Hydraulic lime mortar is a lime mortar that hardens in damp or even wet conditions through a chemical reaction rather than exposure to air. (This is in contrast to standard, or non-hydraulic lime mortars, which harden by absorbing carbon dioxide, a process known as carbonation.) Hydraulic qualities are created when clay is included in the lime mixture.

Spalled brick in an1860s lighthouse that was repointed with portland cement mortar about twenty years ago. The historic stone masonry units have deteriorated dramatically, while the portland cement mortar joints remain intact. It' s important to understand that historic buildings are very different than modern buildings in several key ways: First, historic brick--in particular--is softer than modern brick because modern brick is fired at a much higher temperature than was possible in the past.

Yes. As we have already mentioned on this page, historic brick was fired at a lower temperature and is typically softer than modern brick. Construction techniques have changed, but it's still important that the mortar accomodate the historic brick. Due to the prevalence of portland cement mortars (notably the standard Type N), very few masons have worked with traditional lime mortars.

The colour and texture of a sand has a considerable impact on the appearance of the finished mortar. The fine aggregate particles give a lime mortar its colouring; the larger fragments give its texture. Most lime binders are white, light grey or cream in colour, and therefore the colour reproduction of the sand is excellent, compared to OPC mortars. We can carry out analysis of original mortars and isolate and grade the original aggregates used to help with matching.

These are mixes of lime putty and coarse sand, used for building, pointing, rendering and plastering. The mix for mortar is normally 3 or 3.5 parts sand to one part lime putty by volume.

We supply our premixed lime mortars in sealed dumpy bags or sealed tubs. It will last indefinitely as long as long as air cannot get in to carbonate the lime. This means keeping it from drying out and storing it free from frost. Mortars with hair teased in will gradually lose the hair as it dissolves in an alkaline wet mortar and you will end up with an unhaired mortar. Mortar left for many months will take more "knocking up" to plasticise the lime mortar.

Animal hair, usually horse, cow or goat, is added to the backing coats of lime mortar used for external rendering or internal plastering onto stone, cob, brick or timber lath. Adding hair gives extra strength and minimises shrinking and cracking. It allows thicker coats to be applied to uneven walls and holds the plaster keys in place when plastering onto lath.

This is made from limestone that contains impurities such as clay or silicates. Unlike lime putty which is non-hydraulic lime, NHLs can set in damp conditions. They also have some free lime available for carbonation. There are three European classifications NHL 2, NHL3.5 and NHL5 based on the compressive strength of laboratory mortars after 28 days. These are often somewhat misleadingly termed feebly hydraulic, moderately hydraulic and eminently hydraulic.

Natural hydraulic limes set even when wet and come in a range of strengths. They are useful for building with stone or brick where the earlier set may speed up construction. You can also add a pozzolan such as metastar to a lime putty mortar. We suggest that for external bedding and pointing late in the year natural hydraulic lime should be used. It is capable of a faster initial set in cold weather.

Both lime putty and lime mortar should be protected from frost. If frosting should occur, it is possible to reuse frozen lime mortar so long as it is completely thawed out and thoroughly mixed before use.

Lime is calcium oxide applied in granular form. Lime helps improve lawn color and density, controls thatch, and increases root development. Lime balances the pH levels in the soil that have been affected by the fertilizer applications throughout the year. To read more about the importance of Lime, please read our Article entitled "Winter Care."

What are the standard tests used to determine the percent of available lime (CaO%) and how do they differ? (ASTM C25 and AWWA B202 standard tests) Why is sugar added when running the standard titration for the percent of available lime (CaO%)? (ASTM C25 and AWWA B202 standard tests)

With a growing emphasis on the need to reduce energy consumption and reduce CO2 emissions there is an argument for the use of traditional limes. The production of many natural hydraulic limes offers a significant reduction in energy, compared to that required to produce Portland cements.

Lime mortar will not cure a problem caused by poor detailing on the property, such as undersized gutters, a lack of a roof overhang, outside ground levels that are higher than floor levels or capped unventilated chimney stacks. They will however allow walls to dry out after problems such as this have built up high damp levels within walls and they will allow the wall to be able to breathe again.

Fat lime mortars require construction to take place at a slower rate but hydraulic limes cure quickly enough to allow building work to proceed quickly and do not delay work even on the largest construction sites.

No there is full range of lime mortars with different strengths and degrees of resistance to damp conditions. You should choose the right one, bearing in mind the exposure of the wall, the location of the property and the condition of the stone or brickwork that you are repairing, rendering or re-pointing. If you require specific free advice on appropriate mixes please contact us or read our technical sheets.

A lime render is a coating of lime-based material that was traditionally applied over rough, unsightly brickwork or rubblestone masonry walls. Non-hydraulic lime stuccos and hydraulic lime stuccos are common lime-based renders. In addition to these traditional applications, lime renders can restore some measure of protection to masonry buildings that have been sandblasted. (Sandblasting a masonry building is incredibly damaging.

Obviously, you want to avoid the kind of damage described above, and in order to accurately recreate the original mortar you typically have to have the mortar analyzed. Although a building constructed before 1871 was undoubtedly pointed with lime mortar (because portland cement wasn't even available until that year) the years after 1871 are a grey area.