Tile cracked from heat

[Crofter]

I'm renovating my hearth using large format porcelain tiles. I was under the impression that these were suitable and could handle the heat from the wood burner.

As a temporary measure, I wanted to check the finished height so used an offcut of tile. I sat it upside down so as not to risk scratching it with the stove's feet, and with a layer of cardboard between the tile and the concrete, to account for the expected thickness of tile adhesive.

 

I fired up the stove to get some heat through the chimney and cure the fire cement that I'd applied.

 

To my surprise, the tile cracked in half with the heat. I'm a bit stumped now- I don't really have time to buy an alternative type of tile, and I've already set the height of the flue so can't use a thicker material. I don't really want to go through with installing the tiles if they're just going to crack, obviously.

 

The only thing I can think of is that maybe using the tile upside down is what caused the problem. Maybe it absorbs more heat when it's shiny side down??

 

And on a related note... I've got some flexible flooring adhesive left over from another job... I wonder if that would be better than regular tile adhesive, since it would accommodate more movement?

[Marvin]

Not sure flexible floor adhesive is a good idea?

 

Was the weight of the wood burner feet (or a foot) on the tile? My old wood burner was bloody heavy!

 

Was the cardboard scorched?

 

My guess would be an un bedded tile on an uneven surface rather than heat alone.

 

M.

 

 

[Marvin]

I would lay the tiles using sand and cement morta.

 

M.

 

 

[nod]

Depends where it was manufactured 

Italian are fired for longer at a higher temperature 

[JFDIY]

Also did the cardboard insulate it so the heat couldn't transfer into the slab to sink the heat away, so it saw a higher temp than is likely in practice

[markc]

Very little heat goes down through the legs of a wood burner, i would say it broke due to load rather than heat. when someone left a pile of clothes on my bathroom floor the porcelain tile heated up so much (electric UFH) it curved up at the edges but still didnt break

[James Newport]

I vote for the unstable tile/load hypotheseseseseseses above...

 

When I had wood burner it was possible touch the legs of the stove without having your hand seared into a charcoal stump.

 

[Mr Punter]

I think it is the metal leg that is the issue.  You could put a small piece of cardboard under each foot.  The tile is best supported on a full bed of adhesive.

[Crofter]

Only just spotted these replies- must check my notification settings.

The cardboard wasn't scorched at all. And I routinely leave bundles of kindling under the stove to dry out so it can't be getting *that* hot.

 

Anyway I've finished the installation now, used flexible floor tile adhesive. It's be so stupidly hot the last couple of weeks that I haven't been able to face the prospect of lighting the thing... sp I will find out soon enough...

[Temp]

I think it will be fine. My guess is the cardboard didn't support the tile offcut enough and point  loading from the stove caused it to crack.