What is Lime Plaster?

What is Lime Plaster?

A Beginner’s Guide to Lime Plaster and Lime Render

Lime plaster is made up of sand, water and lime. There can often be confusion due to the fact that the term lime is used to refer to a huge assortment of different products some of which go by different names that mean the same thing.

When it comes to Lime Plaster, we’re usually referring to non hydraulic lime which may be referred to as hot lime, lime putty or fat lime. Lime plaster can also sometimes be confused with cementitious plasters containing lime. Below we’re going to try and explain the different terms used within the construction and restoration industry as well as the benefits of using each product.

Hydraulic Lime or Non Hydraulic Lime

The first thing that is important to understand is the difference between Hydraulic Lime and Non Hydraulic Lime. The main difference is that hydraulic lime sets via hydrolysis which is the reaction with water whereas non hydraulic lime sets via carbonation which is a reaction with air.

Non Hydraulic Lime is softer and more flexible than it’s hydraulic counterpart and sets at a slower rate. Hydraulic Lime sets faster and is more durable, with similar properties to cement. This makes hydraulic lime ideal for exterior work as a lime render, especially when damp conditions are expected.

For more on this topic, see our blogs on Hydraulic and Non-hydraulic Lime or What is Lime Mortar?

Lime Putty

Lime Putty is another name for non hydraulic lime. Lime putty is made by the process of slaking which is the addition of water to quick lime (CaO) – hence the names slaked lime and Ca(OH)2 in the list below.

Ecolime have developed our own unique slaking system which enables us to produce consistently perfect Lime Putty, free from impurities and contamination. Our Lime Putty is a highly refined Limestone based putty slaked from finely ground particles (90 microns – less than 1/10th of a millimeter) which results in a smooth putty that requires no sieving.

Lime putty does not set underwater and will only harden with exposure to the air in a process called re-carbonation.

You may see Lime Putty being referred to as any of the following:

  • Lime Putty
  • Fat Lime Putty
  • Non-Hydraulic Lime
  • Slaked Lime
  • Calcium Hydroxide (Ca(OH)2)

With so many names for one product there’s no wonder there’s so much confusion and misinformation around. Ecolime pride ourselves on being experts on Lime Putty and everything Lime related so remember you can call us on 01653 648566 at any time for more information.

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Lime Plaster

This brings us to Lime Plaster, which as mentioned earlier is made up of sand, water and lime. The lime in question is usually Non-Hydraulic Lime, which of course is also known as Lime Putty. Incredibly, the use of Lime Plaster dates back as far as 7200BC where statues sculpted in Lime Plaster were found buried in a pit at the archaeological site of ‘Ain Ghazal in modern-day Jordan. This is a perfect example of just how durable Lime Plaster is as a building material.

Often products can be used as both a Lime Plaster and a Lime Render as the Lime Putty used is durable enough to withstand the weather conditions encountered in external use. This is just one of the many benefits of using lime plaster or lime render. Though this is dependent on climate and geographical location. For any help choosing the right lime plaster please do get in touch.

Benefits of Lime Plaster

  • Lime plaster is permeable and allows for the diffusion and evaporation of moisture.
  • Lime Plaster has a high pH which acts as a fungicide; meaning mold will not grow in lime plaster.
  • Plaster made from lime is less brittle and less prone to cracking than cement plaster and requires no expansion joints.
  • Lime plaster is less affected by water and will not soften or dissolve like drywall and earthen or gypsum plaster
  • Unlike gypsum or clay plaster, lime plaster is durable enough to be used as a lime render on the exterior of buildings.


Insulating Lime Plaster & Insulating Lime Render

One of the biggest benefits of Lime Plaster or Lime Render is its insulating qualities. Our Unity Lightweight Insulating Plaster is what we at Ecolime see as the future of lime plastering for base coats.

Lightweight Insulating plaster

The benefits of insulating lime plaster include:

  • Saving time by allowing you to go to depths of 40mm per application.
  • Insulating properties with a k value of 0.19.
  • Draws moisture out of the building keeping it dry.
  • Available in both Hydraulic and Non-Hydraulic
  • Cost saving by enabling you to dub out and level all in the same coat.
  • Aiding with salt migration.
  • Increasing soundproofing and acoustic performance.
  • Easier to apply.
  • Cutting down labour cost with less coats required.


