Inserting lime mortar back to the castle wall is not a simple process. Except for various additives, lime mortar needs a constant supply of moisture and carbon dioxide as well as protection from rapid temperature changes to be well hardened and as a result turn into limestone.
If lime plaster is left unprotected, it could be slowly washed away due to impact of the weather.
Its adequate protection could be provided by plants – stonecrops. The name of the family in Latin is sedum originating from Latin sedo, that means “to sit”, and such plants are naturally growing, “sitting”, on the mountain rocks. They protect their natural home from erosion and just this ability was utilized by preservationists.
Stonecrops were used in Devín in 2022 for the first time as a special engineering-biological protection; they were intentionally planted on the wall copings. It’s a well-proven technology of wall protection used, e.g., in the Lietava Castle or Starhrad or city walls in Skalica.
Stonecrops maintain the masonry copings wet enough and provide protection from temperature fluctuations and constant supply of carbon dioxide.
Text author: Andrej Barát