The Great Rising Damp Debate

[Anonymous]

Right, pay attention.
I've read many times on this forum the assertion that "rising damp does not exist". And I must say that this view has often been expressed by people who's opinions I very much respect.
But here's the thing. Sitting here at my electric arithmetic machine, I can see a sizeable patch of damp staining in the plaster on my chimney breast. This is a brick chimney stack that runs up through the middle of the house - no outside wall on it at all - and has a woodburner vented up through a register plate about 1.5m above floor height. So there really is no possibility of rain penetration. Upstairs there is no sign of damp in the stack whatsoever.
The damp stain rises about 700mm above the floor. This floor was laid by our predecessors in the building (the vandals), and consists of a damp-proof membrane under concrete under Suffolk pamments. The stained wall is plastered with (yup) gypsum and painted with (you guessed it) vinyl emulsion.
So - if this isn't rising damp, where's it coming from? I promise that I haven't been peeing on it.

 

[Anonymous]

You may not have been peeing on it David but has any one else in your house.

It can't be rising damp IT DOES'NT EXIST, thats what every one keeps telling me and even I am starting to beleive it.

Long live Rising Damp, oh and watch this space.

PC

 

[Anonymous]

I have also seen damp that could not have been coming from anywhere else. The last time I saw it was also on a chimney breast in the middle of a house. No damp above, no damp to the sides, no outside walls, but a damp patch about 500mm high rising from ground level.

 

[Anonymous]

Maybe the chimney breast wall is colder than other walls as it has a draughty hole leading to the night sky one side of it. Condensation will occur first on the coldest part of the wall and this may well be the bottom metre of the chimney breast. Source of moisture is you folks breathing, Just stop it.

I have a wall, internal but the other side is the cool scullery. Once upon a time someone rendered it with concrete and then gypsum. Every summer the hot wet air from our conservatory hits it and dumps a lot of condensed water on it. The gypsum gets wet, the water can't go through as it hits the cement so it just hangs about, hydrating the gypsum into soft fluffy stuff which does nothing for the structural integrity of the paint, which then falls off. Every year I brush it down and repaint it except this year I have hacked off all the gypsum and replaced it with lime plaster. My theory is that the lime will tolerate absobing a lot of water and then allow it to dry out without falling apart or abandoning it's paint. I'll report back next year to say if it worked.
Anyway it's a damp wall and it isn't rising damp but condensation that has found the coldest part of the room to settle on.

 

[Anonymous]

I think the problem is that much damp diagnosed as rising isn't. And experiments are contradicting each other!

Your placcy underfloor membrane may not be helping. Maybe if the floor could breathe and the plaster was lime, the damp may not be appearing on the wall?

Strange thing this damp in the middle of a house. We had this in a previous house - it started to appear on a wall after ten years of living there. No sign of any damp before that. The house was over a hundred years old.

In this house, the damp rising up the plaster on the walls in the centre of the house was cured by lifting the plastic floor covering laid over flagstones in a central cupboard under the staircase.

 

[Anonymous]

Now, I'm one of those people that has come to question the existance of rising damp merely because I have never seen it on a traditional wall that has been treated in a traditional manner. What I have seen though are traditional walls plastered on both sides with sand and cement and they are as wet as hell. I 'm no scientist but my guess is that damp can 'rise' between two virtually impermeable finishes. Take off those impermeable finishes and the damp dries faster than it can rise if you see what I mean.
I would be interested to hear what others think. Mike.

 

[Anonymous]

Of course you're right Evelyn - it's the plastic membrane and concrete floor that's causing the underfloor damp to migrate to the chimney brickwork and wick upwards. My point is that - according to some people, there's no such thing as rising damp.
So what is this, if not rising damp?!

 

[Anonymous]

No Biff, there's no "draughty hole leading to the night sky", because of the wood burner's register plate. I really can't see any explanation for this damp, other than underfloor moisture migrating to the chimney stack, because of the dpm and the concrete, and wicking up through the brickwork or the mortar. It can't be wicking up through the plaster, because the chimney stack extends below the suspended floor, and the plaster doesn't start until above the floor.
Sorry, but I haven't yet read an explanation that convinces me this is anything but the "mythical" rising damp.

 

[Anonymous]

So, John, do you have any idea where this assertion that "there's no such thing as rising damp" came from?
I swear I've had it in every period property that I've owned (four).

 

[Anonymous]

Well - I'm no scientist, but of course the damp under the concrete is under pressure, so maybe that's part of the equation?

Mostly damp under solid floors or floor voids should have a chance to dissipate - through a breathing floor, or through the first few inches of breathable mortar, above which the flooring should be suspended, through air bricks? It seems to me that damp will only 'climb' high if it's a last resort. If there is an easier methood of escape, it will use that first.

In our house, when we moved here, we had a very damp underfloor in one room. When we lifted boards I thought possibly there was an underground spring, the soil was so damp! The room smelled of damp earth.

The walls were so wet that the wallpaper peeled off it strips. Yet according to a damp 'expert' (he was better than most, but still not great!) this wasn't rising damp. It was condensation from the underfloor, and the walls contaminated with salts were also attracting and holding on to moisture. As the room had been flooded once in its past we thought that may have been true.

