Recently, a few sandstone blocks on two of our towers have been spalling, which involves losing the outside layer of stone in a thin flake, which then falls dangerously to the ground without warning, a real hazard for anyone too close without a hard hat. We roped the areas off in case of any further events and called Wallwalkers to the rescue as a cherry picker would not have worked and scaffolding was not necessary, or economic for the amount of work involved. Wallwalkers, a local firm had access to the top of the two towers and were able to secure their abseiling ropes without difficulty. They then dropped over the side, as it were, and tackled each damaged stone in turn, so there were no loose pieces left. Even though the top of the tower projects from the wall, they were able to dislodge all the loose pieces quite easily. In the image, a damaged (discoloured) stone is seen to the left of the Wallwalker as he works his way down, fortunately on a sunny day.
The cause of the problem is the ingress of rain into the gaps between the blocks where the lime mortar has failed. The stone then gets wet and is damaged by frost, of which there has been plenty last year. The solution is to re-point where we need to, and the next stage is to make a photographic survey of all the stonework to see where we need to go and estimate what it will cost. As the gaps between the blocks are only about 1mm, the material we use will have to be carefully selected. We will also have to make flaunching repairs to the tops of the stones below those where the flakes have come off as they will otherwise be vulnerable to water ingress from the top edge where they are now exposed.
After all we have spent on the roof and parapets it is annoying now to find more work, even if we do not have to re-point everywhere. At least business is picking up and bookings are better for 2014…
JH-B 23rd January 2014