The truth is that mold spores are everywhere. But it takes the right conditions for mold to grow on pallets. If mold spores have enough oxygen, moisture, the right temperature, and a food source, they can germinate in 24-48 hours. Wood is a food source for mold.
Since mold can occur in a fairly broad temperature range, the moisture content of wood becomes a controlling factor to prevent mold. Another option is to treat the wood with a product that prevents or inhibits mold growth. There are things that both pallet manufacturers and users can do to reduce mold growth.
Mold Prevention 101
The summer months are upon us. Knowing how to combat mold growth is a must for pallet companies and pallet users. As the weather warms, mold becomes an even worse problem. Mold on pallets can cause product damage or contamination. This is especially a concern for pharmaceutical and food supply chains.
Mold needs four things to grow — oxygen, food, water and the right temperature. See Sidebar. A successful mold control program will usually involve a combination of strategies aimed at eliminating or reducing one or more requirements for mold growth.
Experts agree that the key to controlling or preventing mold growth on wood is the moisture content. According to the Virginia Tech Center for Packaging and Unit Load Design, if the moisture content is below 20%, the wood will not support mold, mildew, decay or fungus.
However, even if wood is dried to that level, it does not guarantee that mold will not occur. If the right conditions exist, some remaining moisture in the wood can come to the surface, and if it accumulates, mold can occur. Also, even if the wood is dry, mold can occur if the wood becomes wet from some other source, such as rain.
You may need to dip lumber, pallet cut stock or pallets in a fungicide. While dipping in a fungicide is not a magic bullet, it can buy time to prevent mold on pallets until the wood is dry. Fungicides are effective at preventing mold. However, they do not work nearly as well if mold already exists on the wood before it is treated.
A common misconception is that heat-treating pallets for ISPM-15 compliance will prevent mold. The heat-treating process – heating the wood to a core temperature of 56 degrees C (132.9 F) for 30 minutes – is designed to kill insects that inhabit wood. The ISPM-15 regulation was introduced to prevent wood-eating insects from being transported inadvertently from one country to another via infested wood packaging. The heat-treating process does not prevent mold. Heat-treating is designed to kill insects. It may kill existing mold spores on the surface of wood, but the heat-treating process does not prevent mold spores from growing. In fact, after pallets have been heat-treated, they provide a favorable environment for mold spores to colonize.
If pallets are heat-treated, they should be unloaded immediately after the treatment cycle is completed. Allow them to cool before they are loaded into trailer vans. Heat-treated pallets that are loaded into trailer vans while still hot are susceptible to mold.
Storage, Storage, Storage
How you store pallets has a huge impact on whether or not mold growth occurs on pallets. Keep lumber and pallets away from any sources of mold spores, such as decaying wood. Simple good housekeeping practices can reduce the presence of mold spores in the air.
One of the most important strategies is improving air flow to aid in drying the wood. This should occur throughout the entire process from production to usage in a supply chain.
Store pallets in a well-lit, dry, ventilated environment. Covered storage is critical for keeping pallets dry. For outdoor storage sheds, stringer pallets should be aligned in the direction of prevailing winds to help improve airflow.
For indoor storage, choose a well-lit, ventilated part of the warehouse. Allow adequate spacing between rows to further improve ventilation. Consider installing fans to circulate air to assist the drying process. Even a few feet per second of air velocity can help prevent mold.
As summer heats up across the country, mold becomes an even worse problem. Proper storage, treatment and rotation of stock can do a lot to reduce the mold threat. Learn how these tips make your mold go away.
Humidity is not your friend. Do not store pallets in a trailer van. Dark, warm, humid trailers can quickly become incubators for mold growth. Coordinate pallet deliveries with trading partners so that pallets can be quickly unloaded and placed into dry storage.
Pallets or lumber stored outside should be covered to prevent exposure to rain and be elevated above the ground. Air flow is critical too for outdoor storage sheds. Even with heat-treated lumber or pallets, create good air flow to allow the surface of the wood to dry.
Pallet Treatment Options
You can use various treatment methods to help inhibit mold growth or kill mold that has already grown on the surface. Discuss these options with your pallet provider.
