Will removing the concrete outside lead to 'heave'?

[Penners]

I do not understand the proposition that the concrete/cement plinth is somehow holding up the house.

I don't think anyone has suggested this. Although I believe it's not impossible that the concrete is offering some support to deteriorated areas of the plinth. It's a sensible plan to check the condition of the plinth in a couple of places before removing the concrete.

 

[Moo]

How thick is this concrete runway?

 

[Penners]

I don't think Christina knows, until she's done some exploratory mining.

 

[AMc]

It's really good to get this advice, thank you so much to everyone answering. I'll post some photos and if I can get hold of a small angle grinder, cut a small test pit at the weekend. I'll see if Google has any photos of what good and bad foundations look like.
Thanks

If you're buying, as you've got a lot of concrete I'd be tempted to get a cheap large grinder as it will be quicker in the long run.
Look out for cutting discs when your shopping - my little bosch came with 2 diamond discs 'free' which were worth more than the difference between that and a cheaper tool.

 

[christinawoodward]

Hi,
It's an inspection pit with a rectangular drain cover. I'll have a go at lifting it at the weekend. The pipes run horizontally, which direction and from where I don't know. It's always been mouldy and green around that area, up the side of the house, over the back gate, and I'm more convinced the poor guttering and blocked hopper that should look after the rain off the adjoining barn are responsible for the damp in that particular area. For the short term I've had an idea to put a temporary water butt next to where the faulty down pipe is and see if I can divert it into that. I think I know of an angle grinder I could borrow and I'll experiment with wheel sizes. I spoke to the regional Conservation Dept to see if I need permission to remove the concrete and they said no that's fine, so long as there are no obvious remains of any other structures that could be disturbed, which there aren't.
The worst of the internal wall dampness appears a little way off from that. Same wall but further along. The plaster has blown on the inside. I've noticed over the last couple or three years a patch on the carpet quite nearby which, in my darkest moments almost looks like it could be a split pipe running under the floor. There are buried pipes running under the kitchen floor so it's possible. A year or so after buying the place I built a brick planter which runs along the wall in that problem area. (I didn't know it was a problem area then.) I was careful to make sure of a good size gap between the back of it and the wall of the house. Last year when I was pondering on what was making the odd pattern in the carpet, I remembered having to pull weeds up from a hole in the concrete directly outside. This was confirmed by an early photo I'd taken. So I made some buckets of lime mortar and tipped it in the right place down the back of the brick planter. I do think the patch in the carpet looks less angry this year, so I hope it was caused by the hole in the cement outside, behind the planter, that I've now filled in. I think I'm going to have to dig the roses up from the planter, dismantle the bricks, break the concrete (foundations permitting) under it then rebuild the planters, leaving a gap for ventilation again.
Think I'm talked out now. Photos at the weekend, maybe with the new waterbutt.

 

[chuckey]

The puddle out side the back door?, does it go right up to the house wall?, if it does it might mean that the water that accumulates there is actually draining back via the house wall into/under the house foundations.
As you don't know how thick the concrete is , try drilling a hole through it as the start of a test pit. With a disc cutter, it is not possible to cut right through a lump of concrete right up to a wall. You need a gap for its body to go down into. I would start of by drilling a series of 10mm holes as close together as possible, then starting of in the these holes try to go down them at 45 degrees to remove as much material as possible. Possiblely opening out the holes with a 16mm drill. Then open up the holes with a chisel. Always try to break of the concrete towards a gap/space, as it has a low tensile strength, just thumping it so its put into compression would be a hard way of doing things.
Frank

 

[Penners]

It's an inspection pit with a rectangular drain cover. I'll have a go at lifting it at the weekend. The pipes run horizontally, which direction and from where I don't know.

While you've got the inspection cover off, it might be useful to discover exactly what services the manhole is serving. See whether the channel in the bottom looks wet enough to have been used recently. If so, try running all of your house water services (taps, loos, etc.) one at a time and check whether any of them causes water to flow through the manhole. Make a note of the results. Even if the information doesn't turn out to be of immediate use, it's always good to know these things in case of future problems.

It's always been mouldy and green around that area, up the side of the house, over the back gate, and I'm more convinced the poor guttering and blocked hopper that should look after the rain off the adjoining barn are responsible for the damp in that particular area. For the short term I've had an idea to put a temporary water butt next to where the faulty down pipe is and see if I can divert it into that.

If the guttering is faulty or the hopper blocked, then surely the water won't be getting to the downpipe, will it? I'm afraid you need to be getting out your ladder and going up to try and rectify the problems.

And forgive a rather obvious comment, but a water butt on its own will only delay the flow of water from a downpipe. Once the butt full, the water will once again cascade over the area.

The worst of the internal wall dampness appears a little way off from that. Same wall but further along. The plaster has blown on the inside. I've noticed over the last couple or three years a patch on the carpet quite nearby which, in my darkest moments almost looks like it could be a split pipe running under the floor. There are buried pipes running under the kitchen floor so it's possible. A year or so after buying the place I built a brick planter which runs along the wall in that problem area.

Water is an awkward b*gger. It can appear quite some distance away from its source, which makes things very difficult when it comes to tracing the specific area where dampness is originating.

The planter sounds a possible problem. Presumably you water the plants generously? If so, then there's a distinct possibility that this water is seeping down through the soil in the planter and out on to (or into) the concrete - particularly if there's any possibility of a crack in the concrete under the planter. Even if there's a gap behind the planter, I wouldn't dismiss the possibility that this structure has increased the dampness around that area.

