Excavating supporting floor to lay limecrete

[rob00]

Hi

I am in the process of renovating a 17c listed stone built cottage and as part of the renovation and because of the grade 2 listing I will be laying a limecrete floor. I have just started digging the floors to the required levels and it is apparent by the amount of stone that is in the floor that this is likely to be supporting the walls. My question’s are 1. Am I correct in assuming that the stone in the floors are supporting the walls. 2. If they are, then is it still OK to dig the floors as long as I taper the digging rather than dig straight down. Any suggestions/advice with this would be appreciated. I should also say I’ve stopped digging while I check this out!

Thanks
Rob

 

[MdB]

This is where a post from the structural engineer guy would be useful.

Stopping work is a good idea. Getting a structural engineer to take a look would be a good idea also (if possibly expensive).

Photos would be useful for others to comment.

(In my very inexpert view, the stone in the floor is very unlikely to be supporting the walls. The forces in stone work go straight down I think and in soil it is 45 degs but don't risk your house on my thoughts.)

 

[chuckey]

I would (and have) select a bit in the centre of the wall, about a foot long and do an explority dig. The construction of my rock and rubble cottage, was that a shallow trench was dug, big stones hurled into it, then the walls built of these stones. After the walls were built the existing soil was removed for a depth of about 3" and gravel placed on the soil, then the flagstones were put on top of this. So in my case, digging down about 6" into the soil revealed the top and middle(?) of the big rocks BUT NOT their bottom. I think to build walls on a stone floor wouldl be difficult, because as the weight of the stone in the wall increased as the wall's height increased, the stones round edge of the floor would sink into the soil. So it would be very difficult to build the floor very flat.
Frank

 

[Penners]

In my very inexpert view, the stone in the floor is very unlikely to be supporting the walls. The forces in stone work go straight down I think and in soil it is 45 degs but don't risk your house on my thoughts.

I agree with MdB in every respect. I remember one of our most experienced contributors posting that the subsoil support for structural walls runs out and down from the walls at 45 degrees on each side. That being the case, I can't see that a stone floor within the walls would have any supporting effect outside that area, unless it were a monolithic structure, such as a raft, upon which the walls rested.

BUT - like MdB, I urge you to get qualified professional advice. It's not worth risking your building on the strength of your own, or our, inexpert views.

 

[ljn]

limecrete floor with recycled glass aggregate, underfloor heating and a polished lime screed on top. That was my plan.

The materials for the limecrete floor come to £4500
I am waiting for an installation quote from a limecrete specialist for the slab and a polished lime screed on top of the underfloor heating.

I asked the builder for a quote for getting rid of the various bits of concrete floor (no DPM or insulation, I presume), and digging down the 45cm required for the limecrete build-up.

The builder says I'm totally bonkers:
- 2 party wall agreements (one for each side of the terrace)
- Inspection holes, engineer fees, building control inspection, CO approval
- 15 skips worth of rubble (at £200 each)
2 weeks work to dig out.
2 months drying time for the lime slab and floor.
The builder suggests covering the existing mess with a 5 cm concrete screed and spend the £8000, or whatever it comes to, elsewhere in the house.

So I don't know. The limecrete would be the best solution, but could be a very bad economic decision.

I am now thinking of doing the roof and all the rest of the project and seeing if I have money left over for the floor. In th wost case scenario I could go with the builders solution or leave it "rustic" till the UK economy picks up.

 

[Flyfisher]

Obviously I have no idea about the scale or scope of your project but surely if the roof needs work then that's the place to start? Without a solid and dry roof everything underneath remains at risk.

 

[MdB]

Ditto Flyfisher. If you have a dodgy roof then spend your money on that rather than the floor..

Having a warm insulated floor is very nice though.

(Oh and our two builders broke up and shifted over 30 tonnes of concrete / dirt when digging out our floor (60m^2) in two days. There are at least some builders around that are willing to work hard. I looked into using limecrete for the floor but it required more depth and was approx double the cost of a celotex / concrete floor. Our house is unlisted and mainly modern construction so though I would have liked to have used lime, it was ruled out on cost grounds)

 

[ljn]

Sorry, I was a bit unclear. The roof will be done, no question.

My initial plan was to get the necessary basement structural work sorted first, followed by the basement floor. The structural work in the basement is necessary as the previous owner removed the wall supporting 5 floors above - the engineer called it a demonstration of lateral support, or something.

While the basement floor is setting, I planned to start work on the rest of the building from top to bottom. Roof included. So the last thing I'd do is install the basement kitchen.

My certainty on the floor has been a bit shaken, so I might skip that and go directly from basement structure job to the roof job, leaving the basement floor with it's budget and legal issues till last.

Sounds like I need MD's builder, my floor is the same size, or perhaps my builder was just being a pessimist and trying to save me money. I haven't had the quote yet, so I'll see...

An exploratory excavation to check the concrete depth would help. It's rock hard. A bug hammer and chisel won't even chip the surface.

What I end up doing will also depend on what building control say.

 

[MdB]

Ljn, it sounds like our builds are somewhat similar.

