Wood Protection for Outdoor Projects

Applying a Penetrating Stain and Sealer


By Matt Weber

Wood remains the top building material for exterior projects because it has a lot going for it. It’s affordable, easy to work with, versatile, and maintains a natural look that blends with the outdoor surroundings. But wood requires maintenance and occasional recoating to keep it looking good and performing well.

No matter what type of wood you have, whether it’s pressure-treated lumber, cedar, cypress, redwood or even a high-end exotic hardwood, staining and sealing outdoor wood is the best way to protect it from the elements. For structures such as decks, fences, pergolas, and even outdoor furniture, I usually coat the wood with an oil-based preservative stain/sealer.



An exterior-grade penetrating stain/sealer is a water-repellent preservative that includes a “mildewcide,” and some products contain ultraviolet light absorbers that protect from sun exposure. The resins penetrate the wood pores to provide pigment.  This blocks out the damaging effects of UV rays and water damage while allowing the natural woodgrain and texture to shine through. The wood will have a different color tone after application but will feel the same to the touch (unlike the glassy feel of a film-forming sealant).

I prefer an oil-based finish because the tiny particles fuse together chemically into one large sheet-like substance, which achieves a hard, durable finish.

I recently recoated a deck and fence, where the stain had faded and mildew was developing.

But even a quality oil-based finish will eventually need a new maintenance coat. If you plan to stick with a similar color of penetrating stain (and the wood is in decent condition), then a thorough cleaning might be all the prep work required for a fresh maintenance coat. Refer to the stain/sealer manufacturer’s recommendations for best practices.

Prep Work

Prior to applying the stain, heavily soiled wood surfaces can be pressure-washed to remove stubborn grime or gray, dead wood cells, but the high-pressure water stream can cause the surface to fuzz or splinter. The roughened surface can pose a “touch” hazard for areas such as deck surfaces where people may walk barefoot. When using a power-washer, limit the outlet pressure to no more than 1,000 or 1,200 PSI.

The moss growing on the face of this fence board was one of many strong indications the wood needed some maintenance.

If pressure-washing isn’t necessary, and you only need to remove dirt and mildew, a thorough wash with bleach might be sufficient, but the choice in bleach is important. Whereas chlorine bleach does an excellent job of killing bacteria and viruses, and will remove superficial mold, it has not been proven effective in killing mold on porous surfaces. This is because the mold’s enzyme roots grow inside the pores, and chlorine bleach cannot penetrate the porous material due to its ionic structure. This means the mold problem will likely soon return. Chlorine bleach also damages the lignin in the wood, which is how the wood is bonded together, and this will make it more prone to aging and splintering along the surface. Chlorine bleach can also cause some deck stain/sealers to fail, removing the color tone and even some of the wood’s natural color.

To clean the wood surface, I used a scrub brush and a mixture of oxygen bleach.

A better alternative is to use oxygen bleach. As found in laundry detergent, oxygen bleach cleans fabrics without disrupting the color or damaging the material. Oxygen bleach can usually be combined with water, applied to the wood and allowed to sit for 10 or 15 minutes, then it can be easily rinsed from the surface with a garden hose. Oxygen bleach can clean the wood without damaging the fibers or harming the surrounding vegetation, which eliminates the need to use plastic or drop cloths for protection.

I mixed the oxygen bleach with water and applied it with a pump-up sprayer.


Apply oxygen bleach thoroughly, coating all sides and edges of the project. After 10 to 15 minutes, rinse the bleach of the surface and allow the wood to dry.

Once the wood has thoroughly dried from the preparatory cleaning, you can apply your choice of stain/sealer.

Armstrong-Clark is a brand of penetrating stain/sealer I use often because it seals the wood well and can be applied in direct sunlight.

No matter what product you select, always thoroughly mix the stain prior to application. The solids tend to settle on the bottom of the stain container, and mixing will blend them evenly into the sealer to ensure a consistent color tone throughout the project.

I applied the stain/sealer to the wood surface with an airless sprayer. If using a sprayer, hold the nozzle about 10 inches from the wood and move it in a fluid motion parallel to the work surface.
Be careful with the overspray. Use plastic sheeting and paint shields as needed to keep stain off surrounding structures.

For both horizontal and vertical structures, brushing is the best method for stain/sealer application because the bristles push the product evenly into the woodgrain to increase absorption. Using a sprayer or roller can apply the stain more quickly, but both of these methods leave much of the stain on the surface without adequate penetration into the pores. If the product doesn’t adhere well it can wear away unevenly, so you should still back-brush it into the woodgrain for the most consistent appearance and best protection.

