I am trying to renovate an Baxi Burnall open fire with a stone surround composed of multiple interlocking pieces. Some of the pieces have moved over time and the mortar or grout has become loose. I am not sure what the stone is but it is very smooth (but not polished) and waxy feeling. It is very fine grained. It is a light creamy colour and can be scratched quite easily with a sharp instrument. The mortar is the same colour and very fine. The only pieces that have become loose are those immediately adjacent to the fire ie the mantle pieces and vertical sections either side of the fire opening.
I assume that the mortar has broken because of expansion/contraction because of the heat of the fire so would a mortar succumb to the same problems?
Would a flexible tile cement suitable for heated floors be a better bet?
Any ideas would be greatly appreciated... please feel free to email me.
I should mention that the tolerances between the stones are very fine so a very thick mortar would not settle very well when placing the stones so some flow would be necessary until set.
Thanks in advance
Dean Blaby