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Damp and Sub Floor Ventilation in 1880s Victorian

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  1. #1
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    Default Damp and Sub Floor Ventilation in 1880s Victorian

    I'm relatively new to this game but have been trawling through these forums lately and have found so much great information. I have an 1880s solid double brick Victorian in Melbourne that's showing high moisture levels around the lower parts of the inner walls which I'm trying to diagnose and resolve. My current theory is inadequate subfloor ventilation combined with previously poor drainage has left the subfloor quite damp and is leading to moisture being drawn into the walls which can't escape easily due to internal cement render and external painting.

    This is a bit of a brain-dump but I hope it gives a bit of context:

    - There are no obvious signs of rising damp (efflorescence, etc.) however the paint on the walls has lifted in spots and peels away really easily leaving bare plaster. Judging by old real estate photos the paint job looks like it was done in ~2007. The plaster itself looks relatively new, I'm guessing within the last 15-20 years. Beneath that appears to be a cement render (photo attached) before you get to the brick itself.

    - Externally the brick has been painted. Not sure the history of this.

    - A very helpful chap came by and checked for moisture levels at the 2m mark thoughout which returned nothing, making me think it's not penetrating/falling damp.

    - Judging by Google Earth the roof was replaced in ~2016 and may have been leaking prior to that. There are noticable repairs/new paintwork in corners of the ceiling.

    - The previous owner had the downpipes just dumping directly onto the earth/pavers on either side of the house. We fixed this ~3 months ago so they're now diverted out to storm water.

    - There's currently no access traps for subfloor access but there appears to be ~220mm between the earth and the floor which is a suspended timber floor.

    - The floor itself is cork tiles on yellowtongue which then appears to be on top of old floor boards. I've only been able to ascertain this buy sticking a camera through the external vents.

    - Externally there are 2x vents approximately 230mm x 80mm per room (photos attached).

    - The building has bluestone foundations ranging in size but generally quite large, i.e. not bluestone rubble.

    - There's no obvious damp/mould smell in the house but as you scrape away paint from near the skirting boards you definitely notice it.

    - During periods of heavy rain we notice what appears to be condensation around the lower area of walls, just above the skirting boards.

    - A joist appears to be failing in one corner of the house where the floor sags ~20-30mm as it joins the wall.

    - The building has had an extension put on the back (~1982) and a concrete slab was laid.


    I've attached a couple of photos showing the vents, the cement render and have annotated the old plans to show the vent locations (red circles) and the downpipe locations (black arrows).

    I'm getting access traps cut in the next few weeks to re-level the front right corner of the house so that should provide a bit more information as well.

    Given all that, does my initial theory hold water? I'm imagining the vents are insufficient and I should look to replace them with more efficient designs (wire vents, I guess). I'm also wondering whether I should look into subfloor ventilation fans but ideally I'd prefer a natural movement of air.

    Thanks for taking the time to read all this!

    Plans (red circle = vents, black arrows = downpipes)

    plans.png

    Internal cement render below plaster

    cement-render.png

    External vents

    vents.png

  2. #2
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    I'm pretty new to this game too (bought my first 1880s Victorian back in November) but have learned a couple of things so far. In my place there was a small area of rising damp around one of the fireplaces, otherwise nothing really significant. As you say, no smell of mold, and floors solid overall except one area basically right in the center of the house. Figure that's the hardest area to dry under the floor. Same as you, no traps to get under the floor, and similar distance to the earth underneath. Also similarly, the previous owner neglected the guttering and downspouts in some areas, so when it rains a lot of water is not diverted to drainage. The house was unoccupied for most of last winter, and so without the heat on I think the internal humidity levels inside were pretty high during that period.

