A grouted roof is a form of slate roof. It has developed as a form of vernacular architecture associated with the West coast of the British Isles. [1]
A grouted roof is distinguished by having an overall coat of a cementitious render.
A conventional slate roof consists of thin slates, hung over wooden laths. Slates are hung in place by wooden pegs through a hole at the top of each slate. [2] The peg stops the slate slipping downwards, the weight of the slates above it hold the slate down. Later roofs replaced the peg by an iron nail driven into the lath, but the nail is always primarily a hook and it is the weight of the slates above that hold the roof covering down onto the frame. Lead nails were also used, long enough to be bent over the laths from the inside. In time these developed into strips cut from lead sheet.
Such roofs are common and are particularly well known in Wales, where the high quality slate from North Wales was exported worldwide. As the slate was of high quality it could be split very thinly by skilled artisans and so gave a lightweight roof covering that was still strong and long-lasting against harsh weather. Where local slate was used instead, this was of lower quality than Snowdonia slate and so the roof design may have been less successful. In particular, lower quality slate must be cut to thicker, heavier slates to retain adequate strength, so giving a roof of much greater weight.
The primary means of failure in a slate roof is when individual slates lose their peg attachment and begin to slide out of place. This can open up small gaps above each slate.
A secondary mode of failure is when the slates themselves begin to break up. The lower parts of a slate may break loose, giving a gap below a slate. Commonly the small and stressed area above the nail hole may fail, allowing the slate to slip as before. In the worst cases, a slate may simply break in half and be lost altogether.
A common repair to slate roofs is to apply 'torching', a mortar fillet underneath the slates, attaching them to the battens. [1] [3] This may applied as either a repair, to hold slipping slates, or pre-emptively on construction.
Where slates are particularly heavy, the roof may begin to split apart along the roof line. This usually follows rot developing and weakening the internal timbers, often as a result of poor ventilation within the roofspace.
Where a roof has begun to fail overall, it may be 'grouted' to extend its working life. This is not a spot repair, but an overall treatment applied to the entire roof. A thin wash of mortar or render is applied across the roof. This fills the gaps between slates and also covers the slates' surface. Grouting has two obvious visual effects: the distinct edges of the slates blur into a monolithic roof panel and also, as the grout is a pale white, paler than other building materials visible, the roof becomes much more prominent. [4] [5]
Grouting is seen predominately along the western seaboard of the UK, particularly in Pembrokeshire in South West Wales and to a lesser extent the Isle of Anglesey, Cornwall and Devon. It has also been used, primarily as a sealant, on porous stone slates such as the Permian sandstones of Dumfriesshire. [1]
Grouting developed as a repair technique. A roof might have been grouted several times in its lifetime, each time the coating becoming thicker and more rounded. Eventually the weight of these extra render coats becomes too much for the structure of the roof and the roof may fail irreparably by splitting apart at the ridge.
A partial form of grouting was also practiced, where an external lime mortar grouting was applied, but only on the spaces between slates. This was used for larger slates and may have been applied to cottages that were re-roofed from thatch to slate. [6]
Grouted roofs are most distinctive in Pembrokeshire and are considered to form part of the vernacular architecture of the county.
Pembrokeshire slate is often of poor quality compared to North Wales slate, thus requires thicker, heavier slates. These heavy slates also needed to be set on a mortar bed beneath, and grouted above. [7]
A feature of the Pembrokeshire style of roof are a number of prominent vertical ridges on the outside of the roof. [8] These are caused by barbed wire being stretched over the roof before grouting. The wire can be firmly attached to the structure and the barbs on the wire act as a mechanical key to retain the grout in place. Over time and repeated re-grouting, the wires are lost beneath ridges that build up. Barbed wire was used because it was conveniently available to remote farming communities and performed well. It was not manufactured until the 1870s and so this style of roof is newer than the first use of grouting, even with cement. William [7] describes the used of barbed wire as being a twentieth century development, and derived from the earlier 'roped thatch' technique, where a roof of thatched straw or reed would be retained by straw ropes over it. [9]
The use of lime mortars began as limewashing. This was applied regularly to walls, and even to thatched roofs. [10] Although the cottage architecture of pre-industrial Wales, particularly in the South and South West, was based on earth walls more than mortared stone masonry, this was still coated externally with a limewash. By the later part of the eighteenth century, this fondness for limewashing and its frequency was noted by many travellers to the area. [11] [12] Turf houses though, whilst common, were not limewashed. [10]
There is some debate as to the materials used to construct an 'original' grouted roof. Clearly Portland and modern cement-based renders have been used most commonly in the last century. Portland cement first appeared in the 1820s. [13] Before this, lime plasters would have been used, particularly in rural areas where lime burning was a local industry through much of the country.
