It’s easy enough to paint the town red, if anyone remembers that old phrase, but painting your house any color, on the outside, is another matter. It can be a can of worms if you don’t do everything right. In fact, it can be a can of worms if you do everything right.
Painting outdoors is not just a matter of slapping on a little primer or undercoat, then some house paint, and waiting eight years to do it all over again.
Preparation is a must for a good paint job, and scraping and sanding is a large part of the preparation. The rest is to wash the walls and to treat for mildew with a bleach/water solution.
You can wash and treat for mildew at the same time by making a strong solution of Spic and Span and water, to which a cup of bleach has been added. Wear skin and eye protection when working with bleach. Equally important, rinse any bleach-treated surfaces; bleach does not mix well with paint or stain.
One good thing about modern exterior paints and stains: they contain a mildewcide that helps prevent the growth of mildew. Alas, it might not be effective the full life of the paint or stain.
But the biggest problem with outdoor paint is moisture. There are many houses with peeling paint, and the homeowner asks what causes the paint to peel. Some paint jobs have failed in short a time as a year, and sometimes the big blisters that appear in the paint produce water when slit.
Moisture occurs on some houses but not all, and on the victim’s houses the sheathing is often wet under the shingles or clapboards being painted. Not just damp, but wet. There is nothing obvious that is causing the moisture.
Sometimes the moisture comes from outside, soaking siding and sheathing. It comes from roof leaks, overflowing gutters, bad design that allows water to run down the face of the wall, and leaks in flashing and other critical areas of the house. Because these problems are obvious, they are relatively easily fixed.
What is not obvious is the moisture that is coming from inside the house.
What is happening is this: Water vapor, created by breathing, washing, bathing and cooking, builds up in the house–and this may happen more in a house, new or old, that is tightly sealed–until it penetrates the inside wall, goes through the breaks in the vapor barrier (nail holes, electrical outlets, and other passageways), goes through the insulation and condenses against the outside sheathing, turning into water, because the sheathing is cooler than any other surface. This action occurs mostly on the sunny sides of the house.
The penetration is the result of water vapor always trying to pass into a dryer space, such as the wall cavity or outdoors. The water soaks the sheathing and can go through it, under the wood siding, and finally push the paint right off.
Why this happens on some houses and not others is the bane of a painter’s life.
Stopgap solutions
One way to fight that moisture is to insert small aluminum wedges under each clapboard, opening up the clapboards a bit to allow that water vapor to escape before it condenses. This might work, but not well, because the opened clapboard does not provide a passage through the sheathing itself.
If you have shingles, you can’t put a wedge under each one, although you could put one under every fourth shingle or so.
For shingles, a better solution is to drive vent nails, which are hollow, under the butt of each row of shingles, 12 or so inches apart. The nails are virtually invisible, and they penetrate the sheathing so that any water vapor in the wall cavity will escape harmlessly to the outdoors.
It’s a form of ventilation, just as you would or should ventilate the attic, basement, and crawl spaces. In fact, ventilating the house regularly (twice a day, say, even in winter) is a good idea to reduce the humidity in the house. This twice-daily ventilation will not lose appreciable heat.
There is one ray of hope concerning the plague of peeling paint caused by moisture from inside the house.
And that is insulative sheathing. Dow Chemical Co., makers of Styrofoam rigid insulation, has made numerous studies of insulation sheathing on the outside of the wall, and promotes the use of Styrofoam rigid insulation in new construction.
With rigid insulation on the outside of the sheathing, the sheathing itself is kept warm, so that when water vapor escaping through the wall hits it, it does not condense into water. And water vapor that does not condense is virtually harmless.
Another technique is to install the rigid insulation as sheathing, not using wood sheathing at all. The only drawback in that case is that the wood siding should be clapboards, which can be nailed onto the studs. Shingles cannot be used because the rigid insulation is not a nailing surface; nails driven into it will not hold.
Thinking about this, it make sense, even though it goes against traditional methods.
Of course, these techniques are used mainly in new construction. But in severe cases of moisture in an existing house, the wood siding can be removed, rigid insulation applied to the sheathing and the siding put back or new siding applied.
It is probably best to install 1-inch-thick insulation for maximum protection. This poses a problem because the insulation thickens the wall, and window and door casings must be extended to maintain the proper design of the house.
2 kinds of stains
Another way to fight moisture is to use a stain, which may resist that pressure of water vapor and water better than paint.
There are two kinds of stains: solid color (usually latex) and semitransparent (usually oil). Stains will peel less than paint because they allow water vapor to pass through them. However, solid stains can peel, and often do because of the moisture. Semitransparent stains do not peel unless they are applied too thickly or two coats are applied.
That’s one nice thing about the semitransparents: They need only one coat, and are good for five years. But they have to go over bare wood; they cannot be applied over old paint.
Solid color stains can be applied over old paint and bare wood, if the old paint is sanded thoroughly to roughen the finish and reduce gloss. Two coats are needed, whether over old paint or bare wood. Solid-color stains may not peel as much as paint, but they can peel, so that solution is not foolproof. Solid color stains, if they don’t peel, are also good for five years.
If you plan to paint, and have prepared the surfaces properly, the state-of-the-art method is to apply a primer, at least to the bare wood parts, and two coats of a latex house paint. Paint manufacturers call this a paint system, not because they want to sell more paint but because they believe this is the proper way to paint a house for durability and good looks.
Paint or stain can be brushed, rolled or sprayed. Some painters feel that brushing is the best method because it sets up a bond between surface and paint.
Spraying, with a final brushing, is another good way to go.
Aside from brushing as the preferred method of application, there are only three more rules:
1. Apply thin coats; trying to make a paint or stain cover by thickening the coat will guarantee failure such as peeling and alligatoring (the finish cracks to look like an alligator’s skin).
2. Do not paint when the temperature is 50 degrees or lower, and will stay that way for the several days the paint takes to cure.
3. Painting in too-hot weather is as bad as painting in too-cold weather. On a warm, sunny day, paint in the shade. The old saying still applies: Follow the sun around the house.
