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{{Short description|Rough-cast wall lime}}
{{Refimprove|date=October 2011}}
{{Refimprove|date=October 2011}}
[[Image:Stirling Castle great hall dsc06607.jpg|thumb|right|The Great Hall at [[Stirling Castle]] ]]
[[File:Driveway from Craigievar Castle - geograph.org.uk - 1566794.jpg|thumb|upright=1.35|Close view of the harling at [[Craigievar Castle]]]]
[[File:CraigievarCastle.jpg|thumb|[[Craigievar Castle]] ]]


'''Harling''' is a [[roughcast|rough-cast]] wall finish consisting of lime and aggregate, known for its rough texture.<ref>{{cite web |last1=Frew |first1=Craig |title=Lime Harling |url=http://www.buildingconservation.com/articles/lime-harling/lime-harling.htm |website=buildingconservation.com |access-date=18 February 2019}}</ref> Many castles and other buildings in [[Scotland]] and [[Ulster]] have walls finished with harling. It is also used on contemporary buildings, where it protects against the wet [[Climate of Scotland|Scottish]] and [[Northern_Ireland#Geography_and_climate|Ulster climates]] and eliminates the need for paint.
In [[Scotland|Scottish]] usage, '''harling''' describes an exterior building-surfacing technique which results in a long-lasting weatherproof shield for a stone building. A pigment can be embedded in the harled material, thus obviating the need for repainting. Harling as a technique provides the surface of many Scottish castles, but it is also used for a variety of common everyday building types. Long-lasting and practical, it well suits structures in the Scottish climate.


== Technique ==
== Technique ==
Harling as a process covers stonework using a [[plaster]]ing process involving a slurry of small pebbles or fine chips of stone. After a wall is complete and has been pointed and allowed to [[Curing (chemistry) | cure]] then a base of [[lime render]] is applied to the bare stone. While this render is still wet a specially shaped trowel is used to throw the pebbles onto the lime surface, which are then lightly pressed into it. Harl, being mostly lime render, cures chemically rather than simply drying. After this setting process, the harl is sometimes [[Whitewash|lime washed]] in various colours using traditional techniques.<ref>{{cite book|last1=Santo|first1=Phillip|title=Inspections and Reports on Dwellings: Assessing Age|date=2013|publisher=[[Taylor & Francis]]|page=9}}</ref><ref>{{cite book|last1=McWilliam|first1=Colin|title=Scottish Townscape|date=1975|publisher=Collins|page=52}}</ref>
Harling as a process covers stonework using a [[plaster]]ing process involving a slurry of small pebbles or fine chips of stone. After a wall is complete and has been pointed and allowed to [[Curing (chemistry) | cure]] then a base of [[lime render]] is applied to the bare stone. While this render is still wet a specially shaped trowel is used to throw the pebbles onto the lime surface, which are then lightly pressed into it. Harl, being mostly lime render, cures chemically rather than simply drying. After this setting process, the harl is sometimes [[Whitewash|lime washed]] in a colour using traditional techniques.<ref>{{cite book|last1=Santo|first1=Phillip|title=Inspections and Reports on Dwellings: Assessing Age|date=2013|publisher=[[Taylor & Francis]]|page=9}}</ref><ref>{{cite book|last1=McWilliam|first1=Colin|title=Scottish Townscape|date=1975|publisher=Collins|page=52}}</ref>


It is not recommendable to replace more than around 20% of the lime content with [[cement]]. Cement-based render is very stiff and prone to crack or detach from the wall when subjected to stress induced by expansion due to solar radiation and moisture. It is also less permeable to moisture and water vapour. Water entering through fine cracks in the surface does not easily diffuse and can penetrate into the softer stone, thus causing the deterioration which harling aims to prevent. For similar reasons modern, barrier paints should not be used in place of traditional lime washes.
It is not recommendable to replace more than around 20% of the lime content with [[cement]]. Cement-based render is very stiff and prone to crack or detach from the wall when subjected to stress induced by expansion due to solar radiation and moisture. It is also less permeable to moisture and water vapour. Water entering through fine cracks in the surface does not easily diffuse and can penetrate into the softer stone, thus causing the deterioration which harling aims to prevent. For similar reasons, modern barrier paints should not be used in place of traditional lime washes.

