First time clay/cob oven Cardiff

[pusht4time]

Hello from sunny (and it has been for once) Cardiff. Like many, I'm a long-time lurker/dreamer but am finally getting on with building a cob oven.

I'll upload some progress pictures soon (should I start a new thread?) but I've built my base, put down my Kiko-Denzer-bible 'bottles and clay/straw insulation layer' and the next step (I think) is a bed of oven clay/sand before laying the hearth floor.

I've just got a couple of questions - can anyone to confirm that the bricks I managed to salvage from a neighbour are indeed storage heater bricks that'll be appropriate for the oven floor (see pic)?

Also, as they've got a wide recess on the underside, can I just lay them onto a clay/sand bed or do I need to fill in the recess with more clay/sand mix to make them more heat efficient?

Thanks in advance.

[simonh]

Can't confirm if they are storage blocks or not, it I wouldn't want any cavity underneath them if I were doing it.

[oblertone]

Yes, they are storage heater blocks, and while you can lay them with a cavity (as I did) it would probably be better to lay on soft sand to eliminate the gaps.

[pusht4time]

Oct 17, 2017 9:19:26 GMT oblertone said:

Yes, they are storage heater blocks, and while you can lay them with a cavity (as I did) it would probably be better to lay on soft sand to eliminate the gaps.

Thanks Oblertone, If I'm laying in soft sand how would be best to ensure they're bedded in securely?

I'd initially wondered about filling the cavity with the same sand/clay oven mix as the oven wall but wasn't sure if that was too faffy and could cause problems as the mix goes off (shrinking or reacting to heat at a different rate to the bricks etc).

[chas]

Oct 18, 2017 7:10:25 GMT pusht4time said:

Oct 17, 2017 9:19:26 GMT oblertone said:

Yes, they are storage heater blocks, and while you can lay them with a cavity (as I did) it would probably be better to lay on soft sand to eliminate the gaps.

Thanks Oblertone, If I'm laying in soft sand how would be best to ensure they're bedded in securely?

I'd initially wondered about filling the cavity with the same sand/clay oven mix as the oven wall but wasn't sure if that was too faffy and could cause problems as the mix goes off (shrinking or reacting to heat at a different rate to the bricks etc).

The ID was the difficult bit. Provided you take your time to bed them down level and tight(ish) against themselves so they're stable, they won't move much by the time you've built an oven on them. Same principle as block paving.
Cheers, Chas.