    Not having experience in this area and needing to get things sorted prior to moving in, I consulted with Chris at Tech-Dry in Melbourne. I can highly recommend him, he gave me a lot of good general advice on the phone before we had even purchased. He said that the subfloor ventilation in these old houses was never really that great to begin with, and especially in the ones that are quite low to the ground, internal moisture is becoming a more common problem. In the last 10-15 years the weather in Melbourne has also been a bit different to previous, where it used to be pretty frequent brief rains during the wet seasons, it's now more common to see less frequent but heavier falls. Therefore the soil gets more saturated in those periods, and if drainage isn't handling that for whatever reason, it starts to impact the house. Also there's just the fact that at 120+ years old these houses are showing their age in some ways, this being one. Chris mentioned that the skirting boards, being wood, low to the ground, and in contact with the brick/render, tend to soak up moisture both from the walls and also the air, and sometimes give a false indication of damp issues. Some of mine that we removed around the fireplace were showing signs of rot. I wonder if this could be the smell you notice when scraping paint around your skirting boards.

    I had Chris come and do a damp-proofing treatment around the affected fireplace, and was happy with the quality of that work. He suggested that we think about active ventilation below the floor, because they find it makes a big difference in keeping things dry under there and prolonging the life of the timber etc. We haven't gone that route yet, but it's in my future plans after I have some other things taken care of.

    Good luck with it!

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    Thanks! I've tried getting a hold of Tech-Dry but they must be busy at the moment. I'll keep trying them.

    In the interim I bought a large dehumidifier to try validate my assumptions about water being trapped in the walls that just needs to get out. The results aren't too promising though as when I run the dehumidifier for a few days I see the moisture levels in the plaster drop substantially but when I leave it off for a few days it goes right back up. Not sure exactly what this means but it seems like the wall is still drawing up moisture ��

    I should have an access trap cut in at least one of the rooms this week so that should shed some light on the state of the subfloor.

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    Re-reading your original post, am I understanding correctly that the only real complaint so far is high moisture readings at low points on interior walls? Your interior paint/plaster/render is all looking OK and is from ~2007? One of the things Chris told me is that rising damp acts on paint and plaster pretty quickly, so if the existing paint is more than a year or so old and looks undamaged, there is probably no issue there. That's not to say that there isn't still a moisture issue below the floor.

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    Quote Originally Posted by autojack View Post
    Re-reading your original post, am I understanding correctly that the only real complaint so far is high moisture readings at low points on interior walls? Your interior paint/plaster/render is all looking OK and is from ~2007? One of the things Chris told me is that rising damp acts on paint and plaster pretty quickly, so if the existing paint is more than a year or so old and looks undamaged, there is probably no issue there. That's not to say that there isn't still a moisture issue below the floor.
    The plaster is generally in ok shape, barring an area on the side of a fireplace, though the paint is lifting in spots and easily peels away in big sheets.

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    Chris told me that fireplaces are a common problem area, so that checks out. Paint peeling away in big sheets seems strange, almost like a bad paint job rather than being related to moisture. I won't keep speculating though, I'm no expert I'll be interested to hear what you find out.
    Owen in Melbourne

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    Quote Originally Posted by autojack View Post
    Chris told me that fireplaces are a common problem area, so that checks out. Paint peeling away in big sheets seems strange, almost like a bad paint job rather than being related to moisture. I won't keep speculating though, I'm no expert I'll be interested to hear what you find out.
    It definitely wouldn't surprise me if it was just bad paint preparation causing the paint adhesion to fail. Judging by the paint around the place it was done by someone who just wanted to get it done rather than doing it right.

    Funnily enough I just got off the phone with Chris at Tech-Dry who's going to come inspect the place next week, so I'll keep you posted!

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    Quote Originally Posted by Laslo View Post
    The plaster is generally in ok shape, barring an area on the side of a fireplace, though the paint is lifting in spots and easily peels away in big sheets.
    Older house, paint peeling in big sheets ?
    Have you looked at Kalsomine as a cause for the peeling paint ?

