Varnish Treatment
Varnish For Wood Floor
‘Varnish’ comes from the Latin vernix meaning odorous resin.
The etymology is also derived from the Greek Berenice, the ancient name of modern Bengazi in Libya: a place credited with resinous trees.
Resin
Over the centuries, many recipes were developed which involved the combination of resins, oils, and certain waxes. These were believed to impart special tonal qualities to musical instruments. Most resin or ‘gum’ varnishes consist of a natural plant or insect-derived substance dissolved in a solvent. The resins include amber, dammar, copal, rosin {pine resin}, sandarac, balsam, and shellac.
The two main types are spirit varnish (which uses alcohol as a solvent) and turpentine or petroleum-based varnish. The latter is now replaced by several mineral-based turpentine substitutes such as white spirit or ‘paint thinner’.
Synthetic resins such as phenolic resin are typically employed as a secondary component in certain floor varnishes and paints. Resin varnishes ‘dry’ by evaporation of the solvent and hardens almost immediately upon drying.
Drying Oils
Untreated or ‘raw’ oils may take weeks or months to cure, depending on the ambient temperature and other environmental factors
Acrylic
Acrylic varnishes are typically colourless water-borne varnishes with the highest degree of clarity of all finishes. They ‘dry’ upon evaporation of the water but experience an extended curing period. They do not penetrate into the wood as well as oils. And sometimes lack the ‘brushability’ and self-leveling qualities of solvent-based varnishes. They generally have good UV resistance.
Other than acrylic and waterborne types, all varnishes are highly flammable in their liquid state as they contain solvents and oils.
Shellac
The basis for French polish, shellac is a very widely used single component resin varnish that is alcohol-soluble. It is not used for outdoor surfaces or areas where it comes into repeated contact with water (such as around sinks or bathtubs).
Shellac resin is a brittle or flaky secretion from an insect found in the forests of Assam and Thailand.
Alkyds
Typically, modern commercial varnishes contain an alkyd for producing a protective film. These are chemically modified vegetable oils which perform well in a wide range of conditions. They can be modified to speed up the cure rate and thus harden faster.
Polyurethane
Polyurethane varnishes are typically hard, abrasion-resistant and durable coatings – tougher and more waterproof than simple oil or shellac varnishes. They quickly build up a film – within two coats – whereas oil would require several applications.
Oil and polyurethane varnishes remain liquid even after evaporation of the solvent but quickly begin to cure, undergoing successive drying stages until they get hard. The drying and curing time is sped up by exposure to an energy source such as sunlight or heat.
However, as it penetrates less into the wood, even a thick film of ordinary polyurethane may de-laminate – fracturing if subjected to heat or shock – and leave white patches. This tendency increases with long exposure to sunlight or when applied over soft woods like pine.
‘Oil-modified’ polyurethanes, whether water-borne or solvent-borne, are currently the most popular wood floor finishes.
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