BCD 2017

128 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 7 either hewn or sawn and may contain waney edge on one or more arrises. Typically, the boxed heart timbers stay straight but they do tend to ‘shake’ (or crack) on one or more faces, due to differential drying between the radial and tangential dimensions as they season. Halved timbers are first boxed as above and then sawn down the middle. This produces a distinctive rectangular section with waney edge on a maximum of two adjoining arrises. The wide faces tend to bow, with shakes developing on one or both of the two wider faces as they season. Quartered timbers are ‘boxed and halved’ as above and then each half is sawn again to produce four square sections with waney edge on a maximum of one arris on each quarter. They tend to bow in two dimensions but they do not shake as they season. Quarter-sawn or radially converted timber is produced by sawing or cleaving the log multiple times from the bark to the centre, producing thin, triangular sections. The bark and sapwood are trimmed off leaving boards that tend to stay flat and not split as they season. This is the predominant type of conversion for producing oak panelling, instantly recognised by the pattern of the lighter coloured medullary rays running as flowing flecks across the wide faces of the boards. Through-and-through or plain or flat sawn timbers are first boxed and then sawn into four or more evenly sized, rectangular pieces. Those pieces nearest the pith tend to cup more than those nearest the outside of the log but the latter can have one or two waney edges. Braces, struts and floorboards are typically converted like this. Multiple or multi-sawing is found with larger logs (above 300mm diameter) which have first been boxed and then sawn into six or more evenly sized pieces. Four pieces contain one waney arris, the others none, and usually only the timber(s) containing the pith develop any shakes. Timbers converted like this were typically used for floor joists and rafters from the 16th century onwards. They can be distinguished from quartered timbers by the shallower curve of any waney edge and by looking at the end grain if possible. Baulk re-sawing is restricted to large, imported, softwood, boxed heart timbers which were then re-sawn in England. In his classic 1937 book The Village Carpenter , Walter Rose described how the dirty outer faces of the hewn baulk were sawn off for joists and ceiling ties leaving a clean, sawn, boxed heart which was then sawn through and through for boards. Close inspection of Victorian houses undergoing repair work to the floors provides evidence of this practice. REPAIR PHILOSOPHY How should today’s conservator respond when fitting new timbers alongside historic ones? Modern structural timbers are generally bandsawn so their surface finish does not match that found on most historic timber frame structures. Firstly, the timbers can be used as they are, with their bandsawn finish; this is by far the most commonly encountered response. If a surface finish visually closer to historic timbers is specified, then a number of options have been tried over the last 40 years or so. Hewing timbers by hand is best practised on freshly felled logs but this approach is expensive and time-consuming. While it is theoretically possible to hew just a few millimetres off the exposed faces of bandsawn timbers with a side axe, in practice it is hard, slow, highly skilled work. More commonly, planes with convex blades are used obliquely across the grain in an attempt to imitate the undulating surfaces of hewn timbers. In the case of sawn timbers too, working them by hand is hard, slow work. Often a chainsaw mill is used instead. It cuts at a similar angle to pit sawing so it imitates the historic surface finish. Cleaving is still fairly widely practised today for the fencing, shingle and lath markets due in part to its inherent speed, so obtaining good cleft material is usually straightforward. Philosophically, where do the above modern imitations leave us? Working the surfaces of the timbers, after the imitation historic finish has been applied, to such a level that it is difficult to distinguish between modern and historic – for example by drilling fake woodworm holes or hitting surfaces with chains to simulate wear and tear – is deliberate deception and should be avoided. This approach confuses and distorts the archaeological record and is counter to the long-established conservation principle of ensuring that new is distinguishable from old. An approach which is widely advocated is that of ‘honest repair’, but this is a rather vague and ambiguous term in practice, with some repairs being left with razor sharp arrises in stark contrast to the weathered, more softly contoured adjoining timber. The time-honoured response is often: ‘don’t worry, it will soon weather in!’ However, the time required for this process to start can vary from a year to many decades, depending on exposure and humidity. It is often best to follow a twin-track approach which allows the new timber to be easily identified on close inspection, while from a distance it blends in visually with its neighbours. This can be achieved in a number of ways; for example by removing any sharp arrises, by sanding off most of the visible bandsaw marks, and by careful initial selection and matching of the timber. JOE THOMPSON of Sussex Oak and Iron has been working with historic timber frames since 1990. He is carpenter in residence at the Weald and Downland Open Air Museum in Sussex, where he also lectures and runs practical workshops. Circular sawn surface: a product of the steam age, circular sawn timber is easily identified by its very distinctive, large, curved saw marks which radiate across the surface. Bandsawn surface: recognisable by very distinctive and widely spaced saw marks that are at 90° to the length of the timber. Boxed heart timbers have just the outside of the log removed so tend to be roughly square in section. During seasoning they stay straight but do tend to ‘shake’ (or crack) on one or more faces. Halved timbers are first boxed and then sawn down the middle. The wide faces tend to bow, with shakes developing on one or both of the two wider faces as they season. Quartered timbers are boxed and halved and then each half is sawn again to produce four square sections. They tend to bow in two dimensions but do not shake as they season.