36 C O N T E X T 1 3 4 : M A Y 2 0 1 4 Georgian joiners, and to a greater extent Victorian ones, had access to a surprisingly wide range of timbers, both local and imported. As today, price and availability influenced which woods were used. Scots pine or redwood (Pinus sylvestris), also known as northern pine, red fir, yellow fir, Scots fir and Scotch fir, was used for all components of windows manufacture. Expensive teak (Tectona grandis) and oak (Quercus robur) were used in high-quality joinery, in addition to window and door sills. Pitch pine (Pinus rigida) was used for sills and fine joinery in addition to structural uses. American longleaf pine (Pinus palustris) and loblolly pine (Pinus taeda) were also used in place of pitch pine. All three were a source of pitch, highly resistant to rot, hard wearing and therefore popular for sills, flooring and structural work. Red pine (Pinus resinosa), also known as Norway pine and Canadian red pine, was used for furniture and interior joinery.Yellow pine (Pinus strobus), also known as American yellow pine and white pine, was used for all types of joinery. Mahogany (Swietenia macrophylla) was highly regarded, but not for windows. Although popular today with some timber merchants, especially those on the high street, spruce or whitewood (Picea abies), also known as Norway spruce and white fir, was not well regarded by theVictorians, who found it suitable only for ‘common joinery’ and packing crates. Typically Scots pine and certain other softwoods used from the late 18th century until relatively recently came from forests around the Baltic, where the short growing season means that the timber grows slowly and is close-grained. It was air dried over several years, sometimes after steam or water seasoning.Today wood of such quality is no longer available commercially (or legally), and the softwood now used is typically fast grown and kiln dried. Kiln drying is only problematic if it has not been thorough, in which case the wood may twist as it continues to air dry in situ. Today two of the most commonly available timbers used for window repairs are spruce (whitewood) and Scots pine (redwood). Taking our lead from the Victorians, Scots pine is definitely the preferred option. The reclaiming of historic timbers such as rafters can potentially provide well seasoned and very compatible repair material, and is also good recycling practice. When introducing repair material, ensure that the grain is matched to the existing wood, otherwise natural movement, especially in new wood, will cause problems such as the opening of the joints. Opinions vary regarding the suitability of epoxy resin repairs in conservation. Being impermeable, resin prevents the evaporation of moisture, and it can fail when incorrectly gauged or when applied to poorly prepared backgrounds such as friable or decaying wood. Some practitioners report good results when mixing resins with fine sawdust, wood flour or stone dust in an effort to improve compatibility and appearance. Pointing around the window perimeter where the frame meets masonry is important in preventing water ingress. Avoid sand and cement mortars: being brittle, cement is unable to move with the wooden frame and separation will eventually occur, allowing water ingress. When applied correctly, traditional burnt sand and linseed oil mastic will last decades, whereas modern trowel mastic bears no resemblance to traditional burnt sand mastic and is prone to fail. Most window sealant products supplied in a tube are designed for modern construction and, despite remaining flexible, prevent the evaporation of moisture and encourage wood decay. Burnt sand mastic is widely available from specialist conservation suppliers. When performing a window repair, such as to a frame or stile, a competent joiner knows that when bonding new material to old, the larger the surface area of contact, the stronger the repair. Overlapping new and old via a glued and screwed halving-joint is a simple but effective way to achieve this. If the repair is to be obvious, flat-head brass screws in cups provide an acceptable finish. Over-zealous repairs create their own problems. A typical mistake is to plane the normally hidden sides of the sash stiles where they make contact with the window frame. This is rarely required as window frames do not tend to get smaller and sashes do not Poor painting practices and using silicone to join old and new wood have allowed water damage to this repair. Debris within the window frame can accelerate decay. This window had been repaired several years earlier, but the debris had been ignored.This encouraged dampness, causing the lower part of the frame to rot.
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