Why Use Lime?

In short, True lime mortars, plasters and renders, whether hot-mixed or made with pre-slaked lime putty, are breathable, flexible, and aesthetically beautiful.

These qualities mean Lime are equally suitable for new build projects, just as they are vital to ensure older building continue to function as they should.

There is a lot more to Lime than meets the eye. Please keep reading to learn more…

Lime, and other breathable products, help to regulate moisture levels in buildings. This can help lower heating bills and improve living conditions, by helping prevent condensation and so the growth of black mould, for example.

It is also a far more eco friendly alternative to cement based products. Not only in its production but also by actively absorbing and locking away carbon dioxide from the air in a process known as Carbonation.

Lime based materials, due to its pore structure, can continuously absorb water vapour from the atmosphere, buffer it (hold onto it for a while) and release it again, even after the Lime Binder has carbonated (set).

It is this incredible ability to ‘breathe’ and buffer that is so important to ensure moisture levels never build up to critical levels in older houses, especially those with timber frames or solid walls.

The more actual Lime Mortar and Lime Plaster physically present in the property, either on the walls or ceilings, the better the house is able to ‘self-regulate’ its humidity and condensation levels i.e the larger the Sponge the more water it can hold.

Just as in many other areas of nature and science, water vapour moves from areas of high concentration to low concentration throughout a house. Older houses with solid walls must be allowed to breathe or else this vapour becomes trapped or can condense, which is when the problems begin.

Cement does have its place. However, the reason why we do not promote the use of cement in older breathable buildings (in all of its forms) is because it is not breathable. Simply put, moisture vapour is not able to pass through it.

This may sound like a good thing, and in fact it is in certain situations, such as dam walls or large underground sewage pipes.

But if a solid wall is pointed and rendered with cement, where it should be Lime, then moisture can and will build up in the walls, especially in the lower portions – This is due to gravity pulling the water down and the fact lower walls will always be colder and more prone to condensation. This can cause serious structural defects and unhealthy living conditions.

If Timber framed buildings are subjected to a similar treatment, timbers which have been perfectly good for hundreds of years can suddenly begin to rot in a matter of years after the application of cement. It can also happen with the application of cement mortars mixed with Lime (such as a 1:1:6 or 1:2:9 ratio mix) and it can also happen with NHL Lime Mortars.

Lime also has an inherent flexibility and the ability to self-heal. Because old buildings are often on shallow foundations, which move more with the seasons than modern deep foundations, and because timber framed houses can expand and contract significantly, the original Lime is able to accommodate more movement and settlement.

Cement, whilst it has a high compressive strength, is brittle and will crack if subjected to a tiny amount of this movement. Once cracked, water can get in but cannot escape. The end result is usually damp trying to escape the walls via the easiest route, which is often inwards. Because these walls are now wetter, and therefore colder, condensation is ever more likely. And so a negative feedback loop is created. These issues will be especially visible if they have been plastered with more modern gypsum based plasters and painted with modern acrylic emulsions, silk or satin paints.

Lime is also able to resist that degrading nature of salts. If damp is allowed to build up in walls of older properties, especially in external walls around fireplaces, for examples, the salts that would otherwise be held in situ form a briny solution, which can ‘bloom’ on the internal finish as any moisture evaporates. Gypsum plasterboard and skim will begin to break down very rapidly in these conditions, whereas Lime Plaster will allow the salt to bloom and be brushed away harmlessly.

If the walls were Lime plastered and allowed to breathe to begin with, they may never have become so wet as to allow this situation to occur. So often we see that once Lime has been re-introduced in this situations, the walls once again dry out and the salt eventually stops coming through. It can take a little while for the equilibrium to be re-gained however.

If this is happening to You, please see our Products Page for the Salt Removal Poultice.

If the air inside the building is very humid (relative humidity) the Lime Mortars and Lime Plasters can not only buffer the moisture, but allow it to pass through the walls to evaporate externally. Again, this is what is meant by Lime being able to breathe.

We feel this is a really important concept, especially since we are being encouraged, or even forced, to make houses ever more efficient.

We are bombarded with products and government grants for materials that are supposed to make ‘improvements’.

However, the unfortunate truth of materials such as dot and dab plasterboard, spray foam insulation, upvc windows, cement pointing, cement render and weather proof paints is that whilst they may have their place in construction, they are generally not compatible with older buildings, regardless of whether they are grand listed manor houses or modest victorian terraces.

These products are often pushed upon us, along with companies set up overnight to secure the grant money to apply them, often with pure disregard for their suitability. The grants eventually dry up and the house, ironically, becomes damp!

On a serious note, it is often this moisture build up which can cause genuinely life threatening situations in a home, such as mould, and cause irreparable harm to the fabric of a building.

It may be interesting to know that Lime is a strongly anti-septic and can actually help prevent the growth of mould, rot and infestation of wood worm.  This is why Limewash was always used in outbuildings, stables and cow byres, especially on the walls and on the exposed timbers, and it is just another reason why we LOVE Lime!

Finally, Our homes are our Castles; Our refuge and safe place. They are also our greatest assets. For many, they are a source of great pride. Some form part of our national heritage and history and thus we are responsible for taking care of them for future generations.

