Mysterious smell - help! (update)

[fosterdog]

Back in January I posted about an unpleasant smell plaguing our bedroom. I've now done some more investigating and I'm still baffled. In the meantime my pregnant partner has moved out of the room. Further thoughts much appreciated! @PigletJohn?

www.mumsnet.com/Talk/property/3792585-Mysterious-smell-help

A common theme in the January replies was that the smell must be coming from the neighbours. However, I've been over there and there's no sign of any smell or damp problems on their side of the wall. They have had damp problems (now treated) on the other side of their house but nothing on our side. There's no plumbing near that bit of the party wall on their side.

A protimeter measured the moisture in the bricks in the most strongly affected corner of our bedroom at c. 15%. I also found a brick further along the wall which measured 20%, but the neighbouring brick was at 0%, which makes me thinks the meter might actually be picking up salts rather than actual moisture.

One thing I didn't mention in my previous post is that there seems to be a correlation between the strength of the smell and the weather. It's stronger at night and usually (but not always) worse when it's colder and damper. However, the humidity in our affected rooms is always in the 35-50% range so there shouldn't be any condensation. Some days it almost disappears but it always come back eventually.

We've got a fancy new air filter to mitigate the problem. It helps with the smell but doesn't completely remove it. The filter's air quality meter tells us that PM2.5 levels are very low, even when the smell is strong.

My main theory is still that there's a problem under the neighbours' floorboards but their floors and skirting are perfectly sealed so they don't notice it. But that's impossible for me to investigate and they won't do it as there's no problem on their side.

I've been trying to get a chartered surveyor to come and have a look at the problem but none seem willing to do it unless I pay for a full survey. I did manage to have a 20 minute phone chat with one but he was as baffled as we are.

Damp surveyors charge £300 and I don't think I've got a damp problem.

A builder suggested just plastering the party wall down below floor level and sealing the skirting and floor boards, which probably is the right answer, but I'm worried about going ahead with that and finding that it doesn't remove the smell and/or that it's just burying some real horror.

Help!

have you sniffed under the floorboards next to the party wall?

did you find anything in the loft?

does your boiler have a pressure gauge?

I'd check the condition of your floor. We had similar here. Really awful smell. Gets worse when it rains. Turns out our floor is rotting from a previous leak.

www.bbc.co.uk/programmes/p0593pdg

This You and Yours episode from Radio 4 might be of interest.... lots of Valspar paint customers found their walls started smelling of cat's wee.

Also that is very high humidity in those rooms isn't it? Maybe a dehumidifier would be worth a try.

@PigletJohn

No leaks, smells or signs of decay in the loft.

The boiler pressure seems stable.

Haven't been able to smell anything under the floorboards - or at least not as strongly as by the wall itself at skirting board height in the corner.

However, I did do a bit more subfloor delving this evening and might have found something. The back wall of the bedroom has a beam under it. Above the end of the beam, in the smelly corner, there's a square cavity lined on 4 sides with wood. It's very awkward to access without cutting floorboards or removing the bedroom door's architrave but I did manage to snake in my hand to take some pictures. The wood lining on 3 sides is clean but the side against the party wall is unevenly covered in a fine light grey layer which might be dry rot. Picture attached.

It's also possible that it's just old cement spatter though. As I said, the neighbouring timbers seem fine.

What do you think?

Looks like I need to get a rot person in to check it.

@whatisheupto We do sometimes have problems with the smell of cat wee elsewhere in the house but I'm pretty certain our cat is to blame there!

What sort of smell is it? Our cat once killed a shrew and then wedged it under the lino in the cupboard under the stairs. It took me weeks to discover where the smell was coming from. It was like the most evil cheese. Friends stopped coming round.

I can't visualise this enclosure or what it is for.

Do you mean the partition wall has been built on a beam (not on a wall below)? Not unusual.

The white coating reminds me of marks sometimes seen on roof timbers after a leak, I believe it may be mould. If you scrape a bit off, mould will burn away if you hold it in a spoon over a gas flame, cement or lime won't.

@PigletJohn

It's going to be tricky to collect scrapings as I can only get one awkwardly bent, full stretch, arm in at a time and I won't be able to see what I'm doing. I'll give it a go in the morning and report back...

That definitely looks like damp. Looks wetter bottom left. We had wet and dry rot in the house we bought and it had a really strong earthy, damp smell. Is that touching an exterior wall? What's the pointing like outside?

