Cotswold Lime Pointing


Welcome to Cotswold Lime Pointing.

We specialise in building renovation and restoration as well as the sympathetic conservation of old and listed buildings using local craftsmen and traditional materials. 

We use Lime extensively in the conservation of old, listed and historic buildings.  Lime offers an attractive, environmentally sustainable and friendly alternative to cement based mortars.       

Give your property a facelift and preserve its structure !!
The History of Lime and its Environmental Benefits?
Old Lime Mine

Lime has many uses in the building trade.  It can be used as a mortar, a render, a plaster and as slurry and washes.  All these various types of lime product come from limestone which was laid down in the Cretaceous Period (60-150 million years ago). 

The limestone is burned at extremely high temperatures (up to 1250°C) to combine with clay to produce a mixture of quicklime, cementitious material and an inert material.  These limes then require slaking with water to convert the quicklime to calcium hydroxide.  There are two main types of lime mortars,  "Lime Putty"  and "Hydraulic Lime".

Mortar

Non-hydraulic lime or lime putty is lime in its purest form.  It is an excellent material used to great effect with stones or bricks which are weak or weathered.  It is an ideal consistency to be used for pointing and some face repairs to stone or brick.  It is often used in the conservation and restoration of buildings.

Storage of lime putty is extremely important. It should be matured for at least 30 days and must be stored with aggregates in a wet condition or blended.

Lime Putty
Hydraulic Lime

Not as pure as non-hydraulic lime, hydraulic lime has the amazing ability of being able to set under water! This characteristic is due to the impurities of the silica and clay in the limestone.  Lime has a slower drying/curing time than modern mortars and must not be applied if the air temperature is less than 5°C.  Lime mortar is able to accommodate movement and is excellent at retaining its water vapour permeability as well as being frost and salt resistant.  A good choice for restoration and conservation of older properties as well as newer brick and stone buildings.

The term ‘Hydraulic’ or ‘non-hydraulic’ refers to the lime’s ability to set under water, or not. Hydraulic lime sets when combined with water, therefore it dries hard relatively quickly, like cement does.  Non-hydraulic limes stay soft initially and gradually harden over a longer period of time.

Hydraulic lime

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enquiries@cotswoldlimepointing.co.uk

During manufacture lime produces 20% less carbon dioxide than cement production.  This amazing building material is actually carbon neutral. Like cement it gives off carbon dioxide during manufacture.  Yet, unlike cement, lime mortar actually re-absorbs carbon dioxide when it sets!

Lime Cycle
Reduce your carbon footprint...Use lime mortars!
Lime Mortar

Before this century building techniques and materials were very different from those employed today.  Traditional buildings need to "breathe" to allow moisture inherent in a solid wall construction without a damp proof course to evaporate from the external stonework or render.  Many old buildings are constructed from materials such as brick, cob and stone which are relatively porous and often of lower strength.

Lime putty mortars were normally used for bedding and plastering.  Lime mortar is relatively soft and therefore it is able to withstand a certain amount of movement (without cracking) that comes with settlement and seasonal changes in ground conditions.  Lime mortar is porous and allows moisture to evaporate, helping to keep a building free of dampness.

Why Use Lime?

Cement mortars were comonly used for many years to repair and maintain old walls and buildings. Cement mortar traps moisture within the wall causing errosion and weakening of the structure.  Lime mortars helps to preserve the walls integrity by allowing the stone or brick to breath.  Lime is soft and flexible, it allows the building to move (as all buildings do!) without cracking and letting in water. Unlike cement, lime has been dubbed "self-healing" because of this ability.

Cement mortars
Lime

Pure lime putty mortars and plasters dry by suction and evaporation and then they carbonate.  This is the oldest, most flexible and breathable form of lime.  The Romans discovered that adding volcanic ash from Pozzuoli to a lime putty mortar created a chemical set making the lime mortar hydraulic i.e. it enabled the mortar to set in the presence of water and allowed the Romans to build structures such as aquaducts.  Substitute materials have long since been used instead of volcanic ash, hence any burnt clay that reacts with pure limes to create a hydraulic lime set is referred to as a Pozzolan after the original discovery.  If lime putty is kept moist and free from Pozzolans, it will last indefinitely and actually improve with age reducing wastage.

So the original hydraulic lime was in fact a combination of pure lime putty and a Pozzolan that can still be replicated and is usually used these days in the UK to render and point externally or internally on to walls that are inherently damp and require the chemical set.

A dry powdered Natural Hydraulic Lime was introduced much later when limestone was discovered with natural impurities that when burnt mimicked the Pozzolans used by the Romans.  This is perhaps more like a weaker, early form of OPC (Ordinary Portland Cement) as it needs to be dry stored and a chemical set begins once water is absorbed into it.  If stored dry and air tight, this form of hydraulic lime offers a potentially cheaper option for a bedding or pointing mortar.  Care should be taken when selecting the most appropriate Natural Hydraulic lime as it comes in different strengths of NHL2, NHL3.5 and NHL5.  Different manufacturers strengths can vary widely even within these grades.  NHL5 is ideal for Limecrete floors, chimney flaunching, copings or ridge tiles.

Late 19th Century Lime Kilns
More Lime history and facts
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