Lime plaster benefits are many but the most impressive are its breathability and flexibility making it very useful for conservation. In a modern building where this is no movement, flexing, shrinkage or damp then cement based renders and plasters are fine, but older properties that may have many different materials and specifications lime can be more forgiving
Advantages over cement based coatings:
Lime plaster will allow moisture to easily pass through whereas cement will trap and prevent moisture from escaping, leading to a greater problem - gradually building and then ultimately forcing the damp to come out elsewhere. Whilst damp will not rise much more than a metre, it has been reported that damp has been forced nearly 3 metres high into the next floor above due to the cement render not letting any moisture escape.
A damp wall plastered with lime will allow the wall to breathe everywhere and therefore prevent a build up of moisture.
Whilst cement based plasters and renders are strong in compressive strenth they lack greatly in flexibility. Any movement can easily result in the very strong cement based plaster cracking and if used externally will allow the ingress of water and damp. Then the damp will be trapped behind a non breathable render.
Lime whist not as hard is more flexible, so suited for use in an older building.
The alkaline properties of lime are naturally bacteria repellant
Disadvantages of Lime
Setting and hardening of lime is not an exact science. Cement and gypsum plasters have a standard set and hardening process whereas this process in lime is less predictable and takes a lot longer.
Lime mortars gradually achieve good compressive strength allowing for movement.
Compressive Strength after 28 days
Hydraulic Lime & Sand (1:1.5) 1.47 N/mm2
Cement, Lime & sand (1:1:6) 7.7 N/mm2
Compressive Strength after 6 months
Hydraulic Lime & Sand (1:1.5) 5.3 N/mm2
Cement, Lime & sand (1:1:6) 8.1 N/mm2
Compressive Strength after 12 months
Hydraulic Lime & Sand (1:1.5) 5.9 N/mm2
Cement, Lime & sand (1:1:6) 8.7 N/mm2
Water repellant yet breathable
Tadelakt is both breathable and hydrophobic