Where to get it in Ireland
The traditional lime store in Carlow (one of the biggest and longest established - nationwide delivery)
T McCann builder providers, 136 S Circular Rd, Dublin.
The lime store (Dublin)
Hydraulic lime comes in three different grades or forms. You have NHL 2, NHL 3.5 and NHL 5. The number corresponds to the 'compressive strength' of the specific lime, and also to other factors like how long it takes to set, and its 'ability to set under water without exposure to air'
The thing to keep in mind is that each grade is suitable for different kinds of masonry and weather exposure.
Best used for "permeable masonry" that has minimal exposure to the elements. Example; internal brick or stone work - Internal / sheltered Conservation work. Works well with heavily worm or crumbling / flaky sandstone, limestone and bricks. Obviously, it can also used as a Hydraulic lime plaster as well.
Best used with "medium density" masonry that is somewhat exposed to the elements. Often used for General Building work. If you are unsure what lime to use, this is often a good fail safe. Use with: Bricks - Block work - Sandstone - Limestone, for both internal and external building work.
Best used with "impermeable masonry" that has heavy exposure to the elements.
Characteristics: its the strongest and fastest setting of the lime mortars (which isn't necessarily the best thing for your project though), best suitable when working with dense / impermeable materials.
Use with: Granite, engineering brick, flint, paving, roofing, chimneys, balustrades, bridges, harbours, marinas, canals etc.
Read more about Lime Mortar Here