Using lime in construction is not as confusing or difficult as you may think, in fact, it can outperform many modern materials it just seems to have fallen out of fashion. The time is right to refocus on the amazing benefits and versatility of one of our oldest building materials, its time to look again at lime in building.
At Ecomerchant we are always looking for ways to make life easier while at the same time improving building performance and minimising the impact on our environment. How we have developed our range of lime products is a good example.
We found that we were regularly asked for help and guidance on choosing what to use for some of the most typical and straightforward applications simply because customers found all the terminology and possible variations confusing; in many instances they were faced with mixing components in various ratios to end up with a useable products, the end result is that many of our customers found the use of lime in building confusing this meant that use was restricted to conservation and heritage applications and use elsewhere was largely the preserve of highly skilled specialists.
We realised that almost all areas where lime products can be used, plasters, mortars and renders can be achieved with just a handful of well-designed quality products and applied with established construction skills. Good plasterers can apply lime as well as gypsum and the same applies to rendering, bricklaying and repairs and so on, the secret was to create consistent quality products where the only thing you need to add is water.
This is exactly how we and our suppliers arrived at our range of products. We worked together to offer technical performance products that are simple to understand and easy to use. They all benefit from the reduced levels of embodied energy and lighter environmental impact over cementitious or gypsum products, but importantly, they also match the performance and eco requirements now being established through modern methods of construction. They are breathable, long lasting, low polluting, easy to use and attractive products. The list of benefits is surprisingly wide-ranging, there is a list at the end of this article.
At Ecomerchant we have selected all of the most common applications and provide, sometimes a single product, to meet that demand. We are proud to describe them as easy to use, general purpose, versatile, and straightforward because we know they are the result of a great deal of technical research and refinement. With this comes a guarantee of consistency uncommon with previous self-mix application except with very experienced blenders and applicators.
We have also made our descriptions fit the product, simple clear precise and easy to understand so you should always be able to find the product you need for the job you have, and even better you can buy online or over the phone for delivery direct from stock.
Some background on the use of Lime in building
Blended lime mortars, plasters and putty’s dry by suction and evaporation and then they carbonate. This is the oldest, most flexible and breathable form of lime used in construction.
Lime is a traditional building material that is strong, flexible and permeable. Buildings built using lime mortar can move and absorb moisture, in comparison cement mortar is rigid and inflexible. When using lime mortar expansion joints can be avoided. Likewise, the imperviousness of cement mortar prevents it from absorbing water from the structure whereas lime mortar acts as a kind of ‘wick’, absorbing the moisture and allowing it to evaporate. By absorbing moisture, lime mortar is keeping the masonry dryer and lessening the risk of spalling
Up to the 20th Century building techniques and materials were very different from those employed today. Most buildings were constructed from masonry, brick or cob and were designed to breathe, absorbing moisture then releasing it back again this is particularly important for any structure built without a damp proof course allowing it to evaporate. By absorbing moisture, lime mortar is keeping the masonry dryer and lessening the risk of spalling.
These older buildings needed a versatile and flexible compound to bond the building materials and to create renders and plasters lime was the most common and widely used element for these materials. Lime putty mortars were normally used for bedding and plastering, being a relatively soft mortar it is able to accommodate a certain amount of movement (without cracking) that comes with settlement and seasonal changes in ground conditions. By using lime mortars (which are porous) the building would allow moisture to evaporate, helping to keep a building free of dampness.
Lime is most often used in traditional buildings but modern lime renders and putties are now emerging as viable performance options over cement based products. This is especially true of construction methods that require the building to breathe. By being produced at lower temperatures than cement, lime mortar requires less energy, resulting in 20% less CO2 output. Lime putty absorbs CO2 in the curing process. Non-hydraulic lime absorbs nearly its own weight in CO2, hydraulic lime, around 75%. Lime mortar can be recycled, unlike cement. Bricks using lime mortar can be recycled, unlike the cement bonded equivalent which can only be used for hardcore. There are two basic types of lime: hydrated lime where an exact amount of water is added, creating a dry powder sold in bags and generally known as hydrated lime or lime hydrate. If more water is added (slaking) the end product is a colloidal gel, commonly sold in plastic tubs and known as lime putty.
Limestone’s which contain clay produce building limes known as hydraulic because they can set under water. The clay impurities contain silica and alumina which forms a more chemically complex and different product. The more clay impurity the faster the set and the harder the mortar. Modern lime products include spray applied renders and insulating renders, for example, the Ecomerchant Protect System and a wide range of products to meet most construction applications both new and retrofit. Ecomerchant can offer guidance and suitability for all applications. Needless to say, all necessary ancillaries are available for you to ensure a complete service.
The Romans discovered that adding volcanic ash from Pozzuoli to a lime putty mortar created a chemical set making the lime mortar hydraulic i.e. it enabled the mortar to set in the presence of water and allowed the Romans to build structures such as aqueducts. Substitute materials have long since been used instead of volcanic ash, hence any burnt clay that reacts with pure limes to create a hydraulic lime set is referred to as a Pozzolan (or Pozzolanic) after the original discovery. If the lime putty is kept moist and free from Pozzolans, it will last indefinitely and actually improve with age reducing wastage.
