Lime by its nature needs to be built up
in layers to give it time to cure, this and the nature of the tools available to
plasterers of old, along with the imperfections inherent in rubble stone walls
gave the old plaster walls the character, the gentle subtle curves and
undulation typical of the time. In
new works today it�s most important to replicate this by utilising similar
methods, but without exaggerated contrived bumps so popular with the standard
tradesman unfamiliar with conservation work. As a result the cut stonework
is well defined; the bevelled edges clearly visible, the plasterwork
imperceptibly worked to give the finished wall a traditional look and feel.
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Right
well executeed
lime plastering job following the contours of the wall and leaving the bevelled
edges of the quoins stones correctly visible.
left, a technically correct lime
plaster but executed by a non conservation experienced plasterer, the emphasis
on a flat surface guided by a straight edger, this has resulted in the covering
of the bevelled edges of the quoin stone.
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Pointed cut stone quoins
left a standard strap pointing
covering the stonework.
Right the correct pointing method,
fills the joint only and leaves the stone bevelled edge fully visible. |
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EXAMPLES OF LIME PLASTER FINISHES
External Finish, Wetdash (roughcast or harling)
This would be the most common vernacular
finish, consists of small aggregate 3-6mm, rounded stones naturally
occurring like those from a river bed or glacial gravel
deposits. This is also the most efficient with
respect to the performance of lime with its ability to wick away moister from
the wall as it provides a greater surface area for evaporation.
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Often there is confusion with this type of finish as people are familiar
with what appears on most old buildings to be a smooth undulating finish with no
evidence of the aggregate. This is
due to years of frequent lime washing which has formed a multi
layered film over the render.
With experienced tradesmen familiar with conservation lime plastering,
with the correct application of the plaster in multiple layers, then hand
trowelled without the use of strait edger's creates a naturally but gently
undulating surface that reflects a little of the underlying stonework. Over
emphasis on levelling the plaster surface results in modern looking finish of a
concrete block building, it also shows problems where there are features such as
cut stone quoin or string courses on the wall when the
strait surface protrudes over the stonework, hiding details such as bevelled
corners etc.
Likewise the attempt to deliberately make
surface uneven by creating bumps, lumps and a bad finish results in a contrived
finish that despite the practitioners efforts to make it look "oldie worldy"
actually bears no resemblance to any real historical finishes, only to that of a
the London Irish pub or Disney world. In fact the correct "imperfect" finish is
largely only visible close up, looking along the surface of the wall, its effect
on the building is considerable, but from a distance but not necessarily
noticeable uneven to the average passer-by.
Another common mistake is window reveals, where the accepted method is
the creation of a "sticky out bit", patent reveal. This is again a strictly modern detail
and has no place in conservation finishes.
Plaster formed Plinths would be another inappropriate detail common in
modern buildings but not in old ones. See below centre
and right.
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External finish, sponge
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This is a more smooth finish whilst still
following the contours of the wall.
More common with large formal buildings and
in cities.
Left shown with "Ashlar" lines, replicating a fine
courced cut stone, known as Ashlar stone work.
On the right,
an old stone cottage with spomge finish.
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Here to the right is an
example of sponge finish on a modern building. |
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Internal finish, skim coat,
trowelled lime
skim coat finish
This finish is
suitable for most internal work except in perhaps the country cottage of
small farmhouse, its appearence would be similer to a modern gypsom skim
coat.
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Internal finish, sponge
This is a rougher finish, usually in a 3
or 5mm sand, whilst still following the contours of the wall, rounded
corners to window and door reveals. More common and suitable for small
country cottages.
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