For the best stain/sealer penetration into the wood grain, I recommend always back-brushing the product into the surface, even if it’s initially been applied with a sprayer or roller.
Be prepared to “think outside the box” to address the needs of your project. On the shadowbox fence I was staining. I had to chop off the sides of a scrub brush so it would fit between the alternating fence boards and access the entire wood surface for back-brushing.

If you’re recoating an existing project, a single thorough coat of new penetrating sealer should be sufficient to renew the look of your project and defend from the elements for several more seasons in the harsh outdoors.

After modifying the head, the brush slipped easily between the fence boards.

Side Note 1


Armstrong’s deck and siding wood stain has nondrying conditioning oils that separate from the drying side of the formula. These oils penetrate deep into the deck or siding wood fiber where the wood’s natural oils used to be. This process rejuvenates the wood. The drying oils stay at the surface, lock in the conditioning oils and create a dry to the touch barrier. Armstrong’s deck and siding wood stain formulas also contain vegetable oils, transparent oxide pigments, water repellents, mildewcide, and solvent.

Quality is what Armstrong-Clark brings to you. Backed by 7 generations of oil-based coatings experience, coupled with modern technology, Armstrong-Clark can meet and exceed your need for oil based wood coatings.


-Can be applied in direct sunlight and heat of the day. If the first coat penetrates within 30 minutes a second coat can be applied for extra protection.

-Easily applied by brush, roller, or airless spray equipment.
When spraying – back-rolling or brushing will help even out appearance. If there are any puddles or glossy spots after 24 hours, remove with a dry rag.

-Non-drying oils penetrate deep to recondition older wood.

-Drying oils, pigments, and water repellents protect against water and UV damage and lock in the nondrying oils.

-Complies with all government environmental standards.

-No offensive odor.

Armstrong-Clark Wood Deck Stain applies at about 200 square feet per gallon on softwoods, 300-400 sq ft/ gallon on hardwoods.

For more info:

Armstrong-Clark Company

14949 Camage Ave.
Sonora Ca. 95370

W: Armclark.com
P: 800-916-8211
F: 209-588-8973
E: [email protected]


Side Note 2

Simple Fence Repairs

When applying a maintenance coat of stain/sealer to an outdoor structure, you’re likely to find a few areas in need of repair. Since wood tends to move in response to changes in temperature and humidity, boards can twist and bend over time, putting stress on fastener connections. I came across a few of these yawning joints on a recent fence-staining project, where the boards had bent over the years and refused to bend back the way I had originally installed them. In some cases, the easiest way to address these problems is to bridge them with a piece of metal hardware fastened with exterior-grade screws to the mating sides of the joint. Your local hardware store will have a variety of hardware plates in various shapes and sizes. For the fence I used a couple of flat plates, plus a right-angle plate at a corner connection. If you don’t like the look of the metal on your wood fence, you can always cut a 1x block stained to match the wood, then fasten it over the metal plate.

Side Note 3

YellaWood for Outdoor Projects

Pressure-treated pine is a mainstay for outdoor projects and structural fixtures. Used by builders, contractors and DIY’ers alike, its sustainability and beauty differentiate it from all other materials. And, unlike composites and other alternatives, pressure-treated pine brings with it an advantageous price point homeowners appreciate. Here are other benefits to consider when choosing materials for your next project.

Naturally Beautiful—YellaWood brand products are made from Southern Yellow Pine, which doesn’t need factory-applied enhancements to make it look like wood because it is wood. It has history, texture and distinction already built in. Plus, homeowners can change the color of their deck at will. In one weekend consumers can give their deck a completely new appearance.

Economical—Decks crafted from treated pine or other natural wood consistently provide a high return on investment. Rated well by contractors and DIY’ers for its quality, YellaWood brand pressure-treated pine provides a wide array of products through a vast network of dealers, allowing builders to create incredible structures with a budget-friendly product.

Broad Options—With YellaWood, you have access to numerous options representing a wide range of budgets and products. Available in many grades, customers can choose between everything from a rustic appearance to an almost clear finish. And, since YellaWood brand products are available in several retentions, projects can range from decks, their substructures and handrails to treehouses, fences and docks. Visit yellawood.com.

Hot Product

Armstrong Clark wood stain
Armstrong-Clark Wood Stains

Armstrong-Clark’s deck and siding wood stain has nondrying conditioning oils that separate from the drying side of the formula. These oils penetrate deep into the deck or siding wood fiber where the wood’s natural oils used to be. This process rejuvenates the wood. The drying oils stay at the surface, lock in the conditioning oils […]