Sanding is one of the most common methods, as it cuts through varnish and stain, and reveals a fresh layer of wood. Although sanding is fast, it produces a great deal of fine-particle dust, which is easy to inhale, and it can remove more wood than you desire.
Safety[ edit ] Because of flammability concerns, many product containers list safety precautions for storage and disposal for varnishes and drying oils as they are flammable, and materials used to apply the varnishes may spontaneously combust.
Many varnishes contain plant-derived oils e. These are highly flammable in their liquid state. A highly important note, that is often over looked, all drying oilscertain alkyds including paintsand many polyurethanes produce heat an exothermic reaction during the curing process.
Thus, oil-soaked rags and paper can smolder and ignite into flames, even several hours after use if proper precautions are not taken. Therefore, many manufacturers list proper disposal practices for rags and other items used to apply the finish, such as disposal in a water filled container[ citation needed ] History[ edit ] Early varnishes were developed by mixing resin—pine sap, for example—with a solvent and applying them with a brush to get the golden and hardened effect one sees in today's varnishes.
Varnishing is also recorded in the history of East and South Asia; in IndiaChina and Japanwhere the practice of lacquer work, a species of varnish application, was known at a very early date.
The Tang Chinese used medieval chemistry experiments to produce a varnish for clothes and weapons employing complex chemical formulas applied to silk clothes of underwater diversa cream designated for polishing bronze mirrors, and many other useful formulas.
However, different types of varnish have different components. After being applied, the film-forming substances in varnishes either harden directly, as soon as the solvent has fully evaporatedor harden after evaporation of the solvent through curing processes, primarily chemical reaction between oils and oxygen from the air autoxidation and chemical reactions between components of the varnish.
Resin varnishes "dry" by evaporation of the solvent and harden almost immediately upon drying. Acrylic and waterborne varnishes "dry" upon evaporation of the water but will experience an extended curing period. Oil, polyurethane, and epoxy varnishes remain liquid even after evaporation of the solvent but quickly begin to cure, undergoing successive stages from liquid or syrupy, to tacky or sticky, to dry gummy, to "dry to the touch", to hard.
Environmental factors such as heat and humidity play a very large role in the drying and curing times of varnishes. In classic varnish the cure rate depends on the type of oil used and, to some extent, on the ratio of oil to resin.
The drying and curing time of all varnishes may be sped up by exposure to an energy source such as sunlightultraviolet light, or heat.
Drying oil There are many different types of drying oils, including linseed oiltung oiland walnut oil.
These contain high levels of polyunsaturated fatty acids. Drying oils cure through an exothermic reaction between the polyunsaturated portion of the oil and oxygen from the air.
Originally, the term "varnish" referred to finishes that were made entirely of resin dissolved in suitable solvents, either ethanol alcohol or turpentine. The advantage to finishes in previous centuries was that resin varnishes had a very rapid cure rate compared to oils; in most cases they are cured practically as soon as the solvent has fully evaporated.
By contrast, untreated or "raw" oils may take weeks or months to cure, depending on ambient temperature and other environmental factors. In modern terms, "boiled" or partially polymerized drying oils with added siccatives or dryers chemical catalysts have cure times of less than 24 hours. However, certain non-toxic by-products of the curing process are emitted from the oil film even after it is dry to the touch and over a considerable period of time.
It has long been a tradition to combine drying oils with resins to obtain favourable features of both substances. Resin[ edit ] Many different kinds of resins may be used to create a varnish., , and grit sandpaper, for smoothing the wood Oil-based wood conditioner, to pretreat the wood prior to staining Cloth, to apply wood conditioner Oil-based wood stain, for tinting the wood Oil-based polyurethane varnish, applied as a protective topcoat finish Stir stick, to stir polyurethane grit sandpaper, for sanding the.
Varnish is a clear transparent hard protective finish or film. Varnish has little or no color and has no added pigment as opposed to paint or wood stain which contains pigment.
However, some varnish products are marketed as a combined stain and varnish. First, varnish is a film finish, as are shellac and lacquer, which means it cures hard so it can be built in layers to the desired thickness and effect on the wood surface. It is made from oil-modified resins, usually polyurethane and/or alkyd, along with chemical driers, and can be thinned as desired with mineral spirits.
Before applying it, wipe off the surface with a tack cloth. Stir the varnish in a figure-8 pattern, using a stirring stick. Never shake varnish, as that may produce bubbles that dry into the surface.
Dip about ½” of the bristles into the varnish, tapping off the excess so that it falls back into the can. Spar varnish is perfect for outdoor projects and for raw wood used for exterior doors and trim on rustic homes.
In addition to protecting the wood, it also provides natural ultraviolet light protection. And wood varnish adheres better to a well-sanded, sealed surface. Pick a sealer that’s designed for the overlying varnish, preferably of the same brand. If you use a sanding sealer that’s incompatible with the wood varnish, the surface may crinkle or even flake off.