Clinker brick

Reemtsma cigarette factory in Hamburg by Fritz Höger

A piece of vitrified brick

Clinker bricks are partially vitrified bricks used in the construction of buildings.

Clinkers are burnt under temperatures so high that the pores of the fuel property are closed by the beginning sinter process and are often mis-shapen. Thus they are considerably denser and therefore heavier and more irregular than regular bricks. Clinkers hardly take up water and are very durable, but have higher thermal conductivity than the more porous conventional red bricks, thus lending less insulation to climate-controlled structures. The name comes from the sound they make when banged together.^[1]

In early brick firing kilns called brick clamps, the surface of the bricks that were too close to the fire changed into the volcanic textures and darker/purplish colors. They were often discarded, but around 1900, these bricks were discovered by architects to be usable, distinctive and charming in architectural detailing, adding the earthy quality favored by Arts and Crafts style designers. Modern brick-making techniques can recreate the appearance of these bricks and produce a more consistent product.

In the United States, clinker bricks were made famous by the Pasadena, California architecture firm Greene and Greene who used them (often in combination with native rocks) in walls, foundations, and chimneys.

Dutch / Low German origins

Clinker bricks used to form family initials on a 1700s Dutch house in upstate New York.

Clinker brick closeup of bricks in the so-called Clinker building on Barrow street in Greenwich Village, New York City.

Clinker is sometimes spelled "klinker" which is the original Dutch / Low German word.^[2] The onomatopoeic verb "klinken" means "to sound", i.e. a "klinker" is a "sounder". (The Dutch word "klinker" also means "vowel".) These brick stones produce a specifically bright sound when hit with or against something, for instance each other.^[3]

Clinker bricks are also known as hard Dutch paving bricks. In 18th century New York, the Dutch interspersed dark clinkers with regular bricks. Some used clinkers to spell out their family initials on brick dwellings. See Jan Van Hoesen House.

Technical information

Clinkers consist of bits and ends, field-late and white-burning or red-burning clays. Through different mixtures of the raw ingredients, many varied colour nuances can be achieved. For the production of masonry units the source materials—clay and water—are mixed and formed industrially in a string extrusion process. For special purposes, for example the restoration of listed buildings, hand-formed clinkers are used. During the drying process, the water concentration decreases to approximately 3%. Then clinkers are fired at temperatures between 1100 °C and 1300 °C in a tunnel kiln (earlier in ring kilns), in contrast to the 800 °C to 1200 °C temperature range seen with normal bricks.

Klinker in Germany

In Germany, clinkers are named according to the German Institute for Standardization’s DIN 105 They differ between full clinker (KMz) with a density of 2.0 kg / dm ³ to 2.2 kg / dm ³ and high hole clinker (KHLz) with a density of 1.6 kg / dm ³ to 1.8 kg / dm ³. Because of their low porosity, clinker bricks are inferior thermal insulators, compared to normal bricks. Canal clinkers are named according to the German Institute for Standardization’s DIN 4051. Clinkers are frost resisting and, thus are suited particularly for facades. The formats of the clinker stones are named according to the German Institute for Standardization’s DIN 1053. Base for the different formats is the normal format (NF) with length 240 millimetres (9.4 in), width 115 millimetres (4.5 in) and height 71 millimetres (2.8 in). For facade layouts architects also order clinkers produced in special dimensions.

For use with facades, it is possible to cope varied shaped elements (e.g., clinker expressionism, see picture). Earlier clinkers were often used in civil engineering works, for example in bridge building, the construction of sewers and hydraulic structures, for mortar floodgates and hoppers or as paving stones for road construction.

Sculptor Ernst Barlach also worked with clinkers which then were produced according to his drafts, for example by the brickyard of Ilse Bergbau AG.

Peat-fired clinker

Clinker bricks take on a special colouring, often greenish tones, if burnt with peat. The Chilehaus and the Ramada Hotel in Hamburg are famous buildings built with peat-fired clinker. The last ring stove for peat-fired clinker still operating is in Nenndorf near Aurich (East Frisia), producing bricks marketed under the name “Wittmunder Torfbrandklinker” (peat-fired clinker of Wittmund).

Greppin clinker

Greppiner Klinker (clinker of Greppin) is a hard-burnt yellow clinker brick. Greppin clinkers were mainly used for facing railway structures at the end of the 19th and in the early 20th centuries.

References

1. Susan VanHecke. "The Accidental Charm of Clinker Bricks", Old House Journal
2. "Clinker, n.1". Oxford English Dictionary Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009
3. Also compare with the Standard German "klingen" (→ The dictionary definition of klingen at Wiktionary).

External links

• Clinker Bricks from Historical Bricks
• The Accidental Charm of Clinker Bricks, Old House Journal