I’m using some old concrete kerb stones for the bottom half of my pizza oven – obviously they’ll be rendered.
As I have a glut of them, I’m tempted to use them for the oven base too – laid on their sides. Does anyone know if they are heat resistant enough for this to work or are they going to crack and bollox up the whole structure?
Ta

I used some Marshalls (proper hefty jobbies, not B&Q light weight ones) in my barbecue build and there’s a crack in the big one on the bottom. Not enough to cause a problem as the whole lot is held in place by the brick surround, but it suggests the stuff isnt great under heat stress.

Perhaps you should think about casting your own with wire mesh/steel rebar/K screed poly fibres in? Would be pretty easy to make a mould and have a custom sized base.

Cheers stoner – the rebar + mould is an option. Another is to line the base with monoblocks or the blocks out of storage heaters. They should be better for retaining the heat too.

Get some of that asbestos stuff, it works pretty well.

Uh, what do you think ‘poly fibres’ are made of? Do you think its resistant the several hundred degrees?

Scienceofficer – Member
Uh, what do you think ‘poly fibres’ are made of? Do you think its resistant the several hundred degrees?

I’m sorry, you’ve lost me.

geoffj,

Have you had a look at UK Wood Fired Oven Forum or Forno Bravo?

Both sites have tonnes of info about building an oven that works really well.

Also if you join UKWFOF then there are various discounts that they have negotiated.

resistantness

Resistance FFS.

😉

Concrete often fails in a fire because any moisture trapped inside it turns to steam, expands and fails the concrete due to concrete’s low tensile strength. Putting poly fibres into a concrete mix is a good idea – the fibres will melt when exposed to the heat of a fire but in doing so they leave an escape route for the steam, so less spalling of the concrete.

Wonder if using fired and glazed clay tiles might work ?

concrete isn’t good with flames on it, as above, the water in it makes bit’s explode off it, I have no idea if the heat of the oven will do the same thing?
I have a big pile of firebricks, from storage heaters I am told, I got them off freecycle as surplus after someone had built a pizza oven with firebricks.
Thermal blocks withstand heat ok, I use thermal blocks rather then the firebricks when I am heating metal, it reflects the heat back.

Tony – thanks for the explanation. The kerb stones are already cast, so not much option there, so lining with something more heat resistant seems like the best approach.
I’m guessing that the mould approach may still fail, but that the rebar holds it all together.

Paul – I’ve looked at both those fora for info, but the multiple sub fora makes me go blind with confusion!

You really need to use something like firebricks for the actual floor of the oven. Making anything too monolithic will only increase the chance of it cracking. Use something designed for heat.

geoffj – On the uk forum you need to go to the pompeii ovens link under ‘Wood-fired oven builds. Follow 2012/2013/2014 builds HERE’

As well as firebricks you will also want to consider insulation for your oven, under the floor included, to retain heat. This will mean that you can use the oven for longer and use less fuel (and get better pizza).

Forno bravo have building plans to download for free, which are good for a start.

Concrete often fails in a fire because any moisture trapped inside it turns to steam, expands and fails the concrete due to concrete’s low tensile strength.

I found that out, bloody loud bang and a shower of bits of concrete and glowing embers, fun times!