Many sources claim that lime plasters were used originally, with a move to cement renders as they became available in modern times. [4] [14] Others claim that the technique of grouting a roof only developed with the advent of the cheap and easily applied modern cements. [8] Certainly the 'classic' picturesque grouted roof of today, with its bright white finish and prominent wire ridges, is the product of Victorian materials that did not exist locally until the late 19th century.
Grouted roofs came to some prominence in 2007, when comedian and architectural restorer Griff Rhys Jones began work on Trehilyn farmhouse at Llanwnda, Pembrokeshire. [15] The building was in a poor condition throughout and the grouted roof was particularly bad. Restoration involved the construction of a new roof which, in keeping with the previous roof, was grouted during construction.
As has been a theme of building restoration in the UK for some years, a 'historically appropriate' lime plaster was used rather than a Portland cement. [16] [17] The results of the restoration generated much adverse comment. [18] On one hand, the brilliant whiteness of the new roof was criticised, even though their whiteness had always been a notable feature of such roofs and would inevitably tone down with natural weathering. A more incisive comment was to question whether a specifically lime plaster was appropriate for such a roof, raising again the question of when they first appeared. [8] The need for grouting at all on a brand-new roof was questioned, it being likened to, "taking a healthy child to a Victorian reenactment and breaking its legs to give the appearance of rickets." [8] Problems were also experienced during the restoration and some of the blame for these was laid variously, by those concerned and by the outside observers, on either the quality of the materials used or on the plasterers' technique. [8]
Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English, "plaster" usually means a material used for the interiors of buildings, while "render" commonly refers to external applications. The term stucco refers to plasterwork that is worked in some way to produce relief decoration, rather than flat surfaces.
Grout is a dense fluid that hardens to fill gaps or used as reinforcement in existing structures. Grout is generally a mixture of water, cement, and sand, and is employed in pressure grouting, embedding rebar in masonry walls, connecting sections of precast concrete, filling voids, and sealing joints such as those between tiles. Common uses for grout in the household include filling in tiles of shower floors and kitchen tiles. It is often color tinted when it has to be kept visible and sometimes includes fine gravel when being used to fill large spaces. Unlike other structural pastes such as plaster or joint compound, correctly mixed and applied grout forms a water-resistant seal.
Whitewash, or calcimine, kalsomine, calsomine, or lime paint is a type of paint made from slaked lime (calcium hydroxide, Ca(OH)2) or chalk calcium carbonate, (CaCO3), sometimes known as "whiting". Various other additives are sometimes used.
Stucco or render is a construction material made of aggregates, a binder, and water. Stucco is applied wet and hardens to a very dense solid. It is used as a decorative coating for walls and ceilings, exterior walls, and as a sculptural and artistic material in architecture. Stucco can be applied on construction materials such as metal, expanded metal lath, concrete, cinder block, or clay brick and adobe for decorative and structural purposes.
Earthbag construction is an inexpensive building method using mostly local soil to create structures which are both strong and can be quickly built.
Lath and plaster is a building process used to finish mainly interior dividing walls and ceilings. It consists of narrow strips of wood (laths) which are nailed horizontally across the wall studs or ceiling joists and then coated in plaster. The technique derives from an earlier, more primitive process called wattle and daub.
This page is a list of construction topics.
