Bleaklow Industries Ltd
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
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.
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 MORTAR, RENDER AND 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.

Bleaklow Industries Ltd
Hassop Avenue
Hassop
Bakewell
Derbyshire
DE45 1NS

Tel: 01246 582284
Fax: 01246 583192