Rising damp / hole in the ground

[Zebra]

Not pedantic at all. I see what you mean. So if it was a well, ever, that wouldn't necessarily have been a problem. But dumping rainwater into it could cause a problem. When were gutters invented, or when did they become common, out of interest?

 

[robgil]

I did a paving job this summer outside an old cottage and while lifting the floor bricks that had been cemented down outside the building we found a well. Lovely it was , arched , steps down to it etc etc.
The conservation officer was called and fill it in was the decision quickly made. It was directly under the exterior wall of the house although they said it could have been inside an outbuilding , lean-to type thing.
It was pretty dry though and full of rubble and bags of builders waste anyway.
Still , interesting that they would put wells so closed to buildings but I guess if the water is there already what difference would it make where you put it.

 

[middi]

Not pedantic at all. I see what you mean. So if it was a well, ever, that wouldn't necessarily have been a problem. But dumping rainwater into it could cause a problem. When were gutters invented, or when did they become common, out of interest?

Gutters became common, and necessary, when thatch was no longer the main roof covering material.
If you notice, thatched dwellings do not have gutters for two reasons :- 1) the thatch overhang at the eaves is usually at least a couple of feet, therfore watershed is well away fro the building walls. 2) it would be extremely difficult to screw or nail gutters at the edge of a straw roof.
The early gutters were invariably made out of wood, and became ( as a rule of thumb) necessary as the transition from mud-stud-straw buildings were being gradually replaced by brick and slate where the roof overhang at the eaves became less prominent and " gutters" would channel water away from the walls.

Middi

 

[JoceAndChris]

Still , interesting that they would put wells so closed to buildings but I guess if the water is there already what difference would it make where you put it.

I think there's a difference between water flowing under the house, as would happen here set into the hillside near the top as we are, (on very free draining limestone and sandy soil) and actually trapping that water and storing it.

Here's one of our underground rainwater rooms (painted with the black stuff by the previous owner in the 80s)

Here's the other side of that, the inside scullery wall that abuts the rainwater chamber. Damp,for years, and you can see that layer upon layer of limewash was how they dealt with damp.

The well is the square hole in the floor, in winter the water rises so high you can put your fingers into the icy water. I'm not sure what the floor type was before the previous owner poured down concrete, I suspect it would have been quarry tiles laid on earth - long since disappeared due to damp.Whether rising damp from the well or seeping damp from the rainwater pit is to blame is pretty impossible to say.

The well and rainwater harvesting have been crucial to inhabitants from construction until now.

 

[Penners]

Here's one of our underground rainwater rooms

An indoor swimming pool! I'm so jealous!

 

[robgil]

Joce , in the event of WW3 or a plague of flesh eating zombies I am coming to live with you. :lol:

 

[JoceAndChris]

:lol: :lol: :lol:

Very welcome; don't forget to bring your daub and plumbing tools.

 

[Zebra]

The conservation officer was called and fill it in was the decision quickly made.

May I ask Robgil, what was the decision on what you should fill it in with? Rubble? Or concrete? (Noting MdB's comment above that if you fill it in with rubble the water will still rise if it wants to...)

Still , interesting that they would put wells so closed to buildings but I guess if the water is there already what difference would it make where you put it.

Yes, I suppose - if a well doesn't affect the water table, then what does it matter if it is against the wall of the house.
Anyway, I have put a bin inside the hole to catch the rainwater for now, and the water in the bottom of the hole itself has not risen but then we haven't had much rain lately. I will monitor and report back! Your comments have all been so helpful.

 

[robgil]

we Just chucked a load of old broken bricks into it to provide a good base for the layer of new cement under the new paving.
Basically the old bricks that had been cemented down over the well effectively sealed it in and we simply re-instated this seal with new sand stone flags.