Another benefit of the Unity Insulating Plaster is that it can also be used as an Insulating Render. This means it has the strength and durability to be used on the outside of buildings as an insulating render as well as being smooth enough to use indoors as an insulating plaster. Our Lightweight Insulating Render also aids with fireproofing.

In traditional building the products are designed for the building and not the application. Modern materials are designed for the builder and not the building. Our Lightweight Insulating plaster range manages to be sympathetic to the building’s needs while also allowing a quicker application and insulating properties to make life easier for the builder.

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Ecolime are market leaders when it comes to all things lime. Whether you’re looking for Hydraulic Lime Plasters or Non-Hydraulic Lime Plasters, we have everything you could possibly need for your project. If you’re unsure which product is the best fit or how much you will require, we’ll be happy to answer these or any other questions. Just give our lime experts a call on 01653 648566.

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Hydraulic and Non-Hydraulic Lime

What is the Difference Between Hydraulic and Non-Hydraulic Lime?

Lime Mortar for building purposes can be split into two distinct categories – Hydraulic Lime Mortar and Non-Hydraulic Lime Mortar. This blog post looks at the difference between Hydraulic and Non-Hydraulic Lime and will help you choose the right lime mortar for the job you need it for.

If you have any further questions about Hydraulic and Non-Hydraulic Lime then please contact Eco Lime on 01653 648566 and we’ll be happy to answer any queries you may have.

Non-Hydraulic Lime Mortars

Non-Hydraulic Lime Mortars are also referred to as Hot Lime Mortars and are perfect for pointing and building with softer stones and bricks. The softer mortar has a higher porosity, and better flexibility than hydraulic mortar, as it relies solely on natural carbonation.

These come wet as ready mixed lime mortars, all you need to do is rework them and they are ready to use.

You can also turn these into a hydraulic mortar by the addition of a pozzolan. This then turns the mortar to an FHL (Formulated Hydraulic Lime) as oppose to an NHL (Natural Hydraulic Lime).

The use of FHL has been around since the Romans who used volcanic ash to formulate the lime when building the Colosseum, this adds extra strength to the mortar, but does slightly lower the breathability and flexibility. Increasing the amount of pozzolan added to the mortar will increase the mortar’s strength and lower the breathability slightly. This enables you to use the same mortar for several different applications where the strength and a better weather resistance is needed.

Hydraulic Lime Mortars

Natural Hydraulic Lime (NHL) comes from limestone containing natural impurities of clay and other minerals. The amount of impurities within it determines how hard it will set.

There are three European classifications of Natural Hydraulic Lime: NHL 2, NHL 3.5 and NHL 5. These grades are based on the compressive strength of laboratory mortars after 28 days. These are often misleadingly termed feebly hydraulic, moderately hydraulic and eminently hydraulic.

The strength of a Hydraulic Lime Mortar varies depending on the manufacturer of the hydraulic lime. Some Natural Hydraulic Lime will test higher in the qualifying band, and some test lower. Strength will also vary depending on the mix ratio and the type of aggregate used.

Below is a table of what varying strengths NHL can achieve:

Hydraulic and Non-Hydraulic Lime

NHL works by setting in the presence of water, which is why it’s known as Hydraulic Lime.

Eco Lime generally recommend the use of Hydraulic Lime where the need for a higher breathability and lower strength is outweighed by the desire for an earlier and harder set. With any mortar used, the best mortar is the mortar that is the softest and most flexible for the job required.

Using our Premixed Hydraulic Lime Mortars ensures a greater consistency of strength, as these are formulated to strength with the aggregates already added.

These come in a great selection of colours, which will ensure you get the right mortar in the right colour without having to worry about batching consistency.


What Is Lime Mortar?

What is Lime Mortar?

A Beginner’s Guide To Lime Mortar

Interest in the skills of traditional building techniques has increased over recent years. Whether it’s working with green oak or wattle and daub, at some point you will need to know about lime mortar. Despite its enduring utility over many centuries, lime mortar’s effectiveness as a building material has maintained an air of mystery. Only during the last few decades has testing provided a scientific understanding of its remarkable durability. Previously time-honoured practices were based on local tradition, folklore and trade knowledge, vindicated by the vast number of old buildings that remain standing.

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What Is Lime Mortar?

