Four Gables

Yesterday, with the sea millpond calm, we took a look at the castle from the sea side - and a very impressive sight it was, clad in its matrix of scaffolding.

The weather this morning was little different, dead calm with low clouds which were threatening rain.  From the point of view of the lads working on the castle, this sort of weather is bad news: the dreaded Highland midge is out in hoards.

The main emphasis of work at present is within the main, north building.  The westernmost gable end is now fully pointed under the temporary roof which should, in the next week or so, be coming off to allow the permanent roof to be built.

This is the western of the two interior gables, which used to reach up to roof height but was badly decayed.  It's been made safe and pointed, and a door is being inserted at what will be the attic floor level.  The plywood frame is temporary, allowing....

 ....the lads, working with stonemason Damien Summerscales (left), to rebuild the wall to roof height.

Scaffolder John Forsyth is back on site to move some of the scaffolding above the biomass boiler house, but he's also shifted the staircase in the main block from the west room into the area between the two interior gable walls, so it now goes up where the 18th century oak stairs once stood.  The picture is a view from the courtyard through the main entrance to the building.

The eastern of the two interior gables, which used to go up to the roof, now stops just below attic floor level.

I found archaeologist Kenny Macfadyen back on site today for the first time in some weeks - he's pictured working just outside the eastern gable end.  He's here to complete some elevations of the battlement wall heads and plans of the walkway that runs round behind them.

One part he's working on is the northeastern corner where, between the battlements and the roof, there's a rather fine walkway formed of slabs of a metamorphic rock called schist.  This has been covered over during the winter.

And this is an example of the sort of meticulous, detailed work he's doing.  It shows the same corner of the battlements, parts of which, Kenny says, are of original, mediaeval construction.  In due course, all these diagrams will be published in such a way that, with colour coding, we'll be able to see how these walls developed over time.

Work on the North Range

Progress continues to be rapid on site, judging by the amount that's been done since I visited last week.  The emphasis seems to have shifted from the exterior - which was drenched yesterday in over an inch of rain in twelve hours - to the interior of the north range.  Of the nine men now on site, the most since building work started, two are in the chapel dealing with its ceiling.  Here, blocks of stone are being removed to allow plates to be bolted to the walls which will support lintels.  These will be inserted from one end and a damp proof membrane laid over them to keep out any water running within the walls; the space above will then be packed with masonry and mortar.

The chapel is within the nearly 3-metre thick north curtain wall.  In the few places where there are lancet windows let through the wall the lintels which have been inserted are of oak.  Above them is a damp proof membrane, and the space above it has been filled with broken slates from the original roof - again, to help block moisture moving down within the wall.

The lintels in the north range's wall which faces onto the courtyard are of reinforced concrete.  All these are now in place, so the structural strength of this wall has been hugely increased.

This is a view down the three chimneys in the western of the two interior walls of the north range.  The wall will be retained in the refurbished building, along with the three chimneys. However, one of the alterations includes a door which has to be cut through to the right of this picture, which will block the right-hand chimney.  As a result, the three chimneys, important because there will be open fires in all the rooms, will have to be fitted up the space originally used by two.

Visible to the left centre of this picture are two of the slots in the masonry of the exterior wall into which the original joists were fitted to support the wooden floor - in this case, of what will be the attic.  The new joists will be 1ft x 6", and won't be cut into the stonework so, as in the chapel, wall plates will be fitted which will carry the joists.  The laser level seen here has been used to mark the level of the proposed floor.

Pointing of the exterior has also continued.  Here the top of the semi-circular later addition at the angle between the east and southeast walls has been pointed, and it gives a good idea of what the exterior stonework will look like.

The steel girders that will support the flat roof of the biomass boiler house are being moved into position.  The area we are looking at here is the platform onto which the trucks delivering the wood chip will back before their load is tipped into the silo, which is just to the left of where the workmen are standing.

Many thanks, once again, to Mark Thompson and the lads for their patient explanations what's going on.

Diamond Drilling

There's a lot happening on site at the moment.  The blockwork is finished on the biomass boiler house so it's ready for the horizontal steel supports that will hold up the roof.  The landward end is being backfilled ready for this.  Damien Summerscales, who is putting in the strengthening rods - see last week's post - has nearly finished, and the architect is due down this weekend, so hopefully work can start shortly on the roof of the main, north block.

The main interest today was a team from UKdima Engineering Ltd, site drilling specialists, of Stirling, who were there to drill two 450mm diameter holes through the base of the castle wall into the room which gave access to the well.  The holes angle up at 15 degrees.  One will take the biomass boiler extract, which will go up one of the castle chimneys, the other will carry the water and drainage pipes.  The heating system will access the castle through the well itself.

The men on site today were Alasdair Smith, right, and Liam Martin, who were kind enough to show me how their machine worked.

The drill holes are passing up through a blockwork buttress which was built last week.  The bit works very much on the same principle as the attachments I have for my hand drill which I use for making large holes in wood.  The rotating drill bit - blue - has to be forced against the rock wall, and this is done by turning a handle which connects a cog to the ratcheted steel rail that angles up beneath the bit, this rail being bolted to the blockwork.

The two black pipes are attached to a hydraulic unit, from which fluid is pumped to turn the drill bit. The yellow pipe is for water to cool the 'sharp' end of the bit.

As with oil-drilling bits, the teeth here are tipped with diamonds, which....

....can be seen in close-up here.  How long they last depends on the hardness of the rock.

Alasdair and Liam arrived on site yesterday and hope to be away by the weekend, though much depends on how resistant the rocks of the castle wall prove to be.

Many thanks to Liam and Alasdair for their patience in explaining their work.

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.

Progress Report

We've had a run of good weather which ended yesterday when the wind strengthened, shifted into the east, and brought colder temperatures and drizzle.  That it's been so warm - we had 25C on one day this week - has meant that, for the lads who are working their way steadily round the exterior of the curtain walls, the mortar has been going off much more quickly.

Richard showed me an example of some pointing he did yesterday - that's his finger at the left of the picture.  The paler area just above his finger is how the mortar looks before he gives it a good polish which, when he's finished, produces the very pretty mottled effect at upper right.  It amazes me that this, the 'back pointing' as they call it, has to be buffed up as it's then covered by further mortar - but it's important in that it ensures that the outer inch of mortar has a good hold.

Work is progressing on the biomass boiler in the moat, with two stonemasons on the blockwork this morning.  The far end in this picture is where the hopper for the wood chip will go, and access to the boiler room will be down stairs which will be to the left.  The boiler itself will be at the nearer end.  The far end is being built up so the roof will be at the level of the car park while this end, nearer the castle wall, the roof will be slightly lower, leaving the old wall to the right visible.

Where the blockwork butts against the rock wall of the moat, the rock has been stabilised with wire mesh held with plaster, while....

....the blockwork which faces the rock wall has been coated with bitumen outside of which is a layer of insulation.  The area between rock wall and blockwork is then filled with rubble.