Protecting timber with wood coating solutions
Wood is a wonderful, versatile building material that has been used for thousands of years to construct everything from walls and floors of the family home to the furniture and cabinetry that fill it. In order to keep wood functioning at its best and most beautiful, it needs to be protected from abrasion, chemicals, moisture, UV radiation, weathering, and attack from microbes such as fungi and mold. This is the job of a wood coating. With such a wide range of substrates (hardwood, softwood, MDF, aged wood, or green wood) and applications (exterior, interior, furniture, building, residential, industrial) it is no surprise that wood coating is a billion riyal industry with a glut of players and products.
In this article we provide an overview of wood coating technologies and products, and the big brands and companies that make up the industry. As well as traditional coatings such as stains and varnishes we look at newer technologies such as powder coating, polyurethanes, and specialized wood coatings.
The 4 most common types of wood finishes
Varnishes, shellacs, stains, lacquers, polyurethanes, epoxies, and other wood finishes all have properties which work best when paired with the right application. Which wood coating you need depends on the type of wood and the end use of the substrate. A lot of these terms are used to refer generally to a finish, even though they denote specific finishes. Below is a brief description of different wood coating types and their properties.
- A wood stain is a coating which consists of dyes or pigments dissolved in a vehicle with a small amount of binder. When applied it soaks into the wood substrate and, depending on whether it is transparent or opaque, accentuates the wood grain or flatten out the wood with a color. Stains are used to give wood a particular color, and not for protective properties. If protection is needed a clear varnish is often applied over the top.
- A varnish is a transparent protective finish that dries hard and usually glossy (though they can be matte or semi-gloss). The basic components of varnish are a drying oil, resins, and a solvent, and the resin can be acrylic, oil, polyurethane, epoxy, and others. A varnish is a hard-wearing finish which is suitable for both indoor and outdoor use as it is waterproof, durable, tough, and versatile.
- A shellac is a softer form of finish which uses naturally-occurring resin (the shellac) dissolved in ethanol to provide a color and high-gloss finish for wood products. Shellac is now mostly used for furniture and instruments as it is not as durable as varnish, and alcohol spills will cause the shellac to dissolve.
- Lacquer is a form of finish in which the resin is dissolved in a solvent (unlike shellac which uses alcohol). It is harder than shellac, and is used to give a clear or colored shiny, glossy finish for furniture. The high VOC content in lacquer makes it a less popular option than water-based varnishes.
The wood finishing process built up layer by layer
Whether using paint, varnish, or stain it is important to use the correct application methods and processes. A primer cannot be used as a final topcoat, and though some topcoats can be applied as all-in-one systems, not all can.
The first layer of protection: industrial wood preservatives
Impregnation is a wood preservation method where protective chemicals are ‘impregnated’ into timber through the application of pressure. It makes the timber more durable and protects it from pests such as mold, fungi and insects. The preservatives are copper-based (a natural biocide), sodium silicate, thinned epoxy resins (preservative and sealer in one), or oil-based (coal-tar creosote). There are also fire-retardant impregnation chemicals which reduce the surface spread of flame, heat, and smoke.
Impregnation is an industrial wood coating treatment used to protect telegraph poles, railway sleepers, outdoor structures such as decks and playground equipment, as a building material in domestic, commercial, and public buildings, and more.
Building up the protective system: from primers to topcoats
When it comes to wood coating, the intended end use of the wood is vital for choosing the coating system. Exterior wood needs all the protection it can get, and a primer not only protects the wood from the environment, but also prevents cedar bleed and tannin stain – where the tannins from the wood are drawn to the surface and stain the paintwork. Acrylic sealing primers are one such coating, that both seals and protects. A primer also works to connect the wood substrate with the coating, ensuring adequate adhesion.
Surface finishes are those that do not penetrate the wood. Decorative paints, varnishes, lacquers, and shellacs are surface finishes, and so they dry to form a protective film on top of the wood. A clear topcoat protects the layers beneath while enhancing the final finish and providing abrasion and stress resistance. When working with a stain (which is a penetrative coating), a varnish or other surface coating will enhance and protect the color.
Modifying wood coating for special applications
Wood coating is not just about protecting the substrate while letting the beauty of the wood shine through. With technologies improving all the time, it is possible to powder coat wood substrates now, as well as protecting them from fire or making a deck anti slip. Below is more information on these specialty wood coatings.
FLAME RESISTANT SOLUTIONS – Fire is one of the greatest dangers for wood. There are two coatings that act as passive fire protection measures for wooden substrates: intumescent and fire retardant coatings. Intumescent coatings swell up in the presence of extreme heat, forming a protective layer of char between the wood and the fire. Fire retardant paints work by releasing flame-damping gases to prevent ignition.
SLIP RESISTANT COATINGS – Wood surfaces can be very slippery when wet, whether decking, stairs, ramps, or walkways. Anti skid paint works through the inclusion of an anti-slip aggregate or by creating a rough surface that provides more grip in wet or dry conditions.
POWDER COATING FOR WOOD – Powder coating is the process of using electrostatic charge to cause a dry powder to adhere to a substrate and then baking and curing the powder in an oven. The resulting coating is immensely durable and attractive, as well as being environmentally friendly due to the lack of solvent. Powder coating wood is now gaining widespread popularity, particularly for coating furniture.
Find wood coatings for your project in Qatar
The wood coating market is filled with recognizable and trusted brands and products. Globally the leading manufacturers in the wood coatings industry include AkzoNobel (Sikkens), PPG and Sherwin-Williams.
|Wood Coating Company/Brand||Wood Coating Product||Description|
|PPG Proluxe||Transparent Matte – Cetol SRD Wood Finish||A one-coat, transparent exterior wood finish for siding, railings and decks. Solvent-based penetrative coating in a range of colors.|
|Sherwin-Williams||Wood Classics Polyurethane Varnish||A solvent-based polyurethane finish with a satin or high gloss finish. For interior floor use.|
|Axalta||Zenith Waterborne Basecoat||A single component, high performance waterborne lacquer designed for finishing fine woodwork and cabinetry|
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