Making complex structure from cement board

[leen...]

Hi all

As part of my BBQ project, I need to create a chimney hood for the top which needs to have sloping sides and front to reduce the top area to the chimney diameter (1980x820 to 200mm diameter). Quite a complicated structure to make and TBH can get my head around the angles but that's a different story.

It won't get very hot but needs to be noncombustible in case of a stray spark or something (highly unlikely be hey). My thinking is to create a structure out of angled steel or something and then attach cent board to the outside and paint it same colour as the house.

Any ideas how best to go about this? Eg will need to bolt the metal pieces together and somehow attach the cement board to it all counter sunk and filled to give surface to paint.

Any other ideas on how to achieve it? Maybe an easier material to work with than the angled steel which I could screw together? Wood would obviously be ideal but could burn. Maybe there is a way to stick the cement board together to form the structure?

Thanks in advance

Lee.

[Colin Bignell]

That sounds like the sort of problem they would set us in Technical Drawing when I was studying engineering.

Have you considered using aluminium, rather than steel? Easier to bend and work into shape and you can pop rivet it into place.

Alternately, use copper, which is even easier to shape, and make a decorative hammered copper hood.

[Animal]

thin sheet metal you could bend to any shape, whack over the edges easily etc.

[The Natural Philosopher]

So many possibles

Use copper. Expensive but will look gorgeous Use fireproof board and then cover in something more attractive Use (small) bricks e.g.

...with very 'strong' mortar...possibly in layers of two..laid up over a removeable wood former(cover in clingfilm first) or use the bricks over the fireproof board altogether!

[SteveW]

Use a hood bent from sheet metal, with u-channel riveted to the edges and fire-proof board slotted into the u-channel, then metal trim pieces at the board joins, screwed through into the metal hood?

[Brian]

How about a ‘chicken wire’ support coated in a mix of either perlite / cement or vermiculite / cement. The light weight concrete is heat resistant, you can skim it to get a neat finish, and probably get a complex shape. Possible run a length of light weigh flue pipe through it and some metal struts for support. Even use thick cardboard underneath while shaping it. It will burn away later.

[Tricky Dicky]

If the sides were straight and the front sloped then you could use angle iron but with all faces sloping up similar to a hipped roof the angle will be wrong.

Richard