A brief history of Lime Mortar

Lime Mortar is composed of lime and an aggregate such as sand or grit (dependant on use case) mixed with water. The ancient Egyptians were the first to use lime mortars, using them to plaster temples and homes. Lime mortars continued to be used in many different forms of construction throughout the world up until its decline of use in the 19th century with the introduction of Portland cement. This was largely due to cements ease of use, faster setting times and strength.

However, although Lime mortar no longer stands as the most commonly used bonding agent in new construction, its soft and porous properties still provide certain advantages over cement when restoring buildings originally built in lime mortar. This is because older buildings typically move and flex a lot more and with expansion joints not yet common practice at the time of construction the lime mortar accommodates this movement. If a cement based mortar is used on a building originally built in lime this can often result in cracking to the brickwork or stone as a crack will always take the path of least resistance and this is often the brickwork rather then the mortar.

Great care must be used when removing existing mortar

When deciding how to remove the existing mortar on a lime construction building there a many factors you must take into account, for example:

• Is the building listed or in a conservation area ? If this is the case you must consult with local authorities so they can tell you how they would like you to remove the mortar. In most cases power tools cannot be used apart from a select few specialist tools. This is at the conservation officers discretion. The most common way is a hammer and chisel taking great care to not damage any brickwork.
• what is the current mortar ? Sometimes lime buildings may have already been pointed in a cement based mortar, if this is the case it can sometimes be difficult to use a raking disc as the strength of the mortar can force the blade towards the above or below brick, In these cases the cement mortar must be removed with a hammer and chisel followed by a raking disc to clean out the joint.
• what is the joint size ? Older buildings joint sizes can vary from anywhere between 5-20mm, this may mean a smaller or larger raking disc needs to be used to achieve a clean and even joint size, taking great care to not make the joint any larger.

In most cases, an appropriately sized raking disc should be ok, this is always the quickest, tidiest and has the least risk of damage to the masonry. A dust extraction unit should always be used to keep dust to an absolute minimum, this is not only for health and safety reasons but to keep the site clean and tidy during mortar removal.

To prepare for repointing the existing mortar should be raked-out to a depth that is at least two times the height of the joint.  For example a 10mm high joint should be cut to a depth of at least 20mm.  To mitigate the potential for damaging the masonry when raking-out, the process must be undertaken with care.

Before applying new mortar, the brickwork is washed to remove loose particles or dust remnants and the joints are dampened to ensure maximum bond with the new pointing mortar.

Using the correct mortar

To ensure appropriate levels of strength, permeability and longevity it is necessary that the mortar used for repointing walls is similar in composition to that of the original mortar. A golden rule of repointing is never to allow the strength of the mortar to be greater than that of the bricks.

The correct colour, strength and texture combined are all factors that ideally should match the original mortar of the building, Luckily specialist suppliers like the Lime Centre have the ability to match a mortar sample to a huge catalogue of lime mortars they have in stock, They can even change factors like texture to better suit your sample making the match almost identical.

Using a putty or a hydraulic or non hydraulic lime ultimately depends on the use case, for example a hydraulic lime is able to set underwater as so a good use case would be the construction of a retaining wall or 9 inch solid wall. where as non hydraulic lime is set by carbonation so relies on exposure to the air to be able to set, so would be best suited to repointing. Again, specialist suppliers can advise on this if you are unsure.

It is important to note that a cement based mortar mixed with lime is NOT a lime mortar, some builders may try to advertise this as such when in fact the lime in the mix is simply used to make the mix easier to work with and makes the mix and bond stronger. It is not a substitute for standalone lime mixes.

Installing the lime Mortar correctly

Lime repointing is not as simple as cement pointing as how it is installed depends on many different factors like heat, humidity and moisture content in the masonry and much more. All lime suffers with shrinkage prior to installation unless very specific checks and steps are made. Due to most older bricks or stone being very porous this means that when the lime mortar is installed the bricks will immediately begin to suck the moisture from the lime which causes shrinkage and as a result cracking.

To mitigate this you must first assess weather conditions at the time and spray a generous amount of water to the masonry before installing any mortar, this means the bricks are already moist so will not draw as much water from the lime so quickly, depending on weather conditions you may also need to spray water after installation to further slow down the drying process.

Another factor to consider when lime pointing is the consistency of your mix, To dry and you wont achieve a strong bond to the masonry, to wet and you will cause the masonry to stain or ‘shadow’. Again this is also dependant on weather conditions and the sweet spot will vary from day to day or even from morning to afternoon.

Pointing finishes are also a huge factor that affects time, cost and appearance. It is important you choose the correct finish of pointing to compliment the age and originality of the building. Finish is hugely dependant on the age and style of a building but some of the most commonly used are flush, double struck (or birds beak) or weather struck. This decision must be made before choosing your mortar as consistency of the mix is key to achieving the best finish of each style.

Lime Mortar Repointing in Hampshire, Dorset and West Sussex

If you would like to find out more about lime repointing near you then please don’t hesitate to get in touch and we will be happy to help over the phone or in person. Our lime mortar repointing services cover Hampshire, Dorset and West Sussex. If you would like professional advice or guidance on our lime mortar repointing services cover Hampshire, Dorset and West Sussex then get in touch today. Hampshire, Dorset, west sussex, Portsmouth, Bournemouth, Birghton, Southampton, New Forest, Haslemere, Hove, Worthing, Chichester are all areas covered in our Lime Mortar repointing Services.

Alternatively give us a call on our head office number & book a survey 023 9243 0183