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