Professional Damp Advice

[ralral]

The simple question is: Where is the best place to get some good advice on dampness looking at the wider view of house construction/modification and surrounding ground conditions?

The longer question is: The house is detached, 4 bedroom, built c1890, all features ripped out in 1970s (including fireplaces, chimney breasts etc), concreted around house, solid concrete floors on ground floor (since '60s apparently), c1' thick brick walls, now clad with good quality hard smooth finish, c2'deep brickwork below ground, no foundations. I have dug a hole behind the house and the "water level" is only about 6" below ground level. As the concrete floor level is the same as the outside concrete level it doesn't seem surprising that there is a damp problem. i am only surprised that it is not as bad as it could be.

My amateur guess is that:

- All the concrete around the house should be removed to about 2' away
- Drainage/soakaway put around the house
- Leave cladding as-is (even though I would like to remove) as the bricks could be damaged underneath and it could be costly to remove
- Don't do the damp proof as it is as simple as draining water and letting moisture out.

Just need a professional to advise on the above in situ before I get quotes. I am wary because this is a minefield of snake oil salesman peddling damp solutions. How do I find a trusted adviser (in Kent)

 

[jeds]

It's very hard to say without seeing the exact situation, but, it sounds like some kind of drainage will almost certainly be part of your solution. So, if I were you, I would probably strt there and you might find that you need do little else.

If you have an existing working surface drainage system you could try adapting that. Otherwise google french drains.

 

[Joe Malone]

Here's the ideal solution to treating your damp problems at source.

1. Dig up the retrofit internal concrete floors and reinstate the timber floors with adequate sub floor ventilation. Retrofit concrete floors are a common cause of damp in old properties, they prohibit wall base ventilation, and displace ground moisture so that it is pushed up the walls under hydrostatic pressure.

2. If you haven't got a physical DPC fitted lower external ground levels 200mm below internal finished floor levels. 150mm if you have a physical dpc.

3. If lowering external ground levels isn't possible install a french drain round the perimeter of the property. Line it with Terram and fill it with pea gravel. This will help drainage and ventilation at the wall base.

4. If you have a high water table then consider installing a land drain to reduce the height of the water table. It may well be that after carrying out all other measures that this is not required.

As I said, this is the ideal. Only you can tell me whether it is realistic, there are easier solutions but none of them will treat the problem at source.

 

[Shytalkz]

snippety snip...
3. If lowering external ground levels isn't possible install a french drain round the perimeter of the property. Line it with Terram and fill it with pea gravel. This will help drainage and ventilation at the wall base.

The trouble with this method is that it can result in subsidence, in that water is encouraged to drain down towards foundation level. If the french drain is anywhere near foundation bearing level and the subsoil is predominantly granular, then encouraging water flow through this can result in soil erosion and down goes the foundation. It's akin to having a leaking water-bearing pipe close to the foundation.

 

[^woody^]

Here's the ideal solution to treating your damp problems at source.

And the simplest ....

5. Just install a suitable barrier on the top of the floor, and tile or fit a floating floor. Viola!

The OP's post is not actually a question, but a rather cryptic jumble of statements, so its hard to determine what the actual problem is

So nr 5 may not apply if dampness is in the walls too

 

[Joe Malone]

The trouble with this method is that it can result in subsidence

I have to say that this quote is absolute nonsense! I'm talking about installing a French drain not a water feature. You've got half the facts right; of course excessive water can wash away granular soils and potentially cause subsidence problems. I've resolved cases of subsidence without having to resort to underpinning purely by improving land drainage and rectifying drainage leaks. The French drain i mentioned doesn't add more water and if it wasn't there the water would eventually end up at exactly the same place, the French drain just allows it to get there quicker and aids wall base ventilation. They have no affect on foundations whatsoever.

 

[Shytalkz]

Who said anything about definitely needing underpinning? Most subsidence problems related to water escape/seepage into granular soils can of course be resolved by removing the source of escape viz drains, water supply pipe, without recourse to underpinning, depending on the extent of erosion that's taken place and the condition of the structure. You haven't been taking some amazing hitherto un-thought of approach to remedial action, you know .

But you are advocating introducing a potential source of water seepage into the founding soils, by bunging a french drain directly against the wall; and that is not necessarily water that would have "ended up there anyway" at all. The fact is that you are actively encouraging water down to foundation level (and quicker: faster flow rate increases erosion); and in granular soils, with a shallow foundation somewhere near the bottom of the french drain, you may well be solving one problem with this approach, only to cause another.

 

[JerryM]

My amateur guess is that:

Your guess is likely to be a good as anyone’s. Damp is all about finding the route cause and to do this a lot of visual inspection and simple common sense is needed. These attributes are what you’ve already got. What you don’t have is the instruments to enable measurements to be taken of dampness and humidity. This you will need a professional to help.

All the concrete around the house should be removed to about 2' away

The short answer is likely to be yes. This depends on if it slopes away from the house with a good fall. Check with a spirit level. At least 1” per metre is needed. All concrete paths I’ve seen don’t have a slope (concrete likes to lie flat and uneven). A 2” drainage channel is likely to be difficult to construct. I normally go for 1 spade width. Make sure the created channel can drain to lower ground otherwise you are creating an expensive fish tank.

Drainage/soak away put around the house

It depends on if you’ve got an area of lower ground that you can drain to. Soakaways are of last resort as they don’t work as well as proper surface drainage of rain water. They can also get blocked in time.

Leave cladding as-is

Yes. Sort one job at once

Don't do the damp proof as it is as simple as draining water and letting moisture out

Yes. See what effect the drainage has before doing anything else.

