Almost everyone who puts up a new wooden deck is inevitably offered a range of information from friendly, well-meaning neighbours and relatives about when, where and how to finish it properly. But since a good part of this advice is often conflicting, the real trick involves deciding which strategy is actually true. And reality can be more than a little surprising in this realm.
After several disappointing attempts to finish outdoor wood back in the 1980s, I decided to spend as much time as necessary discovering the truth behind successful deck finishing. So, after talking to lab technicians at leading wood finish manufacturers, representatives from the Canadian Wood Council and the USDA Forest Service, I put together several strategies that use all the best advice available today. And since I’ve been using these approaches for 15 years of finishing outdoor wood, I can say for sure that they really do work.
There are three reasons deck finishing isn’t a simple as it looks. The first is that many finishing products are doomed to failure from the start. Independent consumer testing has shown that many formulations fail after less than a year of duty. And of the ones that make it past their first birthday, few offer more than mediocre performance. That’s why step#1 is simple: choose a deck finish that has proven itself effective through independent scrutiny. More on this evolving situation later.
The second source of trouble springs from the way people envision the outcome of their deck finishing efforts. Even with a very good product applied correctly, the need for ongoing maintenance of a wooden deck is higher than many folks expect. If you can get three years of life out of a wooden deck finish, you’re doing well. Even 18 months of respectable appearance isn’t bad considering the moisture, sunlight and abrasion that most decks are subjected to. This is why step#2 involves assessing yourself. Do you really have the time and ambition to maintain a wooden deck finish?
The final challenge of the deck finishing game involves understanding what proper application really means. New wood is actually a rather poor candidate for finishing, and letting it sit unfinished until it turns grey (a popular, though misguided approach) does little to improve the situation.
Choose Wisely
The only source of independent testing of deck finishes that I know of is Consumer Reports magazine. They’ve conducted an ongoing deck finish survey for nearly ten years, observing dozens of products from the three main types of deck finish families: clear, transparent formulations; semi-transparent products; and opaque deck finishes.
In general, the most demanding finishing strategy involves trying to keep new wood looking new and bright. That’s the challenge that clear, transparent deck finishes attempt to meet. But since clear products create little or no protective surface film, they have a more challenging time protecting wood from ultraviolet rays. That’s why durability results are lower with clear products than any other type. Olympic Water Guard 57560C is the only clear deck finish that has proven at least a good appearance over a three year period.
If you want to retain some visibility of wood grain, while also introducing colour to your deck along with greater durability, consider a tinted, semi-transparent product. The current available-in-Canada leader in this category is Sikkens Cetol SRD.
The most durable deck finishes of all are the opaque products that look like paint. These offer the greatest UV protection and abrasion resistance. Cabot Decking Stain has claimed the lead in this category for a number of years running.
Prepare Well
You can choose the very best deck-finishing product available, but unless you prepare the wood properly before putting it on, it isn’t going to deliver full durability. For this to happen, an ideal wooden deck surface must have two qualities: a moisture content that’s less than about 14% (this varies with products), and a surface that’s receptive and absorbent of the liquid you’re about to put on. And unfortunately, new lumber is lucky to have one out of these two parameters. It never has both.
The easiest way to check your new deck surface for moisture content is using a meter. But if you really can’t get a hold of one, then rely on some time instead. A couple of months of summertime drying weather will reduce moisture content sufficiently, even if your wood was quite wet to begin with.
Besides the issue of moisture, you need to recognize that the surface of all milled lumber has relatively low absorbency because of the spinning action of the planer blades that made it smooth. This causes various degrees of surface burnishing – called “mill glaze” -- a condition that prevents any finishing liquid from soaking in as far as it should. And if a finish doesn’t penetrate deeply, then premature peeling of your deck finish is a very real possibility. In fact, for some products, this is a make-or-break detail.
People have intuitively recognized this fact for decades, giving rise to the recommendation that decks be allowed to sit for one year before finishing. This does open wood pores allowing finishing liquid to soak in more freely, but it also causes another problem.
Once wood begins to turn grey, it indicates that surface fibers have become loosened by the action of ultraviolet rays from the sun. And while grey wood certainly is thirsty, it’s loose surface fibers are also poised to detach from the main body of the wood, allowing the film of deck finish to go with it. The result is peeling, though for a completely different reason than with bright, new wood.
Several companies offer chemical mill glaze removers to increase surface absorbency. Another option – widely recognized as the most effective – is to sand your deck before finishing. It’s not easy, but it does do a terrific job. A random orbit sander spinning a 60 or 80-grit disc creates the most absorbent wood surface.
See what I mean? Finishing a wooden deck properly isn’t all that easy. But if you do it right, the results have a beauty that nothing else can quite match. And for some of us, that’s all that really matters.
