Before coating new wood, better do a reconnaissance in force.

What could be new with wood? Well, this: The supply of virgin-growth wood is declining, and the newer woods dont have the same characteristics as that from older-growth trees. Newer wood typically contains more knots, and it's not unusual to see boards that are end-glued. The grain is slightly different as well. The bottom line is that if it's wood from second-and third-growth trees, you should exercise additional care when finishing it to help prevent early coating failure. What follows are some guidelines to keep in mind when coating new exterior wood.

Proper prior planning: Doing the job right so it looks good and lasts starts long before you wet a brush. It starts with knowing the characteristics of the wood you'll be coating. "Take surface preparation back a notch. You have to know your substrate".

Start by understanding wood's basic structural component, cellulose. This component can make life difficult for painters, because cellulose can contain tannins, pitch, resin, and wax -- all of which can destroy your work.

Some woods, such as redwood, cedar, fir, and cypress, contain lots of tannins. These are nature's coloring agents. They also are the ingredients that make certain species decay-resistant, which is why you see a lot of these woods used. Unfortunately, most tannins are water-soluble and can bleed through latex topcoats. The culprit causing the problems is moisture in many forms, in the form or rain, dew, high humidity and moisture content that has not cured out of the newer wood.

Porous, thin latex paint allows moisture to penetrate the wood. The water in water-borne finishes also can trigger the extractive bleeding process. In severe cases, diffused extractive discoloration will appear before the paint dries. Whatever the potential cause, to help prevent it you have to seal the wood with a quality alkyd or latex stain-blocking primer.

Although bleeding from tanning-containing wood probably is the most common stain-related problem you'll encounter, there are many others. For example, many woods, such as fir, pine, and spruce contain resins, often in large quantities and most frequently found around knots. These resins can interact with many alkyd-oil-based coatings, causing the resins to soften and seep into the final finish.

Heat affects resins, causing them to come out of wood during warm weather. Therefore, if you're working late in the year during cool weather, you may not perceive them as a problem. They'll become one the following summer, however. You'll have to play sleuth and determine the most likely places resins are located and take preventative action. Knots are your best bet, but you'll want to check expansion cracks as well.

Once you've found the resin spots, your best defense against future coating damage is to remove what's oozed out and then seal the area. Ideally, you should let the resins come out naturally, then paint, but you'll probably never have that kind of time. If you only have a few knots, you can speed up the process by applying heat -- from a hair dryer or heat gun, for example -- directly on the knots, then remove the large blobs mechanically and follow up with a thorough cleaning with mineral spirits. Then spot prime with a primer designed especially for blocking wood resins.

Rarely simple: There isn't a single solution to ensuring good results. Usually, you'll have to take several steps to achieve the desired results. In many cases, you'll have to apply alkyd-oil-based products to take care of water-soluble tannins, in tandem with latex products to handle solvent-soluble resins. (In fact, let's just get something clear right here: Always consult with your supplier when dealing with staining problems with new wood.)

The new-growth wood presents yet another problem: flat grain. It's a problem because the wood is very dense and allows limited penetration of coatings. To correct the problem, you'll have to sand the wood to open up the pores before you prime it.

You'll also face man-made building products, such as hardboard siding T-111 siding or Lousiana Pacific siding, and they present still different painting problems. For example, hardboard siding usually contains wax and phenolic resin glues to bind the wood fibers together. The good news is that the manufacturing process removes most of the tannins. You also don't have to deal with flat grain and knots. The bad news is that because of its inherent construction, hardboard is very susceptible to absorbing water, and for that matter, primers, if the surface is rough. If it isn't primed properly, the water absorption can lead to mold, mildew, and paint peeling. The trick to successfully painting hardboard is to make sure all the pores are filled with primer before applying a topcoat. Ideally, new hardboard siding should be primed on both sides and on all its edges to help prevent water penetration.

Be sure the surface is free of dirt, mildew, and wax before priming. Scrubbing first with a detergent, such as trisodium phosphate (TSP), then with a bleach solution (one quart of bleach and three quarts of water) is usually sufficient.

