Slab moisture ingress can cause indoor mould growth because it not only adds moisture and humidity to the indoor air environment but it can also cause the house to act as a petri dish where mould will grow, spreading spores around the house. This can happen if it hasn’t cured properly, of if there are gardens with soil covering the weep holes—small rectangular spaces left between the bricks at the bottom of the outside wall—where moisture from inside the building envelope can’t escape. Another reason is the slope of the property, rainfall needs to drain away: Don’t expect that ridiculously heavy rainfall will soak into the ground, it needs to run away from the property of into drainage channels.
I found out the consequences of slab moisture ingress at my last residence, before this rental property, when I lived in The House of Mouldy Horrors. (I do have a post in my drafts folder titled, The House of Mouldy Horrors, which is why I have been referencing it in my posts for like, the last two years or is it three now?), on how we (My Daughter and I) managed to remediate this situation including most of our possession kept in the house, including medical assistive devices such as InovaAir Purifiers but due to the stress or ustress (stress you use to create action), that I’m under, I’d rather not think about that right now. I have a mould-free house to build; or rather, lay in bed an write about it. I’ve not been there since I became chronically ill from a bunch of things at the house.)
(Just a note to new readers: my health went from good to bad in The House of Mouldy Horrors, and I suffered painful symptoms that were the beginning of chronic illness on top of chronic illness, I now react to outdoor moulds as well. I’m trying to get on top of this; and I’m trying to build a safer, mould-free home, where I WILL recover. Right now though, I can smell damp soil all the time because I live in a draughty beach-house. One doctor, recently diagnosed me with “what appears to be CIRS (Chronic Inflammatory Response Syndrome) caused by mould” illness. Another doctor, my main Allergist, says I do indeed get sick from mould but he also says, “It’s not your only problem.”, meaning inhalant allergies to other chemicals other than mould.)
The white patches are efflorescence (a build up of a (harmless) white coloured powdery substance). The three rooms, all bedrooms, that had these wet patches in the concrete, coming from the slab edges that ran parallel with the outdoor gardens originally had carpet in them. When I moved into this house, the owner removed the carpets due to my allergies; ergo, if we hadn’t of done this it may have taken longer for the concrete leak to become apparent. I imagine the carpet would have taken on a mildewy odour–but not before the mycotoxins (the chemical in mould) outgassed into the air making me ill. Instead, each time it rained heavily, the house took on the odour of damp soil. And then I got sicker. It was inconvenient to pack up and move but necessary.
Those photos were taken in the main bedroom where I slept for the first year in that house; it had a garden bed and a tap on the outside of the house, running parallel to my to the room.
As a precaution, for the Build an Eco-Friendly, Allergy-Free House project, we’ve particularly asked our plumber, Kale from KLM Plumbing not to install any taps near the edge of the house anywhere near the slab edges.
We’re also not putting any garden beds or grassy areas around the house. In fact, we’re using more high-energy-embodied concrete to put a pathway around the whole house. (And, so that we can conserve energy within the building via our slab [thermal], we’ll add insulation between the house slab and the concrete path. But more on this later.)
The majority of houses incorporating wellconstructed and well-detailed concrete slabs and footings experience no problems with slab edge dampness. Where problems do occur, there may be one or more of several causes. A thorough investigation is required to determine the most appropriate course of action to rectify the problem. Most slab edges are occasionally damp due to rain, garden watering or by contact with the ground. In some cases this dampness is able to permeate from the outside to the inside and affect the internal walls and/or finishes such as the floor coverings. Preventative measures are far more effective than facing the often difficult and costly repairs required to remedy problems caused by slab edge dampness and moisture ingress.
Not to mention the cost of a water damaged building (WDB) to human health!
Indoor mould caused by dampness and high humidity can impact on medical conditions such as Asthma, Inhalant Allergies, chemical sensitivities, respiratory inflammation, Toxic Encephalopathy, Occupational Asthma, Irritant-associated Vocal Cord Dysfunction, Reactive Airways Dysfunction Syndrome (RADS), Irritant-induced Asthma, Small Airways Disease or Multiple Chemical Sensitivity (MCS).
The initial indication of a problem is usually persistent dampness of the exposed face of the concrete slab/footing, often resulting in associated efflorescence (a build up of a white coloured powdery substance) below the damp-proof course (DPC). There’s your red herring, right there: The DPC may have had lost it’s integrity or may never have been laid properly in the first place.
To fix the above problem, we needed to employ someone to dig out the gardens and pour tar against the slab edges, therefore, sealing them from slab moisture ingress. Due to my sensitivities to petrochemicals, this wasn’t an option. However, had I known before I moved in, it might have been. It was 2010 and my health had recovered from the mysterious chemical sensitivities; but by 2012, my health and level of tolerance for fragrance, petrochemicals and solvents was at ground zero.
To avoid slab moisture ingress:
- Slope the surrounding soil around your building by 50mm before attempting to lay any paths or garden beds
- If you suffer symptoms from mould exposure, keep garden beds away from the side of the house
- When laying concrete around your house, make sure to insulate or better still, water proof the edge of the slab
- Get professional Arborist before planting large trees to avoid tree roots blocking outlets to storm water drains
- Avoid over watering adjacent to slab footings and edges
- Have your plumber install unground pipes that drain water away from your home, which is what KLM Plumbing are doing for us
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