Sidebar: Finish-Free Deck Options
The time to decide whether or not you want deck finishing to be a regular part of your life is before you even plunk down your first concrete deck block. And your decision ultimately comes down to your choice of materials.
Despite the flood of finish-free deck materials on the market, all the options still rely on conventional wood framing underneath to form the superstructure of your deck. That’s a given. But above this you have a handful of choices to consider for building the walking surface. And these can be broken down into three main options: synthetic lumber substitutes, flexible sheet deck coverings, and non-finished wood.
Synthetic lumber is typically made by combining plastic and wood fibres under pressure to create a wood-like material that’s more-or-less maintenance-free. Some types are hollow extrusions, while others are solid all the way through, sized to match conventional lumber dimensions. Pros: no maintenance required except for washing. Cons: solid types are more expensive than wood; hollow types require edge-capping; colour may fade over time
Sheet deck coverings are often made of vinyl, designed for seamless installation over plywood supporting surfaces. Leading types require heat-welded edges/seams and skilled application. Pros: durable performance; creates a weatherproof roof over area underneath deck
Cons: looks very different than a conventional deck; professional installation procedure raises cost above competing DIY options.
Most people are surprised to learn that deck finishes don’t do much to extend wood life. Finishing your deck is an aesthetic thing, and that means that natural weathering of wood is okay as long as that grey, barn board appearance is acceptable to you. Conventional, pressure-treated wood is definitely an option, but you’ll also find higher-end choices for the unfinished approach. One is an ultra-hard tropical wood called ipe.
Several species of this flowering tree grow widely across South America, from Bolivia to Brazil, and northwards into Honduras. The practical value of ipe was only recognized recently, resulting in supplies appearing in Canada for use as premium outdoor decking only about ten years ago.
Ipe is six times stronger than more conventional deck woods, and this means that less of it’s required for a solid deck top. Where a minimum of 1-inch thick cedar is required for decking (1 1/2-inches is better), 3/4-inch x 3 1/2-inch ipe planks do the job. You can expect 20 to 40 years of rot-free performance from an ipe deck, though you’ve also got to expect it to go grey like any other weathered wood.
One problem with the no-finish deck management style is the uneven weathering that often occurs. Areas in full sun turn colour quickly, while nearby shaded places might never change as much. A unique, non-toxic Canadian-made outdoor wood finish called Lifetime Wood Treatment (www.valhalco.com; 250-538-5516) solves this problem and then some. In use for 60 years by government agencies and homeowners, it comes as a powder that you mix with water and spray or brush on wood. Beginning almost immediately, it turns the wood a rich, olive grey, also imparting preservative properties that extend rot-free lifespan.
After several disappointing attempts to finish outdoor wood back in the 1980s, I decided to spend as much time as necessary discovering the truth behind successful deck finishing. So, after talking to lab technicians at leading wood finish manufacturers, representatives from the Canadian Wood Council and the USDA Forest Service, I put together several strategies that use all the best advice available today. And since I’ve been using these approaches for 15 years of finishing outdoor wood, I can say for sure that they really do work.
There are three reasons deck finishing isn’t a simple as it looks. The first is that many finishing products are doomed to failure from the start. Independent consumer testing has shown that many formulations fail after less than a year of duty. And of the ones that make it past their first birthday, few offer more than mediocre performance. That’s why step#1 is simple: choose a deck finish that has proven itself effective through independent scrutiny. More on this evolving situation later.
The second source of trouble springs from the way people envision the outcome of their deck finishing efforts. Even with a very good product applied correctly, the need for ongoing maintenance of a wooden deck is higher than many folks expect. If you can get three years of life out of a wooden deck finish, you’re doing well. Even 18 months of respectable appearance isn’t bad considering the moisture, sunlight and abrasion that most decks are subjected to. This is why step#2 involves assessing yourself. Do you really have the time and ambition to maintain a wooden deck finish?
The final challenge of the deck finishing game involves understanding what proper application really means. New wood is actually a rather poor candidate for finishing, and letting it sit unfinished until it turns grey (a popular, though misguided approach) does little to improve the situation.
Choose Wisely
The only source of independent testing of deck finishes that I know of is Consumer Reports magazine. They’ve conducted an ongoing deck finish survey for nearly ten years, observing dozens of products from the three main types of deck finish families: clear, transparent formulations; semi-transparent products; and opaque deck finishes.
In general, the most demanding finishing strategy involves trying to keep new wood looking new and bright. That’s the challenge that clear, transparent deck finishes attempt to meet. But since clear products create little or no protective surface film, they have a more challenging time protecting wood from ultraviolet rays. That’s why durability results are lower with clear products than any other type. Olympic Water Guard 57560C is the only clear deck finish that has proven at least a good appearance over a three year period.
If you want to retain some visibility of wood grain, while also introducing colour to your deck along with greater durability, consider a tinted, semi-transparent product. The current available-in-Canada leader in this category is Sikkens Cetol SRD.
