Fibreglass mould plug - what material?

[Tim Watts]

Purely hypothetical:

Say I wanted ot make a custom waterfall spillway filter tank, like:

(I don't but I might in a year or two)

Assuming it was a one off, and I was happy to take a single cast from a male plug negative - what would be a good material to use for the plug?

Something carvable/shapable would probably be necessary - there is some internal detail not apparant in that picture.

Some sort of hard foam would be easy to work with - not sure if it is suitable as a GRP plug though??

[The Natural Philosopher]

oh it is.

BUT it depends what finish you want to achieve.

you can rough in foam and then use body filler to get a decent finish, and then dip the thing in wax for a release agent.

gel coat., lay up the shit and away you go.

[Tim Watts]

On Wednesday 24 July 2013 18:04 The Natural Philosopher wrote in uk.d-i-y:

Oooh - yes, I should have said - finish is not hugely important. This type of device is submerged in water and hidden with rocks mostly.

All that matters is it is strong (to resist ground pressure and freezing over winter).

By "dip in wax" do you mean literally coat with melted paraffin wax?