.

    Any idea if something like this exists?

  • Registered Users Posts: 651 ✭✭✭madmac187

    Metal mushroom fixings is issue. Brother in laws place riddled with it in a dry lined house. We use plastic mushroom fixings in work, it stops the cold bridging.

  • Registered Users Posts: 29 millsy

    Right so ideally if I can open up the wall and replace the metal mushrooms with plastic ones then in theory the problem should go away. Makes sense.

    I presume the plastic ones do the job (of attaching insulated plasterboard to block wall) as well as metal ones?

  • Registered Users Posts: 6,228 ✭✭✭10-10-20

    You can't just whip out the old metal mushrooms and replace them with nylon ones, they don't readily come out of the wall like that. Plus there are some concerns for fire safety with the nylon types as they may compromise the wall in the event of a fire.

    You probably should check to see if the metal mushrooms have their plastic thermal caps installed. That's this thing:

    Not sure how effective it is in a humid environment though.

  • Registered Users Posts: 29 millsy

    Ah right so these plastic caps should stick on to the existing mushrooms (assuming they don't already have them). That would definitely be easier than trying to remove the existing mushrooms.

    Seems like a straight forward solution:

    • Cut out the plaster in front of the mushrooms
    • Attach the caps
    • Slap on a bit of Polyfilla
    • Paint over it
    • Problem hopefully gone, or at least minimised

  • Registered Users Posts: 3,371 ✭✭✭chooseusername

    You might need to give the mushrooms a few taps to sink then a couple of mm

  • Registered Users Posts: 6,228 ✭✭✭10-10-20

    Yes, good point. You'd need to scrape back a small amount of the surrounding plaster with a knife from the outside diameter of the mushroom head so that they clip-in. But first do a test drill to see if you have mushrooms there first.

    As I said, these aren't magic, but they are recommended to break SOME of the thermal bridge.

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