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Keeping your pointing in good repair not only ensures the aesthetic values of your property but is also crucial for structural integrity. At Gladstone Tuck Pointing & Restoration based in Burnham-on-Crouch can help you anywhere throughout London and the South East.
Masonry walls must regulate water penetration and evaporation. If the condition of the mortar joints is poor or if the incorrect mortar has been used for repointing previously then this process is often compromised.
There are three main reasons for repointing:
If the mortar joints are crumbling or loose
If the mortar joints are open or have weathered to such an extent that the edge of the masonry units are exposed, forming a ledge that leads to water seeping into the masonry
A hard impermeable cement-based mortar has been introduced trapping moisture and accelerating the deterioration of the masonry. This type of mortar should only be removed if this can be done without causing further damage to the adjoining masonry.
Repointing is typically only necessary on more exposed parts of a building including low-level areas affected by rising damp or areas affected by specific problems such as leaking rainwater. As a result, any sound existing mortar should always be left alone. Lime mortar with some surface loss should still be performing well and if it takes much effort to remove it, the chances are that it does not need to be replaced. It may feel a little soft but this may still be acceptable.
Where masonry is clearly decaying it is important to identify the true cause so that the correct remedies can be selected. The pointing itself might not be the cause of the problem so the condition of the whole structure should be reviewed along with the severity of exposure, and any defects contributing to the deterioration of the pointing should be remedied before repointing is completed.
Natural hydraulic lime is a ground powder that sets by a chemical reaction with water as well as by a longer-term reaction with carbon dioxide. Its initial set is faster than non-hydraulic lime but the actual rate is dependent on temperature and strength. It is available in three different strengths (NHL2, NHL3.5, NHL5). Hydraulic lime mortars have lower permeability and higher compressive strength compared to non-hydraulic mortars so they may be appropriate for use in locations that are permanently wet or very exposed to the elements.
The terms ‘hydrated’ and ‘hydraulic’ are often confused. The term 'hydrated' refers to the process of converting burnt limestone to a lime binder by the addition of water, and all commercial limes are hydrated. The term 'hydraulic' describes lime that sets partly due to a chemical reaction with water.
When considering which type of mortar to use, three issues need to be considered by the specifier:
The type of masonry being repointed – less permeable and denser materials can accommodate stronger mortars, such as hydraulic lime mortars, if extra strength is needed due to exposure.
The condition of the masonry – masonry that is decayed and highly permeable will require weaker mortar.
The level of exposure – areas of high exposure such as a chimney or roof may require stronger mortars.
The aggregate contributes to the colour, texture and performance of lime mortar. There is a wide range of aggregates suitable for making mortar. The most common aggregate used today is sand. Most sands are composed of grains of quartz (silica) but calcareous sand or crushed well-graded limestone is a useful addition to non-hydraulic and pozzolanic mortars as it helps to speed up carbonation. However, fine ‘stone dust’ should be avoided or only added in small quantities to help achieve a particular colour, because if used in large volumes it increases the risk of the mortar shrinking as it dries.
For many general applications nowadays, a well-graded aggregate, containing a range of particle sizes, will be appropriate. The size of the aggregate particles is usually adjusted to suit the width of the mortar joint; for example, coarse grit may be included in a mortar for rubble stonework whereas, for the narrow joints of ashlar stone or some brick, fine-grained sand or crushed limestone may be suitable. Historically, other materials such as crushed chalk, wood and coal ash, crushed shells and crushed brick were also used for making mortar. These materials are available from specialist suppliers and may be needed to create new repair mortars to match the character of existing historic mortars.
For more information about our brick pointing services, contact us today via phone or email.
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