Wall workings

Walking today:   3.8km
Swimming today: 1.50km - yes if you are doing the maths, that is 60 lengths

We've spent the last week or so repairing and rebuilding one of the walls of our outbuilding which we call The Grange. The basic construction is the same as that utilised in the barn, faced stones on the outside faces with the whole construction being held together by clay.

We repointed the outside North wall of The Grange last October and operations were then halted due to the weather - lime is a picky material refusing to mix or set in very cold weather and taking its own time to harden depending on air temperature and humidity. But I find it a very pleasing material to use, somehow it's warmer and more forgiving than cement and, once you get to grip with its setting process, produces much nicer results than concrete. And it is, in the long term, nearly carbon neutral as it sets by slowly absorbing CO2 from the atmosphere at a rate of about 4mm per year- remember that number.

The first stage in the work is to rake out all the clay from the stone joints, clear and brush out all the dust and dampen down the wall with a spray. Controlling and maintaining the moisture levels in the wall is a critical part of the process and requires near continual spraying and re-spraying the wall.

The lime mortar is a carefully measured mix of lime, water, sand from our local quarry at Lauzach and river sand ("Sable de Loire"), more quarry sand produces a whiter, finer mortar, more river sand a warmer honey-coloured finish with larger aggregates in the mortar mix. Maçons here have a kind of colour chart using tints and dyes from reddy-browns through yellows, cream and white, our finish is light yellow using 2 parts quarry sand, 2 parts river sand and one part lime. 

The roof is metal corrugated steel sheet and my guess is that at some stage the previous roof failed (originally it would have been thatch but maybe with a subsequent asbestos one before the current steel) and water got down into the walls. This washed out a lot of the clay that the wall had been built with and left big gaps that animals then moved into. So I've spent a lot of my time filling and rebuilding the stones in big holes at the bottom of the wall, I could get my arm in up to the elbow on a couple of them!

Here's the before picture:

And the intermediate stage with the wall rebuilt back to its original level:

We've re-exposed and made a feature of the niches in the walls:

Lime has a two stage process to finish the pointing, is harder to use than cement but produces much nicer results. The first step of the pointing process is to push lime mortar into the joints until it is proud of the surrounding stones:

At this stage it shows a lot of trowel markings and spill onto the surrounding stones:

And, here's the tricky part, at some indeterminate time after the lime is inserted the surface has dried enough to brush with a stiff churn brush or soft wire brush. The time is critical and very variable depending on air temperature, original moisture content of the wall, humidity of the air and wind. It ranges from 4 hours outside on a warm day to over 4 days at the bottom of our wall in 7 degree temperatures. If the lime dries too quickly it goes bleach white and crumbles, if it's too cold below about 5C it refuses to set and crumbles so the mortaring season here runs from mid February to mid-May and September to mid-November.

No wonder that in the early 20th century lime was almost completely replaced by concrete in the construction and, unfortunately, renovation of buildings. There are plenty of cold looking damp stone buildings around here that have been repointed in cement for speed and ease but look terrible (to my eyes at least).

Lime can adapt to micro-movements in the building without cracking, is porous and allows the wall to ventilate rising moisture effectively and just looks so much nicer and more interesting, here is the finished area of wall from the previous picture:

The stones shine, the subtle colour variations in the stone are highlighted and the smooth brushed off mortar accentuates the outline of the stone. The aggregates from the sand mix contribute to the definition of the mortar bands.

Now, here's the magic part. The initial drying process to allow the lime to be brushed off isn't the setting process, that is a much longer process that relies on fixing CO2 from the atmosphere and proceeds at about 4mm per year plus or minus a bit. So, some of the really deep holes I filled will be nicely cured by about 2070!