If you ask for lime at a builders' merchant you will almost certainly be
offered dried non-hydraulic lime sold in bags. However good quality
non-hydraulic  lime putty is superior and should be used wherever
possible. Non-hydraulic lime putty and dried hydraulic lime are
avaible from a increasing number of specialist suppliers.

CALX RESTORATION use the Traditional Lime Company in Carlow as a supplier.

Lime Putty is usually supplied in plastic tubs in which it can be stored
indefinitely if protected from frost. It should be matured by the supplier
for at least one month before sale, and most suppliers also stock three
months old putty. Check the age before buying

Lime putty can be stored for years, improving all the time.