I need to cast a foundation for a wall, and for the surface levels to be
reasonably accurately.

It will be 300mm deep and 600mm wide, with a 68mm step in the top edge so
that the rear shuttering only needs to be 232mm tall. The whole foundation
will be below ground when completed, so we were looking to back-fill the
outsides of the formwork prior to pouring the concrete to help prevent the
formwork distorting.

(bad ASCII artwork of design)
||---------||
||-------|| ||
|| ||
|| ||
|| ||
||v^v^v^v^v^v^v^v^v^||
base cast onto excavated surface


Using 18mm OSB as the side shuttering/formwork and 50x50x600mm timber pegs
to locate and hold it down, what spacings would you recommend for the
bracings? These shutters are a one-off and will be 22m long, so I do not
want to make them over strong and waste monies that could be spent
elsewhere.



thanks

Tony Strong

"Tony Strong" wrote in message
...

I need to cast a foundation for a wall, and for the surface levels to be
reasonably accurately.

It will be 300mm deep and 600mm wide, with a 68mm step in the top edge so
that the rear shuttering only needs to be 232mm tall. The whole
foundation
will be below ground when completed, so we were looking to back-fill the
outsides of the formwork prior to pouring the concrete to help prevent the
formwork distorting.

(bad ASCII artwork of design)
||---------||
||-------|| ||
|| ||
|| ||
|| ||
||v^v^v^v^v^v^v^v^v^||
base cast onto excavated surface


Using 18mm OSB as the side shuttering/formwork and 50x50x600mm timber pegs
to locate and hold it down, what spacings would you recommend for the
bracings? These shutters are a one-off and will be 22m long, so I do not
want to make them over strong and waste monies that could be spent
elsewhere.

thanks

Tony Strong



Why not use the soil itself as your shuttering? Why go to all the expense
of building a whole timber box, when you can line and backfill to the sizes
you need. Brace out the internal sizes, backfill and compress the soil to
hold it all. As you reach the internal bracings, remove them as you go
along.

On Tue, 10 May 2005 17:08:06 +0000 (UTC), "Tony Strong"
wrote:


I need to cast a foundation for a wall, and for the surface levels to be
reasonably accurately.

It will be 300mm deep and 600mm wide, with a 68mm step in the top edge so
that the rear shuttering only needs to be 232mm tall. The whole foundation
will be below ground when completed, so we were looking to back-fill the
outsides of the formwork prior to pouring the concrete to help prevent the
formwork distorting.

(bad ASCII artwork of design)
||---------||
||-------|| ||
|| ||
|| ||
|| ||
||v^v^v^v^v^v^v^v^v^||
base cast onto excavated surface


Using 18mm OSB as the side shuttering/formwork and 50x50x600mm timber pegs
to locate and hold it down, what spacings would you recommend for the
bracings? These shutters are a one-off and will be 22m long, so I do not
want to make them over strong and waste monies that could be spent
elsewhere.



thanks

Tony Strong


If you can drive a 50x50 timber peg 300mm into the ground, then you
may find thet building inspector wants some more work doing, as the
soil may not be strong enough. I had to use 10mm rebar and a slege
hammer to get far into my ground (an old glacial river bed). I'd get
the building inspector out befor you start shuttering. In all he came
out 5 times to check my foundations.

To a large extent you can put the soil back against the shuttering, to
support it as you pour the concrete. If this is not possible you can
use some blocks.

The method of getting the concrete into the hole is also important, if
you pour a couple of tonnes from a dumper in a second or so, then you
need very strong shuttering, if you pump it in, it can be less strong.

I made my first shuttering from 3x6 that I had piles off, and
supported it with rebar and backfill. a good result was acheived, and
it was easy to level. It took days to do the shuttering.

My second go, I poured straight into ground trences from a dumper, a
much less good result was acheived.

Next time I think I will go for OSB & 3x2 scant - which is so cheep
you can chuck a huge pile of it at the job.