Lime mortar is composed of lime (hydraulic, or non hydraulic), water and an aggregate such as sand. Lime mortar today is primarily used in the conservation of existing old buildings or the recreation of new ones using traditional methods. Its use dates back at least 6,000 years, to the Ancient Egyptians who used lime to plaster the pyramids. With the introduction of Portland cement during the 19th century, the use of lime mortar gradually declined. However, the soft and porous properties of lime mortar provide certain advantages when working with softer building materials such as natural stone and terracotta. While Portland cement continues to be commonly used in new constructions of brick and concrete, it is not recommended in the repair and restoration of brick and stone-built structures originally built using lime mortar. Lime mortar is more porous than cement mortars, and it wicks any dampness in the wall to the surface where it evaporates. Thus any salt content in the water crystallises on the lime, damaging the lime and thus saving the masonry.

Cement on the other hand evaporates water less than soft brick, so damp issues are liable to cause salt formation and spalling (a result of water entering brick, concrete or natural stone and forcing the surface to peel, pop out or flake off on brick surfaces and consequent disintegration of bricks). This damp evaporation ability is widely referred to as ‘breathability’. Also historic buildings are frequently constructed with relatively soft brick and many types of stone, and minor movement in such buildings is quite common due to the nature of the foundations. This movement breaks the weakest part of the wall, and with Portland cement mortar this is usually the masonry. When lime mortar is used, the lime is the weaker element, and the mortar cracks in preference to the masonry. This results in much less damage, and is relatively simple to repair.

What Is Lime Mortar?

Hot Mix Lime Mortar

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There are many types of lime mortar mix available on the market, from ready mixed lime mortar to hot mix lime mortar. Sometimes it can get a little bit confusing to determine which one is the right one for the application. Mortar mixes are classified based on compressive strength and their bonding properties and flexibility. Choosing a mortar mix is not an exercise based only on the resistance and strength of each mortar, it must depend on its use, adhesion, and sealing requirements. Both analytical and documentary evidence indicates that hot-lime mortars were used in traditional construction. These are defined as mortars manufactured by mixing quicklime and sand, rather than the current and more commonly adopted method of combining previously slaked lime with sand. Hot-lime mortars are perceived to have advantages over cold- manufactured mortars they performed better in terms of mechanical and bond strength in recent tests. The benefits seem to come from the hot mix itself but do not require the mix to be used hot – in fact, for plastering it would normally be left a least a day to improve before being used.

Hydraulic Lime

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Hydraulic lime sets by hydration so it can set under water. There are three strength grades for natural hydraulic lime (NHL);

NHL2, a slow setting and softer material, perfect for internal applications or where conservation is a primary concern with soft or deteriorating stones and bricks

NHL3.5 ideal for general building, for moderately permeable masonry materials. Basically, if it’s not essential to use NHL 2 or NHL 5 then use this.

NHL5 sets faster and is stronger, more suitable for dense, durable or impermeable materials with severe exposure to weather or water.

The numbers stand for the minimum compressive strength at 28 days in newtons per square millimeter (N/mm2). For example, the NHL 3.5 strength ranges from 3.5 N/mm2 (510 psi) to 10 N/mm2 (1,450 psi). These are similar to the old classification of feebly hydraulic, moderately hydraulic and eminently hydraulic, some people continue to refer to them interchangeably.

Non-hydraulic Lime

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Non-hydraulic lime or as it’s also known, fat lime putty is a white, putty like material with a fairly solid consistency. It sets by carbonatation, a chemical reaction in which calcium hydroxide reacts with carbon dioxide and forms insoluble calcium carbonate and so needs exposure to carbon dioxide in the air and cannot set under water or inside a thick wall. For natural hydraulic lime (NHL) mortars, the lime is obtained from limestone naturally containing a sufficient percentage of silica and/or alumina. Artificial hydraulic lime is produced by introducing specific types and quantities of additives to the source of lime during the burning process.  A pozzolan could be added, these are materials which enable lime mortars to set more rapidly. Non-hydraulic lime is produced from a high purity source of calcium carbonate such as chalk, limestone or even oyster shells. Hydrated lime is any lime other than quicklime, and can refer to either hydraulic (hardens under water) or non-hydraulic (does not harden under water).

Hopefully this has shed some light onto this ancient building material. Luckily you won’t have to rely on folklore for more information, just ask us!

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