Make Formwork for bell shaped concrete coping blocks
 

Building a wall, making 8"x8"x9" ornamental exposed aggregate concrete
blocks.

Well I've finished my flat-sided tapered blocks and now I'm on to the
copings.

They are bell shaped, with quite tight 1.5" dia curves. The mould will
be to take 3 blocks, approx 8x8x9 each.

Any thoughts on how I can make the curve? I can use 3 existing blocks
in line as a guide.

I tried wrapping them in polythene, boxing them in, and injecting
expanding yellow foam, but it didn't match the contours tightly.

I tried soaking hardboard, bending it when soft, and letting it dry,
but was surprised how water and bend resistant hardboard is.

I'm trying papier mache. If it works, it mightn't last very long with
the wet concrete.

I thought about getting a sheet of thin stiff plastic, heating it,
fitting it, and letting it set into the correct shape. But how would
I heat it until it is soft? boiling water wouldn't be hot enough, and
a blow-lamp would be too unsubtle.

Or maybe any of those approaches'd work if I did 'em more carefully?

Any suggestions welcome.

Thanx
Tony

PS, this group has just cost me a fortune ;-)
After reading here about SDS drills - they sound a brilliant addidion
- I am absolutely itching to buy a decent cordless one. Not cheap!

I recently bought an AKG 12v cordless screwdriver. Best tool I ever
bought. Brilliant. Recommended

Make Formwork for bell shaped concrete coping blocks
 

"tonyjeffs" wrote in message
...
SIP
I thought about getting a sheet of thin stiff plastic, heating it,
fitting it, and letting it set into the correct shape. But how would
I heat it until it is soft? boiling water wouldn't be hot enough, and
a blow-lamp would be too unsubtle.

Or maybe any of those approaches'd work if I did 'em more carefully?

Any suggestions welcome.

SNIP

Hotair Gun??

Baz

Make Formwork for bell shaped concrete coping blocks
 

tonyjeffs wrote:
Building a wall, making 8"x8"x9" ornamental exposed aggregate concrete
blocks.

Well I've finished my flat-sided tapered blocks and now I'm on to the
copings.

They are bell shaped, with quite tight 1.5" dia curves. The mould will
be to take 3 blocks, approx 8x8x9 each.

Any thoughts on how I can make the curve? I can use 3 existing blocks
in line as a guide.

I tried wrapping them in polythene, boxing them in, and injecting
expanding yellow foam, but it didn't match the contours tightly.

I tried soaking hardboard, bending it when soft, and letting it dry,
but was surprised how water and bend resistant hardboard is.

I'm trying papier mache. If it works, it mightn't last very long with
the wet concrete.

I thought about getting a sheet of thin stiff plastic, heating it,
fitting it, and letting it set into the correct shape. But how would
I heat it until it is soft? boiling water wouldn't be hot enough, and
a blow-lamp would be too unsubtle.

Or maybe any of those approaches'd work if I did 'em more carefully?

Any suggestions welcome.

Thanx
Tony

PS, this group has just cost me a fortune ;-)
After reading here about SDS drills - they sound a brilliant addidion
- I am absolutely itching to buy a decent cordless one. Not cheap!

I recently bought an AKG 12v cordless screwdriver. Best tool I ever
bought. Brilliant. Recommended
If the curve is in one direction only, look in B&Q for bendy MDF. It is
about 4mm thick and kerfed on one side to bend to a reasonable radius,
but I suspect not tight enough for what you want. It would be easy to
waterproof and you may be able to add more cuts to increase the bend
radius.

Malcolm

Make Formwork for bell shaped concrete coping blocks
 

tonyjeffs wrote:
Building a wall, making 8"x8"x9" ornamental exposed aggregate concrete
blocks.

Well I've finished my flat-sided tapered blocks and now I'm on to the
copings.

They are bell shaped, with quite tight 1.5" dia curves. The mould will
be to take 3 blocks, approx 8x8x9 each.

Any thoughts on how I can make the curve? I can use 3 existing blocks
in line as a guide.

I tried wrapping them in polythene, boxing them in, and injecting
expanding yellow foam, but it didn't match the contours tightly.

I tried soaking hardboard, bending it when soft, and letting it dry,
but was surprised how water and bend resistant hardboard is.

I'm trying papier mache. If it works, it mightn't last very long with
the wet concrete.

I thought about getting a sheet of thin stiff plastic, heating it,
fitting it, and letting it set into the correct shape. But how would
I heat it until it is soft? boiling water wouldn't be hot enough, and
a blow-lamp would be too unsubtle.

