Keeping an eye on a damp area

We had a slight discolouration in a small area of the bathroom ceiling appear a few months ago. It has I think been correctly traced to wind blown rain making its way under roof tiles, which hopefully is now fixed, but I have been keeping an eye on the area with a damp meter and an IR thermometer, just to ensure it is drying out.
Initially the meter was showing full scale in contact with the stain and nothing on the rest of the ceiling. Now it shows it is just slightly damper than the rest, except when the bath or shower have been used, but it soon drops back to its usual low value. My guess is that the tiny extra bit of moisture where it was slightly damp, makes the area cooler and therefore moisture in the air more readily condenses there. Checking it with the IR thermometer, the stained patch is a couple of degrees cooler, than the rest of the ceiling.
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Apart from the subject line making me think this was some kind of adult newsgroup I'd wandered into by mistake. I do agree with your diagnosis here, We had this in a box room on the side of the house where the coldest winds come from and the ceiling curves to avoid hitting the roof, so the gap is very small and of course gaps between tiles and no lining added to the problem. We did do a little blocking up in the loft and drying out and its gone away for over 20 years now. Took quite a while to dry and we alwso had mould issues to start with. Brian
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On 16/05/2018 11:23, Harry Bloomfield wrote:

We had some damp from a small crack in a leaded. I have a thermal imaging camera, and that clearly showed the damp patch as cooler, presumably due to water evaporation. This is lath and plaster.
The gully was fixed, the damp dried out and there is no longer a temperature difference. It's not been painted or touched in any way.
So I wouldn't be so sure of your diagnosis.
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Clive

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Oops. ...leaded valley.
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Clive

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on 16/05/2018, Clive Arthur supposed :

Nope, nearest leaded valley must be a quarter mile away lol
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Clive Arthur used his keyboard to write :

There are no pipes at all in the area, so it had to be rain water ingress and the best guess, because it had never happened before and the tiles are fine - that the wind (from the east) was driving rain in the edge gaps of the tiles. That was flaunched, since when there hasn't been much wet weather.
There is no mould at all, just the very slightest of damp stains, close to where the ceiling meets the wall.
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