Lime is a traditional building material that is strong, flexible and permeable. Buildings built using lime mortar can move and absorb moisture, in comparison to cement mortar which 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
At Ecomerchant we stock a wide range of high quality, easy to use lime plaster and lime mortar products, including bagged and premixed lime, lime putty and natural hydraulic lime. Here, we look into the history of lime plaster in construction from Roman times to modern construction as an integral eco-friendly material.
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Lime use in buildings
Up to the 20th century
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 design element is particularly important for any structure built without a damp proof course allowing it to evaporate. By absorbing moisture, lime mortar keeps the masonry drier and lessens 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.
Working on historic buildings today
If work is being undertaken to a historic structure, it is important to establish what sort of mortar was used in its original construction (or what sort of mortar predominates in the existing construction). The use of the wrong mortar can lead to deterioration of the masonry, and the properties of lime mortar and cement mortar make them incompatible and so they should not be used together.
Despite this, some poorly-informed contractors continue to use cement mortar on masonry that is better suited to lime mortar, leaving it at risk of long-term deterioration.
Modern lime renders and putties
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 and non-hydraulic lime absorbs nearly its own weight in CO2, and 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 hard-core.
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
- Hydraulic lime (limestones which contain clay and produce building limes that can be set underwater). 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 influence on UK lime putty
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 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
We are a leading supplier of lime plasters, mortars, putty and ancillaries in the UK and offer easy to use, efficient building materials that are eco-friendly. Our team are experts in all of our stock and we are happy to advise on the right lime for any job you’re working on from our range.
Get in touch and see how we can help you and your building project.