Poly vs Wood, The Durability Test
For centuries wood has been a builder’s material off choice, it has natural beauty, is readily available, is durable and can be easily sculpted for a variety of uses. One of the biggest drawbacks to wood has always been how quickly its beauty and durability breakdown in outdoor applications.
In recent years the emergence of HDPE (High-density polyethylene) plastic “poly” lumber as a viable replacement for wood has given builders a better alternative for many outdoor applications. Poly lumber has shown the ability to maintain its beauty and durability for decades.
Poly lumber does not chip, crack, split, rot or decay under normal circumstances, including exposure to harsh climates. Poly never needs stain, paint or any preservation treatment applied. This durability is attractive to manufacuters and consumers alike.
Molecular Nature of Poly and Wood Compared
Your personal experience with tearing a sheet of paper or a sheet of plastic of the same thickness tells you something about the difference in durability of wood and poly. This difference is amplified as you add thickness, while you can still splinter a piece of wood at a ¼ inch thickness with your bare hands, you can’t do so with a poly sheet of the same thickness.
This is partly due to the molecular nature of plastic, which is made up of covalent bonds known as carbon-to-carbon bonds. These bonds are very difficult to break, making plastic an extremely durable material.
The molecular nature of wood is a bit different in the fact that wood’s carbon atoms are bonded to cellulose molecules. While this is a sturdy bond as well, it is significantly easier to disrupt than the carbon-to-carbon bonds of plastic.
Flexibility of Poly and Wood Compared
Contrary to what you may be thinking, durability is not necessarily synonymous with rigid and unyielding.
The flexibility of HDPE plastics is an essential attribute in giving poly lumber more durability than wood.
The old adage, “bend but don’t break” applies here, poly lumber is able to bend in any direction under the force of an impact without breaking. While wood is durable it tends to be more brittle than poly lumber. This explains why we can snap a wood board across our knee but are unable to do so with poly lumber.
That being said, you need to know your project, there are times when you want a building material that is more rigid and unyielding. For those projects wood might be a better choice than poly lumber.
Adding Reinforcement to Poly and Wood
The durability of wood is pretty much dependent upon the tree itself and the environment it grew in. Wood will never become more durable than the day the tree was cut down. While chemicals can be added to help preserve the durability of wood, it won’t make the wood any stronger than it was as a live tree.
However since poly lumber is a manufactured product, reinforcements can be added during the manufacturing process to add strength and durability for a particular application. Fiberglass rebar can be molded inside to reduce flexibility and add a more rigid characteristic, or fiberglass strands can be added to increase strength in applications where flexibility is vital.
Environmental Tests for Poly and Wood
Mother nature has a way of separating the durable from less durable, and non-durable materials.
When a material is exposed to the elements of nature for an extended period of time we begin to see its durability more clearly. The fact that a discarded plastic bottle remains beside the road for years, while alongside it a piece of lumber has long decayed into oblivion indicates a significant difference in durability between wood and poly. Read More...
So how do poly and wood perform in the nature test?
The Water Test
Water is essential to sustaining life, at the same time it is one of the most destructive forces on the planet. It has enough of force to carve a canyon out of a solid rock mountain, wash away a home in a flood, corrode hardened steel, and damage wood.
Because wood contains cellulose molecules which are porous it naturally absorbs water when exposed to it. While that is good and right for a live tree, that is bad for lumber. Water causes wood to swell and warp, while providing potential for mold to grow, or rot and decay to be accelerated. Treating lumber with harsh chemicals is our solution to preventing wood from doing what it was naturally designed to do, absorb moisture. Even wood that has been pressure treated will begin absorbing moisture as time passes.
Poly lumber is of a non-porous nature and is entirely waterproof by default, with no additional surface treatments necessary.
Swelling, warping, rot and decay are all non-issues with poly lumber. Poly lumber is an ideal choice for marine or wet environments.
The Sun Test
It is a known fact the UV rays of the sun can be an extremely destructive force, especially in the area of appearance. Wood left exposed to sunlight will lose its warm tones, taking on a listless gray appearance. Prolonged exposure to harsh sunlight will cause rapid moisture loss in wood causing cracking and warping.
Poly lumber is manufactured with UV blockers blended into the poly resins along with the color. This allows poly lumber to retain its color year after year. Color fading on poly is often so slight you don’t even notice it except on the most brilliant colors. Since poly is non-porous it does not have trapped moisture that will evaporate when exposed to harsh sunlight, eliminating the cracking and warping issue found in wood.
The Temperature Test
Wood exposed to the environment is constantly adjusting its moisture content to its surroundings. This becomes problematic during temperature extremes, extreme heat and low humidity cause wood to dry out and crack, during times of high temperatures and humidity wood tends to expand, while extreme cold causes wood to shrink. The physical changes of wood brought about by temperature change can impact the integrity of a structure over time.
For all its negative temperature impacts, wood has a unique characteristic of being able to maintain a somewhat cooler surface temperature during times of extreme heat, than its counterpart poly.
It is a known fact that heat impacts plastic, however industry advancements have raised the bar significantly in this area over the last decade. High-quality HDPE poly lumber is NOT impacted by temperatures lower than 400 degrees Fahrenheit. The sweltering Florida sun on a summer day is not too much for your poly lawn décor or poly outdoor furniture.
The Rot Test
It is a fact, all living things decay in time, and there are factors that can speed up the process. In wood one of those factors is the presence of fungus. One of the primary causes of fungal growth in wood is water exposure. When wood is exposed to water fungi begin to grow producing destructive enzymes that eat away at the wood, leading to decay.
Because poly lumber is waterproof, the enzymes in fungus that cause rot do not typically impact poly lumber in the same way they impact wood. If fungus attacks poly, it is in the form of mold growing on the surface, which can be removed with soap and water. Maintenance free poly has been known to last decades in a wet environment with no signs of rot or decay.
The Insect Test
Homeowners across the country can identify with the challenge of keeping insects from infesting the wood around their home. Wood patio furniture, wood decking, wood soffit, wood walls, wood structural timbers are all open game to attack from insects.
- Carpenter Ants
- Carpenter Bees
- Powder-Post Beetles
- Wood-Boring Beetles
- Termites
Any of these insects will damage the structural integrity of wood. The best defense against these pests is treating wood with harsh chemicals. Unfortunately, the most effective chemicals are also harmful to humans and the environment.
Poly lumber does not hold the same attraction to these wood destroying insects. It is not that poly isn't able to be drilled or eaten by the insects, it simply isn’t attractive to them, they have no use for it and simply let it alone.
Poly or Wood Which Has Durable Beauty
Poly is clearly more durable than wood in almost every application, manufacturers are bearing this out as they are opting for poly lumber over traditional wood at an ever increasing pace. The one challenge with poly lumber has been trying to emulate the natural beauty of woodgrain. With each passing year poly lumber manufacturers are becoming more creative with the extrusion process and "woodgrain" poly lumber is becoming commonplace. Today's poly lumber is durable beauty.
