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Exterior paints are a great way to protect your outdoor furniture, deck, siding, or trim from the damaging effects of the sun, wind, and rain. However, a quick coat of latex paint from the hardware store is not a silver bullet. When applied directly to old, weathered decking boards or even brand-new clapboard siding, you are likely to run into problems.

The paint will stick to whatever you paint it on. If your boards have rot, mold, or dirt on them, there is nothing solid for the paint to adhere to, and it will likely start to blister, crack and peel. The key to a long-lasting coat of paint is to properly prepare the wood’s surface to accept and bond with the paint.

Wash Up

The first step to any outdoor wood painting project is to remove the surface layer of dirt, pollen, and dust collected on the wood’s surface. Even though the wood regularly gets rinsed off when it rains and may not appear dirty, there is a layer of grim that you should remove before applying any paint. Depending on the type of wood and the size of your project, you can clean the wood a few different ways.

  • Soapy Water – For smaller projects such as patio furniture, a simple solution of mild detergent in water will do. If the wood has been painted before, a deglosser such as TSP will remove the glossy coating from the old paint, making it easier for the new paint to adhere to it. A soft-bristled scrub brush may be helpful. You should never use a wire brush for cleaning as it can scratch softer wood species.
  • Dilute Bleach – In humid climates where mold and mildew can be a problem, you may need to use a dilute mixture of bleach and water to kill mold and mildew and remove the stains they leave behind. Bleach is a harsh chemical that can dry the wood and ruin your clothes. Use it with caution.
  • Pressure Washer – If you are preparing to paint the fence around your ¼ acre lot, you may want to rent a pressure washer to speed up the cleaning process. This method makes quick work of larger projects. Just be sure to keep the pressure low enough that you don’t gouge the wood.

Assess the Wood’s Condition

Once the wood is clean, you should be able to evaluate its condition accurately. Evaluate the condition of the wood to identify spots that need special attention or even replacement.

  • Fuzzy Fibers – Over time, the fibers on the surface of wooden boards may break down, giving the wood a frayed texture. These areas will need to be sanded smooth before painting.
  • Loose Hardware – Look for popped nails or screws. In addition to being unsightly, loose hardware may allow fence pickets to move or warp. Hardware should be tightened or replaced as needed.
  • Rotted Wood – Wood should feel hard and resist pressure applied by your finger or a screwdriver. If you encounter areas that feel spongy or break away under pressure, you likely have dry or wet rot. While the two types of rot occur under different conditions, they are both caused by microorganisms. These spots will need to be removed and filled or replaced before you can begin painting.

Remove Old Paint

You can apply new paint over old paint as long as the old paint is still adhering well to the wood’s surface. Paint that is flaking or peeling needs to be removed. A paint scraping tool is an excellent way to remove loose paint on flat surfaces. When scraping paint off the wood, work with the wood’s grain and keep the blade flush against the surface. The sharp metal corners on the blade can dig into the underlying wood if misused.

After removing the loose paint, you may notice ridges between the bare wood and the wood that still has paint on it. Sanding with 180-grit sandpaper can smooth out these ridges so that the final painted surface is even and level. Be sure to wipe the surface clean after sanding to remove any dust and debris created in the process. A tack cloth or wet sponge works well.

Caulk Joints

To prevent water from seeping between boards or behind window trim, you should apply caulk to the gaps, sealing these joints. Look for a latex caulk that matches the color of paint you will use or paintable caulk.

Be sure to pay attention to the drying times on the label. Preparing wood and painting it is a multi-day project. The painting surface should be allowed to dry completely after each step to ensure the best results.

Prime the Wood

Think of the primer as the glue that will hold the paint to the wood. Choosing a suitable primer for the job is essential. The primer should be compatible with the underlying paint as well as the paint that you plan to apply.

If you don’t know whether the existing paint is oil-based or latex, you can use an acetone test. Rub a small amount of acetone on an inconspicuous area. If the paint comes off, you have latex paint, and a latex primer should do the trick. If the paint is unaffected by acetone, the paint is oil-based, and you may need an oil-based or bonding primer.

Some species of wood, such as pine and cedar wood, produce resins that can seep through your paint, causing discoloration. A resin-blocking primer can inhibit this bleed-through.

With the wood cleaned, patched, scraped, sanded, caulked, and primed, it is finally ready for painting. This step is the most exciting because you finally get to see the finished product. The best part is that it should look fantastic if you have done your preparation the proper way.