By James Ayres, co-founder and operations director at Lime Green
After WW2 destroyed much of our built environment, Britain needed buildings quickly and, on a ‘needs must’ basis. As such, demand for cement soared as it presented a cheaper, faster and easier solution than lime.
Today, construction isn’t about ‘needs must’. It’s about carefully choosing the best materials which enhance the health of the building’s occupants and its environment.
Lime materials are now just as affordable, quick and easy to use as cementitious products which lack lime’s breathability and associated health benefits.
In fact, the UK construction industry is moving to favour healthy building materials so the use of lime in building has seen a significant revival.
But how are lime materials formed? What makes them different? How do you choose?
Mortars, renders and plasters
Most mortars, renders and plasters are formed of:
- A sand or aggregate – which makes up the bulk of the material’s overall volume, acting to prevent any shrinkage as the material dries out. The sand is also a key ingredient for the mortar or plaster’s strength, durability and aesthetic appearance.
- A binder – which acts to hold the materials together. This can be a variety of materials such as clay, cement, silicone or acrylic. But for a long time, the material of choice was lime.
Lime mortars, lime renders and lime plasters
The three primary ingredients in any lime mix are lime, water and sand. Once mixed and set, these materials will form a substance similar to man-made limestone.
This limestone is then heated in a lime kiln to form quicklime, to which water is added to produce slaked lime.
After this stage, different types of limes set in different ways:
- Non-hydraulic limes
Non-hydraulic limes set by absorbing CO2 from their environment. They set much slower than hydraulic limes as this CO2 absorption depends on a number of specific environmental conditions.
- Hydraulic limes
Hydraulic limes initially set by reacting with water – they’re even able to set underwater – further hardening occurs over time as the lime absorbs CO2. Although made in the same way, hydraulic limes are burnt from a different limestone than non-hydraulic limes.
How to decide if lime’s right for your project
Some long-established benefits of lime, such as its natural antiseptic properties, are well-known but there are many other positives to working with lime:
Lime materials are highly breathable as they are vapour-permeable, meaning they allow water, as either a vapour or a liquid, to pass through. This avoids the build-up of trapped moisture which can increase the risk of damp, mould or condensation.
As lime keeps its underlying structures dry, it promotes a more durable and sustainable building structure. One example of how lime has stood the test of time is Blenheim Palace, which was built using lime materials.
Lime has very good workability which makes it very easy to use. This is important to achieve the desired aesthetics of the applied product.
- Beautiful aesthetics
Lime can be produced in a whole range of colours meaning it can be personalised to suit your project. It also avoids the synthetic appearance given by many of its alternatives.
Despite the myriad benefits of lime, there are, of course, certain limitations to its use:
- Slower setting
Some limes can require a more methodical working practice than others as certain mixes take longer to set.
- Complex or confusing terminology
Sometimes, so-called ‘limes’ aren’t always what they appear to be and it’s not always clear exactly what they contain. Make sure you’re taking extra care to prevent paying more for a product which is simply white cement.
- Fear of use
Some builders are wary of switching to lime, branding it ‘too difficult’ to use. However, lime isn’t necessarily harder to use than its alternatives, it’s simply different – and it’s more straightforward than you’d think.
Tips for DIY application of lime
- Decide on your style and finish
Before you begin anything, decide how you want the end result to look – this will ensure you choose the right product, producing a beautiful project result.
- Pick the right product for your project
Hydraulic or non-hydraulic? How exposed will the product be to the external environment? This may help: www.lime-green.co.uk/knowledgebase/hydraulic_or_hydrated_lime
Follow instructions carefully, introducing water gradually and slowly. Machine mixers – both paddle and drum – give a better consistency than mixing by hand. Allow time for it to mix thoroughly to a nice, spreadable and workable consistency.