Anybody have any experience of casting small items from concrete?

I'm not getting into gnomes, but I want to start making what I'd call a
'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on all 4
sides to leave a 3" square at the top.

The application is for 3" posts to support decking joists. Can't find a
ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using silicone
spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast concrete
& he used an orbital sander to vibrate the moulds & get the air out of the
mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

The Medway Handyman wrote:
Anybody have any experience of casting small items from concrete?

yes


I'm not getting into gnomes, but I want to start making what I'd call
a 'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on
all 4 sides to leave a 3" square at the top.


Better making the widest part at the top and having the chamfer moulded into
the bottom...also a 10 inch square chamfering to 3 inches is way OTT, I'd
suggest 150mm to 75mm over a 100mm thickness


The application is for 3" posts to support decking joists. Can't
find a ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using
silicone spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast
concrete & he used an orbital sander to vibrate the moulds & get the
air out of the mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?

make one or two every day as they need a few days out of the mould to
achieve full strength, and I'd use a strongish handmade mix, IE six gravel
(10mm is best), 3 grit sand and 1 cement, quite wet and a few taps with a
hammer on all sides of the mould is more than enough, but this is where the
trouble starts - most woodedn moulds end up getting knocked to pieces after
a few goes - I've heard of people using cling film as a barrier, but it does
leave fold marks in the finished product, but if they are below decking, who
cares?

On 7 Sep, 15:55, "The Medway Handyman"
wrote:
Anybody have any experience of casting small items from concrete?

Can't think of the name to hand, but there's a great American book
(Amazon UK have it) on doing indoor kitchen counters etc. with
concrete cast in situ. The author has two books and the more "hands-
on" one has a lot of useful information on doing small-scale
decorative concrete.

The Multimaster concrete poker is rubbish, but a DIY one made from
stiffish hosepipe with a floppy weight in the end (big bolt with a dab
of silicone) did a lot better for wobbling.

Phil L wrote:
The Medway Handyman wrote:
Anybody have any experience of casting small items from concrete?

yes


I'm not getting into gnomes, but I want to start making what I'd call
a 'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on
all 4 sides to leave a 3" square at the top.


Better making the widest part at the top and having the chamfer
moulded into the bottom...also a 10 inch square chamfering to 3
inches is way OTT, I'd suggest 150mm to 75mm over a 100mm thickness

Hi Phil

I cant have the thing too thick, thatdestroys the object of the excercise.
The two options I currently use are (1) a concrete block. Cheap & strong
but too thick for many applications so a square hole has to be dug into the
ground, right next to a joist. (2) a paving slab, three times the price and
too big to level easily - also split easily if not flat.

Take your point I could make them smaller, but 2" is the maximum thickness.


The application is for 3" posts to support decking joists. Can't
find a ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using
silicone spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast
concrete & he used an orbital sander to vibrate the moulds & get the
air out of the mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?

make one or two every day as they need a few days out of the mould to
achieve full strength, and I'd use a strongish handmade mix, IE six
gravel (10mm is best), 3 grit sand and 1 cement, quite wet and a few
taps with a hammer on all sides of the mould is more than enough, but
this is where the trouble starts - most woodedn moulds end up getting
knocked to pieces after a few goes -

Would that be what they call sharp sand?

I've heard of people using cling
film as a barrier, but it does leave fold marks in the finished
product, but if they are below decking, who cares?

Cling film sounds good, appearance doesn't matter.

Thanks



--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

"The Medway Handyman" wrote:

The two options I currently use are (1) a concrete block. Cheap & strong
but too thick for many applications so a square hole has to be dug into
the ground, right next to a joist. (2) a paving slab, three times the
price and too big to level easily - also split easily if not flat.

How about monoblocks?

--
Jeremy C B Nicoll - my opinions are my own.

The Medway Handyman wrote:
Anybody have any experience of casting small items from concrete?

I'm not getting into gnomes, but I want to start making what I'd call
a 'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on
all 4 sides to leave a 3" square at the top.

