Working with lime

W o r k i n g  w i t h  l i m e ,  t h e  V i v u s  w a y

Lime and its use, is a huge subject and something the retrofit and conservation industry has studied and contemplated for a long while. There are numerous different products available, all of which have both positive and negative qualities. Vivus Solutions Ltd believe we have found a way to waylay some of the negatives and deliver a material that provides ease of use, cost savings on site, a setting speed that is more conducive to modern living but ultimately a product that is suitable for all types of buildings, that is sustainable and most importantly provides the inhabitants of the properties with a healthy environment in which to live.

The information on our website is gleaned out of 30 years of working with lime and buildings and aims to give the reader a comprehensive view on our materials, how to use them and why lime is such an important building material.

All lime, including ‘Air Lime’, ’Natural Hydraulic Lime’, ‘Hydraulic lime’ and ‘Cement’ is produced by burning and slaking of limestone (see FAQ for slaking explanation). 
Air lime is a pure clean limestone when it is quarried, then burnt @ 782o and slaked with water to make quick lime/air lime hydrate.

Natural Hydraulic lime differs and is quarried with a proportion of impurity being silica and trace elements. It is the silica and trace elements that when burnt @1200o [1/3 more energy required over air lime burning], become reactive with water and will cause the hydraulic set of the mortar when mixed with that water into a working mix. ‘Cement’ is created by the deliberate and accurate addition of these admixtures to an exact recipe at the burning stage, rather than being found naturally occurring in the limestone - hence ‘natural hydraulic lime’ rather than ‘Hydraulic Lime’ or ‘Cement’. ‘Hydraulic Lime’ is simply anything that has not been made to the exact recognised recipe for the term cement but has a set as a chemical reaction with the addition of water - hence the term ‘hydraulic’. Up until the early 1980s, cement was often called ‘hydraulic cement’.

It is the hydraulic reaction that makes the mortar set faster and harder - in many instances the material becomes too brittle and ‘cement-like’ over time. The cause of this increase in ‘hardness’ is the longer term carbonation of the lime, in addition to the initial hydraulic set.

Carbonation is the intake of atmospheric Co2 and the final completion of the lime cycle (chemical process) which started with Calcium Carbonate (limestone) became Calcium Oxide with the burning process, became Calcium Hydroxide with the slaking process and thence Calcium Carbonate again with the final carbonation - post use.

Air lime only has carbonation in order to achieve it’s final set. It does not have a hydraulic element in its initial set and therefore retains a level of softness and flexibility not found with any hydraulic setting material. It is this very nature that makes ‘Air Lime’ most suitable for building works and especially older buildings. In more recent years, the only method of using ‘air-lime’ was in the form of a wet putty. This is achieved by the ‘over-hydration’ of the quick lime which takes the dry powder beyond 100% hydration and therefore the material stays wet in the form of a putty. ‘Lime Putty’.

Lime Putty/Air lime can be tricky to use but is widely recognised as the correct version of lime when properly dealing with historic structures and modern sustainable building projects [due to the levels of Co2 absorption and embodied energy]. Lime putty requires maturing for many months [the longer the better] in its wet state. This maturing improves the mortars beyond recognition from younger materials. The skill, knowledge and timescales of storage and site use have rendered Air lime, in form of Putty, realistically unusable in the general building industry and has given the opportunity of the lime-use resurgence of the past 30 years to the hydraulic lime materials.

Pre- late 18th Century to mid/late 19th Century [approximately, as there is no exact date - more a gradual change] all lime used in buildings was Air lime and that history reaches back over 6000 years, with a brief use of hydraulic setting limes by the Romans [not used exclusively and only in certain applications] for approximately 200 years, where it’s use died out until it was rediscovered again around the end of the 18th Century. It’s use will surely die out again and again in around the 200 year mark.

U s i n g  L i m e

Health and Safety - Please see the COSHH document for full details. Air Lime, by its nature carries a risk factor and therefore you should wear protective equipment, particular attention should be given to eye and skin protection. Gloves, googles and or a mask should be worn when working with any lime materials. Eyewash also should always be on hand. Vivus is a dry powder and therefore, as with any other powder materials, such as Hydraulic lime and cement or gypsum plasters, nuisance dust masks should also be worn.

M i x i n g

At Vivus Solutions, in our own works, we use plaster whisks and buckets as the principle method of mixing. We employ this method for any work using the Vivus material. We even use it when render pumps are being used and a single man mixing and loading can easily keep up with the machine, which is covering [circa] 100 m per day base coat render.

It is vital to ensure that when measuring materials and water, this is done by volume. A gauging box or bucket for the water will be necessary for this task. Measuring by shovel is not acceptable as quantities will be inconsistent.

It is also perfectly acceptable to mix with any other form of mixing machine, such as paddle pan, forced action, drum or roller pan [with all weight/crushing action turned to minimum]. It is still however imperative to use a gauging box and water bucket in order to maintain consistency of material.

The water content will depend on the application of the material, some operations, such as pointing require a stiffer mix than for rendering with a pump. Vivus is not adversely affected by water content variation in the longer term ability of the material to survive.

Always put the amount of water into the mixing bucket [for whisking] first.

Add the desired amount of Vivus to achieve the workability required and for continued matching mixes measured quantities is essential.

Only mix what can be easily used straight away. The set speed will depend on the type of Vivus material being used. Casting mix, like plaster of Paris, will set in 10 -15 minutes of mixing with water and renders or building mixes will be stiffening in around 1/2 an hour to an hour. This will also depend on amounts of water and it’s intended purpose and workability.