they broaden the application for building limes by enabling mortars and plasters to be used in harsher environments and in more extreme situations.
they gain strength overtime hence providing flexibility.
considered to be more environmentally friendly than cement as they are burnt at a lower temperature and uniquely reabsorb some of the carbon dioxide given off during burning as they cure/carbonate in/on the wall.
enable building components to be reclaimed and reused as they are 'softer' than cement.
these French hydraulic limes are at the stronger end of the scale (compared to the British hydraulic limes) - see Documentation and FAQs for further information.
What is the difference between the different types of lime?
A non-hydraulic lime or lime putty is made by slaking burnt lime in excess of water. It can then be mixed with aggregate to produce mortar/plaster. This type of lime is used in our premixed lime mortars/plasters which are supplied 'wet' and ready-to-use, they just need 'knocking-up' on site. These limes are slower to set and produce a softer mortar but their strength is good flexibility and excellent vapour-permeability.
Natural hydraulic limes are made from chalk or limestone containing clay impurities. They tend to have a faster and harder set than high calcium lime but they are less flexible and less vapour permable/breathable than non-hydraulic lime. They are available as a powder to be mixed on site with aggregates and water, or as a dry pre-mixed mortar (Glaster).
What type of lime should I use?
The type of lime that you use should always be softer than your building components i.e. stone or brick, this is really important for the longevity of the building (choosing the right strength will mean that the fabric will last longer!)
GENERALLY - internal or sheltered external (at the right time of year!) plastering, pointing and building work can be done using fat lime products, if you are working on an external, more exposed applications or working late in the year and through to the Spring, then a hydraulic lime is recommended. Please see 'Choosing a Lime' in Documentation.
Which hydraulic lime should I use?
We supply the only British hydraulic lime (Singleton Birch) which we prefer from a sustainability point of view, it is an off-white and gives a softer mortar/plaster.
We also supply the Castle Hydraulic Lime which is a purer white and gives a faster set and a stronger mortar/plaster.
Care must be taken to choose the right hydraulic lime (even within the same designation) according to its technical charateristics and the particular building application, there is concern that because the stronger hydraulic limes set quickly they are being used for applications where they are not appropriate in the same way that cement is not appropriate. See the technical sheets and application guides for the different products in Documentation.
If you are not familiar with the different hydraulic limes, it would be worth doing/getting your contractor to do sample panels as they behave and look differently or call 01874 611350 for more advice.
Should I add a little cement to my lime mortar to give it strength?
It is often thought that by adding a little cement to lime mortars, typically in the ratio 1:2:9 (cement : lime : sand), that a lime mix can be strengthened. While this may induce a quicker initial set, this may prevent proper carbonation of the lime and produce a weaker mix in the long-term and so it is not advisable!
If you wish to increase the speed of set, perhaps consider using a pozzolan in your mix (see separate entry) or using a stronger hydraulic lime.
Can I use ordinary building sand to make a lime mortar/plaster?
Lime mortars generally perform best with minimal shrinkage if made with a good quality, well graded, sharp sand. Different sands are available for different applications e.g. we have selected a wide range of sands specifically chosen and some blended to best suit your task, so plastering grade sands (different for base and top coats), building sands, pointing sands for different coloured mortars etc.
Marine sand tends to be too fine. Pit sands and not sea sands should be used as the salt residue in sea sands can cause reactions in lime products and we do not want to introduce salts into the building. For an environmentally-friendly alternative, see our glaster products made with recycled glass instead of sand. Call 01874 611350 for advice.
Can I use an ordinary drum mixer to mix lime mortars/plasters?
Yes but for larger quantities we would recommend using a forced-action, pan mixer or a mortar mill.
Where can I get hold of these mixers or mills?
We hire out and sell small 100 litre mixers and hire out mortar mills. We currently have a towable, diesel mill as well as a static for larger quantities. Alternatively, your local tool hire firm should have a large site mixer that would be adequate.
Why do I need to protect lime work?
Lime products need to carbonate (not just set) which they need to do by absorbing Carbon Dioxide in the presence of moisture. It is therefore important to create the correct conditions for carbonation which comes through experience but is vital to the success - refer to the application guides for each product for details on protection - it is one of the most important points to ensure a successful result!
Different limes, different applications, different backgrounds (even in the same building), different times of the year and different elevations on the same site will all require careful attention and possibly different measures.
Most of the failures that we see are down to a lack of appropriate tending to aid carbonation as even a poorly specified/selected lime type can actually succeed if applied and cared for appropriately after all we did not historically have the range that we have now! As a result, we concentrate on this particular aspect on our training courses and in our application guides and are happy to discuss any aspect of it with our customers - call 01874 611350! We want your job to succeed and most do!
Should I stop using lime in the winter?
It is not recommended to use lime products (lime mortars, renders and limewashes) when temperatures are liable to fall below 5°C (41°F) for several weeks/months after the product has been used, this is especially true for non hydraulic and the weaker hydraulic limes. In practice this means that unless adequate weather protection is provided they should not be used externally until next spring, however, if work must continue then please see application guides and our using lime in winter information sheet in Documentation.
Castle Hydraulic Lime Health and Safety data sheet
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