Brick

Brick is probably the most fragile of the main building materials in Venice. This is because its porous and fragile structure undergoes devastating effects from marine salts.

Usage of Brick in Venice

Medieval and Renaissance Venetians were drawn to brick for its lightweight and economical characteristics and used it widely on the exteriors of houses, palaces, and churches.

Palazzo Contarini del Bovolo, San Luca, 1499. Photograph by Marjorie Och, http://www.flickr.com/photos/7610850@N08/

Palazzo Contarini del Bovolo, San Luca, 1499 (photograph by Marjorie Och)

Bricks were such a popular building material, governmental incentives were issued to increase production: the brick kilns, albeit dangerous, were allowed to remain in Venice even after glassworks was transferred to Murano in 1292, the government loaned up to 2,000 lire in 1393 to individuals who were willing to build and operate kilns in Mestre, and the government raised the controlled price of bricks in 1429 to help brick-makers. (1) Bricks were transported to buildings sites, where bricklayers built structures using lime mortar, which allowed for slight movement of the bricks. This slight movement of the bricks is bound to take place on a city built on a marsh, and lime mortar is able to withstand this movement, whereas more rigid mortars would immediately crack. Many brick walls were covered in a layer of stucco, created from crushed terracotta or Istrian stone mixed with slaked lime and water, which acted as aesthetically-pleasing protective surfaces for the brick, but soon wore away.(2) While economically suitable for the time, the fragile physical structure of brick has led to issues for conservators today.

What is Brick?

Bricks are composed primarily of clay, which is igneous rock that has been eroded and chemically broken down into a moist mass of kaolinite, illite, montmorillonite, and chlorite. Clay readily absorbs water and expands because it has a fine, crystal-layered structure. Because clay should be as dry as possible before firing, sand may be added, which raises the temperature required for a successful firing. To counteract this high firing temperature, crushed limestone may be added to the mix to lower the melting points of minerals in the clay.(3) Bricks could have been under-burnt, making them too soft, or over-burnt, causing brittleness.(4) Regarding stone, wood, and brick, brickwork certainly has the most human manipulation, which also causes room for error.

Decay of Brickwork

Deteriorating Brickwork. Photograph by Katherine Arens, http://karen4dk.umwblogs.org.

Deteriorating brickwork (photograph by Katherine Arens)

Brickwork in Venice is under a constant state of destruction almost entirely due to marine water. Tidal exchange between the lagoon water and the sea causes the canal water to have the same salt concentration as the sea.

Marine Salts (NaCl) Crystallizing in the Pores of Brick.

Marine Salts (NaCl) Crystallizing in the Pores of Brick.

The canal’s salt water repetitively enters the pores of the brick, and as the water dries, salt crystals are left behind to corrode the brickwork.(5) Flooding is not the only manner in which the water reaches above the bricks: motor boats splash waves above the water’s surface and create suction in the water, which degrades foundations and disturbs sediment which can clog sewage drains.(6)

Propeller Suction Damaging Brickwork. From page 42 of Caroline Fletcher's The Science of Saving Venice.

Propeller Suction Damaging Brickwork. From page 42 of Caroline Fletcher

In winter, water-saturated bricks also undergo a freeze/thaw process, which leads to eventual shattering.(7) Istrian stone, wood, and brick all undergo damaging processes caused by marine salts, water saturation, and/or freezing and thawing cycles; therefore, the flooding of Venice has the capability to damage almost every structural component above water in the city.