How you are going to accuratly get a 68mm step in the way you describe
I have no idea, unless you can put the extra 68mm on after the main
chunk is poured.

Rick

BigWallop wrote in message
. uk...

"Tony Strong" wrote in message
...

I need to cast a foundation for a wall, and for the surface levels to
be
reasonably accurately.

It will be 300mm deep and 600mm wide, with a 68mm step in the top edge
so
that the rear shuttering only needs to be 232mm tall. The whole
foundation
will be below ground when completed, so we were looking to back-fill the
outsides of the formwork prior to pouring the concrete to help prevent
the
formwork distorting.

(bad ASCII artwork of design)
||---------||
||-------|| ||
|| ||
|| ||
|| ||
||v^v^v^v^v^v^v^v^v^||
base cast onto excavated surface


Using 18mm OSB as the side shuttering/formwork and 50x50x600mm timber
pegs
to locate and hold it down, what spacings would you recommend for the
bracings? These shutters are a one-off and will be 22m long, so I do
not
want to make them over strong and waste monies that could be spent
elsewhere.

thanks

Tony Strong



Why not use the soil itself as your shuttering? Why go to all the expense
of building a whole timber box, when you can line and backfill to the
sizes
you need. Brace out the internal sizes, backfill and compress the soil to
hold it all. As you reach the internal bracings, remove them as you go
along.


Thanks for the advice, I've uploaded a couple of diagrams,
hopefully showing the plan more clearly than I can explain:

http://www.hebdenhey.org.uk/shutter1.gif - an isometric view of two of the
sections of shuttering

http://www.hebdenhey.org.uk/shutter2.gif - a more detailed view showing the
downstand shutter
"suspended" between the front & back faces.

The 2"x2" stakes will extend further out of the ground if required,
as it is very stony and they will not be likely to be driven fully home.

finally, a section of the proposed wall is:

http://www.hebdenhey.org.uk/wallsection.gif -
this shows the foundation and the interlocking blocks to be dry-stacked,
the wall will be back-filled with clean 20mm gravel
The reason we need the heights of the step is to ensure
the wall slopes back at a slope of 20 degrees.

"Tony Strong" wrote in message
...

BigWallop wrote in message
. uk...

snipped
http://www.hebdenhey.org.uk/wallsection.gif -
this shows the foundation and the interlocking blocks to be dry-stacked,
the wall will be back-filled with clean 20mm gravel
The reason we need the heights of the step is to ensure
the wall slopes back at a slope of 20 degrees.


To obtain the higher section of the pour, you'd need to seal the top of the
lower section to hold the mix at that level. Even concrete finds its own
level, and this is usually the highest point, of course. So, to make the
difference in height will mean building a sealed box with the height change
section built on top of it.

Saying that, the log pour will need more of a base width to hold back the
outward pushing force of the stacked blocks on top of it at the angle you
want to obtain. So the plan of a straight sided foundation isn't the way
I'd personally go with this. I'd tend to look at building a sloped log with
a wider base than the top to obtain the right balance of holding forces
against the build of the blocks. Like the sloping side of a pyramid,
especially on the outward side of the log.

Would it be possible to drop the first row of blocks into the wet pour? If
the blocks themselves could be held at their ends on the sides of the
shuttering, then the pour pumped around and below them, then surely the
first row of blocks would be at the angle you'd need, and they'd be
supported along their full length rather than just at the two points of
contact shown by your diagram.

The shuttering could then be made to taper in from a wider base to a
narrower top where the blocks lie, and thus achieve the correct weight of
balanced force against the rest of the blocks when they are placed. It
would also mean just building two walls of shuttering, only having one side
higher than the other to achieve the angle you need for the blocks.

Leaving one block out ever X metres would allow the mix to be pumped in.
Then place the missing blocks in when the pour has been done. If yaw's sees
what a mean.