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I've moved into a new place that had some mould growth on the ceiling in one of the bedrooms. I found a leak in the roof that corresponded and patched that up and cleaned up the mould. A few weeks later, it's back. I couldn't see any additional moisture up in the roof though. Can mould subsist on paint? Or the latent moisture in the room? Or does this indicate there is moisture getting through still, possibly just a small amount that wasn't visible when I checked it.

Thanks

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    Do you have access to an attic above the spot in the ceiling? What was your method for cleaning the mold?
    – JACK
    Apr 7, 2021 at 23:46
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    What did you clean the mould up with @probablyatthebeach - I've read that bleach based cleansers just "whiten" the mould (so you can't see it), rather than actually killing it. Also what's the airflow like in the room .. non-damp/dry air is also needed to get rid of mould too.
    – Mr R
    Apr 8, 2021 at 0:23
  • @JACK - have limited access - i can just pop my head over and see the area. FIrst time I could see the moisture, second time not. I just used a sponge and soap initially (no bleach).
    – probably at the beach
    Apr 8, 2021 at 0:56
  • @MrR - just used soap and water. The airflow is ok but it's been raining a lot in Sydney so there is moisture in the air.
    – probably at the beach
    Apr 8, 2021 at 0:56
  • @probablyatthebeach is it an old ceiling (e.g. with timbers / lathes)? if so there might still be some dampness in the timbers (especially if there is normally no / minimal airflow into the cavity. Yes it has been wet - although nothing like QLD (where they have as much rain in 1 day [multiple times] as we had over a week...)
    – Mr R
    Apr 8, 2021 at 2:59

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Does mould growth definitely indicate a leak?

No, not at all. Mold can grow in any suitable environment, which just means sufficient moisture and sufficient food.

Unfortunately, neither of these need be present in very large quantities.

It's relatively common to find mold growth on the ceiling in a poorly-ventilated bathroom, or even on other surfaces. Likewise, on walls in a humid basement.

These issues should be addressed with a two-pronged approach: improve the ventilation so that the humidity is kept low enough to prevent mold growth, and on painted surfaces use paints specifically formulated for humid environments and which have mold-retarding chemistry.

Of course, none of this means that the roof isn't still leaking. If you're at all concerned about that, you should go check it again to make sure moisture isn't getting through the roof. But certainly, the presence of mold doesn't prove that the roof is leaking.

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That's a good sign if you didn't see any moisture looking in the attic. You did a good job patching the hole, just remember to check it periodically. It could take some time for all the moisture to evaporate.

Soap and water will not kill mold. Bleach is only good for surface mold and doesn't sink in to kill the roots. I have always used a three percent hydrogen peroxide. Spray it on the surface and let it soak in for ten minutes, then wipe/scrub off. hydrogen peroxide it great because it will kill mold below the surface which it exactly what you want to do.

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