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Mold, Fungi Still Pose Threats to Pallet Businesses
Mold & Fungi on Wood — Causes & Remedies: Explores why mold and fungi tend to grow on pallets in the summer and what companies can do to fix the problem.

By Matthew Harrison
Date Posted: 8/1/2006


    Summer typically wreaks havoc on pallet businesses as mold and fungi find homes wherever untreated lumber rests. Even perfectly dry, healthy wood can be literally covered with fungi within 24 hours, and the poor air quality during summer months allows mold and fungi to proliferate unabated.

    Several kinds of mold tend to prove problematic for people in the wood products industry. Most molds actually do not affect the structural integrity of wood, but they can lead to discoloration and that overpowering mildew stench. Wood rotting fungi, however, poses the biggest problem because it can literally destroy pallet lumber from the inside out. Furthermore, evidence of an innocuous form of fungus usually precedes more damaging species. So if discoloration becomes apparent, it is likely that decay fungi are lurking in the darkened recesses of lumber stock, as well.

    Sanitation is the key to keeping mold from becoming a recurring problem. Spores released from molds and fungi can contaminate production facilities, spread to products, and even threaten the health and safety of your workforce.

    The Food and Drug Administration also mandates that businesses control microbial contamination so that “no obsolete, rejected, or deteriorated product is used or distributed.” This can obviously impact consumer health, as well as the integrity of your company (no one wants to be caught distributing faulty products), but maintaining sanitation guidelines can be a grueling process that some pallet manufacturers take for granted, much less the added strain of ridding the appearance of mold and fungi from their products. 

    Basic housekeeping standards can help your business reduce mold and fungi counts with simple, common sense practices. General site cleanup, like removing unusable wood or piles of wood waste from storage facilities can significantly reduce the potential for mold growth. Periodically washing production and storage facilities with a soapy, diluted bleach solution (one part bleach to three parts water) will ultimately help disinfect your production facility.

    During transportation, businesses should also consider thin layers of paper wrapping to prevent moisture form reaching exposed lumber. While most pallets are shipped via tractor trailer, companies that use flatbed trucks or railcars can protect their pallets with a full tarpaulin.


Air Drying Versus Kiln Drying

    When trying to eliminate mold and fungi on lumber products, the primary objective of either air or kiln drying is to reduce surface moisture content below 20% with total average moisture content being between 30 and 35%.

    Air drying proves just as sufficient as kiln drying for reaching less than 20% surface moisture content, and is often a viable alternative for smaller businesses that operate with a tighter budget.

    When air drying, green pallets should be stacked and protected from the elements such as rain and sun. Portable structures such as tents or warehouse facilities work effectively. To allow the most airflow between pallets, pallets should not be arrayed more than four stacks deep (front to back) and situated at least 12 inches off the ground to allow cool, moist air to flow beneath them. If stored outside, pallets should be stacked with stringers parallel with the wind. Preferably, pallets stored indoors need to be coupled with fans that keep air circulating. It is also imperative that pallets be stored away from standing water, preferably with a drainage system in place.

    The downside of air drying is that it takes a considerable amount of time, which can change dramatically depending on climate. Studies indicate that GMA pallets with 5/8 inch deckboards take about 17-18 days to dry completely during spring in the Midwest. Naturally, such times would nearly double during colder winter months. Another way to prevent mold growth during the drying process is to apply a dilute bleach solution before the drying process begins, which would kill mold and fungi formations from the start.

    Kiln drying is obviously the more expedient away to achieve the optimal less than 20% surface moisture content. Studies show that kiln drying of green mixed hardwood with initial total moisture contents of 75-80% at 108 degrees Fahrenheit for five days results in total moisture contents of 30% with surface moisture contents well below 20%. Businesses should also beware of exceeding heat specifications, since excessively hot kilns can lead to lumber degrading by splitting and cracking. Although kiln drying is the pricy alternative, for bigger operations it proves to be more practical and timely for mold and fungi reduction.

Heat treatment precautions have evolved during the past decade to prevent foreign pests from impacting overall forest and plant health. However, it is of utmost importance to note that phytosanitary heat treatment alone does not kill mold and fungi. Without the use of kiln drying to reduce the moisture content, heat treatment can cause high concentrations of moisture to be released after the process is finished.

    To prevent mold and fungi formations, businesses should also consider allowing their pallets to air dry before moving them directly to a trailer or another enclosed storage space.    

Mold Killing

    Chlorine-based disinfectants are known to help prevent the growth of mildew and fungi with the application of a thin chemical layer. Dipping or spraying the chlorine treatment can be effective for three to six months, depending on the chemical concentration. The aforementioned three parts water to one part bleach solution is effective for 5-7 days.

    To sanitize pallets already affected with mold, businesses should use the bleach-water solution mixed with roughly 1/3 cup of detergent for each four gallon mix used.     Power washing will also help to remove the more noticeable molds, but the drying process will have to be repeated. Heat sterilization of at least 130 degrees Fahrenheit at high humidity with chamber vents closed will also kill off mold and fungi, but typically drying procedures must be adhered to strictly in order to achieve 20% surface moisture content that prevents new mold formations.

    Other methods for preventing mold and fungi growth include use of Boron salts and chemical coatings. However, Boron salts are water soluble and do not bond to the wood, and can therefore be leached out and is used primarily for controlled, enclosed environments like distribution centers.

    Solutions including Copper-8-quinolinolate work as a more long term mildicide, but it may not be acceptable with certain customers. Researchers across the country working to find more permanent mildicides with low mammalian toxicity that will better serve grocery stores without endangering the contents of a unit load. The staff of Pallet Enterprise will keep the pallet community abreast of new developments as they arise.

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