We're planning to put a little log cabin/shed type thing in the back.

The ground isn't particularly nice so I was planning to dig it roughly
level, place level ballast, position a sheet of concrete reinforcing
fabric/latticework on some bricks or somesuch so the lattice is 5cm above
the ballast and then pour 10cm depth of concrete to make a 3m by 3m slab
that's not going to break into a couple of pieces sinking at different rates
over time.

By my reckoning, this will be around 800 litres of concrete and, since a
cement mixer holds around 100l of mix, around 9 cement mixers full.
Neighbour has one I can borrow. However, manufacturer spec sheets say a 25kg
bag of concrete mix (the largest in keyline's web site) will cover 0.1 suare
metres at 10cm depth, meaning I need around 80 bags at a cost of around 600
quid. I can get that much concrete delivered for £118. Am I right in
thinking delivery is the cheapest option?

Whatever way I get it, I will have to work on the reinforcing fabric; moving
a wheelbarrow over it and standing on it. I'm considering some boards to
spread the load and stop me tripping over the bars. Is this the way it's
usually done or will this end up knackering the latticework? How widely
spaced will the supports have to be to stop the lattice buckling under both
my weight and the weight of a wheelbarrow full of concrete?

Am I going over the top to be thinking of reinforcing the concrete? The
fabric sheet only costs around £40 and I'm not sure what the ground is going
to do over time and under load; there's a lot of rubble under there, since I
gather some buildings were once there (used to be railway sidings and
yards).

--
Dr. Craig Graham, Software Engineer
Advanced Analysis and Integration Limited, UK. http://www.aail.co.uk/

On Mon, 28 Jun 2004 09:23:51 +0100, "Craig Graham"
wrote:

We're planning to put a little log cabin/shed type thing in the back.

The ground isn't particularly nice so I was planning to dig it roughly
level, place level ballast, position a sheet of concrete reinforcing
fabric/latticework on some bricks or somesuch so the lattice is 5cm above
the ballast and then pour 10cm depth of concrete to make a 3m by 3m slab
that's not going to break into a couple of pieces sinking at different rates
over time.

I guess your "latice" will need to be reasonably thick to be any good,
I was using 2 layers of a393 sheet (10mm bars, 200mm squares) in 300mm
of concrete, its enouth to hold a house up. a393 sheet is 32 quid a
sheet (4.8x2.4m). You support the mesh on briks, it MUST be 40mm or
more from the edge of the concrete in all directions.


By my reckoning, this will be around 800 litres of concrete and, since a
cement mixer holds around 100l of mix, around 9 cement mixers full.
Neighbour has one I can borrow. However, manufacturer spec sheets say a 25kg
bag of concrete mix (the largest in keyline's web site) will cover 0.1 suare
metres at 10cm depth, meaning I need around 80 bags at a cost of around 600
quid. I can get that much concrete delivered for £118. Am I right in
thinking delivery is the cheapest option?

It easier to work with less than a full mixer full, it gives some room
for manover. The concret will me MUCH cheeper from wicked, 6 bags of
ballast (1.09) to 1 bag of cement (2.60) will give you 150kg of the
stuff.

Whatever way I get it, I will have to work on the reinforcing fabric; moving
a wheelbarrow over it and standing on it. I'm considering some boards to
spread the load and stop me tripping over the bars. Is this the way it's
usually done or will this end up knackering the latticework? How widely
spaced will the supports have to be to stop the lattice buckling under both
my weight and the weight of a wheelbarrow full of concrete?

The a393 mesh will hold your weight. space the supports so thay seem
right.

Am I going over the top to be thinking of reinforcing the concrete? The
fabric sheet only costs around £40 and I'm not sure what the ground is going
to do over time and under load; there's a lot of rubble under there, since I
gather some buildings were once there (used to be railway sidings and
yards).

I guess you will end up with something that will take one heck of a
bit of getting rid of again, so be sure you want this shed to stay
forever.

The mesh will allow "voids" to appear under the concrete, and uless
the void id huge, it won't move.