Or maybe any of those approaches'd work if I did 'em more carefully?

Any suggestions welcome.



Get some 1/32" or 1/64" ply and cut formers. You can fill the thing with
plaster later to stiffen it.

Make Formwork for bell shaped concrete coping blocks
 

On 2 Oct, 16:18, "Baz" wrote:
"tonyjeffs" wrote in message

...
SIP I thought about getting a sheet of thin stiff plastic, heating it,
fitting it, and letting it set into the correct shape. *But how would
I heat it until it is soft? boiling water wouldn't be hot enough, and
a blow-lamp would be too unsubtle.

Or maybe any of those approaches'd work if I did 'em more carefully?

Any suggestions welcome.

SNIP

Hotair Gun??

Baz

Just pop it in the oven!

Probably better to start low and slowly raise the temp - I don't know
how accurate the temp on the dial is!

For ABS sheet at about 110 deg C

For Polypropylene at about 120 deg C

Time will vary - depending on size and thickness

Kev

Make Formwork for bell shaped concrete coping blocks
 

tonyjeffs wrote:
Building a wall, making 8"x8"x9" ornamental exposed aggregate concrete
blocks.

Well I've finished my flat-sided tapered blocks and now I'm on to the
copings.

They are bell shaped, with quite tight 1.5" dia curves. The mould will
be to take 3 blocks, approx 8x8x9 each.

Any thoughts on how I can make the curve? I can use 3 existing blocks
in line as a guide.

I tried wrapping them in polythene, boxing them in, and injecting
expanding yellow foam, but it didn't match the contours tightly.

I tried soaking hardboard, bending it when soft, and letting it dry,
but was surprised how water and bend resistant hardboard is.

I'm trying papier mache. If it works, it mightn't last very long with
the wet concrete.

I thought about getting a sheet of thin stiff plastic, heating it,
fitting it, and letting it set into the correct shape. But how would
I heat it until it is soft? boiling water wouldn't be hot enough, and
a blow-lamp would be too unsubtle.

Or maybe any of those approaches'd work if I did 'em more carefully?

Any suggestions welcome.

Thanx
Tony

PS, this group has just cost me a fortune ;-)
After reading here about SDS drills - they sound a brilliant addidion
- I am absolutely itching to buy a decent cordless one. Not cheap!

I recently bought an AKG 12v cordless screwdriver. Best tool I ever
bought. Brilliant. Recommended

Sculptural concrete (e.g. ciment fondu) casting is often done in a mould
made of some form of rubber. Some materials are available he

http://www.tiranti.co.uk/subcategory_list.asp?Content=Mouldmaking&Category= 9

I'd guess some might be available elsewhere at lower cost - but not
necessarily. :-)

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

Make Formwork for bell shaped concrete coping blocks
 

tonyjeffs wrote:

They are bell shaped, with quite tight 1.5" dia curves. The mould will
be to take 3 blocks, approx 8x8x9 each.

Make a plug in lath, chicken wire and plaster of Paris. Coat with
release agent and then layup a glass-fibre mould on the plug.

Make Formwork for bell shaped concrete coping blocks
 

On Oct 2, 3:49*pm, tonyjeffs wrote:
Building a wall, making 8"x8"x9" ornamental exposed aggregate concrete
blocks.

Well I've finished my flat-sided tapered blocks *and now I'm on to the
copings.

They are bell shaped, with quite tight 1.5" dia curves. The mould will
be to take 3 blocks, approx 8x8x9 each.

Any thoughts on how I can make the curve? I can use 3 existing blocks
in line as a guide.

I tried wrapping them in polythene, boxing them in, and injecting
expanding yellow foam, but it didn't match the contours tightly.

I tried soaking hardboard, bending it when soft, and letting it dry,
but was surprised how water and bend resistant hardboard is.

I'm trying papier mache. If it works, it mightn't last very long with
the wet concrete.

I thought about getting a sheet of thin stiff plastic, heating it,
fitting it, and letting it set into the correct shape. *But how would
I heat it until it is soft? boiling water wouldn't be hot enough, and
a blow-lamp would be too unsubtle.

Or maybe any of those approaches'd work if I did 'em more carefully?

Any suggestions welcome.

Thanx
Tony

PS, this group has just cost me *a fortune ;-)
After reading here about SDS drills - they sound a brilliant addidion
- I am absolutely itching to buy a decent cordless one. Not cheap!

I recently bought an AKG 12v cordless screwdriver. Best tool I ever
bought. Brilliant. Recommended

It sure would be easier if you could get a sample of the shape you
want, using that to cast a mould.