Generally, dipping lumber or pallet components in fungicide is more efficient than dipping finished pallets because a larger volume of wood can be treated more quickly. Spraying fungicide can work, but it is more difficult to get consistent treatment.
The most popular chemical treatments for pallets are provided by ISK Biocides. It offers a full range of options, from PQ-8 to PQ-80 and NeXgen®. Lance Johnson, vice president of sales and marketing for ISK Biocides, recommends PQ-8 or PQ-80 for pallets because they are approved by the federal Food and Drug Administration for incidental contact with food. The company’s NeXgen® fungicide does not have that approval, but it has two active ingredients instead of one, making it the strongest of the products and effective for a longer period of time. PQ-8 and PQ-80 combined are the company’s best-selling products for treating pallets.
PQ-8 and PQ-80 vary mainly by the percentage of their active ingredient, although both are effective for the same length of time. One difference is that PQ-8 meets U.S. military specifications for preservatives for pallets and wooden crates and boxes. PQ-8 is also a thinner concentrate, which makes it easier to pump in cold weather.
NeXgen brightens wood while also controlling sapstain and mold fungi. It combines two chemicals that work to quickly penetrate and bind to wood, minimizing leaching while effectively protecting the wood from mold and sapstain fungi. It is recommended for green lumber but can also be used on dry or partially-seasoned wood to prevent staining and mold.
How long any of the fungicides are effective depends on numerous factors, Lance explained. Those factors include the dilution rate of the product when mixed with water, the species of wood, and the conditions under which the pallets or lumber are stored. For more information about ISK Biocides products, call (800) 238-2523, email info@iskbiocides.com, or visit www.iskbiocides.com.
For pallet applications where chemical exposure is less of a concern, the Virginia Tech Center for Packaging and Unit Load Design recommends periodically applying a bleach solution to the lumber. Another option to kill or remove mold is to spray or dip the pallet or lumber in a solution of two parts water and one part of a household detergent. The solution will be effective for 3-5 days.
Kiln-dried lumber may be an option. Wood that has been dried to less than 20% moisture content will not support mold growth, and kiln-dried lumber is below that level. However, kiln-dried lumber can quickly grow mold if it becomes wet. Kiln-dried lumber may be a bit more expensive depending on your market. But it can be worth it from a product damage and sanitation standpoint.
Pallet Clue – Find the Culprit
Mold doesn’t have to be a problem. Like in the old board game “Clue”, you have to investigate to find the culprit while keeping in mind the four key ingredients required to make mold grow. Usually, it has something to do with the moisture content or the storage of the pallet. Do the pallets arrive mold free and develop mold over time? Are pallets leaving the supplier without mold and developing mold in transit? Are you buying heat-treated pallets? Ask the pallet supplier if anything has changed in the production process. Is the lumber any different than previous shipments? Are you, the pallet user, storing the pallets differently? Are you storing them outside or in a dark trailer for a long time? Has the airflow changed in your building or are pallets being stored or used differently?
Also, is that really mold? Wood may become discolored, but the reason may not be mold. Blue stain creates a bluish or greyish discoloration in wood, but it is not associated with health concerns or pallet performance issues. According to a brochure by the National Wooden Pallet & Container Association, “Mold grows on the surface and can be brushed off or smeared, whereas blue stain penetrates deep into the wood and cannot be removed.”
Asking the right questions can help identify the cause. Mold doesn’t have to be a problem; you just have to take proactive steps to reduce its effect.
Mold Needs Four Things to Grow on Pallets
1. Oxygen
Oxygen is in the air all around us and cannot be eliminated.
2. Food
Wood provides nutrients for mold to grow.
3. Temperature
Generally, temperature cannot be controlled because most pallets are stored in ambient conditions. Mold can grow in temperatures as low as 32 degrees. Growth is accelerated when temperatures are in the 66-90-degree range.
4. Water
Wood that has been dried to a moisture content below 20% will not support mold growth. However, kiln-dried lumber can quickly grow mold if it becomes wet.