Rick

Three by three metres; roughly 100 square feet.
Concrete pad seems like an awful lot of work and a very heavy installation?
More like something one would install for a small very robust building in
which to house a diesel generator at a radio site?
I'm just thinking that one can buy, just for example, an 8 by 12 foot shed
kit that requires anywhere from six to sixteen treated wooden or concrete
posts poured into those cardboard tubes, depending on what load one needs to
put on it's floor! Such sheds, starting at around $1800 Canadian (say 800
quid) or less can be simple storage units or can be dressed up with rustic
siding, extra windows, half (stable style) doors, skylights etc. Also
available up to 14 by 20 or longer (I was considering one 14 by 24 as a
second garage. Substantial posts every four feet, vehicle weighing about
3500 pounds plus tools work bench etc.
Sheds mounted on short posts above ground allow ventilation below, and raise
the floor a little above a small amount of snow. With typical maintenance
they last 30 to 40 years. They also can be given the same exterior finish
and/or painted to match the main house.
Because of frost heaving we have to go at least 30 inches down. With a
manual post hole digger, and a digging bar in our stony/rocky ground one can
dig a hole in about twenty minutes, with suitable tea breaks! We have two
such home built sheds in which we store lawnmower, snowblower, extra sets of
winter wheels and tyres for several vehicles, garden tools, a 2000 watt
standby generator, spare flower pots, spare gasoline (away from the house)
and other useful junk! One 8 by 8 foot shed is on four posts and is 20+
years old and the other about 4 years is on six posts. I may move the 8 by
8 to another location by cutting off the 4 x 4 inch treated posts and towing
it within the garden with our pickup truck; to make space for the proposed
14 by 24 unit.

I considered decking first, which is essentially what you're saying. What
put me off is that pretty much all of the shed companies specify a concrete
or flagstone base and say the warranty is void if the base isn't up to spec.
I also want to keep the shed as low to the ground as possible to minimise
impact on what view there is from the house, and thirdly I didn't want to
have to dig 9 reasonably deep holes in ground that has bits of old wall and
all sorts in it.

Terry wrote:
Three by three metres; roughly 100 square feet.
Concrete pad seems like an awful lot of work and a very heavy
installation? More like something one would install for a small very

--
Dr. Craig Graham, Software Engineer
Advanced Analysis and Integration Limited, UK. http://www.aail.co.uk/

Rick Dipper wrote:
On Mon, 28 Jun 2004 09:23:51 +0100, "Craig Graham"

I guess your "latice" will need to be reasonably thick to be any good,
I was using 2 layers of a393 sheet (10mm bars, 200mm squares) in 300mm
of concrete, its enouth to hold a house up. a393 sheet is 32 quid a
sheet (4.8x2.4m). You support the mesh on briks, it MUST be 40mm or
more from the edge of the concrete in all directions.

That sounds excessive for this- it's a 3 metre single storey shed, not a
house! The specifications say a 100mm concrete base; since I'm unsure of the
ground I was planning a single layer of a393 sheet.

It easier to work with less than a full mixer full, it gives some room
for manover. The concret will me MUCH cheeper from wicked, 6 bags of
ballast (1.09) to 1 bag of cement (2.60) will give you 150kg of the
stuff.

Do you mean Wickes?

I need 80x25kg bags giving 2000kg.

150kg your way costs £9.14, and I'd need 13 of these making the total cost
around £122, excluding delivery since more than two trips to get the stuff
is a bit too much hassle. Given I can get a mixer to come and deliver that
amount ready to place for £118, it still seems the way to go even though
your figures are much better than the £600 that I reckoned from Keyline's
web site.

I guess you will end up with something that will take one heck of a
bit of getting rid of again, so be sure you want this shed to stay
forever.

That's one thing that put me off originally, but since I only need 100mm I
could always hire a breaker if I needed to get rid of it. Or use the SDS
drill and patience.

--
Dr. Craig Graham, Software Engineer
Advanced Analysis and Integration Limited, UK. http://www.aail.co.uk/