Frequently Asked Questions (FAQs)
General Wood Properties
How much water is in wood?
There are two important types of water are in the wood. Bound Water is located in the cell wall of the fibers while Free Water is located in the lumen (cell opening). The important moisture content to remember is approximately 28% which is the fiber saturation point. Below the fiber saturation point, the wood only contains bound water while above the fiber saturation point, wood has both bound and free water. When the wood is harvested its moisture content is about 70-120%. During the initial portion of drying, wood mainly loses free water until the fiber saturation point is reached. This process is a rapid process; therefore, does not require a lot of energy. The properties of wood are not influenced by free water so that is why the strength of the wood and the specific gravity does not change beyond the fiber saturation point. All wood that has a moisture content above the fiber saturation point is called “Green Wood”. We tend to call a piece of wood “dry” if it has 19% or less moisture content. Wood used indoors will eventually stabilize at 8-14% moisture content; outdoors at 12-18%. The strength of the wood increases greatly below the fiber saturation point which makes dry pallets more valuable to the customer.
Why is fiber saturation moisture level so important?
The physical and mechanical properties of wood change only when wood dries below the Fiber Saturation Point (FSP). Shrinkage only occurs below FSP. Pallets made of wood with a maximum Moisture Content (MC) less than FSP will not contaminate most products that are moisture sensitive.
What is green wood?
Wood is called “green” when the MC level is equal to or greater than FSP. The MC of wood in a tree varies somewhat throughout the trunk, but typically varies 50 to 100%, depending on the wood species and season of the year. An average MC for wood still alive in a tree is 70%.
What moisture content does wood need to be to prevent mold growth?
Wood with a moisture content below 20% will not support mold or mildew, decay, or fungal attack.
Pallet Properties and Performance
How can I make my pallets fire retardant and flame spread resistant?
Purchase fire retardant/pressure treated lumber and manufacture the pallets from this material. Or, apply a fire retardant coating to the pallet parts.
What is the best way to dry hardwood pallets?
Pallets dry fastest in spring and summer in temperate climates. When air-drying pallet parts or pallets, the top of the piles should be covered to protect the pallet components from direct exposure to the sun. Direct sun exposure will result in excessively rapid drying, and the exposed lumber will warp, split, and check – to the point that the pallets may no longer be useful. Orient the stickers, or in the case of stacked stringer pallets, the stringers parallel to the predominant wind direction. If a fan is used, drying time is cut by 2/3. If the pallets are dried in a kiln operating at 100 to 110Â°F, the deck board moisture content will change from 85% to 20%, and this could be achieved in about 5 days.
How do I prevent mold growth on pallets?
Periodically apply a bleach solution to the lumber and remove any nearby sources of mold spores (such as decaying wood). Good housekeeping can reduce the amount of spores in the air, which ultimately reduces mildew growth. It is also important to keep the wood dry so the moisture level remains below 20%. You can also apply fungicide. The most popular fungicides used on wood to control mold contains copper-8-quinolinolate or chlorothalonil.
How do I prevent the decay of wood pallets?
Eliminate moisture from the wood and poison the food source (possible with safe fungicides). If food contact is not an issue, construct a pallet with any of the salt or water-borne commercial pressure impregnated lumbers. These pressure-treated products are typically southern pine.
How do I test the strength and stiffness of pallets?
“ASTM D1185 Standard Test Methods for Pallets and Related Structures Employed in Materials Handling and Shipping” is mainly used in the United States. This protocol uses an airbag to apply loads onto the pallets which represent worst case scenarios in loading conditions. “ISO 8611 Pallets for Material Handling” is the internationally accepted standard to test pallets. It has three parts. Part 1 provides information about the test setup, Part 2 provides information about the deflection limits, and Part 3 provides information on the evaluation of the pallet using an actual payload. ISO 8611 uses a combination of rigid bars to apply a load to the pallet.
How do I reduce the number of end splits?
End splits occur in the drying of green wood. You can apply end coatings to reduce the number of end splits.
How do I prevent pallets from causing corrosion of metal products?
Select wood species that have water-soluble pH values greater than 5.2 (Ash, Maple, Hickory, Yellow-polar, Sweetgum, or Tupelo). Use dry lumber or dry the pallet to less than 20% moisture. The pallets must be kept dry during use. Seal the products in moisture barriers or plastic films.
Will bacteria in the wood affect pallet strength?
No. Bacteria in wood will not affect pallet strength or stiffness.
How do I know how heavy a wood pallet is?
The weight of the wood pallet will depend on the volume of lumber used in the pallet, the specific gravity of the wood, and the MC of the wood.