These are surely some of the most compelling arguments for ensuring that the products we introduce into our homes are more than just adequate and they should improve our lives for the better. Equally, they should absolutely not cause more problems than they are supposed to solve.

If You are unsure how Lime can benefit You and Your property, please get in touch and we will happily discuss things with You.

Warm air can hold far more moisture than cold air, and our modern lifestyles see a much greater output of moisture in the form of daily hot showers and baths, kettles and central heating (and drying clothes on the radiators too!).

These are all fantastic advancements in modern living, and I myself love a hot shower every day(!) but without adequate ventilation, or understanding of things like dew points, the massive output in moisture has to be dealt with.

Older houses used to have drafty windows, doors and open fires burning in open fireplaces. There was no combi-boiler for hot showers or heating, nor upvc windows.

As such, the moisture outputs were much lower and the ventilation / changes of air in a room were much greater. Coupled with greater quantities of lime and timber in a building and the moisture levels were better able to reach equilibrium.

Therefore, the benefits of using Lime in new-build properties are just as obvious as they are vital in renovation / restoration projects of older buildings.

It doesn’t matter if You are replacing an historical finish for the sake of preserving a historical building, or if You decide to use Lime Plaster in a modern extension for its timeless beauty, Lime has always been a fantastic material to use.



If a house has damp in its solid walls, these are MUCH more likely to be cold and difficult to live with. If the walls are much colder than then warm air inside, there is more likely to be interstitial condensation (think of the moisture that forms on an ice-cold beer on a humid summer day).

I have literally seen water running down cold walls as a result of condensation. If it wasn’t obvious, dry walls are warm walls. They are easier to heat and more pleasant to live with.




picture an oak beam or lintel.

what is air lime or fat lime?

What is carbonation?

What is a pozzolan?

dealing with humidity in older buildings

Fundamentally, Lime is a natural binder, made by burning Limestone which transforms it into Quicklime.

Water is then added to the dry Quicklime in order to Slake it, which causes a very strong exothermic reaction whereby lots of heat and steam are created.

Once cooled, the resulting material is a workable putty which can then be matured for approximately 3 months in order to ensure the slaking process has fully completed and the putty settles into a dense homogenous product.

Provided it is kept submerged in water and in an airtight tub this putty can be kept for years and, like a fine wine, can actually improve with age!

This Lime Putty can then be mixed with whatever aggregate is deemed most suitable for the application intended e.g. Sand for making Lime Putty Mortar and Lime Plaster or diluted further on its own to make Lime Wash.

Historically, however, the builders would not have had the convenience of pre-made Lime putty in plastic tubs(!) and so the mortars and plasters would have been made by the hot mix method.

To make a hot-mix mortar, the Quicklime and Aggregate are gauged (mixed) together whilst still dry, then the water is added, allowing the slaking and mixing process take place simultaneously.

Often this could be mixed in large quantities either directly on the ground or in pits dug next to where the building was being constructed, allowing the workers to hep themselves as and when needed. Unlike cement, which hardens rapidly after which it is un-useable, this lime mortar could be re-worked for a certain amount of time before it carbonated, which meant it could be made in batches and used more gradually.


The mortar it creates is rich and sticky and one of the benefits

The mix can be used whilst it is still hot or allowed to cool.

This is likely how the Lime was used historically, mixed on hot mix  before the water is added to this blend, prior to the water being added the water is added slaked with water True Lime Mortar, which is also referred to as Hot-mix Lime Mortar, Lime Putty Mortar, Air Lime or Fat Lime, is a non-hydraulic binder which has been used for many thousands of years.

  is a breathable, relatively flexible and aesthetically beautiful material which generally makes it the most suitable material for re-pointing and repairing buildings built prior to the 1900’s, especially those with solid walls and softer masonry.

Not only does it look appropriate on these heritage buildings but it is often vital to their proper function, allowing the walls to move and breathe (release moisture) as they should.

OPC (Ordinary Portland Cement), as we know it today, was patented 1824 although has been in use since Roman times.

It wasn’t until the turn of the century that the mainstream use of OPC in construction really began and overtook Lime in popularity due to its ease, speed and strength in use.

Unfortunately, it is these qualities which often make cement incompatible with older buildings since it is not breathable, prone to cracking with movement and is far too hard for use with softer masonry units.

The results of its use can be unattractive at best, looking dull and grey, and disastrous at worst, causing internal damp and spalling bricks.

These very same things also serve to enhance modern building and renovation Projects. 

Old buildings are a fascinating, inspiring and important reminder of our past. 

As custodians of these buildings, we must respect the traditional materials and methods used in their construction; Particularly when dealing with Listed and breathable solid walled buildings. 

Following the S.P.A.B. guiding principles, we strive to work in harmony with our heritage to ensure the health of both the building and its occupants.

In contrast, we also passionately believe that many new build projects would benefit from the introduction of traditional materials such as Lime Mortar, Lime Render, Lime Plaster and Limecrete flooring, to name but a few.

Not only do Lime products help to regulate moisture levels in your home, which could help lower heating bills and improve living conditions, but it is also a far more eco friendly alternative to cement based products, not only in it’s production, but also by actively absorbing and locking away carbon dioxide from the air during it’s application.

We would love to hear from You