My fire started leaking smoke from around the surround. Had chimney swept but still does then when we first light fire. Once fire is in then there is no problem. I noticed the coal save brick at the back of the chimney was craked and broken. This was removed. I now have a new one to fit - can this just be slotted into place or do we have to use fire cement? I've not really got any idea so any help would be appreciated.