Being a painting contractor is sort of like being a doctor making a diagnosis of a common illness, spotting problems is part of our daily routine. But in the world of paint, as in medicine, assessing the patient's history and doing something about is sometimes more complex. This is undoubtedly the case when it comes to the "common cold" of the average painting project: moisture control.

It sounds easy, but as is illustrated time after time, blisters and peeling can put to rest even the best-laid brush if preventive measures aren't already in place. If we can't make a proper diagnosis of a moisture problem, chances are our clients won't know the answer, either. If we guess wrong and end up with faulty results, it could cost us a customer -- not to mention the unnecessary hours of cleanup work that may have been avoided in the first place.

What to look for: When assessing a surface, either one that has been painted or one that’s about to get its first coat of primer, there are moisture symptoms to look for:

The first and most obvious is water: Water already on the surface, or lurking in places near the substrate, is a bad omen.

Ever hear the term "ice dam?" It’s what happens when snow melts over a warm attic, then runs down the roof until it reaches the unheated overhang — whereupon it freezes, and acts as a backstop for subsequent melted snow. Repeat this exercise enough times, and moisture will begin paying visits inside the house down the backside of siding too.

You’re not necessarily out of danger even if the water does make it to the gutter. "Standing water in gutters will freeze," said Frank Magdits, professional products coordinator for Benjamin Moore. "It can go up behind shingles; then, during the day when it heats up, it goes behind the siding."

"You have to remember that vapor, once it gets outside, turns to ice. Outside cold temperatures freeze vapor in the wall. Then, when spring comes, the sun hits the house and the water wants to escape through the siding"

Clean out gutters and inspect the roof before beginning any paint job, Magdits advised. We recommend to our customers that they attempt to keep the temperature below the roof the same as above it — otherwise, they're only treating the symptom, not the disease. (That rule, treating the source of the moisture and not its effects, holds true everywhere on the structure. It’s what separates the men from the boys, painting-wise.)

Just as the freezing water from the roof will thaw and work its way down, so too do leaky roofs contribute to paint problems if not patched properly. Moisture from a leaky roof, even if it’s not directly over an exterior wall, will find its way to the substrate behind the paint. When the sun heats up, pockets of water aching to get out push against the paint, forming bubbles — or worse, as the photos indicate.

If a client insists that their house is secure and couldn’t possibly have roof or gutter damage, ask about storm windows. Remind clients that a typical family of four generates 3,600 gallons of water from inside the house each year, in the form of showers, cooking, laundry, and even breathing. The water vapor has to go somewhere, and the laws of physics say it will go outside, any way it can get there.

Seals. Not the mammalian variety, but the kind that hold together surfaces that otherwise don’t quite meet.

A typical place for water to creep in is where a contractor neglected to properly seal cracks and joints, or ones that have long since separated. The culprits can be dissimilar materials not caulked together, such as wood and concrete near a foundation, or metal and wood around windows, or similar surfaces, such as overhangs. Joints with 45 and 90 degree angles need to be fully caulked, no matter how beautifully they appear to fit together. This leads back to the first point about standing water or water vapors. Ridges around windows and pockets where water can accumulate will cause damage, and that most likely sooner rather than later.

Here is a prime example of a job where unproperly caulked windows and newer woods moisture content especially proves this case in the following link. This job had several thousand dollars worth of rot replacement needed in only five years after this home was built! Complements www.weaverpainting.com

Mill glaze. This one at first may not be as obvious, and can be expensive to fix. Don Ross, president of Don Ross & Son Painting in Lynnfield, MA, explains why.

"Thirty or 40 years ago when you went to the lumber yard, the lumber you bought had been milled three to four years before it went on sale. Now, you’re lucky if it isn’t still growing as you try to nail it to the building," Ross said.

Builders buy the wood before it has greened out, or completely dried out. Instead, the wood when put through a planer at a high rate of speed, brings to the surface a waxlike glaze of the tree’s inner oils and saps.

"Most builders put the shiny side of the board facing out," Ross said. "The glaze won’t allow primer to bond to it, so when you paint over it it looks good for awhile, but once the moisture in the wood works its way out, the paint peels."

Finding a solution comes before the wood gets the first coat of primer. Ideally, a painter would allow the wood to dry for a sufficient period of time before painting, but since that’s unrealistic for most jobs, Ross has another suggestion.