Our 1970's front and internal structural walls were built very badly, had structural issues, let the damp in and the heat out. After a lot of mucking about looking at various options and digging lots of exploratory holes (I did 11 if I remember correctly) it was decided that the best option was to completely replace the iffy walls. As quite a bit of the floor was being dug up for the new foundations, we had the floor dug up and replaced with insulated concrete with underfloor heating built in. The end walls were old (1850's mud and rubble) and I was a bit worried about undermining them whilst the floor was being dug out as we need 270mm of depth. However, it turned out the floor level had been raised in the past so we didn't quite get to the bottom of the base stones in the wall so it wasn't an issue. As the DPM in the floor couldn't be put under the old wall and because we have a very high water table here, I was worried about pushing damp up the old walls with the new floor. This had happened with the old floor DPM (such as it was) and the walls we had removed. I therefore had a gap left next to the old walls which will be filled with limecrete (made myself from lime hydrate from a shed + leca. Not much more expensive than normal concrete) so that the moisture around the wall can hopefully evaporate.

Cost of reinforcing roof, removing front and internal structural walls, rebuild with block and 100mm celotex, remove floor and replace with concrete + 100mm celotex was £33k. Included rerendering front wall, doubling of the floor joists and the removal and replacement of the windows. Didn't include and internal rendering / plaster work, plumbing or electrics nor removal of the rubble which the local farmer took at about quarter of what it would have cost me to remove.

If you want any more details then please PM me. I can fully recommend the builders but it might take some persuading to get them to Margate..

 

[Penners]

They've certainly installed that glass wall beautifully. You'd hardly know it was there.

 

[masochists-r-us]

You don't say why you're going for limecrete. Costs and inconvenience associated are only really worth it if you need to eradicate a significant damp problem and even then there are other less disruptive way of approaching it.
We also have a 400 yr old hpuse and started off down this route, but backed away from it on the same grounds. However, we still plan to remove the concrete to expose the earth floor in our kitchen to cover it with stone flags laid on lime mortar.

 

[ljn]

The limecrete slab is in place and curing.

Excavating the basement wasn't such a mammoth task. No party wall agreement was needed because I dug out at 45 degrees from where the original floor met the wall, thus avoiding exposing wall footings or foundations. Building control were happy with this. So was the engineer and the CO.

The limecrete slab was done by http://limecrete.co.uk/ They were absolutely brilliant.
It took two people one day to get the Recycled Foamed Glass insulation in, and one day for the limecrete screed. I helped along side a local labouror. The neighbors, other trades people working on the house and I were all very impressed. The logistics of access was quite difficult.

The next step is to lay underfloor heating ready for the limecrete co to come back and pour the final 75mm lime screed that will be polished.

 

[briany]

Ljn, how did you excavate the basement? How long did it take? I'm starting the process of excavating an 8x12 basement in my own place, and am thinking a microdigger (which can get in the front door) plus conveyor to dig down the required 6 feet or so in hard packed stony clay. I'm ever so slightly apprehensive at the prospect of all the work...
Brian

 

[Schoolmarm]

Briany, your basement sounds as if it is completely filled in. I don't think the ones on here are filled in.

 

[briany]

True, true. The same question applies, though - the most efficient way to safely excavate inside the house - manual or mechanised? I've been trawling the hypermeganet for some time and haven't found anything very specific.

 

[Schoolmarm]

DWB, a member on here had machinery inside her very old house. The pictures used to frighten me.

 

[AMc]

At mine, digging out our floors for oversite, insulation and underfloor heating (45cm at one end 1m at the other) was done with picks, spades and wheelbarrows. The labourer was very keen to get the minidigger in, the more experienced guys were too worried about vibration and accidents bringing the house down around them.
They did use a phenumatic breaker to loosen the subfloor which shook the whole house in a quite alarming way but didn't seem to do any permanent damage. In the end it was more expensive but probably safer by hand.

I would probably try a test with a spade to see how hard it is, moving on to heavier duty methods if you need to.

 

[briany]

I bet the labourer was well keen for the minidigger. As my house is pretty solid (3 feet thick walls), I wouldn't be so concerned about vibration. I've test dug a channel and it's pretty hard going. Might be the way to go.

 

[Flyfisher]

I don't think a minidigger would cause much of a vibration problem (unless fitted with a breaker) but, although small, they are very powerful machines. If it was my project I'd want complete reassurance that the operator was very experienced and that their insurance was very comprehensive.

In a previous house, we had some work done involving lowering an integral garage floor by about 1m. The builders, on their own volition, did all the work by hand. I asked them why they didn't use a mini-digger and they said although they could get a machine into the garage, there wasn't much room to manoeuvre around with bucketfuls of soil, so they'd probably have to keep going back and forth on the tracks, which is very slow. Basically, they said it wouldn't be much quicker than hand-digging but there was a constant risk of putting the digger arm through the wall or ceiling.

So they just got stuck in with shovels, picks and wheelbarrows and I was very surprised how quickly they could fill a skip!

 

[Gervase]

I've used mini-diggers inside, but a hugely important thing to consider is the fumes. Unless you have some means of ducting the exhaust out you're in serious danger of carbon monoxide poisoning - and having experienced working inside an unventialted house with one and feeling like seven shades of crap at the end of a day, despite several fans and all the windows open, I would never be so daft as to do it again! If you're going to hire some plant, better to get a conveyor so that the spoil can be shifted out more easily.
And, to repeat what's been said many times, if you haven't got substantial foundations (in other words, if your house is more than 100 years old) always dig down at 45 degrees from the walls to leave a suitable plinth, lest you end up with your house around your ears.