Lime render has many attractive attributes and qualities when compared to modern
day equivalents such as
cement render, polymer render and silicon acrylic render. Lime render contains
Natural Hydraulic Lime (NHL), which gives this substance its unique properties. Avant Coatings Ltd has been
championing the Lime Render cause for many years often met with reluctant attitudes
from builders, developers and architects. But over the last few years the building
industry has woken up the advantages of lime render.
If you are in need of our
Lime Render services, simply call us on 0800 500 3146 or
send us an email and we will be happy to provide you with a quote.
Lime Rendering (AKA Natural Hydraulic Lime Rendering)
Lime render is a long-established traditional building material with an interesting
historical background. It is an entirely natural, traditional building mortar and render.
Its origin can be traced back to the Greeks, Egyptians and Romans who all used an ancient
form of it extensively in construction.
It is widely used in building conservation, because many old buildings were originally
built with this mortar. It is best conservation practice to use the original or most
compatible building materials. Although used in conservation, lime render is not only
used for this purpose. It is an excellent all-round performer with a place in general
modern construction. Hydraulic lime render shares the practical benefits of modern
cement based mortars but simply has none of the disadvantages.
The material consists of natural hydraulic lime and a certain blend of sands and aggregates.
The sand and aggregate are selected based on the size and suitability of their particles.
The natural hydraulic lime acts as the binder. It fills in the voids between the sand and
aggregate and bonds it all together.
Hydraulic lime as used in lime render differs vastly from other limes used in the building
industry. Natural Hydraulic Lime sets by hydrolysis. This means that water and moisture
cause it to set therefore hydraulic limes are able to set underwater. Other types of
lime such as non-hydraulic and hydrated limes, which are more commonly used in mortar
set by carbonation, they set by absorbing carbon dioxide from the atmosphere.
These natural characteristics make hydraulic lime mortar an excellent all around
rendering materials and building mortar.
Lime render has an excellent track record and proven performance. Despite this, its
use has declined in modern times. This is due to the introduction and development of
portland cement in Britain in the early 19th century. Portland cement was a cheap,
impermeable, high strength building material that also simplified the process of
mixing mortar. This material emerged as the construction industry was modernising
so it was welcomed by general builders, despite objections by specialists at the time.
Specialists objected to portland cements because they carry a number of natural disadvantages.
High strength, impermeable cements and mortars are brittle and provide poor thermal expansion.
They are also unsympathetic and do not allow for the evaporation of moisture from masonry.
They carry the additional risk of transferring sodium salt to vulnerable masonry.
Nevertheless, Ordinary Portland Cement (OPC) was adopted and has since dominated the market.
It is now the most popular cement and mortar binder used in modern construction around the world.
With the advent of OPC, hydraulic lime mortar's use steadily diminished. It has eventually
become a little known material and has been used mainly by specialists for building conservation
and restoration projects.
Interestingly, the last few years has seen a resurgence in the use of hydraulic lime mortar
for building and rendering. Architects, specifiers and the general public have rediscovered
the benefits of hydraulic lime and realise what us specialists have known all along.
Fortunately there are still a number of traditional craftsmen with the knowledge and
skill to reproduce the traditional lime mortar mixes that have been used on Britain's
finest historic buildings for centuries.
Lime render is fast setting so it can be used on-site just as efficiently as modern cements
and mortars. Shrinkage cracks are virtually eliminated due to the mortar's hydraulic setting
characteristics. It is essential to specify the correct type and quantity of sands and aggregates.
Lime render allows walls to breathe by absorbing and evaporating moisture from surrounding masonry.
This also helps protect the masonry because less moisture means less risk of salt and frost damage.
Hydraulic lime render has a low modulus of elasticity. This means it is extremely flexible,
especially when compared to modern day renders and allows for movement and thermal expansion.
The lime render mix can be engineered to suit different types of masonry substrates and
degrees of weather exposure. As mentioned earlier, it can set underwater, therefore an
excellent mortar for masonry in extreme conditions. The mixing of a lime render is as
important as the sands and aggregates or the strength of the lime itself. Correct mixing
practices are essential to the performance of the render. Casein, which is a natural
extract of milk can be added which will act as a natural plastisizer. In the past sour milk,
eggs even urine have been added to render mixes to act as plasticers. Lime render is softer
than modern cement, therefore stones and bricks are reclaimed more easily when buildings are
demolished.
Lime render is a more eco-friendly option than its alternatives. The manufacture of
hydraulic lime produces less carbon dioxide than ordinary limes and cement. Furthermore,
it re-absorbs carbon dioxide when curing, thus lowering its carbon footprint.