how much clay?

[talltuk]

Hi folks. As part of my house plans i want to build a couple of j tube half barrel benches for some friends fire pits. I was wondering how many standard(ish) wheelbarrow loads of clay i might need to cast the core and fill say a bench made of four half barrels. looking at a 150mm system roughly as i am using 6" ID twin wall flue pipe to cast the tube. probably use vermiculite or perlite for insulation unless some can suggest good renewable/recycled option

[talltuk]

I ask because one site has clay with lors of sand and the other has only sand and is difficult to get to

[morticcio]

I used approx 2/3 cubic metre of clay for my 8"J tube and bench, and that was using lots of old brick to reduce the amount of clay/cob for the thermal mass.

Build the one at the site that has clay + sand first, noting how much clay you've used. That should give you a good idea how much you'll need at the next site.

[Donkey]

Ready-mix is best. If there's enough sand in the stuff that you dig out of the ground, rejoice!!

[talltuk]

Thanks guys.

Donkey, I haven't come across ready mix except for brick mortar. What should I look for?

I am hoping to have access to some cleaner grey blue clay from a field near my mates with sand/clay so should be able to experiment with mixes. Not sure if I want to add fibreous material, though I have acess to lots of glass fibre insulation.

My forum reading is convincing me to build a batch box now so that would need more. A ply or mdf mould would be fun to put together. Just need some steel for p-channel

[Donkey]

You are looking for a clay deposit with enough sand already in it that you don't need to add more.
It will all depend on the properties of your clay etc.
Tests will tell!

I usually add a little straw to the cob, even in the high temperature areas of my stoves. It improves the workability of the mix and reduces possible cracking. In the highest temp. areas the straw will char away, no harm done and no worries.

[talltuk]

Ok so ready mix out of the ground, not a bag. I will have to see if my mates with clay mind me carting off a load for the others . I badly want to get our piece of land with good clay deposits now. So many plans!

Would glass fibre, rockwool, do as a replacement for straw or might it not have enough tensile strength?

[Donkey]

Mind you, ready-mix out of the ground is a bit of a rare condition. Ideal but rare.
More often than not, we find a soil that is a little on the clay-rich side and add sand.
Worse yet, sometimes you find that the soil is clay-poor and need to amend with bought clay.

[talltuk]

Yeah I really want to avoid buying it Trying to build these from as much found or at least reused material as possible. Think I have found a supplier of 44 gal barrels that are second use. Only £5 each. Wish I had a junk yard to go digging in.

[talltuk]

Oh and any idea about the using rockwool instead of straw?

[Donkey]

I've never done it, so I can't say.. Try it out as a test and let us know how it goes. Might be great. ??


On the other hand, straw works and is inexpensive. If there is a field near you that has tall grasses, you can get it for free.

[talltuk]

My mates live on a meadow so loads and loads!

[Donkey]

If you use the stuff from your friends meadow, try to cut the seed heads off as much as possible. It won't hurt anything, but your stove will probably sprout grass and look like an over sized Chia-pet till it's completely dry, which can take some time.

[talltuk]

Hahahahaha! That would look awesome. I will have to give them the option