DIYbanter - View Single Post

wrote:
Just got a quote of £60,000 for a 30m2 ground floor + 10.5m2 upstairs
extension, which I think is a bit steep! I'll get more quotes but
even so I've decided to dig my own foundations by hand and lay the
concrete, to save money.

My existing house is built in the bottom of a former limestone quarry.
The top-soil/clay is relatively shallow approximately 500mm, below
that you hit solid limestone bedrock. So it's quite good for
building solid foundations on.

Digging the trench I think will be relatively straight forward
(architect's plan state strip foundation 600mm x 200mm)

That's a lot of soil, bearing in mind that they are two foot wide by eight
inches deep at the bottom of the trench, the trench itself will probably be
two feet deep as well.
Aslo don't forget that the bottom of the trench should be widened out to
600mm, so that the shape of the concrete is like this:
________
/ \

for stability.

I have a number of questions and concerns:-
My biggest concern is making sure the concrete will be level and
uniformly at the same depth (digging the trench to a uniform depth is
relatively easy). I've read about knocking wooden pegs in to the
trench bottom so you can easily gauge concrete levels. But won't they
weaken the foundation if left in which I'm told you do? How about
using Steel pins, where do you purchase them, are they the ones used
for steel reinforcing?

You don't need any of that guff, just dig the bottom of the trench fairly
level and drop in the concrete.
To test the levels of the bottom of the trench, get 3X2 timbers and put the
level along them on each run (if for example your trench is in an 'E' shape
or a square 'C' shape) and at each corner.
Pour the concrete in (ask the delivery driver to wet it up so that it runs
more easily) and tamp down with the back of a large rake, this will be level
enough for most brickies, as the others have said, they will gain or lose a
few inches within a few courses and long before they reach DPC level it will
be perfect.

-How do you tamp the concrete easily without sideboards do you use a
"vibrating poker"?

Large rake, or a short length (18inch) of 3X2 fixed to the end of another
piece of timber and tamp it with this, it doesn't need to be polished.

- Should I measure concrete depth to coincide with brick/block
measurements, so that the once the bricks are built up to ground level
they coincide with the existing house brick level?

You can sight it visually, as long as it isn't 6 inches out from one side to
the other, the brickies will sort it out

Any tips websites, books that can give me a full insight into what is
required would be most appreciated.