The application is for 3" posts to support decking joists. Can't
find a ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using
silicone spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast
concrete & he used an orbital sander to vibrate the moulds & get the
air out of the mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?

Yes I know how to - and can do it Dave, it's that old apprenticeship I did
that gave me the knowledge.

Simply think in reverse and how to make the shutter box easy to dismantle -
if you can do that.

BTW - silicone is not a good release oil - there are specific oils for the
job that don't react with the concrete.

Again, if you are going to make a re-usable shutter box (or boxes), think of
how you can make the box[es] with a non-stick lining - it really is simple.
I'll give you a clue - think of an everyday laminate!

Oh, and you don't need an orbital sander as a makeshift vibrator on boxes
that size (you can become overly reliant on power tools), as simple hammer
will get the 'fat' around (rather than get the air out) - and it is the dry
mix of the concrete with the correct amount of added water that gives it its
strength (too much or too little water makes the stuff weak) - along with
steel reinforcing bars as necessary (not that you'll need bars here as long
as the load is in compression rather than tension).

As for "pre-mixed bags" - if you got the money to burn then go ahead, but
why not just hire a ready-mix wagon seeing as you can add the costs to the
job for the customer to pay?.

That's the problem with some "handymen" Dave, if they can't buy it, they
don't know how to make it - that's what 3 months of 'research' doesn't teach
you.

BTW, would you know how to shutter up a sewer inspection chamber to fit the
manhole cover on *and* make the shuttering easy to release and pull out
through a limited opening?

Yes there is a great deal of sarcasm here Dave, along with a lot of 'tips'
if you can rattle that brain of yours and work them out (not to difficult
btw).

Tanner-'op

On 7 Sep, 21:28, Andy Dingley wrote:
On 7 Sep, 15:55, "The Medway Handyman"

wrote:
Anybody have any experience of casting small items from concrete?

Can't think of the name to hand, but there's a great American book
(Amazon UK have it) on doing indoor kitchen counters etc. with
concrete cast in situ. The author has two books and the more "hands-
on" one has a lot of useful information on doing small-scale
decorative concrete.

The Multimaster concrete poker is rubbish, but a DIY one made from
stiffish hosepipe with a floppy weight in the end (big bolt with a dab
of silicone) did a lot better for wobbling.

For vibrating the concrete, you can push an SDS in locked mode against
the mould.
Simon.

Jeremy Nicoll - news posts wrote:
"The Medway Handyman" wrote:

The two options I currently use are (1) a concrete block. Cheap &
strong but too thick for many applications so a square hole has to
be dug into the ground, right next to a joist. (2) a paving slab,
three times the price and too big to level easily - also split
easily if not flat.

How about monoblocks?

Thickness is OK, but I want more surface area to spread the load. A 8" x 4"
monoblock is 32 sq ins, wheras an 18 x 9 concrete block is 162 sq ins. My
planned 10 x 10 pad is 100 sq ins - a large enogh area.


Thanks though.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

sm_jamieson wrote:
On 7 Sep, 21:28, Andy Dingley wrote:
On 7 Sep, 15:55, "The Medway Handyman"

wrote:
Anybody have any experience of casting small items from concrete?

Can't think of the name to hand, but there's a great American book
(Amazon UK have it) on doing indoor kitchen counters etc. with
concrete cast in situ. The author has two books and the more "hands-
on" one has a lot of useful information on doing small-scale
decorative concrete.

The Multimaster concrete poker is rubbish, but a DIY one made from
stiffish hosepipe with a floppy weight in the end (big bolt with a
dab of silicone) did a lot better for wobbling.

For vibrating the concrete, you can push an SDS in locked mode against
the mould.


Brilliant!

Thanks!


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

On Sep 7, 3:55*pm, "The Medway Handyman"
wrote:
Anybody have any experience of casting small items from concrete?

I'm not getting into gnomes, but I want to start making what I'd call a
'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on all 4
sides to leave a 3" square at the top.