An example of the inadequate protection afforded by high cement harling is the [[Charles Rennie Mackintosh]] designed [[Hill House, Helensburgh|Hill House]] completed in 1904 using the newly available but poorly understood [[Portland cement]] harling. Over the years water had penetrated the harling and threatened the overall integrity of the building. The [[National Trust for Scotland]], the building's owner, has (2019) enclosed Hill House in a transparent 'box' which will allow some rain to enter but which will eventually allow it to dry naturally. It is estimated that this will take seven to ten years, after which the box will be removed. <ref>{{cite news |url=https://www.bbc.com/news/uk-scotland-48461850 |title = Mackintosh's Hill House reopens inside a box - BBC News| work=BBC News | date=30 May 2019 }}</ref>


== Examples ==
== Examples ==
[[File:Stirling Castle great hall dsc06607.jpg|thumb|right|The Great Hall at [[Stirling Castle]] ]]

The technique of harling features in a large number of famous Scottish buildings including:
The technique of harling features in a large number of famous Scottish buildings including:


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* [[Myres Castle]] in [[Fife]] (1530 onwards)
* [[Myres Castle]] in [[Fife]] (1530 onwards)
* [[Stirling Castle]] in [[Stirling]]
* [[Stirling Castle]] in [[Stirling]]
* [[Castle of Park (Aberdeenshire)]]


== See also ==
== See also ==
* [[Stucco]]
* Compare [[roughcast]], [[pargetting]].
* [[Roughcast]]
* [[Pargetting]]

== References ==
{{Reflist}}

=== 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.
*Meek, T, (2020) The Practical and Cultural Implications of a Bare Stone Paradigm in Heritage Conservation. The Construction Historian
*Meek, T. (2022) Pointing and Joint Finishing in Scotland. Technical Paper 33. Historic Environment Scotland


==External links==
==External links==
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[[Category:Building]]
[[Category:Building]]
[[Category:Scottish architecture]]
[[Category:Architecture in Scotland]]
[[Category:Plastering]]
[[Category:Plastering]]
[[Category:Building materials]]
[[Category:Building materials]]
[[Category:Visual and material culture of Scotland]]

Revision as of 06:05, 30 June 2024

Close view of the harling at Craigievar Castle
Craigievar Castle

Harling is a rough-cast wall finish consisting of lime and aggregate, known for its rough texture.[1] Many castles and other buildings in Scotland and Ulster have walls finished with harling. It is also used on contemporary buildings, where it protects against the wet Scottish and Ulster climates and eliminates the need for paint.

Technique

Harling as a process covers stonework using a plastering process involving a slurry of small pebbles or fine chips of stone. After a wall is complete and has been pointed and allowed to cure then a base of lime render is applied to the bare stone. While this render is still wet a specially shaped trowel is used to throw the pebbles onto the lime surface, which are then lightly pressed into it. Harl, being mostly lime render, cures chemically rather than simply drying. After this setting process, the harl is sometimes lime washed in a colour using traditional techniques.[2][3]

It is not recommendable to replace more than around 20% of the lime content with cement. Cement-based render is very stiff and prone to crack or detach from the wall when subjected to stress induced by expansion due to solar radiation and moisture. It is also less permeable to moisture and water vapour. Water entering through fine cracks in the surface does not easily diffuse and can penetrate into the softer stone, thus causing the deterioration which harling aims to prevent. For similar reasons, modern barrier paints should not be used in place of traditional lime washes.

An example of the inadequate protection afforded by high cement harling is the Charles Rennie Mackintosh designed Hill House completed in 1904 using the newly available but poorly understood Portland cement harling. Over the years water had penetrated the harling and threatened the overall integrity of the building. The National Trust for Scotland, the building's owner, has (2019) enclosed Hill House in a transparent 'box' which will allow some rain to enter but which will eventually allow it to dry naturally. It is estimated that this will take seven to ten years, after which the box will be removed. [4]

Examples

The Great Hall at Stirling Castle

The technique of harling features in a large number of famous Scottish buildings including:

See also

References

  1. ^ Frew, Craig. "Lime Harling". buildingconservation.com. Retrieved 18 February 2019.
  2. ^ Santo, Phillip (2013). Inspections and Reports on Dwellings: Assessing Age. Taylor & Francis. p. 9.
  3. ^ McWilliam, Colin (1975). Scottish Townscape. Collins. p. 52.
  4. ^ "Mackintosh's Hill House reopens inside a box - BBC News". BBC News. 30 May 2019.

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.
  • Meek, T, (2020) The Practical and Cultural Implications of a Bare Stone Paradigm in Heritage Conservation. The Construction Historian
  • Meek, T. (2022) Pointing and Joint Finishing in Scotland. Technical Paper 33. Historic Environment Scotland
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