Do Linings need back-filling with vermiculite?
Generally speaking no. Some manufacturers recommend back-filling with vermiculite and if customers wish to back-fill Turner and Wilson has no objections but unless the circumstances are very severe there seems very little point. Although linings themselves have little in the way of insulation properties, when the installation is viewed as a whole then thermal thermal properties are quite good. First there is the lining, then a sealed air gap between the lining and masonry, and finally the masonry itself. If the chimney is internal then there are still further advantages. There are, however two disadvantages from back-filling. Firstly any insulation must be kept dry otherwise it will begin to work in reverse and become a conductor. Secondly, a major advantage of flexible liners is that they can be installed and removed with comparative ease. Back- filling reduces this advantage considerably.