Lime is an inorganic material composed primarily of calcium oxides and hydroxides, usually calcium oxide and/or calcium hydroxide. It is also the name for calcium oxide which occurs as a product of coal-seam fires and in altered limestone xenoliths in volcanic ejecta. The International Mineralogical Association recognizes lime as a mineral with the chemical formula of CaO. The word lime originates with its earliest use as building mortar and has the sense of sticking or adhering.
A lath or slat is a thin, narrow strip of straight-grained wood used under roof shingles or tiles, on lath and plaster walls and ceilings to hold plaster, and in lattice and trellis work.
Roof shingles are a roof covering consisting of individual overlapping elements. These elements are typically flat, rectangular shapes laid in courses from the bottom edge of the roof up, with each successive course overlapping the joints below. Shingles are held by the roof rafters and are made of various materials such as wood, slate, flagstone, metal, plastic, and composite materials such as fibre cement and asphalt shingles. Ceramic roof tiles, which still dominate in Europe and some parts of Asia, are still usually called tiles. Roof shingles may deteriorate faster and need to repel more water than wall shingles. They are a very common roofing material in the United States.
Plasterwork is construction or ornamentation done with plaster, such as a layer of plaster on an interior or exterior wall structure, or plaster decorative moldings on ceilings or walls. This is also sometimes called pargeting. The process of creating plasterwork, called plastering or rendering, has been used in building construction for centuries. For the art history of three-dimensional plaster, see stucco.
A plasterer is a tradesman or tradesperson who works with plaster, such as forming a layer of plaster on an interior wall or plaster decorative moldings on ceilings or walls. The process of creating plasterwork, called plastering, has been used in building construction for centuries. A plasterer is someone who does a full 4 or 2 years apprenticeship to be fully qualified
Lime mortar or torching is a masonry mortar composed of lime and an aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, used in ancient Rome and Greece, when it largely replaced the clay and gypsum mortars common to ancient Egyptian construction.
Earthen plaster is a blend of clay, fine aggregate, and fiber. Other common additives include pigments, lime, casein, prickly pear cactus juice (Opuntia), manure, and linseed oil. Earthen plaster is usually applied to masonry, cob, or straw bale or backing boards such as gypsum in interiors or exteriors as a wall and ceiling finish. It provides protection to the structural and insulating building components as well as texture and color.
A tin can wall is a wall constructed from tin cans, which are not a common building source. The cans can be laid in concrete, stacked vertically on top of each other, and crushed or cut and flattened to be used as shingles. They can also be used for furniture.
The Ephraim Hawley House is a privately owned Colonial American wooden post-and-beam timber-frame saltbox house situated on the Farm Highway, Route 108, on the south side of Mischa Hill, in Nichols, a village located within Trumbull, Connecticut, in the New England region of the U.S. It was expanded to its present shape by three additions. The house has been located in four different named townships, but has never been moved; Stratford (1670–1725), Unity (1725–1744), North Stratford (1744–1797) and Trumbull (1797–present).
Seven Chimneys, also known as the Nicholas Zabriskie House, was built between 1745 and 1750 by Nicholas Zabriskie, an early Dutch settler in the Hudson Valley. It is the oldest house in Washington Township, Bergen County, New Jersey. Notable visitors include Theodore Roosevelt. The house was used as a stop on the Underground Railroad. Seven Chimneys was placed on the National Register of Historic Places in 1971.
Cement render or cement plaster is the application of a mortar mix of sand and cement, and water to brick, concrete, stone, or mud brick. It is often textured, colored, or painted after application. It is generally used on exterior walls but can be used to feature an interior wall. Depending on the 'look' required, rendering can be fine or coarse, textured or smooth, natural or colored, pigmented or painted.
Roof tiles are designed mainly to keep out rain, and are traditionally made from locally available materials such as terracotta or slate. Modern materials such as concrete, metal and plastic are also used and some clay tiles have a waterproof glaze.
Lime-ash floors were an economic form of floor construction from the 15th century to the 19th century, for upper floors in parts of England where limestone or chalk were easily available. They were strong, flexible, and offered good heat and sound insulation.
...the tyling is all slatt, which with the Lime its Cemented, which makes it Look white Like Snow, and in the sun shineing on the slatt it Glisters., cited in [1]