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– **Technique**:
– Harling process involves stonework using a plastering process with small pebbles or fine stone chips.
– Lime render is applied to the bare stone wall, and pebbles are thrown onto the wet lime surface.
– Harl cures chemically and is sometimes lime washed in color using traditional methods.
– Cement should not replace more than 20% of lime content to prevent cracking and detachment.
– Modern barrier paints are not suitable substitutes for traditional lime washes.

– **Protection**:
– High cement harling can lead to water penetration and building integrity issues.
– The Hill House, designed by Charles Rennie Mackintosh, faced problems due to Portland cement harling.
– Water penetration through cracks in the surface can deteriorate the stone.
– The National Trust for Scotland enclosed Hill House in a transparent box to dry naturally.
– Estimated time for drying process completion is seven to ten years.

– **References**:
– Frew, Craig. “Lime Harling.”
– Santo, Phillip (2013). “Inspections and Reports on Dwellings: Assessing Age.”
– McWilliam, Colin (1975). “Scottish Townscape.”
– Mackintoshs Hill House reopens inside a box – BBC News.
– Meek, T., (1996) Case Studies of Traditional Lime Harling. Historic Scotland.

– **Further Reading**:
– Meek, T., (1996) Case Studies of Traditional Lime Harling. Historic Scotland.
– Addyman, T., Meek, T. (2019) Historic External Lime Finishes in Scotland. Technical Paper 31, Historic Environment Scotland.
– Adderley, P., Meek, T. (2019) Harl-as-you-Go! Implications for robustness. Journal of the Building Limes Forum.

– **Importance of Traditional Techniques**:
– Traditional lime harling aims to prevent stone deterioration.
– Cement-based render is stiffer and less permeable to moisture compared to lime render.
– Solar radiation and moisture can cause stress-induced cracking in cement-based render.
– Water entering through cracks in cement render can penetrate softer stone, leading to deterioration.
– Modern barrier paints are not as effective as traditional lime washes in protecting walls.