What wood species are used to make wood pallets?
Oak, Elm, Maple, Beech, Hickories, Ash, Sweetgum, Black Tupelo, Aspen, Yellow-Poplar, Firs, Spruces, Southern Pines.
How do I rid of insects in wood pallets?
Green wood in pallets can be heat sterilized at 133Â°F for 3 to 5 hours. Wood pallets can be fumigated by Pest Control Operators (PCOs) using Methyl Bromide. Another effective chemical treatment is the use of powder fumigators, which can be found in grocery and hardware stores. Place two cans of the fumigator containers in a closed van for 4-6 hours to get rid of insects. For long-term efficacy, use topical applications such as Borate Salts or Copper-8-Quinolinolate. Pallets can also be painted to prevent re-infestations.
Does mold affect the strength or stiffness of pallets?
No, mold is only a surface phenomenon and it does not cause any structural damage to a wood pallet. However, it could contaminate the products stacked on the the pallet; therefore, mold prevention is very important.
How do I get rid of mold on pallets?
One treatment to kill or remove mold and mildew from lumber is to spray or dip it in the following solution:
1/3 part household detergent
2 part water
This treatment is effective for 3-5 days.
Does shrinkage reduce load carrying capacity?
No. Shrinkage does not imply a reduction in the load carrying capacity of pallet. However, shrinkage will loosen joints and cause splitting, both of which do influence pallet strength, stiffness, and durability.
What is "iron stain" and how do I get rid of it?
Iron stain is dark blue or black and is often confused with mold. It can rub off onto the products or packaging that is set on top of the pallet until the pallet dries. Iron stain treatments, which rid pallets of discoloration when applied to wood, are available. Also, reduce the amount of oak and hickory when assembling a pallet (iron stain is most common when using oak and hickory).
How much will wood pallet parts shrink as they dry?
The percent of shrinkage depends on the species of wood. To roughly estimate how much wood pallet parts will shrink when air-dried to 18% MC, multiply the green part size by 0.02 or 2% and at long-term equilibrium in warehouses by 0.04 or 4%. This is equivalent to a 1% shrinkage/5% MC change below fiber saturation point.
How do I eliminate odor contamination of products?
Deodorants, such as ODO-BAN can be sprayed on pallets. These deodorants are available in concentrated form from retail outlets such as Sams Club.
How do I know if my pallets are durable?
Stronger, stiffer, and denser hardwoods will result in more durable pallets. The FasTrack simulation developed on the supply chain of Proctor & Gamble can be used to evaluate the durability of the pallet design. For more information please visit the following link: FasTrack Area.
Does the load carrying capacity of the pallet depend on the type of load?
Yes, the load carrying capacity of the pallet is highly correlated to the type of load that is being carried. The type of load can increase the load carrying capacity of the pallet as much as 60-70%. The rule of thumb is that if the pallet is less stiff, the stiffness of the load makes more of a difference then if the pallet itself is stiffer. Some preliminary information can be found in “ISO 8611 Part 3”.
How long do I need to heat-treat a pallet?
Heat-treating time depends on the equipment, the pallet design, and the moisture content of the pallet parts. It takes approximately 2.5 hours for KD softwoods; 4.5 hours for green hardwoods, and 2.5 hr. for recycled lumber.
How do I prevent water contamination during export in containers?
• To prevent water contamination during export, allow KD 19% lumber to dry to 10 to 12% to protect the contents of containers.
• Use desiccant bags in the container to capture the excess moisture.
How do I fumigate wood pallets?
Generally, commercial pest control operators perform fumigation. However, pallet manufacturers can become certified fumigators. Training and certification is available through most state departments of agriculture. For more information, please visit the following link: Pallet Enterprise.
What criteria are important for the installation of sprinkler systems by the NFPA?
Commodity class of the product (how much of a fire hazard is your product) and occupancy classification (type of business, height of building, number of offices, warehouses, etc.)
Do pallets comply with CONEG heavy metal limits in packaging?
Yes. Although there are some metals restricted by CONEG, neither wood nor the low carbon steel nails used in pallet assembly contain these regulated metals.
What are the International Phytosanitation Regulations?
They are guidelines for regulating wood packaging material in international trade. The US and most of its trading partners have adopted these standards with some modification. These regulations require raw wood packaging, pallets, dunnage, blocking, and bracing to be heat-treated or fumigated.
Do I need to use special design parameters if the pallets will be used in an automated material handling system?
Yes, pallets used in an automated material handling system need to meet a more strict requirements created by ANSI MH1 committee. The requirements can be found in ANSI MH1 Standards Section 10.