G, H. (gargoyle - hydraulic set)

Gargoyle: a grotesque Gothic ornament, often used as an outlet for water.

Gathering on: a poor finish produced on run mouldings, caused by either insufficient pressure being applied or by the profile bending.

Gauging: the accurate gauge of quantities, and the proper mixing of different materials by means of a gauging rod or measure.

Gelatine: a natural moulding compound made from best quality Scotch glue. Melts in a water jacket container and requires much preparation, mainly superseded by PVC.

Gesso: a mixture of linseed oil and glue, toughened by the addition of whiting. Used mainly when plasterers formed ornaments by carving in freehand.

Gigstick: radius rod, an arm attached to a running mould and used as a compass leg to run circular features.

Glyphs: perpendicular flutings formed on the Doric frieze.

Gorge: a hollow moulding.

GRP: glass reinforced plastic. A resin cast reinforced by fibreglass.

GRC: glass reinforced cement. A ready mixed material of cement and chopped fibre glass used to reproduce traditional external finishes of all types as well as in a more modern method.

Grease plasterers: a release agent made up by mixing linseed oil or paraffin and tallow together and applying it to a shellac sealed surface.

Green: freshly applied plaster just before it sets or hardens.

Green state: the transitory state of a plaster which, in the process of drying out, had developed a little mechanical strength just from its loss of plasticity, but which has not yet developed significant strength from carbonation or hydraulic reaction. It may have a characteristic dull dark green colour.

Groin: the line formed by the intersection of two arches which cross over each other at any angle.

Groined ceiling: one formed by three or more curved surfaces, so that every two or more may form a groin, all the groins terminating in one point.

Groined vaulting: a vault which is formed by groins springing from various points and intersections.

Grotesque: the Gothic form of arabesques, consisting of plaited scrolls budding into figures, masks and animals of fantastic character.

Ground: a wooden member used as a screed to work to and a fixing member for the joiner. Also a collar when plastering columns and pilasters. Another use is that of moulding ground in fibrous plaster.

Ground lime: quicklime which has been ground down to a specified particle size range.

Grout: a mortar in a fluid state prepared and poured into place to fill fine joints or voids in masonry. Used for joints and crevices too small to access with mortar of normal consistency. Hydraulic lime, either natural or artificial, is generally preferred for grout due to the advantages of hydraulic set in depth of joint filled.

Guilloche: a form of plait, consisting of bands of fillets undulating and crossing each other.

Guttú: small drops, usually placed under cornices, etc.

Gypsoplaste: a cast taken in plaster. Gypsum, sulphate of lime, called plaster of Paris, also ëplasterí after it is calcined.

Gypsum: CaSO₄.2H₂O. The dihydrate of calcium sulphate from which the various forms of gypsum plaster are prepared by dehydration, and to which they revert on setting.

Hack: to cut back and roughen the surface.

Hair: used to reinforce solid plaster mixes. Usually taken from goat, oxen or horse.

Hair hook: a tool like a broad-pronged rake for mixing hair into a lime plaster or render.

Hard (plastering on the hard): when plaster is placed straight on to the masonry rather than on to laths it is said to be on the hard. In damp conditions an air lime plaster on the hard will not set.

Harling: a thrown finish of lime and aggregate, applied by throwing the material on to a well-prepared background. The heavily textured surface improves durability making it suitable for more severe climates. Traditional for external walls in Scotland.

Hawk (plastererís hawk): a hand tool made of a rectangular board with a handle below, to carry plaster for laying.

Helix: the small volutes under the abacus of the Corinthian capital.

Hessian: a woven jute canvas of either 3 or 6 mm mesh, used to reinforce fibrous plaster.

Hood Mould: the horizontal moulding over an arch.

Horse: can have two meanings: (1) the general term for a full running mould. (2) as an alternative to the slipper of a running mould.

Hydrated hydraulic lime: a Class C lime which has been hydrated into a dry powder at the works to be sold to the users in bagged form.

Hydration: in this context it is used to describe the chemical combination of calcium oxide with water to form the hydroxide. If carried out in a wet state this is called ëslaking to puttyí and with minimum water ëdry hydrateí or powder is formed.

Hydraulic binder: a binder which sets and develops strength by chemical interaction with water. It can set under water.

Hydraulic cement: the formal term for a cement which takes a hydraulic set.

Hydraulic lime: Class C limes are natural hydraulic limes prepared from limestones or chalks with clayey impurities. Artificial hydraulic limes are manufactured by mixing pozzolan with calcium hydroxide which enable the limes to harden even in damp conditions. Hydraulic limes were originally used in areas subject to frequent saturation or continuously damp conditions, and for hydraulic engineering works such as harbours and bridge piers.

Hydraulic set (of limes): the chemical combination of lime, burnt clay or other pozzolanic material and water to form a stable compound, even under water. This can either be arranged by mixing an air lime (or any other) with a pozzolan and water, or by mixing a hydraulic lime and water. In the latter case the lime and clay will already have formed intermediate compounds in the firing.
 
 

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