Minefield of snake oil salesman peddling damp solutions

Yes. Repost when you ready. This is one of the most difficult things to protect yourself against. There are a whole host of things which I will list when you need. The key thing is to find someone who has a tie to a national company ie a name to protect and an insurance company backing the guarantee.

 

[Joe Malone]

Who said anything about definitely needing underpinning?

I don't know was it me or was it you? I certainly can't find anything about me raising underpinning as an issue or saying anything about definitely needing underpinning.

Lets keep it simple, what you're doing is speculating without proof. French drains have been installed for years as a cure for rising damp. They were installed long before DPC's were even thought of and there isn't one single recorded case of a french drain causing subsidence problems. You keep saying that a french drain introduces a water source but clearly it doesn't. Your next point seems to focus on the impact it would have on the speed the water reaches the foundations but this is completely immaterial.

The process you refer to is commonly called erosion but the correct term is sub surface erosion because it only occurs from underground leaks. Surface drains have no impact on this process whatsoever. This view is supported by the Building Research Establishment in their book; 'Has your House got Cracks' 2nd Edition

Oliver et al, Dampness in Buildings (1997) states: It is possible that by providing field drains around the building, rectifying defective drainage and promoting rapid drying out of the affected walls, the problem may be resolved.

Key academic text proposing a course of action that might induce subsidence?... I think not.

Your understanding of this subject is at best a little sketchy.

 

[Shytalkz]

snippety snip...
Your understanding of this subject is at best a little sketchy.

Yep, of course it is, I've spent 20-odd years as a chartered SE making up problems where none exist .

Er, actually you mentioned underpinning. I don't know why: presumably as being the end result of whatever potential problems I was indicating that french drains directly adjacent to a building could - and do - cause.

If you are advocating digging a french drain right next to an old wall with shallow/no foundations, down to much the same level, in granular soils, particularly fill or poorly graded virgin soils, then you are asking for problems to occur ie erosion of the founding soil, hence voids, hence loss of support to the foundation, hence building movement. Not to mention forming it at the same, or deeper (it happens...) level as the foundations and promoting potential instability of the wall by excavating alone.

Don't bother with semantics, I qualified where the erosion of the subsoil could take place, it doesn't need the prefix "sub-surface", as, by definition that is where it would occur. Or did you think I was talking about either coastal or wind erosion?

Example: old property on shallow foundations, in granular soils, with a high water table (at foundation level), close to a fractured water main in the street, front of property starts to move while the main leaks, then stops within a reasonable period of time after the main is repaired. Testing of water revealed potable water in with ground water. The only variable has been the rate of flow through the soil. Ergo variations in rate of flow of water through a granular soil can and do have an impact and if the soil/foundation interaction is in a delicate balance, it can be enough to change that. For the worse.

Example: old property on shallow foundations in granular soil, french drain installed to much the same level to "cure" damp problems in said wall, wall moves therafter, quelle suprise. French drain removed, slabs laid next to wall to fall away, wall injected. Hey presto: wall stops subsiding, damp problem solved as well. What was that you said about no documented evidence of this?

I don't have to read books or rely on academic treatise to seek to justify my stance: I've dealt with enough properties where either french drains next to walls, or rate of water flow have resulted in subsidence and removal of the former and dealing with the latter has solved the problem - without recourse to underpinning, even, woohoo. But you carry on doing what you do and I'll willingly follow on after and sort out your balls-ups.

 

[Joe Malone]

I suggest you read your own post again; 'The trouble with this method is that it can result in subsidence.' This was your comment not mine.

It really has gone straight over your head this one hasn't it. If you read again my original post it states; If lowering external ground levels isn't possible install a french drain round the perimeter of the property. Line it with Terram and fill it with pea gravel. This will help drainage and ventilation at the wall base.

I'm talking about lowering external ground levels. Where this isn't possible then French drains can be used locally to reduce ground levels back to their original depth, not lower than their original depth. For some reason you haven't understood this and are talking about compromising the foundations in some way. Carrying out work in this manner does not and has never compromised foundations.

 

[JohnD]

Viola!

(I know what you mean )

 

[PerryOne]

Gentlemen, the key issue here is, the water level is 6 inches below the surface.
There is obviously no where for the water to go!
If the house was on a slope the water would get away.
As it is, a French drain (thanks to Ohio farmer Mr. French who copied Roman idea) will require constant pumping.
This I would guess on a cost/effect basis is not on.

On the other hand, a chemical cream injected solution in all walls at 4 inch spacing will provide protection against rising damp and start the drying process!

As advocated earlier, a painted on damp retardant solution, with self leveling compound over, will sort the floors

 

[^woody^]

lol - the whole industry is a fiddle

 

[Shytalkz]

I suggest you read your own post again; 'The trouble with this method is that it can result in subsidence.' This was your comment not mine.

The key word being can, not will.

I'm talking about lowering external ground levels. Where this isn't possible then French drains can be used locally to reduce ground levels back to their original depth, not lower than their original depth.

You actually said "If lowering external ground levels isn't possible install a french drain round the perimeter of the property. Line it with Terram and fill it with pea gravel. This will help drainage and ventilation at the wall base"; what you didn't say afaict, is dig a french drain back to the original level (until just now). Hence why I read that as digging a trench from the original level down towards the foundation level; and hence my comment that so doing can cause subsidence, an actual example of which was what I gave. If the excavation is no lower than the original ground level, then yes I would concur with you that it's not making the situation with regard to the structure any worse than it was originally.