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I have developed a theory on which I would welcome comments
Specifically Northern Orkney Islands traditional building, where the main material is locally quarried "Caithness Flagstone". The actual stone used in any given building is somewhat variable in quality, with certain stones being soft mudstone and some stones much harder tending almost to metamorphic., it's a fairly soft sedimentary stone anyway. Crucially to this argument, I contend that at least 20 - 40% of any given traditional building in the area is made of this permeable, rather porous mudstone/siltstone. This variability in the stone used in a building may be purposeful but more likely just accidental.
"traditional" building is walls 2-3' thick composed of two roughly dressed outer skins and a fill of chossy broken stone.
unmodified Clay-ey earth seems to have been used as a filler or mortar during the buiilding process.
usually some evidence of lime mortar pointing on the external (and internal) surfaces.
this lime mortar sometimes extends to a full render on the outside, and also sometimes a smoothish render on the inside, made of a lime which seems to use finer sand than is typically used outside. The outside render & pointing where present appears to be made with local beach sand.
Damp-proof measures near ground level appear to have simply not featured in historic traditional building. Probably location was the only consideration - site the house on a relatively naturally dry piece of ground. The floor in a traditional house was the compacted soil. Flagstones (where used) were simply laid on the soil. The first modern floors appear to have been a thin layer of concrete over the soil.
Consider the following observations:
The climate in Northern Scotland is noticably wetter (and warmer - or at least, less frosty!) in the past 20 years than it has been in the preceding 200-odd years.
The traditional use of houses has changed in the last generation, and it is now very rare indeed to find the usual situation of a coal-fired range in the middle of the house with a wife tending it 24-7.
expectations of comfort etc have increased, so that living with damp & mould is now unacceptable, as are the natural draughts of a traditional house that would have contributed to useful ventilation.
labour cost has risen relatively, so it is more difficult to keep building management in check (nobody considers repointing or painting or roof repairs annually any more) likewise much more relatively expensive to work at height now than ever in the past.
That's the backdrop as I see it.
Maintenance of such a traditional local builing for heritage/aesthetic purposes is a challenge.
Lime mortar has fairly recently been used again locally for rendering & pointing with this "breathability" thing being touted as the key to keeping an old house weatherproof and dry.
When done right, I don't doubt that there is something in this: moisture that naturally collects into the structure possibly has a chance to evaporate off through the "porous" lime mortar.
However
I think that the lime mortar is sacrificial: in the current weather it is eroding faster than ever, it's not cost-effective to have the plasterer back every year to keep on top of it, and moreover the climate is damper now through the year that it has been in the past, so the seasonal evaporation mechanism is falling over.
The lime is probably (like all other materials) not as "good" as it was in the old days in some way. don't ask me how but paints are not as toxic as they used to be, therefore not as good, likewise wood, steel, plastics. and probably in some way this is true for lime.
The "fix" that I am favouring at the moment for maintenance of trad old stone is to carefully point stonework in a strong cement mortar, leaving strategic miniature gaps in the irregular pointing where the stone has naturally formed a water-shedding or somewhat protected or hidden vent. These gaps are few and far between.
Never to fully render old stonework, apart from in small patches where a poor stone is obviously spalling.
Leave as much vertical face of stone exposed as possible.
The strategy being that the natural porosity/permeability of the stone face will have to provide any breathability.
the argument of frost spalling saturated stonework is negligible, owing to the (slightly) warmer climate.
The technique is a compromise between reduced permeability of the pointing medium (strong cement vs lime-mortar) with a longer-lasting and more weatherproof finished product (finished product being a bit of worked-over masonry)
I contend that the cement mortar wins out because times (especially expectations, & weather) have changed, leading to the lime mortar being a relatively unsuitable material for this area.
There are probably places (drierplaces with less wind-driven horizontal precipitation - and with a genuine risk of frosting) where the lime mortar technique is more suitable than cement.
enough of an essay. I look forward to arguments against.
