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Old 09-01-2007, 07:15 PM posted to
hob hob is offline
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Default Unglazed quarry tile for baking stones

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pamjd wrote:
I line both myoven and outdoor grill with unglazed red ceramic type
floor tiles I get at Home depot for 35 cents each on sale. I think
they are 8" squire. I leave them on the bottom rack of my oven all the
time. They work great.

A few people have said this. I'll add that I tried some red-orange,
unglazed ceramic tiles and they cracked apart in the middle of the
first use. Is there any further distinction I need to get ones that
won't fall apart so readily?

thinking out loud ---

There are tiles which use clays and firing such that they are rated for
the repeated stress of heat and no heat - common firebrick comes to mind.
However, common firebrick is thicker than most "floor tile", thicker in
order to handle the stress of repeated heating and cooling, of being bumped
when hot, etc.

-- A word of caution - fired tile is like glass, so when a tile cracks,
especially thin ones from heat, the possibility exists that a piece of the
"glass" will come flying off the tile at a pretty good speed. (The crack is
the release of stored energy, and defective heated tile can and does propel
shards with enough force to stick them through the skin.)
Using floor tile in an oven may not be the best idea, given that many of
them are cheaply made. Some might work fine in some situations, but...

Thoughts about why your tiles cracked -

Since tiles have been fired to a thousand plus degrees to "become tile", it
is not the heat stress per se that causes the crack.

It is more likely that

a) firing crack - the tile had a small crack (even unseen or internal) from
handling, poor firing, cheap clay mixtures, etc., before being put in the
heat of your oven, and that crack propagated with the added heat stress,
which split the tile -- and/or

b) moisture - the tile took on moisture from the air and was heated faster
than the trapped moisture in the center could escape, building up internal
pressure - or in the same vein, the tile was sealed on one side, and
moisture was trapped under the sealer (sealer is common in cheap -read
"porous" - floor tiles and travertine-type stone flooring) and that
pressure caused the tile to crack and/or.

c) uneven heating - your oven has an automatic preheat or is defective in
the starting cycle, such that all available oven heat sources are on until
the oven reaches temperature, the resulting uneven heat transfer internal to
the tile caused stress in the tile; or the tiles cover the oven rack such
that the air cannot circulate, and the heat below the tile is
trapped -leaving the upper part of the tile cool while the bottom of the
tile is very very hot, so that the bottom of the tile expands while the top
stays relatively cool, and the uneven heating bows the tile -cracking it.

To minimize cracking in a tile used in the oven, I would get a top quality
unsealed tile rather than the cheapest one, make sure there is at least 3
inches all around the tiles when on the rack, store it in a dry place, and
don't use preheat.
I would say use firebrick as it's cheap, but I have no experience cooking
directly on brick - all I can say about cooking properties of brick is that
the brick I see in the "wood-fired " pizza oven bottoms looks just like