By Ntsako Khosa
Wood is a building material that is versatile and flexible, so clients may choose to paint or coat it; we look at how this can be done while ensuring longevity of the wood.
It is not often that clients request timber to be used on a job, so it is important to do some research first and ask questions such as what type of timber will be used, where will the material be placed (indoor or outdoor), which product works best for the material, will it require maintenance after painting or coating?
“The basic rules hold true for all types of timber types: preparation, application and using the right products are all essential, irrespective of the timber type you are treating,” says Frikkie Greeff, Woodoc, MD.
Once all of this has been determined, preparation is the next step. Stefan le Hanie from Howard Products says that when it comes to preparation, it depends on the finish of the timber. “An antique for example would be treated by one of our products. Restor-A-Finish preserves the original wood finish. It also helps preserve its authenticity.”
“There are different types of wood and each has a different characteristic that needs consideration prior to application of a coating,” says Guy Lawson, director at My Law Chemicals and Excelsior Paints.
The procedure may vary from wood types, but the same basic principles apply and include:
- Checking the moisture content in the wood first (the wood must have a moisture content below 20% before coating or the coating can fail);
- The wood must be abraded with sand paper to open the wood grain and allow the coating to penetrate (different woods have different porosities); and
- Any residue like resin from the wood knots and dust and contaminants must be treated or removed before coating.
Carel Steenkamp, senior product specialist at Rubio Monocoat, says that this step is key.
“Ensure that any filling is done and the fillers drying times are respected before moving on to sanding,” he advises.
Sanding the wood properly is one of the neglected aspects in the process of painting or coating timber. Greeff advises that the wood should be sanded back to bare wood. “This will allow the new coating the best opportunity to bind with the wood. Presence of an old coating will prevent this and when the old coating delaminates, it will take the new coating with it.”
After preparing the wood, it is imperative to follow the application instructions. “Always read the Technical Data Sheets before using the product. It is vital to understand the application methods, drying/curing times, coats required before starting a project,” says Steenkamp. “Each product has its own unique characteristics that make it essential to apply the product in a specific way. If essential information regarding the nature and use of the product printed on the packaging is ignored, it is unlikely that the application will be successful,” says Greeff.
He stresses that indoor products must be used for indoor applications, likewise for outdoor applications. “Indoor products are generally formulated to dry relatively quickly and hard. They also do not contain ultra-violet (UV) absorbers and other additives necessary in outdoor products. Outdoor products are formulated to dry slower (as they must remain flexible for longer periods to be able to survive the large temperature fluctuations that outdoor wood is subject to). This means that they will tend to remain slightly soft and ‘sticky’ if used indoors. They also contain a multitude of additives required for their survival in outdoor conditions which make them a little more expensive than indoor products,” he says.
“Interior wood furniture coatings have a refined smooth finish and are formulated to withstand everyday bumps and knocks, products such as toothpaste, makeup, condiments, alcohol spillage and so on. Exterior coatings on the other hand need to withstand the natural elements of wind, sun, rain, hail and airborne contaminants amongst other things,” explains John Wanliss, MD of WoodGlass Coatings. He shares that quality water based exterior coatings offer flexibility and are non-yellowing.
“Wood is sensitive to photochemical degradation and preventing ultra violet light from penetrating the timber surface therefore destroying the lignin is the major challenge for the paint chemist. All good quality exterior coatings contain one or more additives to filter and absorb harmful UV radiation.”
Wanlis advises the following three-tier approach to combat the effects of UV, recommended by research and development laboratories, ICA Group:
- A water-based, coloured, impregnating sealer is applied to the prepared timber. This deep penetrating sealer enhances the timber colour as it contains semi-transparent oxide pigments. The pigments absorb UV and, together with subsequent coats, limit the effect of UV radiation on the wood.
- A water-based sealer is applied next, which is either a clear coat or may have a translucent colour. A good quality clear sealer will contain UV absorbers and light stabilisers while the coloured type typically contains a UV absorber and transparent pigments.
- The final coat will be clear or translucent and contain UV absorbers and transparent pigments. This multilayer approach offers superior timber protection against the elements including UV radiation.
