Do previous damp stains still give a positive damp reading?

[Deansplit]

We have a sea front Victorian property which had damp from poor guttering and chimney flashing. The chimney was removed down to the tray and rebuilt as part of a restoration grant 12 years ago and I applied stain block and repainted the huge D shaped damp stain area. But after 5 or 6 years the stain came back and got stronger in appearance over the next few years. The paint is now even blistering/bubbling/flaking in our bedroom ceiling, see attached photos.

I have a damp meter which I think is a wood moisture reader (https://www.indonetwork.co.id/product/digital-wood-moisture-meter-nicety-wm801a-6999953) but it's reading high levels at the stained areas and nothing where no stains, so is clearly picking up something.

We get lots of condensation in the morning (I mean you need a towel or cloth to remove it and you could wring it out after mopping the 4 700x1200 windows). Condensation begins mid to late pm at this time of year on the NE facing double glazed windows. We have an ensuite in a corner which has no windows or extractor fan which I know is far from ideal but to be honest the damp is the same whether the shower is used or not. Can salt still be present in previous damp stains and therefore attract moisture leading to condensation issues, or is it likely there is still water ingress from the chimney?

Thanks for any advice.

 

[^woody^]

All damp meters are calibrated for timber, nothing else. You are reading surface condensation which will be relatively high, but not necessarily indicative of a damp problem. Salts may also have been brought to the surface which will increase capacitance and give an even more misleading reading. Salts may also (again misleadingly) attract additional moisture from the air.

That said, from your description you may still have a roof leak problem or a cold bridge from the works which may be causing a local condensation problem.

 

[Deansplit]

Hey Woody thanks for your info there. But if surface condensation is what the meter is reading, how come areas where there are no stains is reading zero or 1%? It's only the stained or damp damaged ares which read anything from 15 - 38% from what I've discovered. Is that just reading the salts in the plaster from historic damage? Am I better just getting those areas replastered to erradicate any confusion?