The application is for 3" posts to support decking joists. *Can't find a
ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using silicone
spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast concrete
& he used an orbital sander to vibrate the moulds & get the air out of the
mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?


I've always liked polythene as a release agent. There's no mess, no
chance of failing to coat it somewhere, it gives a perfect smooth
finish, it can be used repeatedly, and no matter where you are you can
put your hands on some immediately.

Downside is it wrinkles and gets trapped in the concrete surface if
you dont take the time/care to do it properly, ie to line each mould
piece before assembly.

In your case though I dont see the wrinkling being an issue, so you
could use a bit of binbag for each mould lining, treating it as
disposable.

Simplest way to eject the green form is to give the mould slightly
tapered sides. That way a very little movement sees the sides come
away from the product, making clean release easy.

However, why make a bunch of moulds if you can buy them ready made.
Rectangular polythene food storage containers come in the size you
want, eliminating the mould work, long as you dont mind rounded
corners. Cut the mould down to 2" height & fill to the brim. Now if
you put a flat sheet on it and invert, and remove the mould as soon as
it sets. I'd still line the mould for easy release, as any difficulty
would see the mould bend and break the workpiece.

1:3:5 is the classic strong mix ratio.

Been some while since I did any of this, you've been warned .


NT

wrote:


However, why make a bunch of moulds if you can buy them ready made.
Rectangular polythene food storage containers come in the size you
want, eliminating the mould work, long as you dont mind rounded
corners. Cut the mould down to 2" height & fill to the brim. Now if
you put a flat sheet on it and invert, and remove the mould as soon as
it sets. I'd still line the mould for easy release, as any difficulty
would see the mould bend and break the workpiece.

Lamp lights above head

Thank you!


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

On 7 Sep, 21:28, Andy Dingley wrote:

The Multimaster concrete poker is rubbish, but a DIY one made from
stiffish hosepipe with a floppy weight in the end (big bolt with a dab
of silicone) did a lot better for wobbling.

It's not so bad if (a) you stick it in at as shallow an angle as you
can and immerse as much as you can, rather than just plunging it in
vertically like you would with with a proper poker (if you imitate
that, it does virtually nothing) and especially (b) if you can jam
some or all of it against some formwork. You can get it to work up a
flow quite effectively (that's not to say that I think it couldn't be
bettered).

On 7 Sep, 23:17, "Tanner-'op" wrote:

That's the problem with some "handymen" Dave, if they can't buy it, they
don't know how to make it - that's what 3 months of 'research' doesn't teach
you.

You really are a patronising prick.

Andy Dingley wrote:

On 7 Sep, 23:17, "Tanner-'op" wrote:

That's the problem with some "handymen" Dave, if they can't buy it, they
don't know how to make it - that's what 3 months of 'research' doesn't teach
you.

You really are a patronising prick.


Agree 100%.

The most impressive thing about Dave is his willingness to learn.

The second most impressive thing is that he is prepared to admit that
he doesn't know everything. This displays an element of realism -
such modesty does not appear to afflict many time-served builders, who
profess to know everything but often fall a very long way short.

On Sep 8, 8:09*am, "The Medway Handyman"
wrote:
wrote:

However, why make a bunch of moulds if you can buy them ready made.
Rectangular polythene food storage containers come in the size you
want, eliminating the mould work, long as you dont mind rounded
corners. Cut the mould down to 2" height & fill to the brim. Now if
you put a flat sheet on it and invert, and remove the mould as soon as
it sets. I'd still line the mould for easy release, as any difficulty
would see the mould bend and break the workpiece.

Lamp lights above head

Thank you!

Just one thing I didnt mention first time... these moulds are nowhere
near rigid enough to use the 'normal' way up. If used that way they
will bend the green form at ejection time, ruining it. They need to be
filled and inverted, then lifted off the green form when its ready.


NT

"The Medway Handyman" wrote in message
om...
Anybody have any experience of casting small items from concrete?

I'm not getting into gnomes, but I want to start making what I'd call a
'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on all
4 sides to leave a 3" square at the top.

