Lime Mortar

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When used for walls, construction or pointing consideration should be applied to compatibility. The mortar must be softer than the stone.

This being said the best lime mortar for older building is the old non – hydraulic limes however it comes with many conditions we must endure;

Sets very quickly, easy to mix however not best for damp areas and is harder than the non – hydraulic limes.

Three types of hydraulic mortar’s; 

• NHL 2.0 – Described as feebly hydraulic  Sets in 40 hours - soft
• NHL 3.5 – Described as moderately hydraulic Sets in 30 hours - med
• NHL 5.0 – Described as eminently hydraulic  Sets in 15 hours - hard

Very hard to mix, Sets extremely slow – in some cases months and while this dries, we must keep it moist – mist spraying daily and must be protected from freezing. Good for moist areas and is softer than the Hydraulic mortars. This lime was being made for use in two ways

 1)Quick lime to create hot lime mortar

 And when we say hot, this when exposed to water there is a thermic reaction causing very high     heat – is dangerous!

 2) Lime putty to create cold lime mortar. 

Where this has no heat danger it is mighty difficult to mix – you have to rake, chop and hoe. 

Mortars used in building, tuck pointing, plaster and white washing can be confusing. Which to use?

Hydraulic lime mortar sets by the loss of water.

Non – hydraulic mortar sets by carbonation where it loses water and gains carbon dioxide 

Tuck pointing old stone buildings; 

NEVER USE ANY AMOUNT OF CEMENT!

Other than not using any amount of cement both lime mortars can be used, hydraulic or non – hydraulic. When these old stone buildings built before the mid 1800’s they used a non - hydraulic lime mix mixed with sand used as hot lime or first Slaking to putty. These are the preferred methods however much more difficult to use.

The non – hydraulic has the benefit of the ability breathing “allowing water to escape – it is preferred, but is much more difficult to use.

1) More difficult to mix

2) Dries much more slowly and needs care while setting.  

3) Hot mortars are dangerous to mix. 

For much more great information see;

Stone Buildings 

Patrick McAfee