My intention is to build a hollow concrete cylinder for a fire pit like this:
There are a few people who have done this by using steel sheets bent in to shape with supports between, but I would prefer to use just pure concrete.
The only trace I can find of this having been done is that picture from Pinterest, but there's no link to the build, so I'm reaching out to you guys. My idea is:
- 2 Concrete column formers (I think they're called sonotube in the US), 1 approx 600mm diameter x 500mm length and 1 approx 400mm x 500mm length
- Place smaller one in bigger one
- Pour concrete
- Peel off the column formers
- Cook food, drink beer, hi five.
A few questions that the UK suppliers can't answer:
- Is 200mm thickness enough to support its own weight and contain a fire?
- Can I actually use column formers in reverse (i.e. the inside one)? I'm not as concerned about the finish on the inside, but do want a perfectly round shape
- Is there a simpler way to achieve this shape?
Best Answer
The simple way to "achieve that shape" is, of course, to buy it precast, which is almost certainly what the picture is - depending on size, it's either a section of well-casing, drainage pipe, or a manhole extension.
@BrownRedHawk is correct that it may (indeed, probably will) destructively deteriorate if used as direct fire containment - the interior should be lined with firebrick or castable refractory cement. The picture is clearly of the first time the thing in the picture has been fired, as it's remarkably clean as well as being intact - it probably has not held up well to the use, but pictures of that won't likely be forthcoming.
It will also burn relatively horribly unless some air inlets are made near the bottom.