I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

At the lower edge I want to in-situ cast a 6" semi circular drainage
channel inside the sty to lead run off into a settling tank. If it
wasn't a sty I'd set some aco drain before the concrete pour, but this
would block too quickly and not be easy to clear.

But how the heck, given 6 cu M of concrete riddled smooth and rapidly
setting do you form a channel???? Indeed is it possible?

AWEM

Andrew Mawson wrote:

I'm laying a 20 foot square slightly sloping concrete slab At the
lower edge I want to in-situ cast a 6" semi circular drainage
channel But how the heck, given 6 cu M of concrete riddled smooth and
rapidly setting do you form a channel????

20' length of 6" pipe slathered in something concrete will resist
sticking to and set halfway into concrete, then removed before it goes
off fully?

Andy Burns wrote:

Andrew Mawson wrote:

I'm laying a 20 foot square slightly sloping concrete slab At the
lower edge I want to in-situ cast a 6" semi circular drainage
channel But how the heck, given 6 cu M of concrete riddled smooth and
rapidly setting do you form a channel????

20' length of 6" pipe slathered in something concrete will resist
sticking to and set halfway into concrete, then removed before it goes
off fully?

+1

Use plastic soil pipe (dose sit have to be 6" or would 4" do?)
Spray pipe with mixture of diesel and old engine oil (bit carcinogenic, so
gloves, but it's in an american "concrete" book I have) or wrap pipe in DPM
plastic which is both tough and even PU foam will not stick to it.

If it is half in, no hurry to remove, it will release.
--
Tim Watts

On Sep 27, 10:29*pm, Andy Burns wrote:

20' length of 6" pipe slathered in something concrete will resist
sticking to and set halfway into concrete, then removed before it goes
off fully?

I believe expanded polystyrene is sometimes used for this, removed
after setting with a wire brush and then acetone.

In message
,
Andy Dingley writes
On Sep 27, 10:29*pm, Andy Burns wrote:

20' length of 6" pipe slathered in something concrete will resist
sticking to and set halfway into concrete, then removed before it goes
off fully?

I believe expanded polystyrene is sometimes used for this, removed
after setting with a wire brush and then acetone.

Bugger of a job to keep that submerged

As someone said, half plastic pipe, but I would fill it with mix to keep
it submerged until it had gone off sufficiently
--
geoff

Andrew Mawson wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

At the lower edge I want to in-situ cast a 6" semi circular drainage
channel inside the sty to lead run off into a settling tank. If it
wasn't a sty I'd set some aco drain before the concrete pour, but this
would block too quickly and not be easy to clear.

But how the heck, given 6 cu M of concrete riddled smooth and rapidly
setting do you form a channel???? Indeed is it possible?

AWEM

easy peasy. get a halfdisk of wood or summat - and use it to form the
void you want where you want it.

after the concrete sets, pull it off.

Andrew Mawson wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

Out of interest, how do you make concrete slope? Does it just stay where
you put it? I'd expect it to sort of level itself out whilst your back is
turned.

On Sep 27, 10:22*pm, "Andrew Mawson"
wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

At the lower edge I want to in-situ cast a 6" semi circular drainage
channel inside the sty to lead run off into a settling tank. If it
wasn't a sty I'd set some aco drain before the concrete pour, but this
would block too quickly and not be easy to clear.

But how the heck, given 6 cu M of concrete riddled smooth and rapidly
setting do you form a channel???? Indeed is it possible?

AWEM

If you used an oiled moulding pipe, there would be no way to ensure
absence of voids. If you used a scraper, the result would be a pig's
ear. If I were going to do it I'd be tempted to use rectangular timber
to mould the recess, then cement/sand line it afterwards. But like
most of the replies in this thread, unfortunately this is not from
experience. Wrapping with polythene makes a great release agent, and
gives a nice smooth surface. Thick polythene doesnt crumple and fold
like thin.


NT

On Sep 27, 10:22 pm, "Andrew Mawson"
wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

At the lower edge I want to in-situ cast a 6" semi circular drainage
channel inside the sty to lead run off into a settling tank. If it
wasn't a sty I'd set some aco drain before the concrete pour, but this
would block too quickly and not be easy to clear.

But how the heck, given 6 cu M of concrete riddled smooth and rapidly
setting do you form a channel???? Indeed is it possible?

AWEM

T'would seem so far I am the only one who has actually done something
similar...albeit a 4" wide one near the edge of a slab by.....

using a length of old pvc troughing and weighing it down with bricks
etc as necessary to stop it "surfacing", sliding it sideways back and
forth helped minimise voids while the mix was wet.
Removed it when concrete still green, no release agent required came
out easily as it was just "sat in" it.

