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