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Taylor Publishing
Presents:
Three Coat Lime Plaster on Riven
Lathe
by Bob Bennett
Photo
courtesy Patrick Macafee's Irish Stone Walls website at
http://homepage.tinet.ie/macafee/#irishs
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Taylor Publishing note: This article describes using a premade lime putty
mix product not available in the US. But, the basic information can be
followed if you make your own lime putty, use coarse and fine sand, and
use animal hair as described.
Animal hair is usually goat hair, or
body hair ( not maine or tail) from horse or cow. Coarse sand is 3mm
particles, finer sand is 1mm or less and fines are tiny particles. Sharp
sand means each grain is jagged, not rounded like beach sand
particles.
- Repair any damaged laths.
- Pre-wet the laths with mist spray clean cold water before starting to
spread the scratch coat.
- The ready mixed scratch coat is marked 125LS as is made up from one
part mature slaked lime putty and 2 parts well graded sharp sand 3mm
through to fines. The tubs are marked Coarse Stuff.
Remove the lid from the tub of ready mixed plaster and you will find a
small amount of surface water. Mix this back into the plaster before
emptying the entire contents of the tub onto a board and run a shovel
through to ensure thorough mixing.
- Sufficient animal hair for each tub is supplied in a separate plastic
bag. Add one bag of hair to one tub of plaster. (We spread the plaster
about 100mm thick on a board and sprinkle one third of the hair evenly
over the surface. Mix the plaster back together, roll out flat again and
add the second third of the hair. Mix thoroughly and repeat with the last
of the hair).
- Spread the plaster onto the pre-wetted laths at about 10mm, rule off
and leave. Do not attempt to work the plaster at this stage as it will
only stick to the trowel.
- Keep an eye on the plaster and, after about three hours (longer on a
cold or wet day), the surface will start to take a slight crust and can
be worked if required. At this stage we just scratch the surface, being
careful not to run in the same direction as the line of the laths.
Leave the first coat for about four or five days, depending on the
weather, before applying the intermediate coat.
- Follow the same procedure for emptying the tubs of Coarse Stuff as
with the scratch coat but this time no hair is added. Spread at about 7mm
and, once again, scratch and leave until ready to take the finishing
coat.
- The finishing coat is marked 12K and Fine Stuff. It is prepared from
one part mature slaked lime putty and two parts of a well graded sharp
sand, ranging from 1mm through to fines.
Remove the lid, mix any surface water back in before emptying the entire
contents of the tub on to a board and running a shovel through to ensure
a good mix.
- Mist spray the surface of the intermediate coat with clean cold
water. Allow time for the water to be absorbed and spread the plaster
about 5mm thick. Rule off as before and leave for at least a couple of
hours. When ready, rub up with a plastic or wooden trowel to get the fat
back (no need to spray water on the surface). Trowel to the required
finish. Under certain conditions you may experience slight crazing of
this last coat after a further few hours in which case it can be rubbed
up again and trowelled out.
- The ideal finish for lime plaster is limewash, which is available in
plain white or to any pastel shade of your choice. (See the Limewash
article link at the top of this page for more information on washes.)
Bob Bennett's articles can be downloaded from:
The Lime Centre
visit their website at
www.thelimecentre.co.uk/index.html
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