Hydraulic lime

When Portland cement, even traces, is present (can be up to 20% of binder weight), it has to be labeled as 'PHLc'.

This meant that lime could be used in a wide variety of applications including floors and even vaults or domes.

[citation needed] Natural hydraulic lime (NHL) is classified for different uses[3] the first two of which are sometimes called semi-hydraulic lime because they initially set with water but continue to set in contact with carbon dioxide in the air.

Moderately hydraulic lime (NHL 3.5) can be used for external work in most areas.

This type of lime sets (assumes given shape) within a few days after the addition of water.

Eminently hydraulic lime (NHL 5) is used for external work in exposed areas, such as chimneys and for floor slabs/underpinning.

Smeaton's Eddystone Lighthouse . John Smeaton is credited with pioneering hydraulic lime in the 18th century, which led to the development of Portland cement and thus modern concrete . Painting by John Lynn.