UKC

An absolute conundrum, to me anyway.

Daughter-in-law has a typical redbrick Victorian terraced house in Sheffield. 4 quite evenly spaced damp areas along the living room wall, about 60cm above the floor.  The terrace has alleyways through under the upstairs.  The affected wall is external to one of these - i.e. it is an external wall but the area is completely covered by house!  There is a cellar below.

Hacked off the plaster internally to height of 1m and removed a brick from the centre of one patch.  It came out rather easily as the mortar is completely crumbled.  There was an uninsulated copper wire contained horizontally in the wall, with a tight loop corresponding to the damp spots...but appears not to be connected to anything.  Perhaps part of an old "electrostatic damp course" - which I think have been fully debunked?

The service water pipe is along the cellar ceiling; and dry.  The bathroom radiator is above the wall section, but also dry and the wall above and below the damp area is dry.  The damp brick is currently showing 45% moisture (albeit a cheap meter).

There don't seem to be any pipes running near the spots.  If the bathroom radiator pipes were leaking under the floor I can't see why the water would emerge 2m lower and only in some places.  There's a waste pipe in the alley with some joins over problem areas...but it's dry even in prolonged use (shower etc.).

A dehumidifier has been running and we've had quite a dry summer (until yesterday) but the patches remain stubbornly damp and, interestingly, so does the removed brick - 41% cf. 45% for the wall.

So scenarios appear to be:

1.  There's something extremely hygroscopic in the brickwork that is pulling in water from the air and resisting attempts to dry it.  Would a salt neutraliser help?  Is it even possible to get that damp with moisture from the air and not from a leak?

2.  A pin leak under the floor upstairs is entering the wall and running down the centre between the brick courses (it's 9" solid I guess) to emerge where it can, being contained by moisture-resistant plaster above

I'm finding #1 hard to believe given just how wet the bricks are, and I'm finding #2 hard to believe given how focal and local the spots are.

Poor D-i-L was persuaded to get a gravel trench adjacent to the wall outside; no apparent effect.

Would be very grateful for any ideas or expertise!

are there any differences in the brick, mortar or plaster. that is, if patches have been repointed in cement and the rest is lime mortar this might cause patchyness in damp.

if the brick is damp, i.e. cold and clammy, then it could be just from temperature gradient. although i wouldn't have thought you'd get this at this time of year what with the summer we've had.

if it's proper wet wet, esp now in mid summer, then i'd think it's more likely to have come from a water source: cracked pipe, leaking gutter, water pipe, CH, etc. you might want to try and judge this in a few weeks or months time after it's been given a chance to dry off a bit. 

no. and, yes - but it'll need a big temperature difference, and some way that condensation an accumulate and not escape. this can build up in unvented void-space where it can be dripping wet. 

of these - i'd put my 50p bet on this one. might be worth trying a couple of test holes in to the cavity. a borescope might help, but the cheap ones are... cheap.

I'd be very wary or the 2 pronged "moisture meters", I think it's better to try and measure the relative humidity and air temp in any void / cavity space if there is one. 

this might be the pathway the water had taken, have you fully traced this back to its ends and removed?

This is a bit of a puzzle. But a few leads I would suggest:

Salt can pull a huge amount of water out of the air. This is why it's so common for chimneys to show damp as the soot is a source of salts.

It's also why you need to ignore the prong meter thing. You don't know if you are measuring damp, or salt or somehting else.

Better to rely on smell and touch.

Being an old Victorian house, I assume it's solid wall construction. Originally this would have lime mortar and lime plaster. I suspect it's been repointed with cement and has gypsum plaster inside. This seals the wall up, so any moisture getting in anywhere has nowhere to go other than travelling through the wall itself internally.

If the above is true the source of the damp could be quite far form where it is emerging and it's just found a weak spot.

With the amount of damp you have described, you may find with lime plaster and pointing, you would completely mask the problem. Not ideal, but better.

That wire sounds like a rent-o-kill rising damp piece of nonsense. Ignore it.

Don't be tempted to use chemical damp courses or tanking etc. This will likely just move the problem and make the overall situation worse in the long term.

I assume the living room wall continues upstairs. Have you lifted floorboard upstairs either side of the wall to look for other sources?

I would also be looking externally, at either end of the alleyway. Leaking gutters, downpipes etc. If the water really has travelled that far through the wall (inside the wall will probably be lime, so it will travel) then it could take years of dry weather to dry out. Especially if it has gypsum and cement pointing.

Long shot, but if that wall continues into the loft, it could even be a roof leak and it's saturating the wall. 

Try drilling into the wall upstairs and see if it's damp under the plaster.

The wall, if in the loft likely isn't plastered so will be more revealing.