Application and treatment
When it comes to putting paint to wood, a basic understanding on how to apply a coating with a brush is all you need. Greeff states that there are many short videos on the internet that show the correct technique. Woodoc provides training to DIY timber enthusiasts while the South African Paint Manufacturers Associations (SAPMA) has rolled out online training for retail paint sellers.
“Basic spray systems for DIY to professional applicators, which need basic skills and training all the way to more technical spray airless / air-assisted systems and then onto highly specialised coating methods like curtain coating for bulk manufacture plants,” Lawson says.
“The SAPMA training programme is a webinar that teaches how to paint. Once they pass they move one to the next module. The modules offer training in painting internal and external plastered walls; the painting of gypsum board ceilings; the painting of palisade fencing; the painting of exterior walls; and the varnishing and sealing of external wood. Once all the videos have been viewed and assessed, an overall assessment is conducted,” says executive director of SAPMA, Deryck Spence.
It is important to use the right product for the right application.
“Deck sealers are generally very specialised products and are marked as suitable for application to a deck,” says Greeff. He adds that characteristics that you should look out for on an indoor product include fast-drying, good water repellent properties, good resistance to scratching and in the case of a sauna, low odour.
“As with choosing the correct tool for the job, it is advisable to use the best technique for the job. For large shop-fitting projects like furniture applications and saunas if varnish or paint is used, the surface can be sprayed or applied with paint brushes or rollers. For oil systems the application can be done by hand using an application pad as per instructions,” advises Greeff.
Oils available for treating timber include teak, raw linseed, boiled linseed, modified linseed and tung oil. “Hard wax oils are the new generation of triple coat applications. The oil doesn’t penetrate (or it penetrates very little) into the surface of the wood and keeps the natural look and feel of the wood with the option to add colour,” he says.
“Factors such as changing air moisture and rain may cause the wood to expand and contract,” says Lawson. He advises that wood should be regularly maintained to expand its lifespan by applying maintenance coats. “Some coatings (such as varnishes) need re-coating after a year or two and some coatings (penetrating oils and wax sealers) need re-coating twice a year.”
It is often said that to enjoy the material longer, preparation plays a huge contributing factor. There are many products on the market that clients and contractors can choose. You are indeed spoilt for choice. With a good oil, wax or sealer and proper maintenance you can never go wrong.
Tools for the job
- Sandpaper in various grades, from course to fine grit
- Paint stripper
- A scraper
- Something to neutralise the paint stripper after use
- A paint tray
- Good quality paint brushes in various sizes (widths)
- Mineral turpentine to wipe the wood after sanding (and to clean the brushes, if working with a turpentine-based sealer / varnish;
- Rubber gloves to protect your hands
- A painter’s apron or overalls
- Old newspaper to place under the item being worked on, to make cleaning up a bit easier
- A sturdy ladder, if necessary
|Varnish||Oils / waxes||Sealers|
|A product that merely sits on the surface of the wood, achieving minimal penetration. The old practice of diluting the first coat of a varnish to achieve ‘penetration’ does not work. The particle size of the varnish remains the same after dilution and only the solvent will penetrate the wood. Hence, varnish is a pure surface coating. When varnish is subject to weathering or damage, it will delaminate and ‘bubble’, peel or flake off wood. To re-coat the old surface, the coating must be completely removed.||Product does not form a surface coating to protect wood against mechanical damage / weather but penetrates the wood. It is excellent for stabilising wood in the short to medium term but offers no real protection to the wood surface. Thus, it must be re-applied regularly but generally no stripping or sanding is required before re-application.||A sealer combines the best characteristics of a varnish and an oil by penetrating wood to stabilise the wood and then builds up on the surface to offer surface protection and finish. Woodoc sealers all fall into this category. It is not necessary to strip or sand a Woodoc sealer off the wood before applying a new coat. In exterior conditions the surface will need a clean with a stiff brush (or fine steel wool) and turpentine to get rid of any pollution before application. In indoor conditions, a light sanding on and around the area to be repaired followed by a wipe-down with mineral turpentine is all that is required before application.|