Wood Fence FAQ

Where does Western Red Cedar come from?
It’s unique to the West Coast of North America. In British Columbia it makes up almost 21% of the coastal forests. In the rest of the growing range, it comprises three to twelve percent of the total growth, along with Douglas Fir and Western Hemlock. Inland Red Cedar is a sub-species of Western Red Cedar that grows in an area that follows the Rocky Mountains, goes south from mid-British Columbia to the Salmon River and extends westward from Helena, Montana to Spokane, Washington.

What’s the difference between nominal and actual thickness?
Nominal is a size designation most lumber uses for convenience. In lumber, the nominal size is usually greater than the actual size.

Thickness:
1″ = nominal

Producers have determined that the thinner sizes still have acceptable performance. Also, due to rising cost, raw-material producers receive a better return with thinner products.
3/4″ = actual
21/32″ = actual
5/8″ = actual

How does full width differ from scant width?
All lumber is produced with a stated width, which is the target size. As milling has become more accurate, target sizes have moved closer to surfaced or planed sizes, i.e. 5 1/2″. As the width diminishes, the actual width is scant-or less than-the nominal width. See examples below:

Full Width Scant Width
6″ 5-1/2″
4″ 3-1/2″
3″ 2-1/2″

Why do knots fall out of boards, creating holes?
Knots and the surrounding wood have different densities. Since knots are more dense, they expand and contract less than the surrounding wood, loosening the bond. To protect against this, use a Premium or #1 board with both faces graded. The knots will be smaller and intergrown. The cost is slightly more, but your fence will have a longer serviceable life.

What causes wood boards to develop black stains at the nails?
The stain is caused by natural wood extracts interacting with metal in the fastener. Moist wood increases the likelihood of this interaction. For Cedar, Redwood and Cypress, you should use double-dipped galvanized, stainless steel or aluminum fasteners.

Can the stained wood be cleaned off?
Yes. If the stain is has a brown tint to it, use a solution with Trisodium Phosphate (TSP), which is available at local retail hardware stores.

If the stain is black, use a solution with Oxalic Acid to clean the boards. This material is also available at retail hardware stores.

Commercial cleaners are available as well. Identify the cause of the stain to ensure you choose the correct product. Certain concrete cleaners are specifically formulated to clean wood extracts from patios, sidewalks, or other concrete structures.

What about using bleach and water?
Chlorine-based or Oxygen-type bleach is effective against mildew and fungi. Oxygen-type bleach contains sodium percarbonate, which when added to water forms hydrogen peroxide, an effective agent in removing mildew stains, dirt and weathered gray residue from wood that has ultraviolet (sunlight) degradation. Unlike chlorine-based bleach, once the wood is treated with the oxygen-type bleach, it will return to its original natural appearance.

Some species of wood contain tannins, a natural resin. Water can extract these resins from wood leaving brown or black discolorations on the surface. Blue-black stains can result from a reaction of tannins to the iron in nails or fasteners. Neither chlorine nor oxygen bleaches are effective against tannin or iron stains, but the use of an oxalic acid-based product mentioned previously will render the stains colorless.

Why do boards split when fastened with nails?
Correct nails and nailing practices are essential for successful installation. Choosing a needle point nail is a common mistake. While the most commonly used nail is a diamond point, a blunt point will reduce splitting also. Overdriving nails is another problem that distorts wood and causes excessive splitting. Predrilling will help reduce any splitting that can occur.

The boards at the top of my fence are warping. Why?
The backrails should be no more than 8″ from the fence board tops and bottoms. Fence boards 6′ high should have three back rails. Spacing your rails this way will help control the wood’s natural tendency to warp, due to expansion and contraction.

What can be done to eliminate the effects of weathering and keep that “new fence” look?
While there’s no way to eliminate the weathering of wood, it’s relatively easy to minimize the effects:

  • Use three back rails (6′ fence), two backrails (4′, 5′ fence), or 4 backrails (8′ fence) for more hold-down points.
  • Use only hot-dipped galvanized, or stainless steel fasteners with a ring or spiral shank to minimize warp and rust stains.
  • Treat the surfaces of fence boards with a water-repellant solution to reduce the rate that moisture is absorbed and released. This solution should also have a good UV inhibitor if you don’t want the fence to gray.
  • Follow a regular maintenance program of cleaning and refinishing every few years with a “clear” or “toner” water repellant containing UV inhibitors. This will revitalize a dingy appearance caused by dirt, mildew or graying. It’s like washing and waxing your car. Opinions differ on how necessary it is to perform regular maintenance, but most agree your fence will look much better for the effort.

Where does Redwood come from?
It’s unique to the Northern California coast and adjacent regions. Redwood is harvested in commercial forests from San Francisco to Southern Oregon in a strip along the Pacific Ocean.

Where does Northern White Cedar come from?
It’s unique to the Northeast region of North America. Northern White Cedar grows from upper Michigan along the Canadian-United States border to New Brunswick. It’s a slow-growing tree found mainly in swampy areas.

What’s pressure-treated wood?
It’s wood that has been pressure-impregnated with an effective preservative. This treatment helps wood resist attacks by termites and decay-causing fungi.

What are some of the advantages of pressure-treated wood?
It’s economical; works easily with common tools; is naturally attractive; durable; strong for its weight; and is readily available in a wide variety of sizes and styles.

What about any cracking, warping, and graying that may show up over time?
Even though pressure-treated wood is protected from termites and fungal decay, it is still a porous, natural material. Wood swells when it absorbs moisture and shrinks when it dries out. The drying process creates stresses in the wood, which contributes to cracking and warping. The sun’s ultra-violet (UV) rays cause the wood to turn gray. Pressure-treated wood is subject to these effects, just like other lumber.

What are Whitewoods and where do they grow?
The species Spruce, Pine and Fir make up the grouping known as Whitewoods. Fence board cut from these species have a white appearance when first installed. While these species are prevalent throughout North America, Whitewood fencing products are produced primarily in a belt ranging from Eastern to Western Canada.

What are the black spots on my boards?
Small, sooty-looking circular spots are caused by mold or mildew. Mildew occurs when there’s low air circulation, moisture, temperature and food source (wood). Installing your fence will expose the wood to airflow and stop mold.

Can the mold or mildew be cleaned off my boards?
Yes, you can choose from a number of readily available commercial products. Read the directions closely. They’ll describe various wood-cleaning problems and recommend the proper cleaning solution.

How long can I expect my Whitewood fence boards to last?
Untreated, unpainted Whitewoods will last 3 to 7 years, depending on local environment conditions. (Source: USDA Forestry Book.)