Strengthening the Walls

When ArcEngineers carried out their structural survey of Mingary's curtain walls, they identified a number of cracks (blue lines in picture) which had developed over the castle's 700-year life.  These needed to be strengthened to prevent further movement.  The plan shows part of the west wall, and each -x----x- marks the position where a strengthening bar has to be inserted into the stonework.  In all, in this wall alone, there are nineteen bars needed.

Both the engineer's drawings and the manufacturers of the stainless steel rods, called helibars (see website here), suggest that the reinforcing bars should go horizontally across the line of weakness.  In reality, on a castle like Mingary, this simply isn't possible, so the first thing that stonemason Damien Summerscales has to do, after cutting the rod to length, is to chip out the mortar along the straightest path possible and then bend the bar into the resulting crack.  His task is made more difficult because, if the joint between the rocks is covered with the original harling, this mustn't be removed, and even chiseling out the mortar is difficult because, although it's seven centuries old, it's still incredibly hard.  The result is anything but a straight line.

Once the helibar has been bent to shape, it's removed, and a bed of mortar pushed into the gap.

 Then the helibar is replaced....

....and forced in as far as possible by hitting it with a cold chisel and hammer.  The bar isn't too keen to go in so, as fast as it's hit at one end, it tends to jump out at the other.  Needless to say, Damien has a trick for getting round this problem by pinning it with small stones.

Once the bar is firmly in position, Damien forces mortar on top of it using a neat little mortar trowel, finishing the mortar so it's still an inch from the face of the rocks.  Later it'll be pointed along with all the other cracks.

Many thanks to Damien for his patience in demonstrating the process.