Lime VS Cement

True Lime Mortar is a non-hydraulic binder which has been used for many thousands of years.

It is often vital to the proper function of heritage buildings allowing the walls to move and breathe (release moisture) as they should. It also looks appropriate.

OPC (Ordinary Portland Cement) as we know it today was patented in 1824 although has been in use since Roman times.

It wasn’t until the turn of the century that the mainstream use of OPC in construction really overtook Lime in popularity, especially post-war, due to its speed, ease and strength in use which kept costs down.

Unfortunately, these qualities often make cement incompatible with older buildings since it is not breathable, prone to cracking with movement and far too hard for use with softer masonry units.

The results of its use can trap damp in walls, cause bricks to spall and timber frames to rot.

Wet walls are an extremely poor insulator and will draw heat from a room far more quickly. This means money wasted on heating and can cause even more condensation to form on the inner surface leading to mould growth.

Lime mortars and Plasters help to regulate the moisture levels and keep the walls dry. They do this by absorbing and buffering moisture from the air and allowing it to evaporate again. This is what is meant by breathability.

In conjunction with proper ventilation, this can dramatically improve living conditions and reduce heating costs.

Lime is also a good antiseptic which means it simultaneously prevents mould and fungal growth as well as reducing the chance of rot and insect attack on timber.

Lime is a flexible material. It has a lower compressive strength than cement, so if the building moves, which is often the case with older properties on shallow foundations or timber framed buildings, the lime is able to move with it rather than crack. It also has the ability to self heal.

If built on clay, movement caused by heave and settlement can be quite dramatic. In this situation, cement might resist any movement until it failed catastrophically and there are instances where older properties have been damaged irreparably by the inability to move.

Timber frames expand and contract massively throughout the year and the Lime Mortar and Plaster allow this movement to continue unhindered. The Lime is considered sacrificial and will continue to do its job for many, often hundreds, of years until it requires maintenance or renewal.

Soft fired clay bricks are extremely absorbent and can expand and contract up to 10% as temperature and moisture levels fluctuate. This is a significant amount across a large wall or between different faces of a building.

Cement pointing can cause soft bricks to be held far too tightly, and therefore self-destruct, or force moisture to try and escape via the brick faces rather than the joints, which can be especially damaging when there is a frost.

In all situations, the mortar should be softer than the structural elements of a building and therefore considered sacrificial i.e. it is supposed to wear out over time, in order that the bricks do not.

Lime is a far more eco friendly alternative to cement based products, not only in its production, but it also actively absorbs and locks away carbon dioxide from the air during its application as it undergoes carbonation.

In summary, whilst Cement certainly has its place, there are very few situations which it can out-perform Lime when it comes to properties built before 1900.

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