Vermiculite chimney

[Neil.B]

Hi all,
I've searched loads of posts and none have what I'm looking for.

I have loads of vermiculite, firebrick dust, kiln dried sand and cement.
I want to cast my own chimney.
Is it best to cast in place, if so what's the easiest way i.e type of form work or is it best to cast it seperate and mortar in place after?
What is the best mix?

Neil

[david s]

It is quite common for brick chimneys to be parged on the inside with a mix of vermiculite and cement fondu. No reason why you can’t cast the whole thing. For adequate strength I wouldn’t,t be going anything leaner than 4:1 and no thinner than 2” thick.
Suggested mix parts by volume. 3 parts vermiculite, 2 parts sand 1 part Portland cement 0.5 parts lime 1.5 parts water. (1 part AR glass fibres get from concrete countertop suppliers)
Build an inner and outer form in ply (could look nice tapered a little and make mould stripping easier) cover both mould surfaces in plastic for easy removal, ram the mix between the mould surfaces. Strip casting from mould after two days, cover casting to cure for further five days, mortar chimney casting in place, then allow casting to dry for two weeks before any fire.

[Grahamstein]

I cast my chimney in place. My outer form was cement board attached at the corners with some 22ga steel studs. I had an inner flue pipe and just packed the cavity between the inner and outer with the perlcrete. Perlcrete or vermicrete would be difficult to move and place without damaging it. But where there's a will there's a way.

[Neil.B]

Thanks both.
I was thinking of using a 6" plastic drainage pipe and sliding it out after. I would gently rotate it while the mix dries to make sure it's kept loose.

Is there any advantages to packing in between formwork rather than laying by hand, the same way as when an exercise ball is used?

I assume it will be lightweight, will it be strong enough to have 45° or 90° angles?

I prefer my saying ' where there's a Neil, there's a way'