Don't let the solution dry on the surface, because the TSP will return to its crystalline form. Use a rinsible formula TSP and make sure the wood is wet when you apply the solution. Otherwise the TSP may be absorbed into the wood.

If there's an excessive amount of wax, you may have to resort to cleaning with a solvent and some light sanding.

Be sure to rinse thoroughly with water after applying the detergent and again after applying the bleach solution. (Be careful not to mix the bleach with anything containing ammonia, or hardboard siding will be the last thing you ever see on earth.)

Even if the hardboard was factory-primed, you may want to apply another primer coat. First, you don't know the quality of the existing primer, and it may or may not meet your standards -- or needs. Second, it's added insurance against failure.

Now or never: It's a misconception to think that wood should weather for six months to a year before coating it. Because of the high tannins in Cedar this is an exception. Cedar should weather if there is still very high moisture content in it. In most cases, new wood should be protected. Wood that's left unprotected for as little as four weeks may become damaged enough to interfere with the performance of a paint.

When working with hardboard and most other woods, you'll want to paint it as soon as possible to help prevent weathering, which will lead to reduced paint adhesion. Be sure to prime and paint all the crevices and edges. If you don't and water swells the board, it's likely to swell more than your coating will, and the paint will crack.

When painting previously painted hardboard, you'll want to remove all peeling and cracked paint by scraping and sanding. Exercise care here, however, and don't scrape or sand into the hardboard's surface. Then remove surface contaminants by powerwashing or scrubbing with a mild household detergent or TSP. If mildew is present, use a bleach solution.

Also look for rusty and loose nails. Replace the loose ones with galvanized nails. Clean rusty nailheads and apply an epoxy sealer primer to them.

Don't assume that because the surface has been coated previously that wax isn't present. If the hardboard originally was primed with a latex product, some wax bleed may be present. To correct the wax bleed, you'll have to use an alkyd primer -- even though the surface has been coated with latex paint.

Regardless of the type of siding you're coating, be sure to caulk all points where utilities enter a building. If you don't, moisture may reach the inside surface and soak into the substrate and work its way back through to the exterior.

Another problem you'll frequently see is mill glaze. During the planing process, mill glaze occurs because the heat of the blades burnish or glaze the boards; providing a sort of pre-varnish. "Mill glaze can interfere with coatings, especially those designed to be penetrating instead of film-forming.

Scrubbing or powerwashing -- at 500 psi -- will take care of most mill glaze problems. In particularly stubborn or highly glazed cases, light sanding may be necessary. If so, go with 80-to 120-grade: Finer paper tends to polish the surface instead of roughing it up.

We prefer to avoid powerwashing for mill glaze and stick with sanding. When you do powerwash, leave ample time for the substrate to dry: a minimum of three days -- and preferably a week -- of dry weather. If you paint over moisture in wood, it will eventually leave the wood and cause the paint to blister.

You also have to consider the plane of the the surface you're coating. Many, if not most, industry professionals think horizontal surfaces are the biggest challenge. "A horizontal surface is more difficult for a coating to perform on than a vertical one. As a general rule, I don't recommend painting decks because when you put a film on a deck the tendency will be for it to peel off," unless all sides of the wood is sealed before painting the top. Standing water and snow, as well as people, will contribute to failure and moisture will enter the wood from underneath saturating the board.

Seasons in the sun: Horizontal surfaces also get more exposure to sunlight than vertical surfaces. Moreover, keep in mind that although the air temperature may be only 85F, that the temperature of the wood on a deck -- or an exterior wall -- may reach 150F on a sunny summer day, and that's too hot for paint.

There's another practical reason for relegating exterior painting to September or October: rainfall. A sudden rain, like the typical spring cloudbursts, could ruin a new paint job. The old oil-based paints often need two or three days to dry thoroughly. Newer coatings dry more quickly, but you still are relying on the kindness of nature. Further, oil-based paints require a bone-dry surface to insure proper adhesion. If it rains on Monday, you can forget about painting until the middle of the week. Mercury and lead are no longer used in oil based paints and ultra-violet protection is rare to find in oil paints used for exteriors today, plus they dry hard and brittle! 100% Acrylics are your best bet because they flex with expansion and contraction of wood!