Curing a damp shed - is it possible?

[Teejayef]

Following on from the post concerning insulating a concrete floor - I have an building that was the Blacksmiths Shop in my smallholding. Having had to renew the cladding at the ends of the building I have discovered that it used to be a wooden shed on a concrete base but blocks walls have been built inside all the way around giving solid walls and the two side walls have been built externally with block leaving just the ends as wood frame and waney board. That's the background - the issue is that it has rising damp through the concrete floors and up the plastered internal walls and, apart from knocking down and rebuilding with damp courses etc I can't see how to try to insulate the internal space from the damp. Would lining it with a water resistant material or sealing and painting it help? Any ideas gratefully received but with the usual proviso ... it's got to be 'affordable' (read 'cheap' for 'affordable'!). It's got 3 rooms, the largest is approx 4m x 4m, the second 2m x 3.5m and the third 1.5m x 2.5m so it's not too small and it's the largest room that gets the most damp.

 

[artie]

There is a school of thought that denies the existence of rising damp.
There is a guy online somewhere who claims to have taken mortgage surveyors to court and proved them wrong when their report stated rising damp.
His claim is that proper ventilation is the key, obviously combined with drainage and proper roof.
A google search should find him.
Well worth a read.

 

[Teejayef]

Thanks, ventilation will certainly help to an extent but maybe I should have said 'wet' rather than damp. This area suffers from a rising water table when the rains come as well as runoff the hill down to the building so I know why it gets wet or damp because it spends some time with the concrete pad it's built on sitting in a very damp/wet patch. When the weather is wet (roll on Storm Christoph) it's like the tide has come in and the floor and lower walls get damp. So I was thinking that I ought to treat it like a cellar that needs tanking but my lack of any experience (ex PE Teacher/youth worker!) in these areas is holding me back somewhat!

 

[artie]

Could you dig a moat around it and let the water away at the lowest point?

 

[Fitzroy]

There are reams and reams of claims and counter claims around rising damp, its existence etc etc beware if you trip down that road. I've spent much time on it, and the many lay-byes and cul-de-sacs that lie along it. My main take always are :

- Many historical building were built without damp courses and do not suffer from damp, so it is not a given that you will have problems with no DPC.
- Rising damp can occur theoretically however most of the time the problem is due to other reasons.
- Solving the damp should follow the route of. Review building externally and ensure ground levels are sensible (reduce where they are high and change slope to ensure surface water does not stand against the building). Review local rain management, gutters to ensure water is channeled away, eliminate hard surfaces around wall bases where rain splash will wet the lower walls. Review ventilation, eliminate external coatings that prevent the wall drying out, remove local obstructions that prevent the walls drying out, for suspended floors ensure underfloor ventilation is not blocked up.

Fitz.

 

[Fitzroy]

Could you dig a moat around it and let the water away at the lowest point?

You joke, but a French drain around the perimeter of the building would likely help significantly.

 

[artie]

You joke, but a French drain around the perimeter of the building would likely help significantly.

I wasn't joking.
All you need is to lower a 600mm perimeter right around the building provided the water can get away, if it can't then a drain is necessary.

Perhaps moat wasn't the best word. lol

 

[minilathe22]

Go out and look at the building when it's raining hard, I had a damp problem in one area, the wall was wet to the touch on the inside, when raining I could see the gutter was bowing under the weight of the water and pouring water down the outside of the wall, looked like everything was fine on a dry day! Clearing out the gutter fixed it but I plan to add some extra gutter supports as they are very far apart.

 

[Teejayef]

Thanks for all your responses - I think that you are right about having to solve the outside water issue prior to looking at the internal but the issue is that it is an 'agricultural' building - in style, use and quality/effectiveness of build and the wet end extends underground by 75cm at least (it's built halfway up a sloping yard. The moat idea is probably the best option but that would be a major job seeing as how the yard is paver block laid. It could be that ground guttering needs to be sunk into the pavers to divert the flow but that still won't address the rising ground water at wet times (yes, Storm Christoph has contributed an increase in the size of wet patches). If internal tanking/sealing isn't an option then the building will have to resort to a junk storage room .... but I've got several of those already!

 

[Jameshow]

I would put a drainage channel in to catch any surface water.
Then I'd either tank it in rubber Dpm when it's dry enough.


Or tank it in battens then DPM battens insulation and ply OSB on the top.

With at least an inch or two of gap to allow any damp to flow away.

Cheers James

 

[MikeJhn]

I was going to add to this thread with the benefit of my extensive experience of so called rising damp and lowering water tables, but then realised the post is over two years old, the building has probably floated away by now.

 

[MikeJhn]

Just as an afterthought, answering old post got me banned from the "UK's Friendliest Electricians Forum" an oxymoron if ever there was one.