The application is for 3" posts to support decking joists. Can't find a
ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using
silicone spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast
concrete & he used an orbital sander to vibrate the moulds & get the air
out of the mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?

In early 90's I made some concrete slabs to replace some sandstone flags for
the entrance to a charity hut. Due to the amount of traffic the original
sandstone flags wore out quite quickly. We cast our own as couldn't find
anything in suitable finish, affordable cost and suitable size.

We made moulds out of scrap timber, placed a layer of sand in bottom,
flattened in a wavy/lumpy/not flat pattern using a spoon, so cast surface
wouldn't be flat, lined with 500 gauge polythene and used strong mix
conventional cement mixed with small (5mm ?) aggregate. Used a Hilti SDS
drill on "hammer lock" to vibrate out air and liberally spray cement
everywhere before moving to a less powerfull Bosch SDS.

First passes weren't very good, we put sloping edges on allow easy mould
release but the sloping edges causes issues with filling the joints, it was
felt the cement would just knock out. Also despite being quite thick (inch
odd) one broke when first laid down an jumped on. Also as stones were
visible on the surface water penetration and frost damage was likely.

Anyway 2nd pass, which are still laid today the following changes were made:
- Sides were vertical and mould unclipped to release blocks.
- A layer of cement with no aggregate was poured into the mould first to
provide a water resistant surface.
- This first layer was allowed to go off slightly before 4 primed steel
reinforcing bars were added.
- Topped up with aggregate cement to suitable depth.

Was it all worth it, probably not, took ages as we only had 3 moulds and
blocks were ruined by taking them out too early. Also a pain to lay as each
block was a slightly different thickness and required extensive fiddling to
get level. Also when they had to be cut (as someone decided to edge with a
line of engineering bricks) there was the issue of steel reiniforcing to cut
and protect from rust. Anyway had great fun and learnt a lot.

On Sep 11, 1:53*pm, "Ian_m" wrote:
"The Medway Handyman" wrote in media.com...



Anybody have any experience of casting small items from concrete?

I'm not getting into gnomes, but I want to start making what I'd call a
'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on all
4 sides to leave a 3" square at the top.

The application is for 3" posts to support decking joists. *Can't find a
ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using
silicone spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast
concrete & he used an orbital sander to vibrate the moulds & get the air
out of the mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?

In early 90's I made some concrete slabs to replace some sandstone flags for
the entrance to a charity hut. Due to the amount of traffic the original
sandstone flags wore out quite quickly. We cast our own as couldn't find
anything in suitable finish, affordable cost and suitable size.

We made moulds out of scrap timber, placed a layer of sand in bottom,
flattened in a wavy/lumpy/not flat pattern using a spoon, so cast surface
wouldn't be flat, lined with 500 gauge polythene and used strong mix
conventional cement mixed with small (5mm ?) aggregate. Used a Hilti SDS
drill on "hammer lock" to vibrate out air and liberally spray cement
everywhere before moving to a less powerfull Bosch SDS.

First passes weren't very good, we put sloping edges on allow easy mould
release but the sloping edges causes issues with filling the joints, it was
felt the cement would just knock out. Also despite being quite thick (inch
odd) one broke when first laid down an jumped on. Also as stones were
visible on the surface water penetration and frost damage was likely.

Anyway 2nd pass, which are still laid today the following changes were made:
- Sides were vertical and mould unclipped to release blocks.
- A layer of cement with no aggregate was poured into the mould first to
provide a water resistant surface.
- This first layer was allowed to go off slightly before 4 primed steel
reinforcing bars were added.
- Topped up with aggregate cement to suitable depth.

Was it all worth it, probably not, took ages as we only had 3 moulds and
blocks were ruined by taking them out too early. Also a pain to lay as each
block was a slightly different thickness and required extensive fiddling to
get level. Also when they had to be cut (as someone decided to edge with a
line of engineering bricks) there was the issue of steel reiniforcing to cut
and protect from rust. Anyway had great fun and learnt a lot.