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    Quote Originally Posted by droog View Post
    Older house, paint peeling in big sheets ?
    Have you looked at Kalsomine as a cause for the peeling paint ?
    I hadn't thought of that but it doesn't appear to have a wash on the walls. One point worth mentioning is the paint beneath the current paint was this deep pink colour which in areas where it wasn't painted over with the newer paintwork, i.e. under skirting etc. it doesn't remove anywhere near as easily. I'm also wondering if the new paintwork had some bad reaction with the old paintwork

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    We now have an access trap for the subfloor in one of the rooms which has been illuminating. Generally everything under there feels dry and doesn't smell overly musty but I've attached a few photos in case I'm missing something obvious. A couple of interesting points though are that the bearers and joists don't show high moisture levels on a meter but the bluestone footings do.

    Am I right in thinking wood would dry out faster than the bluestone and that overall moisture could be trending down after fixing the drainage, or is that wishful thinking and we could still have a rising damp issue?

    img_2597.pngimg_2596.pngimg_2595.pngimg_2594.pngimg_2593.png

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    I don't think a moisture meter is going to give you any useful reading when you stick it on a slab of bluestone I would expect it's just giving you a measure of surface moisture just from condensation and such. Bluestone is not as porous as brick, so my understanding is that you don't really get true rising damp issues (as in moisture wicking up from the soil) as much if you have bluestone all around. That's why in my place the main area of concern was the fireplace, because there the bricks go all the way down to the earth below the floor.
    Owen in Melbourne

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    Quote Originally Posted by autojack View Post
    I don't think a moisture meter is going to give you any useful reading when you stick it on a slab of bluestone I would expect it's just giving you a measure of surface moisture just from condensation and such. Bluestone is not as porous as brick, so my understanding is that you don't really get true rising damp issues (as in moisture wicking up from the soil) as much if you have bluestone all around. That's why in my place the main area of concern was the fireplace, because there the bricks go all the way down to the earth below the floor.
    Good point, I donít really know what I was expecting measuring the bluestone haha.

    Iím now pretty puzzled where the moisture in the walls is coming from though.

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    Quote Originally Posted by Laslo View Post
    Good point, I don’t really know what I was expecting measuring the bluestone haha.

    I’m now pretty puzzled where the moisture in the walls is coming from though.
    I will place an amateur's wager that Chris will tell you it's got more to do with humidity in the air than anything else, and may be unrelated to the paint and (possible) skirting board issues. I'll be interested to see if I'm right
    Owen in Melbourne

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    Bluestone does hold some moisture and the old mortar even more so there could be some wicking of moisture into the bricks. It does look dry though. Do you have a watering system against the house at all or well watered garden beds? Given the dryness in the subfloor I would be checking outside as well

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    So what's the update? Inquiring minds want to know
    Owen in Melbourne

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    Quote Originally Posted by Laslo View Post
    I hadn't thought of that but it doesn't appear to have a wash on the walls. One point worth mentioning is the paint beneath the current paint was this deep pink colour which in areas where it wasn't painted over with the newer paintwork, i.e. under skirting etc. it doesn't remove anywhere near as easily. I'm also wondering if the new paintwork had some bad reaction with the old paintwork
    this could be the issue.
    As mentioned above by droog Kalsomine paint could be the culprit.

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    Any update on this one? Just curious to know how it turned out.
    Owen in Melbourne

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    Sorry for the late follow-up here! Chris from TechDry came around and indicated it does appear to be rising damp but that it's something we can live with until we decide to renovate in the next 5 or so years at which point we'll tackle the problem.

    Still no real indication as to where the moisture is coming from though unfortunately. In more of my usual unscientific tests I placed a hygrometer at each of the vents to measure the humidity of the air exiting the subfloor and nothing seems too outrageous so now I'm wondering if things are slowly drying out after repairing the draining in December. I'm going to continue monitoring the moisture levels over the next year and see if things are trending down.

    As for the paintwork I'm just going room by room and removing all the loose paint and repainting. It's time consuming but I'm much happier knowing that the walls are correctly painted now.

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