Roughcast or pebbledash is a coarse plaster

Plaster

Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...

 surface used on outside walls that consists of lime

Lime (mineral)

Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...

 and sometimes cement

Cement

In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

 mixed with sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

, small gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

, and often pebbles

Pebbles

Pebbles may refer to:* Pebbles, small rocks* Pebbles , Boston-area radio DJ* Pebbles , British-trained thoroughbred racehorse of the 1980s* Pebbles Flintstone, a character in The Flintstones animated television show...

 or shells

Seashell

A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer created by an animal that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on beaches by beachcombers...

. The materials are mixed into a slurry and are then thrown at the working surface with a trowel or scoop. The idea is to maintain an even spread, free from lumps, ridges or runs and without missing any background.

According to the Encyclopædia Britannica Eleventh Edition

Encyclopædia Britannica Eleventh Edition

The Encyclopædia Britannica Eleventh Edition is a 29-volume reference work, an edition of the Encyclopædia Britannica. It was developed during the encyclopaedia's transition from a British to an American publication. Some of its articles were written by the best-known scholars of the time...

 (1910–1911), roughcast used to be a widespread exterior coating given to the walls of common dwellings and outbuildings, but it is now frequently employed for decorative effect on country houses, especially those built using timber framing

Timber framing

Timber framing , or half-timbering, also called in North America "post-and-beam" construction, is the method of creating structures using heavy squared off and carefully fitted and joined timbers with joints secured by large wooden pegs . It is commonplace in large barns...

 (half timber). Variety can be obtained on the surface of the wall by small pebble

Pebble

A pebble is a clast of rock with a particle size of 4 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered to be larger than granules and smaller than cobbles . A rock made predominantly of pebbles is termed a conglomerate...

s of different colors, and in the Tudor period

Tudor period

The Tudor period usually refers to the period between 1485 and 1603, specifically in relation to the history of England. This coincides with the rule of the Tudor dynasty in England whose first monarch was Henry VII...

 fragments of glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

 were sometimes embedded.

According to the Encyclopædia Britannica Eleventh Edition, the central tower of St Albans Cathedral

St Albans Cathedral

St Albans Cathedral is a Church of England cathedral church at St Albans, England. At , its nave is the longest of any cathedral in England...

, built with Roman

Ancient Rome

Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 tile

Tile

A tile is a manufactured piece of hard-wearing material such as ceramic, stone, metal, or even glass. Tiles are generally used for covering roofs, floors, walls, showers, or other objects such as tabletops...

s from Verulamium

Verulamium

Verulamium was an ancient town in Roman Britain. It was sited in the southwest of the modern city of St Albans in Hertfordshire, Great Britain. A large portion of the Roman city remains unexcavated, being now park and agricultural land, though much has been built upon...

, was covered with roughcast believed to be as old as the building. The roughcast was removed about 1870.

Pebble-dashing is a type of roughcasting where the surface coating is of small stones, chips of stones or gravel that are thrown at a coat of wet plaster while it is still 'soft'. Though it is an occasional home-design fad, its general unpopularity is estimated to reduce the value of a property by up to 5%.

Roughcasting incorporates the stones in the mix while pebbledashing adds them on top.