We had a different issue using home made slabs. It turned out they
werent quite perfectly square, very close but over several slabs it
started to add up. With commercial ones the edges can be used for
alignment, but you cant necessarily count on that with home mades.
Hence the order of laying needs a little more thought, and aligning
the slabs can be a bit slower.

There were none of the troubles you mentioned Ian, I wonder if it was
perhaps because they'd been left standing a month or so to cure. They
lasted well.


NT

On 11 Sep, 13:53, "Ian_m" wrote:
"The Medway Handyman" wrote in media.com...



Anybody have any experience of casting small items from concrete?

I'm not getting into gnomes, but I want to start making what I'd call a
'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on all
4 sides to leave a 3" square at the top.

The application is for 3" posts to support decking joists. Can't find a
ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using
silicone spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast
concrete & he used an orbital sander to vibrate the moulds & get the air
out of the mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?

In early 90's I made some concrete slabs to replace some sandstone flags for
the entrance to a charity hut. Due to the amount of traffic the original
sandstone flags wore out quite quickly. We cast our own as couldn't find
anything in suitable finish, affordable cost and suitable size.

We made moulds out of scrap timber, placed a layer of sand in bottom,
flattened in a wavy/lumpy/not flat pattern using a spoon, so cast surface
wouldn't be flat, lined with 500 gauge polythene and used strong mix
conventional cement mixed with small (5mm ?) aggregate. Used a Hilti SDS
drill on "hammer lock" to vibrate out air and liberally spray cement
everywhere before moving to a less powerfull Bosch SDS.

First passes weren't very good, we put sloping edges on allow easy mould
release but the sloping edges causes issues with filling the joints, it was
felt the cement would just knock out. Also despite being quite thick (inch
odd) one broke when first laid down an jumped on. Also as stones were
visible on the surface water penetration and frost damage was likely.

Anyway 2nd pass, which are still laid today the following changes were made:
- Sides were vertical and mould unclipped to release blocks.
- A layer of cement with no aggregate was poured into the mould first to
provide a water resistant surface.
- This first layer was allowed to go off slightly before 4 primed steel
reinforcing bars were added.
- Topped up with aggregate cement to suitable depth.

Was it all worth it, probably not, took ages as we only had 3 moulds and
blocks were ruined by taking them out too early. Also a pain to lay as each
block was a slightly different thickness and required extensive fiddling to
get level. Also when they had to be cut (as someone decided to edge with a
line of engineering bricks) there was the issue of steel reiniforcing to cut
and protect from rust. Anyway had great fun and learnt a lot.

I made a slab by "accident", when I was testing mixes for my thin
concrete soundproofing wall. It was sharp sand, cement and glass-fibre
strands.
The result was virtually indestructable. It was poured onto polythene-
lined cement board resulting in a perfectly flat surface. Wasn't
vibrated more than just jiggling the mould by hand.
Simon.

The Medway Handyman wrote:
Anybody have any experience of casting small items from concrete?

I'm not getting into gnomes, but I want to start making what I'd call a
'padstone' (not sure if thats the right name).

Essentially it would be about 10" square x 2" thick with a chamfer on all 4
sides to leave a 3" square at the top.

The application is for 3" posts to support decking joists. Can't find a
ready made one anywhere.

I'm thinking an 18mm plywood mould to cast maybe 4 at a time, using silicone
spray as a release agent.

I saw on The Salvager a while ago Rico making something out of cast concrete
& he used an orbital sander to vibrate the moulds & get the air out of the
mix - I guess this would make a stronger product?

Any idea what mix or just use pre mixed bags?



Have you thought of using silicone rubber for the mould?

http://www.tiranti.co.uk/subdivision_product_list.asp?Content=Silicone+Rubb er&Subcategory=51&Subdivision=

Or a vinyl rubber?

http://www.tiranti.co.uk/subdivision_product_list.asp?Content=Hot+Melt+Viny l+Rubber+%26+Ancillaries&Subcategory=163&Subdivisi on=

--
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