Wooden planter boxes are common outside houses, on patios, and in other areas of the landscape. While wooden planters may look attractive when first purchased, over time, moisture and soil take their toll on the wood. If you have a wooden planter, it is important to waterproof it to prevent the constant moisture from damaging the wood. Waterproofing simply involves applying a sealant that prevents moisture penetration.
Clean the wooden planter, if it is not new, by rinsing it with a garden hose and using a stiff-bristled brush to scrub away any dirt. Place the planter in a sunny area of the yard and allow it to dry for 24 to 48 hours to allow all of the moisture to evaporate from the wood.
Spread a plastic dropcloth over the ground or work surface, and place the wooden planter on top of it.
Open a tub of roofing cement, and use a putty knife to scoop up 1/4 cup.
Spread the cement onto the inside bottom of the wooden planter, smoothing it out to a thin, 1/4-inch layer. Repeat the process, adding more cement as needed until the entire inside bottom of the planter is covered.
Pick up an additional 1/4 cup of cement on the putty knife, and apply it to the interior sides of the planter in the same manner. Apply additional cement as needed until it extends all the way up the interior sides of the planter.
Let the planter sit undisturbed for 24 hours to allow the cement to set up.
Turn the wooden planter upside down. Open a can of penetrating oil. Use a paintbrush to cover the entire outside of the planter with one coat of the penetrating oil to seal the wood grain. Include any feet the planter may have, since these are often porous.
Allow the wooden planter to dry an additional 24 hours or until it is no longer sticky to the touch.
If desired, you can paint the planter with standard latex paint instead of using a penetrating oil.