Conservation and Restoration of Brickwork

Because bricks vary considerably in their composition and manufacturing processes, there is no exact cleaning method; therefore, the decision is very much up to the conservator as to what process should be utilized. The fragility of the bricks due to wear must be taken into account, as well as the porosity, glazes, dyes, mortar, and washes.(8) In conservation, water cleaning is often considered because it is a gentle cleaning process. In the case of brickwork though, water only removes superficial or loosely adhered dirt.(9) High pressure water spraying improves the results, but should not be used if brickwork is in a very fragile state, as in most of Venice. A better cleaning method for removing salts from bricks involves either a) saturating the bricks and rinsing with chemical cleaning solutions or b) wet-abrasive cleaning. Upon drying after either method, the salts can then emerge from the pores and be dry-brushed or vacuumed away.(10) In the first method, chemical cleaning is utilized, which involves pre-wetting the surface, cleaning with an alkali-based agent (pH above 7) followed by cleaning with a hydrofluoric acid solution (pH below 7) and thorough rinsing. This chemical cleaning must not be used if the mortar contains lime, as it can dissolve the mortar.(11) The cleaning of bricks in Venice may not be worth the money put into the project, as the next motor boat that drives down the canal will spray marine salts back onto the structure. Instead, bricks should be either be consolidated after a cleaning or completely replaced upon partial deterioration.

As far as Venice is concerned, much brickwork is in such disrepair, restoration is a better solution than conservation. If the bricks are damaged beyond repair, the only proper method for restoring the building and its foundation is to carefully cut out the damaged areas and replace the areas with new bricks of similar color, size, and texture. These bricks should meet current ASTM (American Standards for Testing Materials) standards for water absorption, maximum saturation coefficient, and minimum compressive strength.(12) Also, new mortar should be as dry as possible and is generally lime-based.(13) Since the great flood of 1966 and with increased operations since the 1990s, Venice has promoted operations to dredge the canals and replace sewage systems and brickwork at the foundations.(14)
If damaged bricks are not replaced, they can be consolidated with synthetic resins.(15) A resin, or liquid which hardens upon drying, coats the brick surface and is pulled into the pores, filling in areas where marine water could penetrate. Sometimes a simpler, less scientific variation on the methodology of protecting the brickwork is applied, where plasterwork is spread on the surface of the brick. In this manner, the salts will degrade the plasterwork before they can reach the brickwork.(16)

Conclusion

Brick is a material whose makeup proves too delicate for Venice’s watery environment. Easily damaged by marine salts, water movements, and freeze/thaw processes, brick can not withstand a marine environment with persistant flooding. Overall, consolidation of bricks in Venice is rare. The physical composition of bricks renders a material which wears too quickly to be worth the time and monetary spending of consolidation work.

1. R. J. Goy, Building Renaissance Venice: Patrons, Architects and Builders c. 1430-1500, (New Haven: Yale University Press, 2006), 82-83.

2. D. Howard, The Architectural History of Venice (New Haven: Yale University Press, 2002), 57-58.

3. M. E. Weaver, Conserving Buildings: A Manual of Techniques and Materials, Revised Edition, 99-100.

4. G. Lynch, Brickwork: History, Technology, and Practice, Vol 1 (London: Donhead, 1994), 95.

5. C. Fletcher and J. Da Mosto, The Science of Saving Venice (Torino, Italy: Umberto Allemandi & C., 2004), 42.

6. Ibid.

7. M. E. Weaver, Conserving Buildings: A Manual of Techniques and Materials, Revised Edition, 105.

8. N. Ashurst, Cleaning Historic Buildings, Vol 1 (London: Donhead), 1994, 105-106.

9. Ibid.

10. Ibid, 107.

11. Ibid.

12. M. E. Weaver, Conserving Buildings: A Manual of Techniques and Materials, Revised Edition, 107.

13. Ibid., 109.

14. Ibid., 107.

15. M. E. Weaver, Conserving Buildings: A Manual of Techniques and Materials, Revised Edition, 108.

16. C. Fletcher and J. Da Mosto, The Science of Saving Venice, 49.

 

Return to title page

Responses

My husband and I recently returned from a trip to Venice. While there we questioned the use of brick in the buildings, making a note to ‘Google’ it when we returned home. I found your Website and learned MUCH about Venice brick. Very informative and easy to read.
Thank you for sharing!

Linda Shepard

This website is quite informative. Now I could probably know enough to do a science experiment.

[…] this article from the online exhibit produced in ARTH 470Z at the University of Mary Washington http://venice.umwblogs.org/exhibit/the-conservation-of-venetian-building-materials/brick/. Tweet […]

Leave a response

Your response:

css.php