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Bleaklow Industries
Lime mortar mix lime putty premix lime mortars
A leading UK producer of non-hydraulic, high
quality, matured slaked lime putty and premixed lime mortars.
Bleaklow have over 25 years' specialist experience in lime products
for applications in industry, construction, agriculture and
conservation.
A flexible high volume production facility and large stocks of
slaked lime putty and pre mixed mortars are constantly maintained.
History of Lime Mortar & Lime Putty
Unlike modern buildings, which tend to rely on impervious materials
or double skins to keep out moisture, those constructed before the
mid 19th Century (later in some areas) rely on allowing the
moisture, to evaporate from the surface. Lime based mortars and
renders are vapour permeable, they allow the building to breathe and
so manage moisture transfer naturally. The walling materials of old
buildings in Britain are usually stone, brick, timber and earth.
They are all, to a greater or lesser extent, absorbent. Mortars are
usually lime/sand for brickwork and lime/sand/ aggregate for laying
stone. Lime based mortars have a number of unique qualities. They
resist the suction of the dry building materials of the construction
for longer, after being laid, than other mortars. This reduces
shrinkage and maintains greater contact. The durable bonds thus
formed provide permanent, weather-proof, frost-resistant joints.
These are now acknowledged to resist rain penetration more
effectively than with other types of mortar. Movement and
temperature/moisture cycling tends to produce cracking in all kinds
of mortar and render but lime mortar by absorbing moisture and air
allows small cracks to be closed as carbonisation occurs in the
newly exposed lime. No other mortar has this ability.
Benefits of Premix Lime Mortars
As the original mortars were more permeable than the materials they
bonded, moisture in the walls was transported out through the
mortar. However, where cement rich pointing has been substituted,
not only does the whole wall become less able to 'breathe' out
moisture, but the mortar is often less permeable than the bonded
materials. Moisture transport now occurs through the stone or brick
where frost action and salt deposition can cause spalling of the
masonry. Whilst gradual erosion of a building's fabric is inevitable
with the passage of time, the use of softer lime based mortars not
only minimises moisture build-up but can also act as the sacrificial
and most easily replaceable element of the structure.
External rendering was also usually lime based and to further
facilitate moisture transport out of the walls a rough texture was
used which maximises the surface area for evaporation. Walls were
decorated, internally and externally, almost exclusively with lime
wash which can be tinted with natural pigments.
Limewash is again highly porous being the final coat in a totally
breathable system, as opposed to modern emulsion paints which, in
effect, lock up the walls in a plastic film.
Why use a mortar that is weak, flexible and vapour permeable?
Because that was, and still should be, the method of construction in
traditional buildings. A single, solid, thick wall standing on very
shallow, often rudimentary foundations is bound to move as it and
the ground it stands on expand and contract in response to
variations in humidity and temperature throughout the year. Thus,
the mortar and render must not only allow movement but also allow
the moisture, which inevitably will enter through the minute cracks
generated, to exit the structure.
Lime mortars and renders have been rediscovered as perfect for this
purpose. The modern obsession with cube tests and crushing strengths
is a product of a totally different mode of building. While strong
mortars are absolutely essential in post-war construction with their
deep concrete foundations, damp courses and double skin walls, extra
strength in old buildings, except in very exposed positions
(copings, chimneys etc.) is actually detrimental.
Traditionally, in Britain, the first job on a building site,
especially an important one like a church or cathedral, was to dig a
pit in which the lime was slaked so the resultant putty would have
time to mature. This makes it very unlikely that the limes used were
hydraulic, since by definition, they set under water. Today it is
impossible with a dry powdered product, either hydrate or hydraulic,
to attain the same plasticity which gives a proper lime putty its
fantastic bonding ability. Even if the original mortar contained
added strength, the structure has, by now, been exposed to the
process of decay and can be seriously weakened. If a replacement
mortar or render is stronger than the actual fabric of the building
then vapour transfer and its attendant damage will eventually start
to break down the brick or stone.
Choosing Mixes for Lime Mortar, Render &
Limewash
Remember pure lime/sand is the softest and most permeable, cement
based the hardest and least permeable. It is a question of choosing
the most appropriate technology. The suggestions that follow are
only for guidance, but have been used successfully in locations in
Britain.
* Internal limewash preparation
Matured slaked lime putty should be diluted with clean water in a
bucket or other robust container until the consistency of thin cream
is achieved. Where pigment is to be used it should first be mixed
with clean hot water and thoroughly slurried as this will help it
mix more easily in to the bulk of the limewash.
* External limewash preparation
Follow the instructions for mixing internal limewash. Then to
improve the external weathering characteristics raw Linseed oil can
be whisked in to the mixture at the rate of approximately 5ml per
1litre of limewash. Limewashes should normally be carefully sieved
before use however this is unnecessary with Bleaklow Matured Slaked
Lime Putty which is free of any grit or lumps.
Request information Bleaklow Industries Lime
mortar mix lime putty premix lime mortars
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Email this company
Bleaklow Industries Ltd
Hassop Avenue
Hassop
Bakewell
Derbyshire
DE45 1NS
Tel: 01246 582284
Fax: 01246 583192
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