We found the causes of the damp, stopped those, and opened up the air bricks. Sadly, we also had the plaster hacked off part way and re-done with gypsum as the 'expert' said that was the thing to do. Thankfully, no damp proof course was injected. Another national firm had said that all plaster should be hacked off, injection, cement with waterproofing, right up to ceiling height, the whole expensive works was required, at vast expense. The mortgage company had also retained a lump of cash until damp proofing works were carried out and a cert issued.

The plaster isn't too extensive thankfully - doors, window with panelling under, fireplace etc take up a great deal of room - but I do wish we hadn't had it done, simply allowed the walls to dry. We are older and wiser now. The gypsum will be removed one day, along with the nasty plasterboard ceiling (if anyone is ever tempted - don't do it! It was done not by us...) and re-done in lime, but it's all money down the drain really. As no doubt you are finding!

 

[Anonymous]

I think it came originally from Jeff Howell - the bloke that writes for one of the papers, Sunday telegraph I think? Jeff has been banging on about there being no such thing as rising damp for years.

Now, I certainly agree with a lot of what Jeff says, and a lot of what is often said on this forum. Rising damp is rare, dampness is very often misdiagnosed and the injection industry has been having it away for years. I agree with all of that.

BUT, I have seen damp on a couple of occasions that I can't explain by any cause other than rising from the ground. It may be that pressures and membranes or water tables or some other influence may be at work, but it is still rising from the ground.

We've seen a lot of examples of castles sat in rivers or moats recently. I'm not convinced this situation is the same as a plastered, decorated habitable living room. In fact I think the stonework would be quite damp but just not as visible due to the high degree of external surface evaporation. Also notice that the habitable areas are well above the water - I think the old builders may have known a thing or two about damp as well.

 

[Anonymous]

I thought the comment had been that rising does exsist but it was the failure of a physical DPC was very rare.

 

[Anonymous]

I generally agree with all of that, John - except the word "rare". I have seen plenty of examples of what I regard as obvious rising damp. Coming from a civilian, that probably sounds rather arrogant, but - as the old saying goes - if it looks like fish and smells like fish... it's fish.
If rising damp genuinely occurs in properties under the circumstances that I have in my house, then - given that they're a pretty common set of circumstances - surely rising damp can't be that rare.
As regards castles, I believe you've hit the nail on the head when you mention that the habitable rooms are located well above the source of the wet (ie: the moat). This places them above the maximum level at which osmosis is able defy gravity. And as the castle walls aren't plastered, it can easily dissipate.
I'm not trying to be argumentative in this. I just feel that it's easy in forums like this to fall into a habit of reciting mantras. And it's sometimes a good idea to re-examine such mantras to satisfy ourselves as to their validity.
Blimey - I'm sounding a bit bleedin' pretentious, eh?!

 

[Anonymous]

I think from a purely physical point of view, the osmosis could go on and on - gravity's pull is effectively constant at any height we are discussing - I think its more to do with the relative water pressures as all building materials are damp to some degree (I think Evelyn commented on this earlier).

Surely its not that water cannot rise through adjacent materials, but rather that the usual commercially proposed solutions fail to address why it is happening or deal with it appropriately?

 

[Anonymous]

David - I agree, every opinion on this subject should be questioned. The trouble is there are so many variables that the brain starts to spin. I have done lots of jobs involving cement render stripping and replastering with lime. Sometimes the stonework and cob has been damp - sometimes it has been as dry as a chip! The damp problems (or lack of them) have not been related to very sheltered or very exposed positions. I have usually found walls exposed to the prevailing weather tend to be the damp ones, but not always. We stripped the cement render off one cottage to find that all the walls were bone dry except for the one facing North! Mike.

 

[Anonymous]

"...gravity's pull is effectively constant at any height..."

Hmmmm - I agree that gravity remains the same, but the weight of water in the osmosis "column" surely doesn't? The higher the water creeps, the more the total weight of water that is trying to defy gravity...

... or am I missing something?

 

[Anonymous]

The effect of gravity is not constant, it decreases according to the inverse square law. Newton said that. You'd need a very tall building to notice this however.
Capillary action may be involved but osmosis is more about differntial diffusion across semi-permeable membranes. A different phenomenon entirely. Osmosis is a word that should only be used by biologists but has been hijacked by unscrupulous damp-proofing salesmen in an attempt (often successful) to blind their victims with pseudo-science.

 

[Anonymous]

That would be true if one bit of water was attached to the other bit of water - but i think its more of an everyman for himself thing with water molecules!

True Biff - it’s more likely to be capillary action - creeping through the tiny crevices. But still an issue about relative pressures so the osmosis idea helps (which isn’t strictly just found in biological world, is it?).

No doubt if I understood this stuff better it would help!

 

[Anonymous]

That's it! I couldn't think of the bl**dy word!
CAPILLARY action!

Thanks Biff.

 

[Anonymous]

I agree Biff, it's not osmosis were talking here, it's that elusive (for some, nudge nudge) word capillary action.

And of course it's restricted by gravity. I distinctly remember Mr Llewelyn in his white lab coat saying 'if it wasn't for gravity it would shoot up the glass tube and spill out the top'.