Knowing When It's Time to Paint

Repainting makes your house look better and more valuable and protects siding and trim from deterioration, of course. But what a pain, because after moving ladders and drop cloths once around the building, in most cases there are at least two more circumnavigations to go.

This week, we'll look at what a good paint job entails and how to assess surface conditions like alligatoring and chalking. Next week, we'll cover options for prepping the house and start painting.

A realistic appraisal

Around we go, with the first lap for basic cleaning to help fresh paint adhere, and particularly to remove mold that no paint can cling to for long. Most houses also need at least some scraping and sanding, and if you've waited too long before repainting, siding or soffit repairs, as well.

The first circuit is worth a major effort. Aside from improving adhesion, you can prevent bleed-through discolorations by stain-killing any knots and nail heads, and by slicing away tree sap. If the paint surface is dingy instead of cracked and peeling, a thorough cleaning may brighten the house so much that you don't have to repaint -- this year, at least.

Lap two (on large or two-story houses we may be into the second weekend) is for final prep work such as finding and pounding in raised nail heads (they create drips), but mainly for priming new wood or raw wood exposed by scraping and sanding. One thick coat, even of the best paint, will soak into raw wood more than painted wood; it can create adhesion and wrinkling problems and show up as dull spots when dry.

After all the prep work, you can make the last lap (probably no sooner than the next day) and finally do some finish painting. And for those with more energy, planning on a contrasting trim color, and maybe redoing the shutters too, count on yet another circuit and at least another day.

So why not combine the cycles and work through cleaning, repairing, replacing, priming and painting one section of siding at a time? The primer needs time to dry, for one thing. But the main reason is that you can't be fixing and finishing in the same area. Prep work makes a mess that can ruin any finish application nearby.

On top of that there's the weather, and a classic rule of exterior painting: to follow the sun around the house. In this sequence, morning dew is burned off, the siding is warmed before you get there, and you avoid paint bubbling and other problems that stem from working in harsh sunlight.

Is your resistance to vinyl siding starting to crack? Re-siding is an option, but an expensive proposition with its own set of drawbacks.

Surface diagnosis

You don't need a diagnosis to fix surface defects, which respond to basic scraping, sanding and cleaning. But recognizing specific conditions, and knowing what causes them, can help you avoid the problems as you prep and paint.

Many factors can contribute to paint problems, of course, like using poor-quality siding that twists and buckles, or building without vapor barriers, which allows interior moisture to put pressure on the paint film from the inside out.

• Lead check. If you're working on an old house, bear in mind that lead-based paint wasn't banned until 1978, and you may need to conduct a simple swab test to check for lead.

• Alligatoring. Small horizontal and vertical cracks, hairlines at first, gradually connect to produce a rectangular grid, and then chunks start to break away. Most common causes: The top coat is applied before the primer coat has fully dried. A rigid top coat, such as alkyd enamel, is applied over a more flexible undercoat, such as latex primer. One exceptionally thick coat is applied as a time saver instead of two thinner coats. The paint is just old and loses its elasticity.

• Blistering. Bubbles form in and under the paint film. Most common causes: Application in harsh sunlight that overheats the paint. Painting over a damp surface.

• Chalking. The paint surface forms a fine powder. It's the way most paints wear and renew themselves, but excessive chalking can cause fading, and stain other surfaces. For example, you want a non-chalking paint on second-story siding where chalk residue would wash down onto first-story brick. Most common causes: Using a poor-quality paint or an indoor paint outdoors. Thinning or overspreading the top coat of paint.

• Cracking and flaking. This often takes the form of advanced alligatoring (though cracking can also run mainly in one direction), with little chunks falling away first. Most common causes: Using a poor-quality paint without enough elasticity. Painting over bare wood without priming. Overthinning or overspreading. Painting in dry, windy conditions that make latex paint dry too quickly.

• Peeling. This can involve some or all coats of paint on the siding, which sometimes let go in surprisingly large or long patches. Most common causes: Moisture seeping though poorly caulked joints. Interior moisture escaping through walls. Painting over a damp surface, particularly with oil-based paint.

If you're not sure what a paint problem looks like, close-up photos are posted on the Web site (paintquality.com) of the Paint Quality Institute, an information group established by the Rohm and Haas Co., a major supplier of raw materials to paint manufacturers.