Moisture readings for old fireplace - are these for real?

[anxiouscat]

When I bought my house last year (Scotland, old stone cottage built c. 1850), the Home Report stated that "slightly elevated moisture readings were obtained at the bedroom fireplace". The fireplace in question isn't being used and hasn't been used for a very long time. It's on an internal wall. The other side of the wall is another fireplace (also unused) in the lounge. The chimneys are capped.

A specialist came around today and used a moisture meter to take readings (one of those meters you press against the wall, i.e. doesn't go into the wall). The meter read 99.9%. The specialist said it's common in these old houses for debris to fall down the chimney and pile up at the bottom (these were readings starting at the bottom, and going up roughly a metre). He said they would need to remove the plasterboard and clear away the debris, which was a quick and easy job. He got the same readings in the fireplace on the other side of the wall too.

But... those moisture readings left me wondering: If they're so high (the highest the moisture meter will go), shouldn't I be seeing evidence of the moisture/damp? The wall is dry, no visible signs of any damp.
(Not sure if weather makes any difference, but it's been rainy/sleety today.)

Is this right? Is there something going on behind the fireplace that isn't visible from inside the room?

 

[stuart45]

If there is any salts in the plaster it can give a high reading on a dry wall. Those type of damp meters are not always accurate, so they are only a quick guide to point out an area which might have damp issues.

 

[anxiouscat]

Thanks Stuart. Is it worth having them open up the back of the fireplace to deal with anything that might possibly be there, or is that a lot of disruption for potentially nothing?

I'm guessing the way forward is to get a second opinion (and hope that it doesn't add more confusion!)?

 

[stuart45]

At 99.9% in masonry it would have be a really wet wall. If the wall is dry I'd leave it at the moment. It's quite common for the plaster around fireplaces to give high readings due to salts from years of burning fossil fuels.

 

[anxiouscat]

Thanks Stuart. There are no visible signs of damp or moisture, and the plasterboard is dry and hard to the touch. That makes sense, I appreciate the reassurance!

 

[Kearn]

They were certainly not a ‘specialist’ in anything you need, selling snake oil is about the only possible qualification.

Those meters are purely for measuring moisture content of timber. They measure conductivity and there are many things that will thrown them off with elevated readings.

He might as well have pressed his nose against the wall and told you what he wanted you to hear.

However, from what you’ve described I would still be investigating. Chimneys should not be closed off when not used, there needs to be airflow bottom to top, so a vented cap and air brick or similar in the old fireplace opening.

It may also be parlance, but the mention of plasterboard is concerning. Not an ideal material in an old building.

Out of interest, why did this person come around?

 

[anxiouscat]

They came to check on some timber in the loft - I posted about that in the forum a little while ago. He confirmed what Matt Green told me here (no dry rot). He also has a lot of years of experience and good reviews. But I was left wondering about the 99.9% reading as that seemed excessive to me when there are no signs of damp.

The previous owners of my house did a lot of renovations (not well though, for the most part!). They never used the fireplaces, so those are just decorative features (hence, I guess, the plasterboard). The top of the chimney has a cap on it, but not completely closed off, so there is some airflow.

I've managed to find someone else (a recommendation from a trusted person) to come out tomorrow for a second opinion.

 

[paulc]

They were certainly not a ‘specialist’ in anything you need, selling snake oil is about the only possible qualification.

Yup, I've had one of these experts charlatans visiting on the pretext of doing a "free" thermographic survey. In reality, it was a sales pitch for spray foam insulation. Claimed that fibreglass & mineral wool insulation only has a life span of 5-8 years, and then claimed he could put his hand down inside the cavity up in the loft. This was in spite of me telling him that it is a solid 9" brick wall up there.
He'd also been waving one of those darned damp meters around, and I was just waiting for him to tell me that the DPC had failed and the building was suffering from rising damp. But a size nine up the backside had scuppered any further discussion.

anxiouscat - If you want an accurate measure of moisture in a wall, a hole needs to be drilled in to it, and a sample of the powder placed in a Carbide Meter. Even then, there will be a margin of error, but be assured, it won't be anywhere near 99.9% (at that level, you'd see water oozing out of the wall).

 

[Kearn]

They came to check on some timber in the loft - I posted about that in the forum a little while ago. He confirmed what Matt Green told me here (no dry rot). He also has a lot of years of experience and good reviews. But I was left wondering about the 99.9% reading as that seemed excessive to me when there are no signs of damp.

The previous owners of my house did a lot of renovations (not well though, for the most part!). They never used the fireplaces, so those are just decorative features (hence, I guess, the plasterboard). The top of the chimney has a cap on it, but not completely closed off, so there is some airflow.

I've managed to find someone else (a recommendation from a trusted person) to come out tomorrow for a second opinion.

What is it you’re trying to find out / solve though?

 

[anxiouscat]

anxiouscat - If you want an accurate measure of moisture in a wall, a hole needs to be drilled in to it, and a sample of the powder placed in a Carbide Meter. Even then, there will be a margin of error, but be assured, it won't be anywhere near 99.9% (at that level, you'd see water oozing out of the wall).

Thank you, I'll check this with the guy coming out today. And well done to you for sending your "expert" packing. It helps when you know a bit, so can ask the proper questions and know when you're getting proper answers - I'm learning! Thanks to you and everyone else here who shares their knowledge!

 

[anxiouscat]

What is it you’re trying to find out / solve though?

I'd originally booked the surveyor to come round and have a look at an area I was worried about in the loft. He had to postpone the appointment, and so while I was waiting for it to be rescheduled I posted here, and had a very helpful answer from Matt Green. I went ahead with the survey (finally done yesterday) as I wanted the guy to cast his eye over the rest of the loft too. While he was here, I asked him to look at the fireplace as the Home Report mentioned slightly elevated moisture readings and recommended getting a specialist opinion. So, I was really just trying to get more info on what the HR mentioned, and then to find out if there was any remedial work that needed doing.