Specifically Northern Orkney Islands traditional building, where the main material is locally quarried "Caithness Flagstone". The actual stone used in any given building is somewhat variable in quality, with certain stones being soft mudstone and some stones much harder tending almost to metamorphic., it's a fairly soft sedimentary stone anyway. Crucially to this argument, I contend that at least 20 - 40% of any given traditional building in the area is made of this permeable, rather porous mudstone/siltstone. This variability in the stone used in a building may be purposeful but more likely just accidental.
"traditional" building is walls 2-3' thick composed of two roughly dressed outer skins and a fill of chossy broken stone.
unmodified Clay-ey earth seems to have been used as a filler or mortar during the buiilding process.
usually some evidence of lime mortar pointing on the external (and internal) surfaces.
this lime mortar sometimes extends to a full render on the outside, and also sometimes a smoothish render on the inside, made of a lime which seems to use finer sand than is typically used outside. The outside render & pointing where present appears to be made with local beach sand.
Damp-proof measures near ground level appear to have simply not featured in historic traditional building. Probably location was the only consideration - site the house on a relatively naturally dry piece of ground. The floor in a traditional house was the compacted soil. Flagstones (where used) were simply laid on the soil. The first modern floors appear to have been a thin layer of concrete over the soil.
Consider the following observations:
The climate in Northern Scotland is noticably wetter (and warmer - or at least, less frosty!) in the past 20 years than it has been in the preceding 200-odd years.
The traditional use of houses has changed in the last generation, and it is now very rare indeed to find the usual situation of a coal-fired range in the middle of the house with a wife tending it 24-7.
expectations of comfort etc have increased, so that living with damp & mould is now unacceptable, as are the natural draughts of a traditional house that would have contributed to useful ventilation.
labour cost has risen relatively, so it is more difficult to keep building management in check (nobody considers repointing or painting or roof repairs annually any more) likewise much more relatively expensive to work at height now than ever in the past.
That's the backdrop as I see it.
Maintenance of such a traditional local builing for heritage/aesthetic purposes is a challenge.
Lime mortar has fairly recently been used again locally for rendering & pointing with this "breathability" thing being touted as the key to keeping an old house weatherproof and dry.
When done right, I don't doubt that there is something in this: moisture that naturally collects into the structure possibly has a chance to evaporate off through the "porous" lime mortar.
However
I think that the lime mortar is sacrificial: in the current weather it is eroding faster than ever, it's not cost-effective to have the plasterer back every year to keep on top of it, and moreover the climate is damper now through the year that it has been in the past, so the seasonal evaporation mechanism is falling over.
The lime is probably (like all other materials) not as "good" as it was in the old days in some way. don't ask me how but paints are not as toxic as they used to be, therefore not as good, likewise wood, steel, plastics. and probably in some way this is true for lime.
The "fix" that I am favouring at the moment for maintenance of trad old stone is to carefully point stonework in a strong cement mortar, leaving strategic miniature gaps in the irregular pointing where the stone has naturally formed a water-shedding or somewhat protected or hidden vent. These gaps are few and far between.
Never to fully render old stonework, apart from in small patches where a poor stone is obviously spalling.
Leave as much vertical face of stone exposed as possible.
The strategy being that the natural porosity/permeability of the stone face will have to provide any breathability.
the argument of frost spalling saturated stonework is negligible, owing to the (slightly) warmer climate.
The technique is a compromise between reduced permeability of the pointing medium (strong cement vs lime-mortar) with a longer-lasting and more weatherproof finished product (finished product being a bit of worked-over masonry)
I contend that the cement mortar wins out because times (especially expectations, & weather) have changed, leading to the lime mortar being a relatively unsuitable material for this area.
There are probably places (drierplaces with less wind-driven horizontal precipitation - and with a genuine risk of frosting) where the lime mortar technique is more suitable than cement.
enough of an essay. I look forward to arguments against.
