Hydraulic Lime is produced from limestone containing clay and other impurities which enables it to set without exposure to air (unlike fat lime products). It therefore means that these limes can be used in harsher conditions e.g. they are ideal for use in foundations, limecrete floors, sea-defence walls, chimneys, parapets, copings, paving etc. The products in this range are produced in Portugal by Secil who have been producing high quality limes for over 100 years. Natural Hydraulic Limes (NHLs) are categorised, where the number refers to the compressive strength of the mortar after 28 days (please note the selection of aggregate and mix ratio will also effect the final strength)
- NHL 2 is the slowest setting of all the hydraulic limes, but also the most flexible and vapour permeable and so is primarily used for internal work and external work in sheltered areas on strawbale, cob, soft masonry or brick.
- NHL3.5 gives a slightly faster set and can be used for external work in most areas with most masonry types.
- NHL5 has a much faster set and achieve s a greater strength, it is typically used for external works in exposed areas such as chimneys, copings or river and canal works, floors.
These limes have become increasing popular over the last decade because of their comparative ‘ease of use’ and ‘strength' compared with non-hydraulic fat-limes. However, they should be used for the right situation as limes that are too strong can cause damage to the fabric of the building in the same way that cement does. The golden rule is that the mortar or plaster should always be weaker than the building components it is used on.
Please call for advice or see Choosing a Lime in the Documentation below.
Hydraulic Limes are supplied as a powder to which water and sand must be added in the correct ratios – see Documentation.
We supply a wide range of aggregates suitable for use with these limes.
Please note that this product must be stored completely dry and frost-free and used straight away.
Bulk order discounts apply to this product, the more you add the more discount you will accumulate!
- Technical Documents
- Application Advice
This section is under development but please email firstname.lastname@example.org for system builds and NBS clauses.
- Variable strengths for most everyday applications
- NHL2 – for use in internal plasters, and as mortar for brick and ’soft’ stone.
- NHL3.5 – for external renders and mortars on harder stone.
- NHL5 – for external flaunching and mortars in extreme conditions/situations where high strength is required, and low vapour permeability is acceptable.
- Gain strength over time hence providing flexibility and avoiding the need for expansion joints.
- 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.
- Set under water hence ideal for applications in contact with the sea, canals, rivers etc.
What basically 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.
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 all 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 Singleton Birch (Secil) Hydraulic Limes which are an off-white, general purpose lime.
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?
No, 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.
Building 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.