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Preparation:
Any existing defective pointing must be raked out to a depth usually equal
to twice the width of the joint, but not less than 20mm. The back of the
joint should be roughly square in profile. Plugging chisels ensure that
the stone or bricks aren't forced apart.
Damping:
The joints must be dampened, with enough time left for the stone or brick
faces to dry to prevent smearing. The mortar should be as dry as it is
practicable to point with. This allows maximum compaction in the joint,
reduces shrinkage cracking and reduces the tendency to smear on the stone
faces.
Premixing:
All lime putty mortars benefit from being pre-mixed for a minimum of a
couple of weeks and then "knocked up" (aggitated/mixed) again prior to
use to plasticise them - this reduces shrinkage in the mortar.
Gauging:
We suggest a 3/1
mix of coarse sharp well graded sand to mature lime putty internally and
a 3.5/1
mix externally where a pozzolan
is to be added. In damp, frost prone or very exposed situations it may
be appropriate to add the pozzolan
to a lime putty mortar to increase its compressive strength and frost
resistance. It won't give an overnight set but will slowly begin to add
a little extra compressive strength to the mortar after a few days. Alternatively
a weak NHL mortar may be used.
Pointing:
Start at the top of a wall to allow for cleaning up and spraying to continue.
Use a pointing key or metal spatula and force the mortar in from a hawk.
Joints deeper than 20mm will need an initial dubbing out as shrinkage
can occur otherwise. Finish flush or rebate a little if the joints have
widened with age or for personal preference as rebating highlights the
stone more.
Brushing:
When the mortar is "green hard" (firm enough to brush without smearing
but still maliable enough to work), brush or tamp the joints with a churn
brush to enhance the aggregate and give a coarser texture to the pointing.
Protection:
External pointing should be mist sprayed to control drying and protected
from direct sun and wind. In winter it should be protected from rain and
frost. Hessian cloth is recommended.
Quantities:
20kg of lime putty mortar will point 2-3 square metres of average sized
stonework or 1- 1.5 square metres of brickwork based on a 10mm joint and
20mm depth.
Safety:
Limes are caustic. Always wear eye protection and protective gloves and
clothing and follow the safety instructions on the labels. Our advice
and information are given in good faith. It's important that users satisfy
themselves that they've chosen an appropriate product and have a suitably
skilled workforce.
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