Packing behind a fireplace

[derrynoose]

My open fireplace has a space between the back of the fireplace and the blockwork. I assume that this gap should be filled and would appreciate advice on what I might use to pack the gap. Thanks.

[Craftypig]

Is the space not part of the whole cavity between the inner and outer walls?

[RATTER15]

Im not sure I understand what you mean, what type of open fireplace are you talking about? Are you referring to some kind or insert, a cast iron fireplace for example?

[Mosaic]

It would help if you could post a snapshot on something like photobucket.

[The Builder]

If it's the cavity, we're in big trouble ........ fire brigade-wise :o(
I guess it's just the space between the fireback and the masonry. In which case it should be solid filled with concrete...... preferably insulating conc. made with "Vermiculite"............. but that's not essential

[derrynoose]

Thanks Builder. I couldn't describe my problem well as I didn't know the name "fireback" of the item behind which was the void. Thanks to all who have replied.

[AlBags]

Closed in with block-work, brickwork or insulating blocks.