Re bending plastic, last time I did it I just dipped it in boiling
water. Works with some plastics - unfortunately I dont remember what
kind of plastic it was. Making a mould in thin air is going to be hard
to get just right.


NT

Make Formwork for bell shaped concrete coping blocks
 

Thanks to All
Several good ideas to consider.
Replies to all...

NT, I do have a sample of the shape in that I have some of the
original coping blocks to work from, so we got that covered.

Steve, I think that's the way to go, but I don't completely understand
what you're saying - what you're doing with the lath and plaster of
paris. I was thinking to line up the existing blocks with shaped
plywood separators between them, wrap them in plastic (blue DPC
membrane), apply a few layers of glass fibre & resin, hold the fibre
tight to the curves with laths screwed to the spacers. Maybe another
layer of plastic first to stop the laths sticking to the mould. Maybe
a layer of stiff cardboard to help keep the shape. Sound OK?

Rod, I think the rubber would be good for small items, but would be
very expensive for this.

Kev, it wont fit in the oven - it's 3' long. I'll use the tip another
time though.

TNP, that sounds a good way. I fancy having a try with the resin
though.

Baz, I'll remember your hotair gun suggestion for future reference.

Malcolm, I had a look at the bendy MDF. As you say it wouldn't give a
small enough radius. It'd be fiddly cutting lots of extra slots, and
the pieces they had were too small in the non-bend direction. Good to
know it's there though.

Tony

Make Formwork for bell shaped concrete coping blocks
 

On Oct 2, 8:57*pm, tonyjeffs wrote:
Thanks to All
Several good ideas to consider.
Replies to all...

NT, I do have a sample of the shape in that I have some of the
original coping blocks to work from, so we got that covered.

So whats stopping you covering it in polythene (release agent), then
resin, then concrete to make a mould?


NT

Make Formwork for bell shaped concrete coping blocks
 

tonyjeffs wrote:

Rod, I think the rubber would be good for small items, but would be
very expensive for this.


The usual way of creating a mould uses just a relatively thin layer of
rubber - made up to a usable shape with something like plaster of paris
on the outside. So cost, which I have not worked out at all, might not
be quite as bad as you initially think.

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

Make Formwork for bell shaped concrete coping blocks
 

On Oct 2, 9:13*pm, wrote:
On Oct 2, 8:57*pm, tonyjeffs wrote:

Thanks to All
Several good ideas to consider.
Replies to all...

NT, I do have a sample of the shape in that I have some of the
original coping blocks to work from, so we got that covered.

So whats stopping you covering it in polythene (release agent), then
resin, then concrete to make a mould?

NT

It's a possibility, and after reading all the suggestions I'll do
something similar along those lines.

Against using concrete is:
- I'll have to flip the mould over when it's set and shake the blocks
out. It'd be very heavy. 3'x9"x9" of concrete.
- the concrete wouldn't have any give in it, so it might grip too
tightly when I try to shake the blocks out.

I'll do something similar( if it stops raining), but will use
something lighter instead of concrete, like strips of wood or
hardboard, which won't have to take the exact shape - the resin will
do that, - but will hold the shaped resin in place, and flexible
enough to bend a little when removing the product.


Tony

Make Formwork for bell shaped concrete coping blocks
 

tonyjeffs wrote:
On Oct 2, 9:13�pm, wrote:
On Oct 2, 8:57�pm, tonyjeffs wrote:

Thanks to All
Several good ideas to consider.
Replies to all...

NT, I do have a sample of the shape in that I have some of the
original coping blocks to work from, so we got that covered.

So whats stopping you covering it in polythene (release agent), then
resin, then concrete to make a mould?

NT

It's a possibility, and after reading all the suggestions I'll do
something similar along those lines.

Against using concrete is:
- I'll have to flip the mould over when it's set and shake the blocks
out. It'd be very heavy. 3'x9"x9" of concrete.
- the concrete wouldn't have any give in it, so it might grip too
tightly when I try to shake the blocks out.

I'll do something similar( if it stops raining), but will use
something lighter instead of concrete, like strips of wood or
hardboard, which won't have to take the exact shape - the resin will
do that, - but will hold the shaped resin in place, and flexible
enough to bend a little when removing the product.


Tony

If the end product's sides are tapered and you use polythene,
inverting the mould and tapping should work. If its not a shape
that can slide out you can add a divider so the mould is in 2
halves and clamp it together with some wood.

Bear in mind with all this though that its a long time since I did
this stuff, so there's always room for data errors.


NT