Devon and Cornwall Property Developers/General Builders
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Specialist Products
LIME PUTTY OR NON-HYDRAULIC LIME
Quicklime is the raw material in the production of lime putty. When added to water a chemical reaction occurs and this is known as slaking. After the mixture has been sieved and left to mature for a minimum of 3 months the liquid slaked lime thickens to a creamy consistence similar to toothpaste. This mixture is called lime putty and is pure white in colour. Non-hydraulic lime is slower setting and is especially good for internal plasterwork and for use with cob.
Carbonation
Lime putty products harden after absorbing Carbon Dioxide through exposure to air and revert back to calcium carbonate. This is known as carbonation.
Lime Wash
Lime wash is made by diluting lime putty with water to create a wash. Coloured pigments can be added to a diluted lime putty (diluted with water) to create a natural. lime wash.
Lime Haired Plaster
By adding hair to plaster greater strength is achieved. Today we normally use goat hair but through the years many people have used horse hair. This is usually used when plastering onto solid walls and also ceiling laths and walled laths.
Mortar
Various mortars can be produced when sand is mixed with lime putty. Generally coarse sand is mixed with lime putty to produce a mortar suitable for rendering and pointing however grit sand is not uncommon when being used with certain types of stone work construction. When applying a base coat to a wall it may be applied as a scratch coat using coarse sand and the second or top coat can be applied as a FINE SKIM using a finer grade sand. Varying grades of finish can be achieved depending upon the grade of sand used.
Finish coat
NATURAL HYDRAULIC LIME (NHL) OR HYDRAULIC LIME
Natural Hydraulic Lime (NHL) is produced from argillaceous limestone deposits which is found in quarries in Italy, France and England. This limestone contains clay and/or other silica impurities. Calcium silicates and aluminates form in the presence of water as well as calcium carbonate occurring from carbonation which results in a harder set being obtained despite the limestone being burnt and slaked. Because this can be set under water the term hydraulic is used.
Patio walling built using Natural Hydraulic Lime (NHL) with natural slate paving
The hydraulic lime is available in varying strengths depending upon the type of application that it is being used for. These strengths are termed as NHL 2 which is feebly hydraulic, NHL 3.5 which is moderately hudraulic and NHL 5 being eminently hydraulic. Whilst NHL 5 is the stronger of the three types it is less permeable and has the least amount of flexibility. This could be used in applications such as masonry below water level. chimneys, earth retaining walls or even high level weather exposed stone work or cappings. NHL 3.5 can be used in areas such as walls close to ground level, lintels and cornices, as with NHL 5 it has excellent resistance to sulphates found in ground waters and masonry. At the lower end of the scale NHL 2 which is the weakest of the hydraulic limes tends to be used where time is not of the essence and where greater flexibility is required. NHL 2 is more likely to be used with weak or porous surfaces and with plaster work This weaker mortar will allow for greater flexibility between the mortar and the original surface. If cracking does occur there should be less risk of damp penetration because the cracks will more than likely only appear as hairline cracks. Because of the low shrinkage and flexibility the cracks should heal through the carbonation process and keep out any unwanted moisture.
Natural hydraulic lime can have additions mixed with iit such as metakaolin which will increase the mortar strength or lime putty which will increase the plastic properties. Crushed brick or fired clay and ground blast furnace slag can also be added as well as natural ground pigments to vary the colour if desired. Care should always be taken when introducing additives and it is therefore recommended that sample mizes are made in order to verify the required strength.
Hydrated Lime
This product is often used by general builders by adding it to a standard cement based mixture. It is not hydraulic and comes in the form of a dry powder. It is often used to give a certain amount of flexibility to a mortar but it does not share the same qualities as a lime putty.
Daub
Riven and Sawn Lath
Cob Blocks
Epoxy Resin and Stainless Steel Fixings
When repairing old stonework or cob on older buildings it may be necessary to use some modern day products. This may include stainless steel fixings such as helical ties and threaded bars. Helical ties are driven into cob and stone walls with the use of a special tool attached to a drill. In certain cases where the stonework needs to be repaired without removal or where stonework is being toothed epoxy resin can be used as a bonding agent. The epoxy resin is grey in colour and is a stress free chemical anchoring system. It is generally a two component resin which when pressed through a mixing nozzle begins a quick setting process. This is used instead of a standard mortar based product. Threaded bars and ties can be set in cob or stonework using the epoxy resin and left to set. Once set, stone or other building material can be fed onto the threaded bar and stainless steel washers and nuts can be introduced at the other end and tightened off. This resin can also be used in other applications such as the repair of clay flue liners and chimney pots.
EXAMPLE OF A COLLAPSED CHIMNEY REBUILT ON A LISTED PROPERTY USING LIME PRODUCTS AND PERMO-TRIASIC STONE
Stoodleigh, Tiverton, Devon