 

[Zebra]

Hello all, I'd like to post about progress on my damp situation, I think I've figured out what has been causing all the rising damp, and I think I've solved the problems in one way or another, but the walls are still damp, mould is developing, and I just want advice on how to dry the walls and how long it will take!
Basically, there have been four different ways in which water has been diverted to under the concrete slab of the house, for years.
1. The rainwater pit, which probably was once a well, has been taking all the water from the guttering on the front of the house, and holding it right adjacent to the side wall of the house.
2. Before I made the French drain and did all the drainage on the back of the house, the water from the guttering on the back used to be dumped in a leaky unlined brick chamber right adjacent to the back wall of the house.
3. The sideway used to be concrete, and had a yard gully which went nowhere, and concentrated all the water from the sideway to a point adjacent to the side of the house.
4. Leaky plumbing when I bought the house was sending a constant trickle of water into the floor.
The first three had probably been going on since 1969, when the house had its last round of renovations. The last one was probably going on for the two years that the house had stood empty before I bought it.
So the ground under the house has in various ways been soaked for years.
Yet if you dig a hole only a metre away from the house, to the depth of the house's foundations, it is dry. Much drier than the walls indoors. I don't think there's a high water table, I'm on quite high ground.
So, if I have now solved all the problems, but there is still damp rising, then perhaps this will continue to happen until the ground underneath the concrete slab dries out. Where I've taken parts of the slab out, the hardcore under is quite damp.
Electric heaters aren't helping because the heat rises and the damp is coming in low down. Will a dehumidifier help?
How long might it take to dry out?
And what is next - should I do something with the concrete slab? I can't afford an insulated limecrete floor throughout along with all the other building works. I've read on here about converting a concrete floor into a breathing one by means of a trench along the walls filled with limecrete, and I could do that, or I could perhaps remove the slab if I were to "discover" a flagstone floor which as far as Building Control are concerned was there underneath all the time..... This would have the advantage of not raising the height of the floor.
Would be grateful for any more thoughts. By the way the well/rainwater hole has not filled up again at all. It has been very dry weather lately though.

 

[Flyfisher]

That all sounds like good news.

As for drying out, I'd suggest there is little to recommend but time and as much ventilation as possible. An oft-quoted rule of thumb in these here parts regarding the drying of previously wet walls is one month per inch of thickness. Like most rules of thumb it is generally applicable though widely variable depending on the prevailing conditions.

If you have the patience, maximise the ventilation and leave it until about this time next year. My feeling - completely unsubstantiated by any specialist knowledge - is that where a structure has been damp or saturated for any length of time then it's probably best to let it dry out slowly and to gently come to terms with its new condition and gradually find its new equilibrium. Forced drying with heat and/or dehumidifiers may dry things out too fast for the structure to adapt, causing cracking.

The structure has clearly been damp for a long time, surely another year won't do any more harm?

 

[Zebra]

That sounds like wise words.

 

[Zebra]

I've gone for the dehumidifier in the end, because the damp was condensating on the timber rafters and forming mould. I reckon it's not such a big dehumidifier as to force dry the brick, but might help to take the damp out of the air before it settles elsewhere.
So, just thinking, if I were to go for the "breathable trench" thing that one can do when one has a concrete slab, then I could take up the slab now around the edges, which might help the ground under the house to dry a bit without it all going up the walls, and then I could finish the floor downstairs, which means I could rebuild the bottom half of my stairs instead of standing on a cable drum before pulling up onto the third step (which isn't a problem, it'd just be nice to have stairs again!)
So, as I understand it, such a trench would be filled with limecrete, is that so? This might be a daft question, but how would you make limecrete? That is, if you weren't going for the leca insulated full new floor job? If it was just a bit. Would you mix NHL and ballast? Would it take forever to set fully? Is it the wrong time of year to be thinking about it?
Should I just do as Flyfisher says, and leave it alone til next year!!?

 

[Penners]

First - yes, I would do as FF suggested and leave the whole structure to dry out as much as it can, until next year.

