DIYbanter - View Single Post

wrote:

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)

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

Since you are on bedrock you have no worries about the footings moving.
All you need is a base to run the brick courses to. I wouldn't worry oo
much about gettin the levels spot on. Any competent brickie will soon
put the first couple of couses right.

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 won'r need that will you just fill it to a level and drop a plank
on it and move the concrete around until the plank is floating level.

For anyone putting footings onto clay or shale, the pegs come out after
the bulk of the concrete is poured then the holes filled in. A cpoule
of 3 x 2 run along the trench nailed to the pegs allow the concrete to
be trammelled level.

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

No need the footings for the wall only need to be scraped level to
withing spitting distance. Of course if there is little of no depth
below DPC to play with you might have to fiddle it. The bricklayers
will just lay thicker and thinner mortar to bring the bricks right.

I have even seen them leaving bricks out of courses and using floor
tiles instead of bricks to make the level.

- 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?

Once the bricks are brought to DPC level you can put the hardcore in
the floor and then the binding sand which will need tramping with a
"wakker plate" or roller. Then the visquene does on the day the
concrete comes. I'd get the brickies to float that for you if you are
that unsure.