FANTASTIC NEW MULTI-PURPOSE BUILDING MATERIAL

 DISCOVERED

A building material that can be used as a paint, in harling, as a mortar for stone walls, in plaster and can even improve your garden is being rediscovered near Charleston, Dunfermline. This material is considerably cheaper than conventional masonry paint and compares favourably with portland cement in price. What is this new material called? LIME. Yes, LIME. All right, so it is not new, but its proper use has been all but forgotten. We have the Scottish Lime Centre to thank for its return to favour.

Techniques of converting limestone to calcium hydroxide (hydrated lime or lime putty) for the construction and finishing of buildings have been known for around 6,000 years. The Romans were probably the most skilled at working with lime. To produce lime for building (and other purposes) limestone is heated to 900 C, driving off carbon dioxide to leave calcium oxide or quicklime. The quicklime is converted to calcium hydroxide (hydrated lime or lime putty) by the addition of water. This is called slaking.

LIME PUTTY

Lime putty is a white clay-like material that is used to make lime mortars and lime washes. It can be bought in large buckets from good builders suppliers.

 Wall With Lime Mortar Wall With Cement Mortar

 Sandstone

Soft lime mortar: moisture can not collect

Damage occuring when moisture concentrates on top of the mortar containing portland cement pointing

Frost fracture

A common mistake is to buy dry powdered hydrate (builders lime). This material is useless and should only be used as a garden conditioner, to soften cement mortars and to whitewash the inside of stables.

 If you are involved in a large project it is cheaper to make your own lime putty by slaking quicklime. BUT NEVER SLAKE QUICKLIME UNLESS YOU ARE TRAINED AND ARE WEARING THE PROPER SAFETY CLOTHES AND GOGGLES. Quicklime is very caustic and will get very hot, damaging and burning your skin and eyes. Quicklime must always be added to water never the other way round.

LIME WASH

Lime wash is lime putty well mixed with water and pigments to a skimmed milk consistency, sieved, and left for up to 3 months to cure. Fat (tallow) is added during slaking if the wall is exposed to rain.

 The lime wash is well worked in two or more coats on to a damp surface in frost free conditions.

LIME WASH VERSUS PAINT

 1. Lime wash is a bit of effort. 2. Lime wash has a light-reflecting property not found in in paint and provides a more subtle colour and finish. 3. Lime wash does not peel off the wall as water cannot become trapped behind a porous surface. 4. Lime wash inhibits the growth of unsightly algae and lichens. 5. Lime wash is cheaper than paint.

 LIME MORTAR

A considerable number of sandstone buildings in Kinross-shire have been damaged, in particular the buildings constructed with red sandstone. The damage occurs when the original pointing is replaced with a mortar containing portland cement.

 Mortar containing portland cement is stronger than sandstone and less porous.

 The damage occurs in the winter when moisture concentrates on top of the pointing and saturates the sandstone which fractures in frosty weather (for example the wall below).

Lime mortar is a mix of lime putty and damp aggregate normally at a 1 to 3 mix, well beaten together (knocked up) for one hour and left for 3 months. A good mix can be achieved when the lime putty is still hot from slaking.

HARLING AND RENDERING Until the late 19th century many Scottish buildings were protected by an external cover of a coarse lime mortar (harling) and lime wash. Removal because of the current fashion for exposed rubble walls or loss of this protection has contributed to many problems.

The use of cement-based harling roughcast or render prevents evaporation of moisture from within the building's fabric and contributes to problems of rot, condensation and the likelihood of the harling becoming detached from the wall.

Lime work should only be done by a craftsman with experience in working with lime and no lime work should be carried out after mid October unless full frost and rain protection can be guaranteed for the whole winter.

Traditional mortars and equipment can be obtained from;

Masons Mortar, 61-67 Trafalgar Lane, Edinburgh EH6 4DQ and advice. Material analysis and evaluation and practical training avalable from the SLC Trust, PO Box 251, Edinburgh EH6 4DW

Tel 0131 553 4999. RHWM

 Anyone wishing to know more about pointing and masonry consolidation, harling, rendering and plastering or limewash, is strongly advised to get in touch with the Scottish Lime Centre, Telephone 0131-553-4999