As a custom painting contractor in the Boston market, I've spent a good part of my lifetime studying the way paint works. That includes courses and seminars provided by the Painting and Decorating Contractors Association, which I think every professional painter ought to join (I'm the president of our local chapter's residential forum; painters interested in best-practice solutions are encouraged to visit www.pdcaresidentialforum.org).
Formal training is important — for example, we have all our employees take the three-hour training course on CD from the Rohm and Haas Paint Quality Institute (www.paintquality.com) each year, and I often bring some employees along when I travel to an industry conference. But experience is still the best teacher. And when you think about it, painters are in a unique position to learn from experience, because we get to revisit projects years after construction is complete. Few builders get that opportunity: they might go on and build a new project for a client, or they might have a punch list at the end of a job for minor mistakes or things that didn't get finished. But builders don't usually get a chance to go back after five years, seven years, forty years, even a hundred years to see what's working and what isn't working on a home. We painters do — in fact, that's most of what we do: we come along and fix things that are failing, and we get to learn from that failure.
The source of most problems
No coating lasts forever, especially on wood. Depending on the environment, you can expect a well-executed paint job to last somewhere between 5 and 12 years. But often, paint begins to experience trouble long before that. And from what I've seen, that trouble is virtually never related to a flaw in the paint itself. Manufacturers have had years to perfect their formulas, and they do continual research and development. If you invest the dollars for good-quality paint, rather than the cheapest can on the shelf, you can expect excellent performance from the product.
So when I see problems, it's because of things other than the paint or stain. Most commonly, problems go back to the way the house was built. Less frequently, the issues relate to how the substrates — the wood trim, siding, or window and door frames — were prepped for paint. And least commonly, there was some problem with how the paint was applied. In any case, the prep and the painting are the painting contractor's job. But things the carpenters do, before the painters even show up at the site, can make all the difference to the endurance of the coating.
These days, most of my company's painting projects are likely to involve some carpentry as well. I now have a few well-rounded carpenters on my own payroll, in fact, and they sometimes spend days replacing siding and trim, or even remodeling a porch, before my prep crew starts to work. So the tips here aren't just kibitzing — they're what our own carpentry crew does in the field. If your carpenters do the same things on the next house you build or remodel, they'll be helping to give the paint or stain a fighting chance.
Top Tips for Trouble-Free Paint
Use preprimed material. The minute you put wood up on a wall, the sun starts to attack its wood fibers, and it begins to experience swelling and shrinking as it gains and loses moisture to adjust to the surrounding air (Figure 1). To protect that wood, every piece of siding or trim that gets nailed to a building should be primed first on six sides — that is, on all four faces and on both ends. Factory-primed clapboards and trim are easy to find in the market these days; if you use unprimed material, you should prime it yourself before you nail it up.
Figure 1. Without back-priming, daily and seasonal moisture cycling will soon cause beveled wood siding to show cupping and warping (visible in the upper courses of siding on this house), as well as cracking. Moisture migrating from inside the home through the backs of the clapboards also attacks the adhesion of the paint or stain on the exterior wood surfaces, causing premature loss of the coating. The new preprimed clapboards at the lower right of this gable-end wall, installed as part of a window replacement, will perform much better in service.
That includes priming the back face. Although it doesn't face the weather, the back of a board is often attacked by moisture coming from within the house. Back-primed wood can resist that moisture, but wood that hasn't been primed in the back will curl or cup. That unbalanced movement stresses the nailed connections, and moisture migrating toward the outdoors also attacks the bond between the coating and the wood, causing early peeling or wear.
Don't over-rely on the factory primer. A factory-installed primer serves to stabilize the wood during shipping and storage, and it provides temporary protection when siding, trim, or windows are first installed. But it's not usually intended to be the primer for the material in service (Figure 2). That's why the label on a new window or door will often warn you that the unit should be primed again before it's painted. With those components, and also with preprimed clapboards and trim, we always reprep the surface and apply a field primer before we apply the finish coating of stain or paint.
Figure 2. Factory-applied primer on new bevel siding serves to stabilize the wood during shipping and immediately after installation. However, it does not serve other functions of a field-applied primer. For instance, factory primer usually will not block bleed-through by extractive oils in cedar, as shown above. It also will not provide the "tooth" that helps finish coats bind strongly to the material. The author touch-sands and/or power-washes the wall, spot-primes areas of bleed-through with an oil-based stain-blocking primer, then primes the entire wall with regular acrylic primer before applying a finish coat of paint or stain.
In fact, even if wood is installed and primed, but then sits for an extended period before the finish coating is applied, it may need to be washed or even sanded again and primed again first. Primer is not supposed to serve as a finish coat; it is supposed to help the finish coat bond. And if it weathers before the finish coat goes on, you can't count on it to do even that.
