tonyjeffs wrote:
I'm making some ornamental exposed aggregate concrete blocks to match
those in our 80 year old garden wall.
I'm very pleased with my wooden mould - designed to make 10 blocks at
once.
So that it doesn't get wrecked by the water and concrete, and remains
reusable, I've varnished it with polyurethene, and lined it with blue
damp proof membrane.

Would polyurethene varnish on its own protect the wood?
The dpm plastic is a pain - it flaps about and makes it hard so see
where the screws are going when assembling the mould, and if it gets
creased, it shows in the blocks. It has the advantage though of
allowing easy release from the mould.

Any ideas on a better way to water-protect the formwork?

Secondly, I think there is such a thing as a washer with teeth around
the edges, which I could nail over a screw hole so as to ensure that
the screw can only go in the correct place.
Anyone know what these things are called so I can tell the store what
I want to buy?

Thanks

tony

Tony

Have a look at:

http://www.pavingexpert.com/formwk01.htm
And the following excerpt is taken from there. You could try googling for
your nearest supply of Release Agent, Mould Oil or Shuttering Oil.

==============

Release Agents

All formwork, whether is be steel roadform or timber shuttering, needs to be
coated with a Release Agent (Mould Oil) before any concrete is placed. The
purpose of a Release Agent is to prevent the concrete bonding to the
formwork and then 'scabbing' when the formwork is removed. They also help
ensure the formwork stays clean and free from concrete, so that it can
easily be re-used elsewhere.

There are many products on the market that can be used as Release Agents for
formwork, but the most commonly used is known as 'Soap Oil'. This liquid is
painted onto the formwork in advance of the concrete being poured and it
dries, leaving behind a soapy or waxy residue that has no deleterious effect
on the concrete. Where the finish of the concrete is not important, some
contractors will save themselves a few bob by using engine oil or diesel in
place of a proper release agent; while there is nothing technically wrong
with this practice, it's not exactly environmentally friendly and should be
avoided whenever possible.

Tanner-'op