ZM Lumber is proud to offer Vermette Wood Preservers’ (VWP’s) Penta Treated Ag Fence Posts.

Vermette Wood Preservers (VWP) is a Canadian manufacturer of oil-based, pressure-treated wood products. They provide us with pressure-treated fence posts, utility poles, foundation piles, lumber, bridge timbers, cross-arms, pipeline blocking and sleepers, wood shavings, and firewood.

What’s So Great About Taper-Peeled Fence Posts?

Compared to non-tapered dowel posts, they’re superior in virtually every way.

For starters, you get more wood for the money.

Tapered peeled posts are peeled by a high-speed machine that follows the natural contour of the log. The finished post has the same characteristics as the log. Because the tree is tapered, the post is tapered. A tapered peeled post diameter should have a 1” variance at the small end of the post (these posts are measured by the small end and the large end is sharpened or left blunt the large end would be placed in the ground). Example: a 4” to 5” x 7’ post can range in diameter between 4” to 5” at the small end of a 7’ long post. By contrast, a non-tapered dowel post is exactly 4-1/4” from the top to the bottom of a 7’ long post. Regardless of dimensions, it is recommended that posts be CAA-treated to 0.4 per-cubit-foot in order to achieve maximum life expectancy.
Non-tapered dowel posts have 50% less strength vs tapered peeled posts. A non-tapered dowel post is a log that’s been pushed through a spinning ring to form a smooth, decorative post.
This lack of taper makes the post about 15% lighter and have 50% less strength than a traditional tapered peeled post. It’s the milling process that makes these posts weaker because the heartwood is often off-center. Their aesthetics and uniformity of size make non-tapered dowel posts only acceptable as a decorative acreage fencing. They’re also less expensive to ship. But these posts should never be used as horizontal braces because they will weaken over time. Where greater strength is called for (like bracing units and hydraulic driving), tapered posts are the clear choice.

Don’t take our word for it.

The Facility of Forestry at the University of Toronto conducted a study prepared for Osmose Inc. that demonstrates how tapered peeled posts are superior in strength and will accept wood preservatives to meet industry standards. This makes them by far the best choice when comparing tapered peeled posts to non-tapered dowel posts.

Tapered peeled posts (appeal) to the traditional farmer and rancher. Fence installers prefer them over non-tapered dowel posts because there’s more post surface, thereby making the post stronger for hydraulic driving.

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Penta & the Treating Process

Pentachlorophenol is an excellent wood preservative which has been in commercial use for over 60 years. It is approved by the American Wood Preservers Association for use in the treatment of all outdoor wood products. Penta is a crystalline solid which is made into a liquid preservative solution by dissolving it in dark wood treating oil with a high asphalt content. Our treating solution contains 3.5% penta by weight.

Pentachlorophenol dissolved in dark wood treating is very similar to creosote and as a result, is often mistaken for creosote. Penta is as effective and, in some situations, even more effective than creosote in providing long-lasting protection for wood products. The major difference and the reason that Vermette Wood Products chooses to use Penta is that Penta-treated products are less oily and less messy than creosote-treated products and in addition, they do not carry the same level of negative health risks as creosote-treated products.

When compared to creosote-treated fence posts, our penta-treated posts will last at least as long, and in most cases, even longer than creosote-treated fence posts. Our product truly shines when used in moist soils and flooded areas. The dark wood treating oil used in our treatment process creates an effective moisture barrier and reduces swelling of the product. In addition, the fact that pentachlorophenol is not water soluble means that you do not have to worry about high levels of preservative leaching into the ground or surface water on your property such as in the case of arsenic leaching from water-soluble CCA (chomated copper arsenate) treated product.

In fact, the USDA recently released the results of a 50-year study on the lifespan of fence posts treated with over 50 different preservatives which shows that penta-treated posts have the longest useful life. The results reveal that after 50 years of exposure, 100% of the fence posts treated with 3% penta in wood treating oil were still standing compared to 64% standing for ACA (close chemical cousin of CCA) treated posts, 76% standing for creosote, and 72% standing for CuNap (Copper Napthenate). (2005, A Comparison of Wood Preservatives in Posts in Southern Mississippi: Results from A Half-Decade of Testing , USDA Forest Labs, M. Freeman, D. Crawford, P. Lebow, J. Brient) – view this study at

The penta preservation process begins with conditioning of the raw material. This is accomplished by naturally air drying the wood until the moisture content is between 19% and 26%. Once this initial moisture level is achieved, wood is loaded into the pressure cylinder and the treatment process begins. First, any excess moisture content is vacuumed out of the wood. Next, the initial air pressure is established in the cylinder, which causes the cells of the wood to expand, then the cylinder is filled with the Penta solution.

The next step is to increase the air pressure to 120-150 psi (depending on the moisture content) and in effect, the preservative is forced into the wood. The pressure is applied for three hours and at the end of the process, the excess solution is forced from the cells. When the pressure is relieved, a second vacuum is applied to remove any remaining solution and the cells return to normal size. At this point, the treatment process is complete and the treated wood is then removed from the pressure cylinder.

Vermette Wood Products pressure-treated fence posts meet all CSA, AWPA, and USDA specifications. They have a minimum, pentachlorophenol retention of 0.41 lbs/ft³ and correspond to a retention level of 4 on the USDA standards scale.