We have developed a ground breaking fast setting air lime material without resorting to hydraulic chemical reaction. This is important because it enables this most ancient of materials to be used in a modern commercial world. The results of this use of air lime, over hydraulic lime, are improved performance of humidity control and effective drying of the building, thus significantly raising the insulation performance of the structure. The material is much softer and so much more flexible.
Lime has been used in mortars, plasters, renders and paints for centuries. It was continuously used in building work from pre - ancient history up until the 20th Century. It is only in the last 150 years with the development of modern cements and hydraulic limes that truly traditional lime products have started to be used less. However, those traditional Lime mortars, renders, plasters and lime washes have many properties that have encouraged a healthy resurgence in their everyday use but they only work if used properly and with the right aggregates: We know that using the right lime materials can help with and even eradicate the following problems;
Apart from the adverse effect it has on the environment in general, cement mortar is usually hard, brittle and less porous than lime mortar. It often contains additives to make it sometimes completely waterproof and is damaging to traditional buildings for several reasons. Cement mortar is often harder than old bricks, cob or some types of stone, therefore when movement occurs it may damage these softer traditional construction materials. Hard cement mortar can trap moisture behind it causing damage to the structure and encourages ground water to rise up a solid wall by capillary action many sand mortars “drink” in water and then have the tendency to stay wet and appear to trapping moisture behind. Capillary action is the tendency of a liquid to rise in narrow tubes or to be drawn into small openings such as those between grains of a rock.
Capillary action, also known as capillarity, is a result of the intermolecular attraction within the liquid and solid materials.
Capillarity in mortars is greatly reduced by the use of softer, porous materials. Equally, capillarity is greatly increased by the use hard impervious sharp sands in a mortar and even more especially when those sands have been washed, which is why we use neither.
Trapped water in the wall will cause poor insulation, decay and eventual failure. The substrate can also be subject to frost damage if moisture levels are too high. Everything that has made cement a brilliant modern building tool (High strength, im-permeability, high speed high density) makes it completely inappropriate for the repair of old buildings.
A mixture of lime (calcium hydroxide) in water which is used for the production of lime plasters, renders, mortars, grouts and limewash. Lime putty is made by burning limestone at a temperature of about 780°C to make quicklime (calcium oxide) which is then 'slaked' with water. It is best matured for several months by storing it covered with a thin film of water. This is quicklime that has been slaked. Lime putty is sometimes also called non-hydraulic lime or 'fat lime' and increasingly commonly – air lime.
It is the process of hydrating quick lime. Quick lime is added to water and a chemical reaction occurs resulting in the release of a large amount of heat from the quick lime creating a boiling liquid. The liquid is drained off through a sieve into a settling tank. Chemically the calcium oxide is converted into calcium hydroxide.
These are mixes of lime and aggregate, (we limit the use sand as our aggregate) used for building, pointing, rendering and plastering. The mix for mortar is anything from 2 to 3.5 parts aggregate to one part lime by volume.
We have strong views on the types of materials we use for our work. We are against using sharp washed sands (especially silicates) in our work and feel they have no place in a lime mortar that purports to be replicating one found in traditional buildings. Old mortars from any building prior to the end of the 18th century contain little or no sand of this sort. Any sands found in those materials are heavily balanced with other ‘fine stuffs’ and air lime putty. It is now our contention that those sands occurring in those old mixes were there as a result of the aggregates used for their other constituent materials or local availability and not for the sand alone. We go further; attempts would have been made to minimise the sand (especially silicate) content as impervious hard materials of this nature degrade the lime mortar over time and therefore poor performance is experienced.
If lime is being used because technically it performs as a soft porous material that allows a building to breath, why then should one use a hard impervious silica aggregate suspended in that soft water-soluble material? Over time the lime degrades in that harsh environment and therefore requires other ingredients to help it last. Without that help, lime is the only porous element of the mortar and the only binder. As already stated, lime is soluble and will therefore leaves behind sand without binder, allowing it to fail. This is a reason for modern lime mortar failure. Another is an alkaline reaction with silica. The silica sand degrades in contact with lime – making the particles smaller within the mortar, thus leaving it weak and vulnerable to decay.
For the reasons as previously described. In our view, if we choose to revert back to a traditional binder, we must also revert back to the types of aggregate traditionally used with that binder. We cannot do one without the other. Modern washed sharp sands were developed with the advent of modern stronger binders in order to create stronger mortars – ergo were damaging to the building, with all the problems previously described. Historic mortars were developed over thousands of years to perform in specific ways. These performance characteristics are only achievable if we also use the correct aggregates.