Could this be causing backfill and intermittent moisture in my walls?

[Lainey]

Hi I need some advice as this has been ongoing since august and nobody can find a problem but meantime water is damaging my walls.
The lady upstairs had a plumber in July who relocated her washbasin shower and fitted a new radiator.He caused a bad leak and came to fix it in august and I thought I could move on with the remedial work but moisture meter was still showing excessive moisture in the walls in a different area near where the upstairs boiler is.This has been intermittent but is ongoing.
The lady upstairs has become hostile and there has been no communication since august and she’s deluded that there’s no leak as her floors dry.
She had a new boiler fitted in 2018 but the guy left the small overflow from the previous job in place.Then when the plumber came in July he relocated the washbasin and a new pipe has appeared over the old overflow pipe and into the vent/soil pipe.There is no other waste pipe exiting the building after the relocation of the washbasin only this new one over the original overflow pipe.
This is the area where the walls are being affected with the moisture which has been between 18-27% since august.The moisture level seems to increase when it rains.She agreed to let in a plumber in on my behalf but he found nothing inside.My argument is that if there’s nothing inside then it’s something he did outside and that was fit this pipe.
Can anybody see a problem here as I’m running a dehumidifier taking samples to TRY to source where the waters coming from with no end in sight.
I’m not very good at this as I have no experience with plumbing and just want my home back so any input would be greatly appreciated.
I was unaware she had a condenser boiler as the guy that fitted it left the small white overflow pipe in place so don’t even know if that would be the cause but everything was fine until July.
1.This used to be how the overflow looked.
2.This is the new pipe he fitted over the original overflow with black foam over it.
3.This is it where it exits the wall.
4.Her washbasin has been relocated to same place as mine and my waste pipe is the one to the left of the soil /vent pipe.

 

[Chuck]

What method have you been using to measure the '18-27%' moisture content?

 

[Lainey]

What method have you been using to measure the '18-27%' moisture content?

Hi Chuck thanks for your reply.I’ve been using a dry zone moisture meter.

 

[gpbeck]

Hi Chuck thanks for your reply.I’ve been using a dry zone moisture meter.

That meter measures electrical conductivity not water content, the '18-27' is just a random guess. Wall conductivity basically represents the salt content of the plaster. When it rains room air has a higher water content which might affect conductivity marginally on the wall surface. Certainly there would be no immediate change in the actual wall water content.

If there are no other signs of damp I would just forget it, maybe sell it on Ebay to wind somebody else up.

 

[Chuck]

@gpbeck anticipated my train of thought; surface resistance measurements are useful for checking whether timber has been adequately seasoned and not much else. The only reliable way to measure the water content of plaster / masonry is to drill out a sample and weigh it accurately before and after oven-drying the sample.

If the wall was soaked by a 'bad leak' in August and has been left to dry passively you need to be more patient. It'll be faster with heating / dehumidification but I'd still expect it to take six months, maybe up to a year, to dry out properly.

 

[Lainey]

@gpbeck anticipated my train of thought; surface resistance measurements are useful for checking whether timber has been adequately seasoned and not much else. The only reliable way to measure the water content of plaster / masonry is to drill out a sample and weigh it accurately before and after oven-drying the sample.

If the wall was soaked by a 'bad leak' in August and has been left to dry passively you need to be more patient. It'll be faster with heating / dehumidification but I'd still expect it to take six months, maybe up to a year, to dry out properly.

Ok thanks.I have a dehumidifier running.