Andy Phillips wrote:
Hi,
I have a pizza oven made from refractory cement (see
http://www.purimachos.demon.co.uk/pizza.htm). This works OK, but the walls
are not thick enough to retain much heat - therefore, having heated the
oven with a wood fire and raked it out, it's only possible to cook about two
pizzas before it's cooled down. I'd like to be able to cook at least four
pizzas and maybe some bread afterwards. I therefore need to thicken the wall
to increase the heat capacity - I thought by adding at least one course of
bricks around the sides and top of the oven, followed by an inch or so of
render. Question is, do I need to use special heat-proof bricks (eg
firebricks) and cement, or can I get away with normal house bricks and
mortar? I'm concerned that the mortar and render will crack - when in use,
the outer wall of the oven gets too hot to touch for more than an instant -
I would guess about 100-140C.
Any advice appreciated.
Andy



Andy,

First, Barry should have followed your link. It appears you bought a
commercial product. However, what we call "the implied warranty of
merchantability and fitness for use" in the US may be a legal concept
that does not have an exact equivalent in the UK. In any case, this
looks to be the product of a home-based microbusiness, so there wouldn't
be much point in pursuing a remedy with them.

So, second, let's look at your proposed solution.

What I've seen done to good effect is to design in a gap between the
inner shell (which you own) and the outer shell (which you propose to
construct) and to fill that gap with vermiculite insulating fill.
Vermiculite got a bad rap because the principal source of it in the US
was laced with asbestos. For all I know, all sources of it are laced
with asbestos. So you will want to be careful handling it (gloves, long
sleeves, respirator), and you do want to ensure that the space you are
filling is then sealed in an airtight fashion with some sort of
inspection plug at the top where you can add more vermiculite if it
settles over time.

This insulating layer cuts down significantly on the overall weight of
the oven (a possible concern depending on what it's sitting on) as well
as on material costs.

The outer layer can be ferrocement, and you can skip the bricks altogether.

Or you can do it your way, of course. I'd suggest firebrick, as it's
lighter in weight and therefore easier on your back as you do the work.
Of course it may also be harder to come by, in which case I'd suggest
chimney brick (solid clay brick, as opposed to the sort with holes in it
that is used for walls).

Good luck!

Dick