So the original hydraulic lime was, in fact, a combination of pure lime putty and a Pozzolan that can still be replicated and is usually used these days in the UK to render and point externally or internally on to walls that are inherently damp and require the chemical set.
Lime: THE BENEFITS
- 1. Lime allows buildings to breathe
In the search for architects and conservators for building materials sympathetic to traditional construction, lime was found to be one of the most important. One of the reasons lime binders are promoted by the Society for the Protection of Ancient Buildings for repairs is because they are vapour permeable and allow buildings to breathe. This reduces the risk of trapped moisture and consequent damage to the building fabric.
- Lime provides a comfortable environment
Porous and open-textured materials such as lime plasters, help to stabilize the internal humidity of a building by absorbing and releasing moisture. This makes for a more comfortable environment and reduces surface condensation and mould growth.
- The use of lime has ecological benefits
- Lime has less embodied energy than cement.
- Free lime absorbs carbon dioxide in the setting process of carbonation.
- It is possible to produce lime on a small scale.
- The gentle binding properties of lime enable full re-use of other materials.
- A very low proportion of quicklime will stabilize clay soils.
- Small quantities of lime can protect otherwise vulnerable, very low energy materials such as earth construction and straw bales.
- Lime binds gently with early adhesion
The fine particle size of lime, far smaller than cement, is linked to the root meaning of the word lime, which is ‘sticky material’. Due to the fine particle size, lime mixes penetrate minute voids in the background more deeply than other materials. They bind gently and the stickiness gives good adhesion to other surfaces.
- Lime mortar can protect adjacent materials
Lime mortars with a high free lime content are porous and permeable. These characteristics allow lime mortars to protect adjacent materials by handling moisture movements through the building fabric and protecting them from harmful salts. Adjacent materials frequently affected this way include timber and iron as well as stone and brick masonry.
- Lime renders can assist drying out by evaporation
Dense and impermeable renders can trap moisture within the building fabric. Trapped moisture is often the agent for various decay mechanisms. Dense renders used in conjunction with softer materials or on weaker backgrounds can cause serious problems by creating local stresses. High calcium lime renders allow evaporation and reduces the risk of trapped moisture and decay. In simple terms, the greater the extent of pure lime and permeability the better this is for the building. This needs to be balanced with durability, however, and some reduction in permeability may be necessary to obtain adequate weathering qualities, hence the advantage of feebly hydraulic limes for external use.
- Lime mixes have good workability
The ability of a mortar or plaster to remain smooth and mouldable, even against the suction it may experience from porous building materials, is termed workability. Good workability greatly assists good workmanship, helping to achieve full joints with good bonding to the other materials. This is what makes lime based mixes such a pleasure to use. The workability provided by the lime allows the inclusion of widely graded and sharp aggregates in the mix. These enhance both the performance and the aesthetic of the finished work.
- Lime binders can be durable and have stood the test of time
When used carefully, lime is exceptionally durable. Caesar’s Tower at Warwick Castle has stood the test of time for over 600 years, and many cathedrals have stood longer. An outstanding example is the Pantheon Temple in Rome which has a lime concrete dome spanning over 43 metres (142 feet). This has survived for nearly 2000 years.
- Lime finishes are beautiful
The double refraction of light through calcite crystals give a unique aesthetic combining a soft texture with a lustre that has a liveliness and delight of its own. The graceful softness apparent in lime based materials is a visual indication of their intrinsic permeability, workability and soft binding properties. They can rapidly develop a rich patina which has a glowing translucent quality.
- Lime contributes to a healthy environment
Lime is caustic and has been extensively used, often in the form of lime wash, for its disinfectant qualities. Lime is also used for water purification. Lime mortars, plasters, renders and lime wash have been used to create hygienic surfaces and improve comfort conditions within buildings for thousands of years.
- Self healing
The nature of ground conditions and the elements are such that all buildings are subject to varying degrees of movement over time. When buildings made with lime are subject to small movements they are more likely to develop many fine cracks than the individual large cracks which occur in stiffer cement-bound buildings. Water penetration can dissolve the ‘free’ lime and transport it. As the water evaporates this lime is deposited and begins to heal the cracks. This process is called autogenous, or self-healing.
- Free lime encourages the growth of calcite crystals
Calcite crystals are a different shape to those formed by the more complex compounds in hydraulic limes and cement. The crystals form in voids in lime-rich environments. The growth of calcite crystals adds strength over time and generally provides a more open and permeable material than the denser eminently hydraulic and OPC mixes with little or no free lime.
- Disfiguring by cement can be avoided by the use of lime
On-site, the temptation to use quick and easy solutions for short-term gain can lead to long-term problems. The attraction of using excess cement to be ‘safe’ is understandable if not desirable. The fact that it is plentiful, inexpensive and readily available adds to the problem. There is a high probability that over-strong and dense mixes that are not fit for purpose will be used in excess. The physical damage and unsightly aesthetic that results from this can be avoided by the use of lime. Typical symptoms resulting from the use of OPC materials for repair would be large variations in colour and texture meaning repairs are obvious rather than blended in, spalling, cracking and disintegration of the brick face, cracking and separation of the mortar and excessive local erosion around patch repairs.
- Indefinite shelf life
Non-hydraulic limes have an indefinite shelf life when stored without access to air, usually as a putty underwater or in sealed containers. In fact, the quality of the putty improves the longer it is stored.