Will removing the concrete outside lead to 'heave'?

[christinawoodward]

Hello,
I live in a cruck framed thatched cottage. It's like Tales From The Green Valley. A previous owner has got a bit carried away with concrete around the outside the house. It's everywhere, butts right up to the walls and stretches outwards up to 6m. The floor level indoors is about level with outside but I don't know what's under my carpet, it might go down some way, which would make it lower than outside. I don't want to mess up the carpet by cutting a test pit. The walls inside get damp at around waiste height. It seems obvious that what I need to do is hire a concrete breaker but I'm worried about causing heave. I'm aware of the age and possible fragility of the house. Does anyone have any experience of this? It's a very beautiful place. I'm doing the renovation work myself, researching and learning as I go. If I'm unsure of anything I leave it for the time being. I've learned a lot about lime mortar and repointing. Also drainage. I could do with some help please if anyone has any time to spare.
Tina

 

[middi]

Hi
It looks lovely and cosy inside !!!

You have no choise but to excavate two or more exploratory " holes" close to the outside perimeter walls to find out the constitution and stability of " footings", before you remove the rest of the " motorway" around the perimeter walls.
If these holes are six or seven feet apart it should be absolutely fine if it appears that the" footings" are fine. If the int. and ext. levels are equal, or the inner level is lower, I would definetely remove the cement " ring" and lower the exterior level ( if at all possible) and according to what you find with your test holes I would include some form of drainage below some new porous paths. The existing cement must play havoc with drainage from within the house sub soil.

Middi

 

[robgil]

just a thought but where does your rainwater from the roof go? Thatched cottages usually have no guttering.

 

[christinawoodward]

Thanks Middi. How will I know if the footings are sound? I would guess I'm looking for the walls to continue downwards and the stone to be still in a line and not falling away or crumbling. The walls are made of soft sandstone random rubble. The lowest ones are pretty damp looking. I think I'm sitting on sand. If the footings seem ok and I remove the concrete, I'm worried the sudden allowance of rainwater soaking into the ground will wash away the sand. There's also a drain that will be exposed if I remove the concrete. Do you think the pipes would need lowering?Many things I'm fine to take on, just grit your teeth and put on a dustmask, but I think I could cause real damage if I do the wrong thing here.

 

[robgil]

If there is a lot of water down there now to cause damp in your walls , then surely removing the concrete wont make it much worse? would it not make the ground less swollen and shrink as it dries out? Im no expert though.

 

[christinawoodward]

Thanks Robgil,
The rainwater forms a small pond just outside the back door! Some of it washes down the passage between me and an adjoining barn - I think it's an old long house - I don't know where the rest of the rain goes. The drainpipe on the barn has ferns growing out of it and the gutting on the barn is useless. It had the thatch taken off it. I'll talk to the farmer, probably quicker to fix it myself though.

 

[robgil]

Ive always found getting to the source of damp is better than trying to remedy the effects.

 

[Flyfisher]

I think I'm sitting on sand. If the footings seem ok and I remove the concrete, I'm worried the sudden allowance of rainwater soaking into the ground will wash away the sand.

Welcome to the forum Christina. What a lovely looking house you have there - very inviting.

I'm certainly not a structural expert but my understanding is that 'heave' is something that happens in heavy clay soils, rather than sandy soils, due to the fairly large volume differences between wet and dry clay, which results in ground movement. If I'm right about that, and you are on sand, then 'heave' should not be a problem.

As for your sandy soil being washed away, I would have thought that your house is significantly older than its concrete 'collar' so why wouldn't this have been a problem many decades ago? I'd guess the house would have had plenty of time to fall down - if it was going to - before the concrete was laid.

I'd also guess that simple rain would be unlikely to wash away your foundations, although if your ground is such that water can pool and flow to form a 'mini river' then that could be a problem if left to its own devices. But such circumstances are usually what drains and pipework are intended for.

I'm probably not being of much help - I'm just trying to look at things from a different perspective.

 

[AMc]

The house is older than the concrete and can almost certainly do without it
The house is damp which you need to sort out
The house is framed with wood - which doesn't like being damp and will end up needing major repair if its left to rot.

If there is a lot to do then a breaker is a good idea but I would remove the stuff near the house manually as a breaker transmits a lot of vibration around it and may damage render etc. on the house.

I would get a cheap 9" grinder and cut neat lines around the house in two lines a foot apart so you can remove a strip between them with a long crowbar/cold chisel then neatly clean up the concrete closest to the house by hand.

I wouldn't wait as we have a lot more wet weather to come and you want to get the benefit of the summer to dry your walls.

 

[another_richard]

In my days when I was in field archaeology we encountered lots o concrete that needed to be broken up outside delicate buildings.

We used large disk stone / concrete cutters cutting the concrete into slabs and using a crow bar / hammer chisel to lever break it out. It obviously depends on the thickness...