"Take 120- or 220-grit sandpaper to remove the glaze and go over it two or three times to get some tooth and grit."

Jim Weaver of Weaver Custom Painting from Seaside, Oregon agrees but includes new wood should be treated using "Clear Penetrating Epoxy Sealer"

"Clear Penetrating Epoxy Sealer from Smith and Company was designed to dissipate moisture and seal sap and oil content from penetrating through knots. Its a marine product. Moisture content is a common unsuspecting culprit found in newer Cedar that has been known to cause early coating failure from moisture and saps escaping the wood.

Wedging. This is another Ross staple, and one that he recommends for all clapboard houses, either during the construction phase, or after for existing structures. Like it sounds, wedging involves driving wedges at even spaces between clapboards to release excessive moisture. "It allows the house to breathe and get the moisture out, without damaging the paint,"

Buildings with shingles as siding have a wedging advantage, since the cracks and spaces between the shingles create pockets for moisture to escape naturally. However, "I can’t tell you how many times I’ve seen people painting the shingles and either using a lot of paint to fill in those cracks, or caulking them," Ross said. "I just want to tell them to stop, because they’re ruining the whole thing."

Shingled buildings, too, need wedges, but not until the house is 30 to 50 years old, he said.

Ventilation. Again, this one sounds obvious, but for do-it-yourself types, it’s not. Moisture that’s contained in a house without proper ventilation will, as mentioned earlier, look for ways to escape. Again, if moisture can’t escape the interior through normal means — vents, windows, other openings — it’ll escape through abnormal means, like through walls and ceilings. This may be good for your painting business initially, but failure to alert your client to the root problem will be good for somebody else’s painting business. "Air expands through the soffit vents and takes the moisture with it," said Donald Grudeski, president of Aesthetics Painting Inc., in Orlando, FL. "Often you can’t find moisture. You can use a moisture meter, but that’s hit or miss. Basically, what you have to know is how the weather gets behind the substrate. The best solution is proper ventilation." In older buildings where ventilation can be a problem, interiors hydrostatic pressure creates peeling problems, Grudeski said. Ventilation is also tied to Ross’s wedging system. Older buildings without effective soffits can find relief through the installation of a wedging system.

Oil-based paint. This is usually only a problem if you’re dealing with an older building, but it’ll be some time yet before the revolution in water-based coatings eliminates alkyd coatings once and for all. Since paint has to expand and contract with the wood throughout the seasons, oil-based paint — which is static — has no give.

"It gets pushed off the substrate," Ross said. "Use only latex paint."

Ross recommends 100 percent acrylic. "It’s the only breathable type of paint on the market today," he said. "If you use the others, it’s like putting your house in a balloon. Eventually, it’s going to pop." A good example is a simple six-inch by 12-inch piece of wood, left out in the elements, just like clapboard siding. A piece that size can expand and contract by as much as one inch. The paint has to keep stretching to cover the surface.

Just touch it up! Good Luck! Once you’ve made a diagnosis, the next step is writing the prescription, and it may be one the homeowner may not like. The reason is that more likely than not, preventive care or repairs will be considerably more expensive than they originally had in mind: "But all I really want you to do is touch up the peeling spots!"

"Painting a house is a huge investment," Magdits said. "You don’t want the contractor to come back in a short period of time. Unfortunately, what happens is that a lot of people don’t want to pay to have the job done right. When you start cutting corners, that’s where there’s danger."

That said, while it’s the client’s responsibility to follow up with routine care and maintenance,

it's the contractor's job to prescribe the correct solutions for problems before they start. A reputable contractor will take a client around the house and point out potential problem spots. This serves two purposes: It shows the homeowner that the contractor is schooled in his profession, and eliminates headaches in the form of leaks, rust, bubbles, and blisters a few years down the road. On the other hand, however, keep in mind that all moisture problems can't be easily solved. There's a limit to what you can reasonably do to correct moisture problems. Moist air from the interior has so many ways to slip into walls that there isn't always an easy answer -- not to mention that some paint failures look like moisture problems, but aren't. There are other forms of blistering like solvent and air entrapment. What you can do, however, is advise your clients on the most likely areas of concern, such as those listed above.