Greetings, felllow dialists,
At the recent meeting of the British Sundial Society in Edinburgh I
spoke on the conservation of the 1793 stone dial on my local parish
church. This conservation work was being carried out at the time and I
learnt from the stonemason involved the importance of lime mortar in
stone preservation as opposed to cement.
Most people have seen early lime kilns and know that they produced
quicklime to be subsequently slaked, to be used as land fertiliser or
lime mortar. We know that the kilns were charged with limestone and with
a fuel of wood, coke or coal. My puzzle was, what happened after the
couple of days of ignition. Inside the kiln would be quicklime and ash.
How was it separated? And once separated, what happened to the
quicklime? While the evidence of the kiln function is obvious, how and
where did the slaking take place (we are talking of several tons in each
batch)? It had to be slaked on the spot, being dangerous and
untransportable stuff. The slaking process takes several days to
complete. Was there an area set aside for iron pots to contain the
boiling reaction? I have seen no evidence of any special area. All of
the authorities I have consulted give comprehensive accounts of the
roasting but none of the equally important slaking.
Lime mortar is a material of importance to dialists. Although cement was
first produced in the nineteenth century it was not until as late as the
nineteen seventies that the superiority of lime mortar over cement for
stonework was fully realised. For repairs and pointing to stone dials
lime mortar, which is flexible, should always be preferred to cement.
(Cement is to be preferred for brickwork). The two mortars differ in
that cement mortar sets with water while (non-hydraulic) lime mortar
sets in air, taking several months to be fully finished.
Can anyone throw further light on this, please.
Frank 55N 1W
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