I can only add the cutters are really noisey so wear ear protectors.

 

[christinawoodward]

Thanks so much for your advice. Lots of information to consider. I think I need to get the guttering on the barn fixed first and unblock the drainage pipe with fern growing out of it. After that dig some trial pits to look at the foundations. Still not sure how to proceed with the drainage pipe that will be left standing proud if the concrete comes off.
Lots to do.

 

[Flyfisher]

Still not sure how to proceed with the drainage pipe that will be left standing proud if the concrete comes off.

I can't really see why the pipe couldn't be simply cut back, but maybe there is a good reason. Would it be possible to post a photo of the pipe in question?

 

[christinawoodward]

Flyfisher, I'll take photos at the weekend. I've never lifted that drain cover but it'll be a brown ceramic pipe I'm sure. There's no smell eminating from it. I hope it's just an old land drain. It's one thing I've never got round to taking a close look at.
I'm changing my forum name to Chard to fit in.
Chard

 

[Penners]

Welcome Christina.

You actually have a number of issues to address, all rolled up in this thread. And many of them have been well answered by others. But just to add my inexpert voice to those above, here are my thoughts:

1. Heave, as Flyfisher says, is chiefly a problem on clay soils, which tend to swell significantly if they suddenly become wetter. If you're on a sandy soil, this should drain efficiently and I doubt that heave would be a problem.

2. If you have a motorway (as Middi humorously called it) around the outside of the house, and concrete floors inside at the same level, then it's not really surprising that your walls are damp. The subsoil moisture is unable to percolate up to the surface on either side of the wall, so it's probably tending to migrate sideways and get soaked up by the walls. So, in my view, removal of the motorway will probably make a significant contribution to resolving this problem.

There's no need for you to dig exploratory holes inside, but Middi's suggestion of a couple of pits against the walls outside is probably well worthwhile. They will enable you to check and make sure that the concrete is not hiding and supporting a seriously degraded subsoil plinth, which could deteriorate further if the concrete is removed. Provided you find the subsoil masonry to be in good order, then you can probably proceed with confidence to remove the concrete.

3. The drainage pipe that you're concerned about is one of those "suck it and see" problems (yuck! :x ). If removal of the concrete exposes the pipe and leaves it proud of the surface, then you have to ascertain whether it can be covered up, or whether it will have to be relaid at a lower level.

Removal of the concrete will, of course, leave the outside soil level considerably lower than the level of the concrete now (and, if I understand you correctly, lower than the internal floor level). For dealing with the damp walls, this is a desirable thing. But, depending on the thickness of the concrete that you're removing, you may afterwards be able to build up the external soil level a bit (finishing off with something porous like gravel), while still leaving the finished level lower than the internal floors of the house. This might be enough to cover up the drainage pipe again. If not, then I'm afraid you may have relay it at a lower level (always assuming this is possible).

As others have suggested, it would be a good idea to post a picture of the pipe here, so that you can gain a view as to its purpose.

 

[Flyfisher]

But, depending on the thickness of the concrete that you're removing, you may afterwards be able to build up the external soil level a bit (finishing off with something porous like gravel), while still leaving the finished level lower than the internal floors of the house. This might be enough to cover up the drainage pipe again. If not, then I'm afraid you may have relay it at a lower level (always assuming this is possible).

Ah, I think I now understand the possible problem. I had imagined the pipe being vertical right through the concrete and into the underlying ground, in which case I was thinking it would be easy to cut off the excess pipe exposed by the concrete removal. But if, as I think you're hinting, the pipe lies horizontally within the concrete, or at least just below it, then it would be a different matter.

A photo would almost certainly help.

 

[Penners]

I'm not really sure either, FF. But both of our mental images would obviously be improved by a posted one!

 

[christinawoodward]

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

 

[Penners]

Christina

The foundations or plinth (and they may not be very deep in a house of that age) will - I presume - be masonry. If so, then so long as they're reasonably vertical, with no serious signs of deterioration of the mortar or the bricks/stones, then they should be fine. In fact, they should just look like a buried masonry wall.

 

[robgil]

when you say drain cover do you mean an inspection chamber cover?
how long have you had this damp issue? it seems to me that the concrete wont be helping the earth dry out properly but if this damp is only recent in relation to the concrete being laid then it wont be the cause either.
Sandy ground should have good land drainage as opposed to clay.
Where does your rainwater drainage go?

 

[Lime]

I do not understand the proposition that the concrete/cement plinth is somehow holding up the house.
If anything it is detrimental to the property.
It needs to be removed with care, no bashing with hammers and other bodge methods.
Cut the surface in small pieces (to start with) and lever up.
Start at the outside with long steel lever pivoted on wood.
Don't try to remove too much at once.