LIME & CEMENT

Lime goes back a long way. The pyramids were built with limestone and some of the houses we live in today will have originally been built with lime and later repointed in cement. 

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There was a time when cement was thought to be the better alternative as it sets quicker and is much stronger. It is widely used across the world, cheap and easy to get hold of. The problem with cement is that its brittle. After long periods of bad weather or subsidence it will crack and continue to get worse.

Lime mortar on the other hand sets more slowly, but this gives it more workability for certain projects. It is also practically waterproof. Lime draws moisture out of a building, rather than trapping it inside and leading to damp. Cracking is less likely to occur but if it did, and structural stability wasn't a concern, it would self repair by carbonating over a long period of time.

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When to use Lime

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When a particularly older building in very poor condition is in need of restoration. Bricks can be repaired with lime mortar if replacements are impractical or unavailable. Stone should always be repointed or built with lime as replacing spalled stone is expensive or not even an option due to limited availability.

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From my experience, lime should always be used on larger projects. You are certainly getting more value for money. On smaller jobs i encourage the use of lime when damp is a major issue in particular areas.

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Types of Lime

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Hydraulic Lime - the most popular and affordable option

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Hydraulic lime is available in different strengths. Commonly 2.0, 3.5 and 5.0. The most popular choice being 3.5. It's numbered grade determines it's strength against exposure. For example NHL 2 would be used where weather exposure is minimal. NHL 5 on the other hand is used where weather exposure is high and faster setting times are required. For example: coastal areas or an area in which the property is partially or completely beneath the water. I'd also recommend NHL5 on Chimneys & DPC but it's not essential.

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The one downside to NHL is that it's not quite as beneficial as lime putty (more info below). It's still okay to use but it was more recently discovered so it may not be suitable for certain projects.​

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Lime Putty

This type of lime has been used for centuries and is fully tested and proven to be most beneficial on historic buildings. It is made form quicklime and then left to mature before use.

Lime putty has better breathing capabilities and is much softer than hydraulic lime. 

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If your house is pre-18th century then I'd advise using putty. I'd also advise using it on very soft bricks & stone if possible.

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Hydrated Lime

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The main difference with hydrated lime compared to hydraulic is that it quite simply does not set in water. Hence the reason why it is added to cement. It can be added to cement mortar for added workability and also has the self repair trait if damage were to occur later on.

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Is cement still okay to use?

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Short answer - Yes. Cement is still widely used today. Mainly because of its setting time, helping large building projects progress faster. It is also the main ingredient for concrete, which is one of the most popular composite materials in the world. As far as repointing goes, putting cement mortar back into a house is okay so long as the building was built with cement and there is no evidence of major damp problems.

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Conclusion

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If you require a full house repoint on a pre-war property I would advise using some form of lime. There is no right or wrong lime - all lime is good. Cement however is usually encouraged on different jobs where the house may have been built with cement and structural repair is needed (for example).