Jim K

On Sep 27, 10:22*pm, "Andrew Mawson"
wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

At the lower edge I want to in-situ cast a 6" semi circular drainage
channel inside the sty to lead run off into a settling tank. If it
wasn't a sty I'd set some aco drain before the concrete pour, but this
would block too quickly and not be easy to clear.

But how the heck, given 6 cu M of concrete riddled smooth and rapidly
setting do you form a channel???? Indeed is it possible?

AWEM

The official method is to use precast concrete/plastic U sections, the
run in concrete buts up to it/under it. Or set in concrete haunching
prior to laying the slab.
Available in various sizes, with or without grates/lids.

Failiing that,you have to let the concrete go off a bit (sedimentation
phase. clear water on top of concrete.) and you form the gulley with a
tool that looks like a hoe & then smooth off with a small float
+addditional cement.. You might have to rig planks to get access over
the wet concrete.
Skilled work to make it look right.
Also weakens concrete(thin point), cracking may appear later

Re gradients, there are special anti-slump concretes available.

Bits of pipe will just float off, waste of time.

"GB" wrote in message
...
Andrew Mawson wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto
which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

Out of interest, how do you make concrete slope? Does it just stay
where
you put it? I'd expect it to sort of level itself out whilst your
back is
turned.






We're only talking a 6" fall over 20 foot. So long as the concrete is
no more than 50 slump it tends to stay put. The mesh re-inforcement
tends to help hold it, also no damp membrane otherwise it does slide
rather.

AWEM

GB wrote:

Andrew Mawson wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

Out of interest, how do you make concrete slope? Does it just stay where
you put it? I'd expect it to sort of level itself out whilst your back is
turned.

Unless the mixture if too wet, you can put a pretty major slope in it IME.

--
Tim Watts

Tim Watts wrote:
GB wrote:

Andrew Mawson wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)
Out of interest, how do you make concrete slope? Does it just stay where
you put it? I'd expect it to sort of level itself out whilst your back is
turned.

Unless the mixture if too wet, you can put a pretty major slope in it IME.

Brickwork and mortar is vertical slope and that doesn't run out :-)

On 28/09/2011 08:01, Jim K wrote:
On Sep 27, 10:22 pm, "Andrew Mawson"
wrote:
I'm laying a 20 foot square slightly sloping concrete slab onto which
a pig sty will be built. (18" block wall topped by several rows of
scaffold poles between piers)

At the lower edge I want to in-situ cast a 6" semi circular drainage
channel inside the sty to lead run off into a settling tank. If it
wasn't a sty I'd set some aco drain before the concrete pour, but this
would block too quickly and not be easy to clear.

But how the heck, given 6 cu M of concrete riddled smooth and rapidly
setting do you form a channel???? Indeed is it possible?

AWEM

T'would seem so far I am the only one who has actually done something
similar...albeit a 4" wide one near the edge of a slab by.....

using a length of old pvc troughing and weighing it down with bricks
etc as necessary to stop it "surfacing", sliding it sideways back and
forth helped minimise voids while the mix was wet.
Removed it when concrete still green, no release agent required came
out easily as it was just "sat in" it.


I'll second Jim's suggestion: that's exactly how I formed drainage
channels when I built our goat shed, with the further complication of
setting the troughing (in my case 4" guttering) deeper at one end than
the other.

For another job where I wanted a yard to slope to one corner, I made
yard-long sections of mock-aco* by casting them upside down in a simple
timber mould. Once I'd made enough sections for two sides, I bedded
them on weak concrete and they formed the shuttering for the main pour
of concrete. You can buy shallow channel blocks like this from
Marshalls, which I've used with block paving, but they're ott (and too
shallow) for a pig yard.

* wide, shallow gulley with no lid

--
Kevin Poole

Andy Burns wrote:
Andrew Mawson wrote:

I'm laying a 20 foot square slightly sloping concrete slab At the
lower edge I want to in-situ cast a 6" semi circular drainage
channel But how the heck, given 6 cu M of concrete riddled smooth and
rapidly setting do you form a channel????

20' length of 6" pipe slathered in something concrete will resist
sticking to and set halfway into concrete, then removed before it goes
off fully?

My next door neighbour could help on this one.

--
Adam

On Sep 27, 11:40*pm, geoff wrote:
In message
,
Andy Dingley writes

On Sep 27, 10:29*pm, Andy Burns wrote:

20' length of 6" pipe slathered in something concrete will resist
sticking to and set halfway into concrete, then removed before it goes
off fully?

I believe expanded polystyrene is sometimes used for this, removed
after setting with a wire brush and then acetone.

Bugger of a job to keep that submerged


Fill it with bricks

Robert

On Sep 28, 5:10*am, NT wrote:
On Sep 27, 10:22*pm, "Andrew Mawson"

If you used a scraper, the result would be a pig's
ear.

very apropriate I would have thought, given the use of the buidling.

Robert