pouring foundations - levelling up

[sm_jamieson]

When pouring mass concrete foundations, I have some questions:

1. What is the best way to make guides for the tamping down boards ? (I'm sure I've seen wooden pegs sticking up at the required height - if so, can these be left in place ?)

1. Since the concrete will be delivered quickly (a chute or pump), how can you get just the right amount of concrete in to level to the tamping boards ? Have an overflow pit ready just in case ?

2. What to do with excess concrete, since the lorry will want to empty it's load ?

1. If it turns out I have ordered just short of the required amount and the foundations are a little low, will this be rectifiable, or will BCO go loopy and require it all the be dug up ! Would it be reasonable to have tamping guides one 75mm lower just in case this happens ?

TIA, Simon.

[The Natural Philosopher]

Yes.

You can't. Its a bloody nightmare and you WON'T get it dead level.

That is what half bricks and a good bricklayer are for.

Fill the thing up, and level it as best you can. Takes a lot of blokes with rakes and so on. If its a bit higher so be it. The Earth is not flat ether.

Just don't tell him. or mix up a shade more. Or use conctre precast blocks to make up the difference if you like., HE probably would not mind that. Use a very strong mortar underground tho 2:1 sand:cement IIRC. Others will know.

After the rigmarole of pouring mine, next time I will leave it all about

4-6" below and use blockwork to build up on a variable mortar bed. Its a lot easier to lay blocks to a string than pour concrete to a level.

IIRC the issue with foundations going deep, is not so much that whats higher up has to be strong, but that what's lower down rests on soil that is more stable - i.e. into the area where soil huimidity is fairly constant, and tree roots don't go..

[sm_jamieson]

Well the plans have 3 brick courses / 1 block between the foundation and ground level, and I'm sure it's better to have it too low rather than too high, since fiddling with part-blocks would be a pain (although thermalite easy to cut !). Probabaly aim for a point a bit lower, then "top up" !

Cheers, Simon.

[The Natural Philosopher]

Actually mine came out a bit high, but as my ground man said 'its always easier to add hardcore and soil to get the ground level up, than dig trenches to drain a house where the soil is higher than the DPC".

Being on a slight slope, we ended up using a lot of old foundations to fill in a 2ft deep terrace and I built a haha as well, which makes a nice microclimate for Mediterranean plants, that don't mind all the buried builders sand etc..

MY BCO was concerned to get the foundations below tree root level: How high they went post that wasn't really an issue..the next issue was that the DPC was above soil final level by two bricks or so.

Having the house high also makes drain building easier. Both foul and rainwater.

Be sure to get these in next. BEFORE you start laying the blocks. Many of them will have to run THROUGH that. Use lintels over, and gravel backfill..

[sm_jamieson]

My final floor level is fixed, since it's an extension. And the original 1930s house only has 1 brick level between ground and DPC, so I will have to reduce ground level around the extension to make the floors line up and have 2 bricks clear.

It seems that drain gullies etc are sized to sit on top of the sticking out bit of the concrete footings, and meet ground at about 3 brick courses. Drain levels roughly fixed as existing. If BCO agrees, I will pour foundations around the existing clay drains (leaving 150mm around IIRC), and sort out the new plastic connecting drains just before the floor slab is done. The bit that will remain clay goes into a public sewer, and I shan't be touching that !

[Andrew Mawson]

I wouldn't want thermalites below dpc level - far too porous - first freeze will blow them away

AWEM

[sm_jamieson]

If that is the case, their must be a reg about it. I will ask BCO. I wouldn't want them at all ! It was never specified on the plans to use different below DPC. Since perimeter insulation comes up to DPC level, no reason not to use concrete blocks or just bricks. Another BCO question. Simon.

[Hugo Nebula]

On Wed, 19 Sep 2007 06:26:45 -0700, a particular chimpanzee, sm_jamieson randomly hit the keyboard and produced:

Have a look at the manufacturer's details for the particular block, but AFAIK, most can be used below DPC. Indeed, Celcon & Thermalite make trenchblocks specifically for foundations.

[Hugo Nebula]

On Wed, 19 Sep 2007 03:02:01 -0700, a particular chimpanzee, sm_jamieson randomly hit the keyboard and produced:

Depends how low. Assuming standard unreinforced strip footings, then provided the thickness of the concrete is no less than its spread. If you have 600mm wide footings, they'll have 150mm spread, so your foundations would need to be at least 150mm thick.

[sm_jamieson]

No problems here - they are mass concrete trench between 750 and

1000mm thick ! Simon.