Second - if you want the full bag of tricks on limecrete, the following PDF is very useful. Look in particular at page 3, which gives you a recommended mix and laying method. http://www.oldhousestore.co.uk/pub/files/1233760213_Limecrete.pdf

Third - I'm no expert on lime stuff. I've been 'educated' by being a member of this forum for years.

 

[wobs]

Slight diversion here, but QI last week mentioned that rising damp does not exist.

 

[Penners]

Oh, that old myth!

I don't care who denies the existence of this phenomenon - I've seen enough walls which have no DPC and are thoroughly damp up to roughly 1 metre high to convince me that rising damp DOES exist. Sherlock Holmes had something to say about it:

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth".

In several of the walls I've described above, the only perceivable explanation for the damp was moisture being wicked up through porous masonry to a height where gravity prevented it from climbing any further.

Masonry can be porous. Capillary action exists. http://en.wikipedia.org/wiki/Capillary_action

It's not QI, it's QED.

 

[Flyfisher]

Fair points. But is the 'rise' exacerbated by non-porous coatings on the wall, making a sort of plant-like structure where a combination of capilliary action and evaporation can raise water to great heights?

A porous brick sat on damp ground would have a surface area of 21.5x10.25 = 220 cm2 through which to pick up water but 2 x (21.5x6.5) = 280 cm2 through which water could evaporate. Clearly there are more variables involved, but the basic starting point doesn't seem a great way of making water rise up a brick wall.

The other thing I've often pondered is the impermeablity of cement based mortars and damp. We all know it can trap moisture inside walls, timber frames and the like, so why is it not quite so helpful in trapping moisture in the ground? After all a brick wall has many layers of 'impermeable' cement mortar, so why would these layers not act as multiple DPCs?

 

[Penners]

Interesting points, FF. My (amateur, inexpert, subjectively-observed) thoughts are that:-

* Yes, a concrete and/or gypsum coating on the bricks will inevitably exacerbate an existing rising damp problem by preventing (or - see below - greatly reducing) the evaporation of moisture from the brick substrate.

* However, I don't believe that the available naked surface area of the brick is the whole story, when it comes to evaporation. A brick may be porous, but surely the great majority of the capillary routes are located well away from any of the brick's external surfaces. Therefore the moisture in these capillaries won't get the opportunity to evaporate before it has been drawn up to the maximum height that gravity will permit.

* Your observation about cement mortar as a barrier to rising moisture is an interesting one, which has been a kind of background puzzle to me over the whole matter of the "impermeable evils" of cement/concrete. If a damp wall is rendered with a cement mortar, you certainly know it. The patches of damp are clearly visible, showing up as a much darker colour in the mortar's surface. If cement mortars were truly impermeable, then surely this couldn't happen?

The only conclusion I've been able to reach is that cement must greatly reduce the movement of moisture, rather than completely eliminating it. Thus it presumably retains moisture within a structure far more effectively than migration and evaporation can remove it.

But of course, these amateur ramblings may be complete rubbish.

 

[Zebra]

By the way thanks Penners for that link from the Old House Store with the recipe for limecrete. I've been making my own in small amounts and it's setting fine.
Anyway, disaster the night before last. The bin in the hole has been happily collecting the water from the rear of the house which is piped under the house. After it rains I've been going out there with a bucket and bailing it out.
But the night before last it rained hard all night, and in the morning I went out to see, and it was flooded. The bin had overflowed and the carefully dried hole was full of water again. Oh no! In I went again to empty it. (Still no wellies.)
Silly of me not to have done it before but now I have a pump with an automatic switch suspended in the bin, until I can get someone in with a digger to make a soakaway.
The idea that it never rains but it pours is not quite true. Sometimes it rains a bit, and lulls you into a false sense of security, before tipping it down in the middle of the night. Oh well. Things are no worse than they were before........

 

[Penners]

Maybe in your move over here from Africa, Zebra, you didn't know about the British weather...

:wink: