SOFTWOODS and HARDWOODS

Post 513  by Gautam Shah

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Timber varieties are broadly categorized as Softwoods and Hardwoods, with underlying presumptions that former ones are softer and duller in colour and lighter in weight, whereas the later are harder or tougher and darker in colour and heavier in weight. Softwoods as the name implies are soft grained, but are necessarily not inferior to the commercial quality of hard woods. The tones of sap and heart portions of soft woods are not acutely different from each other.

Wikipedia image by Author Patrick Dinnen (talk)

Hardwood timbers come from deciduous trees that lose the leaves annually or biannually, and Softwood timbers come from conifers, which usually remain evergreen. Hardwood trees tend to be slower growing, and are therefore the timbers are more dense in grain, but not always. Softwood trees grow in large tracts and very rapidly.

Wine barrels Wikipedia image by Author Gerard Prins

Classifying trees as hardwood or softwood is often misnomer definition. As for example Balsa wood is one of the softest timbers, though technically it is classified as hardwood. Likewise, the wood of Yew trees, which though technically a softwood, is tougher than many hardwoods like oak. Wood classification actually depends on the seeds produced by the tree. Hardwood trees have seeds in the form of a shell or fruit. Ancient Greek word shows, that angiosperm =vessel seed or contained in a protective vessel. Softwood trees produce seeds without any cover and called gymnosperm = naked seed.

Timber carving Detail of the Last Supper from Tilman Riemenschneider’s Altar of the Holy Blood, 1501-05, Rothenburg ob der Tauber, Bavaria Wikipedia image by Author Tilman2007

Softwoods or conifers are less dense and so are easy to cut or drill. Softwoods on being planned and sanded expose tender remnants of food transfer area. Such tender areas contain un-synthesized sugars and starches, which readily absorb and release moisture resulting in swelling and shrinkage. Small amounts of aliphatic compounds, waxy and resinous substances which along with the softness of grain help, at least initially, to provide a very smooth surface texture. The softness of the surface is however, lost with exposure to atmosphere. Examples of softwoods are pine, douglas, spruce, redwood, fir, cedar, juniper, cheal, deodar, larch. juniper, yew and cypress.

Grand Fir (Abies grandis) cross section, Rogów Arboretum, Poland Wikipedia image by Author Crusier

Softwoods are used for roofing trusses, temporary support structures for construction industry, warehousing pallets, packing cases, etc. About 80% of all timber come from softwoods. Softwoods are used as intermediate material for wood composites such as block-boards and production of paper pulp, MDF, etc.

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Hardwoods are denser (heavier in weight) and therefore sturdier. Hardwoods are darker in colour, and the heart portion is fairly distinguishable from the sap portion. The denseness results in smooth cut and on planning offers smoother finish. On planing and sanding the hardwood surface shows intermittent branches of pores, the food transfer areas are clearly visible. The pores are very narrow in width and short in length and are full of remains of un-synthesized sugars and starches. The pores in hardwoods are of shorter length but are prominent. The pores on drying tend to shrink in, but being fewer and tightly packed by the surrounding fibres. The effect of moisture transfer is not very acute as with soft woods. Hardwoods being tough-grained, require greater efforts for smoothing but then the surface retains its fairness much longer. Examples of hardwoods are oak, maple, walnut, alder, balsa, beech, hickory, mahogany, teak and sycamore.

Australian Acasia Wikimedia image by Author Forest & Kim Starr

Hardwoods are used in furniture, decks, flooring, and structures that need to last longer. Hardwoods supplies are varied in species, and comparatively smaller in volumes. Hardwoods are more expensive than softwood. Hardwoods are used for production of exotic veneers.

Table surface made of Sheesham Wood Wikipedia image by Author Andy king50

Hardwood or Softwood, both have their unique features. But a wood should have a tight, even grain and colour. Excessive knots or irregular patterns are good for decorative effects but not for structural usage. Similarly wood cracks or splits should be avoided. Woods with resins, gums or tendency to de-colouration (in presence of sunlight or water) need to be carefully used.

Traditional Malay boat building with Neobalanocarpus heimii, is a tropical hardwood Wikipedia image by Author Christoph Swoboda

One of the oldest (since 1906) and popular method of testing hardness of wood is the Janka Hardness Test. The test is the average amount of impact force required to ‘embed a .444-inch (11.27mm) steel ball to half its diameter’. Most of the time, the numbers you’ll see quoted here are referring to side hardness. As per this test the hardest wood is Australian Buloke (Bull-oak) tree, describes as rock like hard. Few of the harder Indian varieties include Sadad (Combretaceae -Rangoon creeper family > Terminalia elliptica) used for ladder steps and thresholds.

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WOOD SURFACE FINISHING

WOOD SURFACE FINISHING

Post 472 by Gautam Shah

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Woods’ surfaces have some inherent qualitative characteristics. These relate primarily to the species of wood, broadly the Softwoods and Hardwoods. Other features include presence of oils or resins, food transfer cells, pores, nature of grains (straight, entwined, interlocked, curly or mottled), and local variations of grain colours. Timbers in spite of good seasoning practices show changes in the wood surface during various seasons, stresses and over long term conduct. Wood products are created from young timbers (freshly seasoned) as well as reuse of aged timbers. Wood finishes, are applied on fresh timbers, for conservation of existing status, and for rejuvenation or reformation exercises.

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Soft-wood knot

Wood finishes are broadly of three classes: 1. Finishing done to timbers, 2. Finishing fashioned after a product or item is formed and 3 Finish processes for repairing or reconditioning an existing product.

Clonfert Cathedral Choir Stalls being Ammonia fumed to darken the colour and enhance grains

1 Finishing done to timbers is accomplished with sizing and shaping operations, and include levelling and straightening of the surface.

2 Finishes fashioned after a product or item is formed, are of two types: Finishing with tools, relating to micro-removal of surface material, by grinding, sandpapering, burnishing, singeing, etc. Finishing, a surface, with applique materials, such as surface sealing, putty application, staining and coating. In some instances it may include covering with film, foil or printing.

3 Finish processes for repairing or reconditioning an existing product may involve full or partial removal of existing applied finishes, re-levelling or straightening of an original timber surface to correct deformation of bending, warping, surface irregularities caused by differential shrinking. The removal of existing applied finish is most difficult as it is a matter of conservation, preservation, correction, all in a very limited scale of intervention.

Soft wood planks

Differential wood grain colour

SOFTWOODS are in dull in colour, light in weight and soft grained, but not always inferior in quality. The sap and heart portions are not very different in colour. Soft woods are easy to finish by planing and sanding. A finished surface exposes the tender portions, the remnants of food transfer areas. And these are likely to shrink and decay over a long period, in spite of seasoning. Small amounts of aliphatic compounds, waxy and resinous substances give a fresh wood, a short lasting, smooth feel and slight sheen. Softwoods due the grain structure and the constituents are difficult to stain. Its surface cannot be well sealed and levelled by chalk or oxide pigments, but a coat of very low viscosity NC Lacquer can seal the face.

Pine wood

Softwood articles are difficult to restore, as the wood grains of aged article show uneven settlement. To correct this, entire applique coating must be removed, and surface re-ground, or heavy surface filling by low opacity minerals is required. Old timber articles show very dry surface, which is prone to chipping along the grain.

HARDWOOD Quebracho colorado wooden sleepers of Argentine origin in Uruguay

 HARDWOODS are darker in colour and heavier in weight. In hard woods, the heart portions are fairly distinguishable from the sap portions. On planing and sanding the hardwood surface, intermittent branches of pores, the food transfer areas are clearly visible. The pores are very narrow in width and short in length. The pores on drying tend to shrink in but being fewer and tightly packed by the surrounding fibres, effect of moisture transfer is not very acute as with soft woods. Hardwoods are tough grained and require greater efforts for smoothing, but the finished surface retains its fairness much longer.

Abies grandis (grand FIR) Trunk section

Rough finishes are cheaper, take less time to prepare and require simple tools and techniques. Some rough surfaces give better bondage to preservatives and coatings. Rough surfaces are good for moisture movement but are highly vulnerable to insect and bacterial growth. Rough finishes hide local defects such as stains, knots, ugly grains, fine cracks etc.

Rough or as sawn finish of Hardwood

Smooth finishes are costly, require fine tools and superior techniques. Smooth finish often give poor bondage to preservatives and coatings but one requires much lesser quantity for coverage. Such finishes collect little dirt. Smooth finishes are not as susceptible to bacterial growth as the rough finishes. The timbers for smooth finish should have a fine grain pattern. Heart portions are much better for smooth finish then sap portions. Sap portions may however be finished fairly smooth, provided are immediately covered with moisture proof coating. Hardwoods usually provide smoother finish and of permanent type then soft woods. Woods with resinous or oily substances generally have smooth feel, however, if the substances are reactive or soluble in water or aliphatic solvents, may create problems during coating. Sisam and rosewood have oily or waxy face, which does not allow oil paints or varnish finish. Such woods need to be covered with very thin coatings based on solvent evaporation drying; like nitro cellulose lacquer. Timber surfaces are flame charred or singed to provide slightly darker to black tone to selected areas. The flame is either ‘cool’ capable of depositing carbon, or `hot’ to singe the surface.

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