Does the photo you attached need rotating 90 degrees anticlockwise? It's hard to picture what you mean without a diagram, but I'd say that looks like the source of your problem. I can smell it in my mind iykwim.

You could buy the spray off amazon and see if that helps? Wet/dry rot spray.

@PigletJohn

I managed to scrape off a bit and couldn't get it to ignite over a gas flame.

On the other hand I've also managed to get the protimeter down there. The unmarked wood panels all read c 6% moisture. The panel covered in the grey stuff reads 0%. Which sounds like a bad sign re dry rot?

@stoparguinganddoit

It's an internal party wall, about 4m from an external wall.

"The unmarked wood panels all read c 6% moisture. The panel covered in the grey stuff reads 0%. Which sounds like a bad sign re dry rot?"

no, it sounds nice and dry. There is no sign of fruit, spores or square cracks and shrinkage.

If you want to test for rot, poke it with a flat-ended screwdriver. Dont use anything sharp, round or pointed because the next person will see the marks and think they are wormholes.

Sure it's not a dead rat.... the smell is gross and can last for months

try dripping vinegar on the craped powder. Does it fizz? Lime would do that if you had a water leak.

I don't think I've seen efforescence or lime bloom on timber (this is mineral crystals forming on the surface of brickwork when hard water evaporates)

@PigletJohn

It does seem quite solid to the touch.

The smell round there is quite strong today, particularly where I've lifted a board to get to the cavity. Lifting more boards in the area to get a closer look at the cavity / check for other issues in the area would involve, at a minimum, ripping the ancient architrave off my bedroom door and possibly also cutting floorboards (the original boards in my hall run under the wall into my middle bedroom so can't easily be lifted). Do you think I should do it (or more realistically get a builder in to do it)? What would you suggest as a next step?

if the smell seems to be coming from under the floor, I suppose you need to take up some boards for a look. It might be deceased wildlife, though smells are often plumbing related. Have a look round the outside for a potential point of entry, might be crack in wall, chimney, airbrick, hole for pipe. I assume your house does not have cavity walls.

Carpenters are usually neat and skilled at lifting floorboards. Ask for them to be put back with screws, not nails as you might want to look again. If any are damaged keep the splintered bits as there is a way of restoring them. You can have a little hideyhole for your valuables.

You might like to read this page www.petercox.com/our-services/dry-rot/what-is-dry-rot/early-signs/

It says often the first signs of dry rot is the smell. What does it smell like?

Any obvious tiles off over the party wall?

@Dodie66

It's a sort of musty smell. Sometimes smells sort of damp, sometimes doesn't. I find it very hard to define, which isn't much use.

Is it near any gas pipes?

Raising this thread from the dead after 4 months...

@PigletJohn - Really hope you're well and have survived the last few awful months intact. We've finally got a proposed solution on this that I'd love your take on before we hire someone to do it.

Until last week we got nowhere with this. Just after posting the thread, we had a couple of different damp guys round to have a look but they largely drew a blank.

Then lockdown struck, which we've had to be super strict about as one of us is immunosuppressed and our first baby is due at the end of the month. Apart from getting a fancy air filter which partly dealt with the smell (but not the underlying problem) nothing has happened to the room since. The skirting board is still off the wall and it still smells terrible in the mornings when the filter is off.

However, last week I had to get a structural engineer round to check our some new cracking around our bay window (don't get me started on that!) and he had a new suggestion about the smell.

The mystery has always been how the room could smell damp without any leaks or water ingress, when the humidity was usually below 50%, always below 60%, and the temperature never near the dew point. The engineer suggested that the issue may be that hygroscopic salts in the bricks are absorbing moisture, causing the bricks to become damp at well above the dew point temperature. Does that sound plausible?

Treatment is difficult as the smelly area is (a) partly behind a joist that runs 1-2 inches away from the wall (and probably can't be lifted without damaging the old lath ceiling it's attached to), and (b) partly right in the corner of the room, behind the base of a perpendicular wall. We'd also have to rip out a fitted cabinet in the hallway. So I'm really keen to make sure we're doing the right thing before going ahead.

The engineer suggested that we should treat the problem by preventing damp air from accessing the bricks behind the skirting board and below floor level.

Specifically, he suggested:

1. Where the wall is accessible, paint it first with a silicone-based waterproof sealant, then cover with an anti-salt treatment to be sure. Alternatively, fix a plastic sheet barrier over the bricks and pin in place.

1. Where the wall is inaccessible (behind the joist and in the corner), fill the cavities with insulating spray-foam.

@PigletJohn I'd love to know what you think.