Hydraulic Lime Mortar Information
Hydraulic lime mortar is a totally natural, traditional building material.
Its origin can be traced back through history for thousands of years.
The Greeks, Egyptions and Romans all used an ancient form of it extensively in construction.
The material contains natural hydraulic lime (NHL), sands and aggregates.
The sand and aggregates are selected based on the size and suitability of their particles.
The natural hydraulic lime acts as a cementing agent or binder.
It fills in the voids between the sand and aggregate and bonds it all together.
Hydraulic lime is very different from other limes used in the building industry.
It sets by hydrolysis, this means that water or moisture cause it to set therfore hydraulic limes are capable of setting underwater.
Other non-hydraulic and hydrated limes (more commonly used in mortar) set by carbonation, they are set by carbon dioxide in the atmosphere.
These natural characteristics make hydraulic lime mortar an excellent all around building material and bedding mortar.
Bedding mortars act as a cushion between stones and bricks and are required to compensate for the irregularities in their beds.
They also spread the structural load imposed on the wall and aid the evaporation of moisture.
Hydraulic lime mortar does this exceptionally well, especially in areas subject to extreme conditions.
Despite the excellent track record and performance of hydraulic lime, its use has declined in modern times.
This is due to the introduction and evolution 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 ten years has seen a resurgence in the use of hydraulic lime mortar.
Architects, specifiers and the general public seem to have rediscovered the benefits of hydraulic lime and realise what us specialists have known for a very long time.
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.