Talking THI – Volume 2; What’s the Point?

For each project currently underway, you will have hopefully noticed our Historic Heart Boards on display – there to give a short history of the building, alongside an overview of the work being carried out. For a lot of the THI projects, you will see a phrase along the lines of: ‘cleaning, minor repairs, and repointing of brickwork’. Today’s blog is going to explore what we mean by pointing, and why it is so important to get it right – especially for historic buildings.

Mortar joints repointed with lime

What is pointing?

Pointing, as it refers to the upkeep of buildings, is the process of repairing the mortar joints between bricks or other masonry elements. These repairs might be necessary due to recognisable damage to the building – from an external force, plant growth, extreme weather events etc – however, more often than not, the repairs are made because the mortar simply degrades over time. As it is supposed to do.

Historic buildings (pre-1940s) – whether made from brick or stone – would have utilised lime mortar in the construction. Made from lime mixed with (typically) sand and water, it creates a strong yet permeable bond that allows for natural shifting of the building and ensures mortar can freely evaporate. Also significant is that lime mortar is softer than the surrounding masonry – historic bricks are a lot softer than their modern counterparts – meaning that when natural weathering occurs due to water, frost and salt, it is the mortar that erodes before the bricks do; it’s pretty awesome stuff! There’s a reason it was a major part of construction dating all the way back to ancient Rome and Greece.

So what changed?

In short, Portland Cement. Easier to use. Quicker to set.  And far, far stronger. As brick technologies improved, we switched to more efficient mortar. The new bricks were better placed to cope with the cement – the impermeability of it didn’t have as big of an impact as it would with older buildings.

If only it was as simple as keeping the two types of mortar to their own types of building…

The problem

As already mentioned lime mortar, by its design, is sacrificial. Over time it degrades and needs to be replaced – the building needs to be repointed. Unfortunately, as cement came into the picture, more and more buildings had this repointing carried out in cement. After all, this mortar wasn’t going to degrade – the job would only need doing once!

But cement isn’t permeable – any water evaporating from the building is now either trapped (causing damp issues) or works its way through the bricks (which degrades the bricks).  It’s harder than the bricks, meaning that natural erosion due to rain, frost and salt damages the bricks rather than the mortar. The strength also means that the shifting of the structure that had been previously possible due to the slight flexibility of lime now doesn’t happen. Which puts added stress where there wasn’t before, ultimately damaging the bricks.

Mortar joints repointed with cement – note damage to surface of bricks.

The ’point’ of THI

Where buildings have had ‘repairs’ with cement mortar, this is being removed and replaced with lime – repairing or replacing damaged bricks as necessary in the process. Other buildings have retained their lime mortar; this is being repaired and replaced as necessary due to natural wear and tear. The repointing is often a much lighter colour than the mortar joints around them; however, these will weather to a similar shade over time.

Fresh repointing – colour will weather to a similar shade to the ‘old’ pointing over time .