The one exception is factory-primed wood shingles. Many companies now apply both a permanent primer and a durable top coat to shingles, under ideal factory conditions and with controlled drying and curing. That's the best coating a wood shingle or shake can get — better than any field-applied coating. If you're going to use wood shingles, I'd advise you to go that route.
Field-prime all cut ends. Whether you use factory-primed material or prime it yourself, make sure to prime every cut end or edge. That's easy to do — just keep a can of primer and a brush at the chop-saw station, and have the carpenter who's doing the cutting prime each end before he passes it to the carpenter who's nailing.
If you don't prime the cut ends, you're leaving open the part of the wood that is most open to moisture entering: the end grain. Nature intended wood to draw water into the end grain. In service, unprimed ends will absorb water and swell, and paint will start to come off the wood at that location first (Figure 3). If painters arrive to paint or stain a house that is sided with clapboards whose cut ends are unprimed, or trimmed out with boards whose ends are unprimed, there is very little we can do to address the issue. So it's up to the people installing that wood to make sure that the ends are primed (Figure 4).
Figure 3. Here, carpenters have installed factory-primed window casing material without sealing the ends. Stain was applied without any sanding or repriming. Failure has begun at unprimed ends and flat grain and at unsealed knots. At the bottom of one piece, water has entered unprimed end grain and caused the piece to check (left). If the carpenters had primed all cut ends, and if the original painters had prepped the wood and applied a fresh field primer, the onset of failure could have been postponed for years.
Figure 4. Carpenters have several convenient choices for primers to apply in the field during siding installation. Above, stain-blocking primers come in small cans for brush application or in spray cans. The author prefers the brush method because it gives thick coverage without overspray or environmental concerns. A pocket-sized sponge applicator bottle is handy too; a carpenter can keep it in his pouch, ready to use. However, it takes repeated swipes with the bottle to achieve thick primer coverage.
Take special care with finger-jointed material. Many wood windows and doors are now assembled with finger-jointed wood. We also see a lot of finger-jointed siding and trim these days. If the wood has a factory primer applied, it may hide those joints, but it doesn't protect them from the weather. So it's very important to prime finger-jointed material again as soon as possible after installing it. If those joints start to open up and let moisture in, they may not hold up the way they're supposed to, and they'll start to look bad as well.
Some finger-jointed material uses very small pieces of wood and lacks a good match between one section and the next. Pieces with different grain density and grain orientation move in different ways, and they also accept paint or stain in different ways (Figure 5). If you use this kind of material, you should make sure your customer can accept the way it looks: coatings on sections with flat grain will wear or come loose sooner, and the joints and variations may quickly become apparent to the eye. While the material may be economical, the results may not be to everyone's liking.
Figure 5. These finger-jointed clapboards appear to be made with very short sections of wood with different sawing and grain patterns. Some finger-jointed boards are even made with pieces from different tree species. Here, we see that the flatsawn grain of some sections holds stain very poorly. The author advises carpenters to reject pieces of siding that show such dramatic differences from section to section.
Use ring-shank or spiral-shank nails. When siding and trim are nailed with smooth-shank nails — even galvanized nails — daily and seasonal wood movement can work the nails loose from the material over time, leaving nails standing proud (Figure 6). On repaint jobs, our prep crew usually has to pull a lot of nails that are high, and we always replace them with ring-shank nails (either hot-dipped galvanized or stainless steel). There's no good reason for a carpenter in new construction not to use ring-shank nails in the first place. In my experience, I've never found a ring-shank nail that has worked its way high of the siding or trim.
Figure 6. As the wood expands and contracts with changes in moisture, smooth nails may gradually work proud of the board surface (right). Nails like this should be pulled and replaced with stainless steel ring-shank nails, which hold better and won't work loose.
Be careful to drive nails just flush with the top surface of the wood, or perhaps just a hair lower. Good carpenters get a feel for how to set the nails just right with the final tap of the hammer. But gun nails are harder to control, and carpenters may get in the habit of driving the nail heads into the wood (Figure 7). That's bad practice — it provides a place for water to pool and attack end grain, and it creates a surface condition that is hard for primer to seal.
Figure 7. When carpenters overdrive gun nails beneath the surface of a board, water finds a place to collect and penetrate exposed wood fiber ends. The coating has started to peel next to this nail hole, even on the shady north side of the house.
There's a lot more to say about a durable paint job. Good surface prep and good application technique are important factors in the success of a coating. But those measures are really the painter's job to implement — and if you choose a well-qualified painting contractor, they'll be done properly. And they're no more important than the tips I've provided here: if your crews use the careful priming and nailing techniques I've described when you're building the house, you could add years to the lifetime of the coating your painter applies.
All photos by Ted Cushman except as noted.