Introduction to Wood Finishing
Finishing Touch: Join us as we delve into the challenging, and often misunderstood, world of wood finishing. Our new informative column, “Finishing Touch”, will help take the mystery out of finishing and allow you to choose and apply the right finish, no matter what type of project you’re working on. We start with why you should finish a project at all.
This issue begins our new series on wood finishing. For anyone new to the craft of woodworking, knowing which finish to use and how to apply it is fraught with confusion, uncertainty and disappointment. But wood finishing doesn’t have to be all that complicated or distressing. In this series we’ll look at how to best prepare your projects for finishing. We’ll cover the most common types of finishes – what they are and how to apply them – and, we’ll look at a variety of specialty topics, including pore filling, staining, dying, toning, glazing, ebonizing, spraying and French polishing.
In this introductory article we’ll look at a few things that we need to be aware of before we even begin to put finish to the wood.
Heat and Moisture Protection
Some finishes may need to stand up against heat and warm liquids, if they’re spilt. Certain finishes are great at this task, while others soften and discolour.
Some furniture has a country feel to it, and is a bit less refined and glossy. In these cases you may not need extreme durability from your finish, but want ease of application and a nice colour.
Many finishes emit solvents, or other chemicals, once they’re applied. If you’re using a finish like this protect yourself and the environment with equipment like a face mask and spray booth. (Photo by Fuji Spray)
Why We Finish Wood
There are a number of reasons that we apply finishes to wood. The most obvious is that it protects the surface of the wood from dirt, stains, moisture, and abrasion. And, to some extent, it even protects us from bacteria that might otherwise reside in the nooks and crannies of wood – especially in very open pored wood like ash, elm or oak used in kitchens and dining rooms, or on children’s furniture.
The choice of finish we use will often depend on what the project is going to be used for. The priority for a kitchen tabletop would be a finish that offers superior abrasion and moisture resistance, while for a display cabinet the dominant concern might be for a finish that enhances the natural colour and grain pattern of the wood, and less for its resistance characteristics.
Another important reason we finish wood is to reduce moisture exchange. Wood responds to changes in the level of moisture around it by expanding and contracting. This affects the structural integrity of the projects we build and can cause the wood to warp, crack or split. While no finish will completely eliminate moisture exchange, it can significantly reduce its occurrence. This is why it’s important to apply a finish equally on all surfaces of your project, even those that won’t be visible.
We also finish wood to enhance its appearance – to ‘bring out’ or ‘pop’ the grain. Sometimes we may find the open pores in a wood unappealing, and want to fill them to produce a flatter, smoother finish. At other times we may want to match the colour of wood to an existing piece of furniture, or we may simply want to make one species of wood look similar to a different species.
Finishing is a bit of a balancing act. In general, there is no ‘best’ finish. Rather, you’ll try to choose a finish that balances the need for protection while maximizing the appearance of your project.
Finishing Starts at the Beginning
You can avoid some finishing surprises by giving a bit of thought to the choice of wood before you begin your project.
Often we build projects that combine wood in different forms, the most common being solid wood and plywood. We may also incorporate different wood species in the same project. The same finish applied to wood in its different forms, and to different wood species, may not always produce the same results. This is due to the characteristics of the material being used. As well, the way that the wood is cut – plain-sawn, quarter-sawn or livesawn – will affect the appearance of your project.
Your Health and the Environment
Almost all finishes, as well as the solvents and thinners we use with them, contain harmful chemicals. Some may have no immediate, apparent impact, while others can produce a temporary acute impact. Regardless, over the long term, repeated exposure to these chemicals can have irreparable, and often dramatic, detrimental impacts on your health. It’s wise, then, to consider that none of the finishing materials you use are good for your health. Protect yourself by working in a well-ventilated space. Ensure you wear a NIOSH-approved organic vapour respirator and latex or vinyl gloves when handling solvents and applying finishes.
Some finishing materials are also dangerous because of the flammability of their solvents, and may require specific storage and disposal precautions. Never pour solvents or finishes down the drain – store them in appropriate containers and take them to a recycle centre. Spread rags used to apply finishes in a single layer so heat dissipates while the material cures. After the rags become hard and brittle they can be placed in the garbage.
In the next article in this series we’ll look at surface preparation – what you need to do to prepare wood surfaces to receive a finish. It’s the most critical step in obtaining a great finish, and one that you’ll want to master.
A Basic Finishing Kit
Regardless of the specific type of finish you’ll use, there are some common finishing supplies you’ll want to keep on hand. Store them in a cabinet or plastic container for easy access and to keep them dust free. It’s best to purchase the solvents, thinners, and other supplies you need as required for a specific finish. At a minimum you’ll want to have these supplies on hand:
• A NIOSH-approved organic vapour respirator
• Latex or vinyl gloves
• Painter’s tape
• #0000 (extra fine) oil-free steel wool or super fine 3M fiber rubbing pads
• Disposable plastic mixing cups
• Lint-free rags
• 2″ flat brushes: natural-filament (for solvent-based finishes); synthetic-filament (for water-based finishes)