The most durable deck finishes of all are the opaque products that look like paint. These offer the greatest UV protection and abrasion resistance. Cabot Decking Stain has claimed the lead in this category for a number of years running.
Prepare Well
You can choose the very best deck-finishing product available, but unless you prepare the wood properly before putting it on, it isn’t going to deliver full durability. For this to happen, an ideal wooden deck surface must have two qualities: a moisture content that’s less than about 14% (this varies with products), and a surface that’s receptive and absorbent of the liquid you’re about to put on. And unfortunately, new lumber is lucky to have one out of these two parameters. It never has both.
The easiest way to check your new deck surface for moisture content is using a meter. But if you really can’t get a hold of one, then rely on some time instead. A couple of months of summertime drying weather will reduce moisture content sufficiently, even if your wood was quite wet to begin with.
Besides the issue of moisture, you need to recognize that the surface of all milled lumber has relatively low absorbency because of the spinning action of the planer blades that made it smooth. This causes various degrees of surface burnishing – called “mill glaze” -- a condition that prevents any finishing liquid from soaking in as far as it should. And if a finish doesn’t penetrate deeply, then premature peeling of your deck finish is a very real possibility. In fact, for some products, this is a make-or-break detail.
People have intuitively recognized this fact for decades, giving rise to the recommendation that decks be allowed to sit for one year before finishing. This does open wood pores allowing finishing liquid to soak in more freely, but it also causes another problem.
Once wood begins to turn grey, it indicates that surface fibers have become loosened by the action of ultraviolet rays from the sun. And while grey wood certainly is thirsty, it’s loose surface fibers are also poised to detach from the main body of the wood, allowing the film of deck finish to go with it. The result is peeling, though for a completely different reason than with bright, new wood.
Several companies offer chemical mill glaze removers to increase surface absorbency. Another option – widely recognized as the most effective – is to sand your deck before finishing. It’s not easy, but it does do a terrific job. A random orbit sander spinning a 60 or 80-grit disc creates the most absorbent wood surface.
See what I mean? Finishing a wooden deck properly isn’t all that easy. But if you do it right, the results have a beauty that nothing else can quite match. And for some of us, that’s all that really matters.
Sidebar: Finish-Free Deck Options
The time to decide whether or not you want deck finishing to be a regular part of your life is before you even plunk down your first concrete deck block. And your decision ultimately comes down to your choice of materials.
Despite the flood of finish-free deck materials on the market, all the options still rely on conventional wood framing underneath to form the superstructure of your deck. That’s a given. But above this you have a handful of choices to consider for building the walking surface. And these can be broken down into three main options: synthetic lumber substitutes, flexible sheet deck coverings, and non-finished wood.
Synthetic lumber is typically made by combining plastic and wood fibres under pressure to create a wood-like material that’s more-or-less maintenance-free. Some types are hollow extrusions, while others are solid all the way through, sized to match conventional lumber dimensions. Pros: no maintenance required except for washing. Cons: solid types are more expensive than wood; hollow types require edge-capping; colour may fade over time
Sheet deck coverings are often made of vinyl, designed for seamless installation over plywood supporting surfaces. Leading types require heat-welded edges/seams and skilled application. Pros: durable performance; creates a weatherproof roof over area underneath deck
Cons: looks very different than a conventional deck; professional installation procedure raises cost above competing DIY options.
Most people are surprised to learn that deck finishes don’t do much to extend wood life. Finishing your deck is an aesthetic thing, and that means that natural weathering of wood is okay as long as that grey, barn board appearance is acceptable to you. Conventional, pressure-treated wood is definitely an option, but you’ll also find higher-end choices for the unfinished approach. One is an ultra-hard tropical wood called ipe.
Several species of this flowering tree grow widely across South America, from Bolivia to Brazil, and northwards into Honduras. The practical value of ipe was only recognized recently, resulting in supplies appearing in Canada for use as premium outdoor decking only about ten years ago.
Ipe is six times stronger than more conventional deck woods, and this means that less of it’s required for a solid deck top. Where a minimum of 1-inch thick cedar is required for decking (1 1/2-inches is better), 3/4-inch x 3 1/2-inch ipe planks do the job. You can expect 20 to 40 years of rot-free performance from an ipe deck, though you’ve also got to expect it to go grey like any other weathered wood.
One problem with the no-finish deck management style is the uneven weathering that often occurs. Areas in full sun turn colour quickly, while nearby shaded places might never change as much. A unique, non-toxic Canadian-made outdoor wood finish called Lifetime Wood Treatment (www.valhalco.com; 250-538-5516) solves this problem and then some. In use for 60 years by government agencies and homeowners, it comes as a powder that you mix with water and spray or brush on wood. Beginning almost immediately, it turns the wood a rich, olive grey, also imparting preservative properties that extend rot-free lifespan.