I made some buckets of lime mortar and tipped it in the right place down the back of the brick planter.

And is that patch of lime mortar now in contact with the bottom of the house wall? If so, it could be wicking water up from the ground and into the wall.

 

[Flyfisher]

And forgive a rather obvious comment, but a water butt on its own will only delay the flow of water from a downpipe. Once the butt full, the water will once again cascade over the area.

Not only that but it may not actually delay the flow of water for very long. I connected a large water butt to one of our downpipes but didn't have the overflow arrangement in place before the first downpour. I was astonished to notice that the water butt was overflowing within 10-15 minutes.

 

[robgil]

Overflowing waterbutt made mince meat of my clay lump wall.

 

[skier-hughes]

I do not understand the proposition that the concrete/cement plinth is somehow holding up the house.

I don't think anyone has suggested this. Although I believe it's not impossible that the concrete is offering some support to deteriorated areas of the plinth. It's a sensible plan to check the condition of the plinth in a couple of places before removing the concrete.

Our house suffered a small amount of subsidence about 35 years ago when the septic tank was leaking, saturating the ground, blah di blah. The people who did all the work put a concrete plinth all around the house to help hold it up Ours is, about 4' wide and about 4" deep.

 

[christinawoodward]

Update about my drainage. Interesting to me but possibly a bit boring to the rest of the world. I had an exciting few hours today looking into the drainage problem I mention earlier. To some extent I've been able to seperate the different elements that combine and lead to general sogginess. The bad guttering on the farmer's barn next door lead to water being dumped on my doorstep. I can't believe I've turned a blind eye to such an obvious need for maintenance. Busy trying to fix many other urgent maintenance problems. I took the inspection cover up for the first time and it looks very nice and clean. I ran the kitchen tap as suggested, and found it does use this drain. Then I ran the bath and found it uses the same drain too. Also the toilet flushes through there which suprised me. I tried pooh sticks with a bit of toilet paper but didn't get there in time, but it definately uses the same drain as there's a sudden rush of water. I don't think there's a burried pipe running under the living room floor now so that's a big relief and isolates the problem to the hole in the concrete outside. I've unblocked the hopper and cleaned the line of guttering which was so packed with debris you wouldn't believe it. It was also out of position and wouldn't have been catching the rain off the barn roof. Tomorrow I'll investigate the depth of the concrete. I'm including a couple of pictures to show how bowed the walls are in that area. I'm bearing in mind the last comment on this thread, which mentions how a concrete band was used to help combat subidance. I'm wondering now if the concrete might help keep the base of the walls solid. It might be better to leave a narrow ring of concrete at the base of the walls. On the pictures you'll see gravel, well that sits on top of the concrete. Not fully evolved logic I know. Needs changing. I've added an early photo that shows the hole in the concrete which I think caused the damp patch in the living room carpet. You can see weeds growing out. It's near the corner with the new brick bathroom extension. Also last years photo which shows the brick planters. There's a gap between them and the house walls.

 

[christinawoodward]

I'm not up to speed with posting photos. Apologies.

 

[christinawoodward]

test

 

[christinawoodward]

KK

 

[christinawoodward]

KK

 

[christinawoodward]

Reduced photo size.

 

[christinawoodward]

Works better with small photos. Only 3 at a time I think.

 

[christinawoodward]

One of these photos shows the hole in the concrete. Far right, weeds growing out, where base of wall meets the ground. I've filled it in since. The patch in the carpet inside corresponds with the position of the hole outside. I'm sure that's what caused it.
Second photo shows lots of greenery but it's all contained in the brick planters, which sit on concrete and I'm careful not to over water.
I'll test the depth of the concrete now.

 

[Penners]

Christina - I'm not sure why you gave up. All of your pictures have worked fine for me.

The manhole you have opened sounds like the main drainage outlet from the house. So whatever you do, you don't want to damage or even disturb any of the pipe runs to and from it.

A word of caution about solving damp issues: it's very tempting start dealing with as many possible solutions as you can, all at the same time. But actually, if you want to keep costs down, you're probably better to approach them one at a time, with a period of "watch and wait" afterwards. This enables you to see which of the treatments is effective - hence the root of the problem. If you're lucky, the first and cheapest solution will work!

The photographs of the barn guttering look... er... characterful! If the part of your house that's damp is anywhere near that guttering, I would certainly get the problem rectified (so that the guttering is doing its job) and then wait to see whether the dampness seems to be drying out. It looks a very likely suspect.

The concrete runway around your house is certainly not an ideal situation. But I really wouldn't recommend leaving a ring of it against the walls of the house - unless it appears to be essential to the structure (which is probably unlikely). The bit nearest the house is the most important bit, when it comes to the causes of damp. It could be preventing subsoil water from evaporating away, and causing rainwater bounce to soak the walls.

As I said before, I would cut/dig a few exploratory holes against the walls. If it doesn't appear that the concrete is offering any structural reinforcement, then I would either (a) remove a ring of concrete immediately against the wall, perhaps a metre wide, or (b) remove all of the concrete and replace it with gravel paths.

 

[christinawoodward]

Thanks Penners. I'll proceed slowly and with caution. I just don't quite dare break the concrete. Certainly won't get far in my dressing gown so I better get on now.
Thanks