Good luck

All good comments here. You don't say how long DiL has lived there and whether this is a new or historic problem. Note that in the good old days houses were very well ventilated, so watch reducing ventilation by closing off fireplaces and sealing draughts, and make sure the kitchen has a very good externally routed extractor, and use it!

We have recently moved into a ~ 150 yr old cotswold stone cottage, which has sections of plaster blown above skirting level. I'm pretty sure blown sections are where rising damp has been prevented from drying internally by gypsum plaster applied 30 yrs ago during refurbishment and also by the dulux type paint that the walls were painted with. (the paint comes off in sheets in places).I'm slowly removing blown plaster and replacing with lime plaster and we'll repaint with silicate based paint. So to add to the above, I would say having allowed the wall to breath with lime plaster don't then seal the water in with standard DiY petroleum based paint - even the "breathable" ones have very limited permeability. And it'll take months for the wall to dry out..

Good luck - there's lots of information on damp in old houses on-line, some of it holier than thou, but mostly good.

Just had a thought, and interesting experiment to do.

Take a piece of brick (size of a ping pong ball) from a damp spot, and then another from say 1m away.

Weight them both.

Stick then in the over at 100 degrees.

Weight them every couple of hours.

When the weight stops changing they are dry. Might need overnight. You could speed it up my carefully using mortar dust instead, but you need to extract it without generating any heat.

Final weighing to calculate the actual moisture content.

This will tell you whether it really is local, or the whole wall is wet.

 If it is local, it's probably salt sucking moisture form the air. Sounds un-realistic, but it does happen.

If it's the whole wall, look for leaks externally, pipes etc.

Who owns the room above the gennel? If it's the neighbour, that room is often the bathroom and it's possible a small amount of water is leaking through a shower somewhere and getting into the wall. Those solid walls can be a right mess of brickwork and it's possible the water is running down between the internal and external bricks and just showing itself where it can't progress any further. 

Are there any drains/sewers near that wall? I can't full picture the layout you describe but I'd assume that drains from the rear of the house(s) come through to the front of the property, most likely under that alleyway, to access sewers in the street. Old clay drain pipes used to be about 3 or 4 feet long and are prone to leaking at the joints if there has been any movement of the surrounding soil. If that's the case, it would explain the even spacing of the patches and that its still soaked, despite the dry summer. Bricks would easily absorb water to that height if the dpc was missing or defective. 

2 pronged meters are intended to estimate moisture in completely unpainted wood (like timber in a timber yard) and have no relevance to measuring damp in walls your house, despite various sales charlatans who poke around with one until they get a "good" reading they can show to a homeowner to justify the expensive remediation they're selling.

Sure.  But 45% on the problem area and 12% in the adjacent wall says there's a problem, which is what matters.

Thanks for all the helpful replies.

Turned this up: https://www.heritage-house.org/damp-and-condensation/all-about-the-pca/the-...

Looks like an identical situation and provides a very plausible analysis.

So if it's never going to dry in those areas, I guess sealing it is the way forward.

Look up Lectros damp proof course, this is what your wire will be. No, they don't work.

Thanks for all the helpful replies.

Turned this up: https://www.heritage-house.org/damp-and-condensation/all-about-the-pca/the-...

Looks like an identical situation and provides a very plausible analysis.

So if it's never going to dry in those areas, I guess sealing it is the way forward.

Wow, I'd absolutely never ever heard of that type of snake oil before. 

Sounds like you need to remove all weak mortar and plaster from the area, replace and hope for the best. 

In these sorts of situations I'm never convinced sealing is the way forward, any seal also seals in moisture.

Hope it works out for you, and good luck 

My goodness https://wykamol.com/products/damp-proofing-power-unit never heard of it before. The electricity kind of scares the rising damp repelling it back down the wall again. People pay hundreds of pounds for this BS.

Maybe they're onto something?

MOACS, how would you like to exclusively trial my Reiki damp repellent (holistic) realignment. I'll post you an odd number of special polished pebbles (exact number determined using a formula I won't share) and you plaster them into the damp area. They'll emit vibrations that only rising water molecules are sensitive to, and painlessly scare it away. As a forum user I'll let you have them virtually for free, just £498.00! (A quid cheaper than Lectros!) So you save money?

You've got to admit... it's a tempting offer isn't it?

I'd at least replace all the damp bricks and mortar. 

Hmmm.  That's a big job - acros and the works

Surveyor here, I undertake gravimetric analysis and specialise in listed buildings for a living. This is good advice

I'm in the process of buying a very wet Grade 2 listed Georgian house. 

Expect lots of hair pulling threads to follow.

Heritage-house did my survey, I spent the day with the surveyor. Nice chap. But I could tell he thought I was mad for not running away.