Heat Treating Of Wood

A common requirement for many projects is the use of heat treated wood. This is particularly true in the crating and international shipping business. In this article we will discuss the basics of what heat treating means, and why you may need it.

The heat treatment of wood is performed to kill whatever insects or disease may be in wood. It is performed relatively simply. Wood is stacked with air gaps in between each piece. These stacks are loaded into a large insulated barn-like building. Temperature probes are placed in the center of the board that is the thickest. The inside of the building is then heated up with large hot air blowers. These are often propane heaters like you may see on a construction jobsite. Meanwhile the temperature is monitored by a computer system. Once the temperature reaches a particular point, the temperature must be held for a certain period of time. Once that time has elapsed, the heaters are deactivated and the barn is opened. The wood is considered heat treated at this point.

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Shipping container based heat treat oven.

In high production settings, such as pallet production of building material production, an alternative setup is used. The wood is stacked as before, but the stacks are placed on a conveyor belt. The conveyor belt carries the pallets into a large industrial microwave oven. This uses the same technology as your personal microwave, just much larger. This “cooks” the wood very quickly and enables a very fast production timeline. As a point of comparison, where these RF ovens can process multiple cycles a day, a traditional heat treatment building may take over a week to perform a single cycle.

There is an additional step that may take place. Heat treaters are governed by a set of rules and regulations. A regulatory agency provides them with a stamp with a code unique to them. The stamp is used on each wood piece, indicating that the wood is heat treated and was produced by their facility. Regular inspections and fees are required to maintain possession of that stamp. Depending on the exact process used, different stamps are issued by the inspection agency. These stamps are considered property of the inspection agency and are tightly controlled. The use of counterfeit stamps is a grave concern as it can lead to the spread of disease and parasites internationally, as well as the degradation of international trade norms.

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A mid-sized heat treat building.

Heat treatment of wood is performed for a variety of reasons. Many building materials are required to be heat treated. The KDHT wood that you find at home improvement stores is one such example. In other cases, as is the case in shipping, it is a requirement for all international shipments. This is to prevent the transmission of parasites and disease internationally. Many domestic shippers also want the wood to be heat treated. A common technique is to heat treat the wood when the moisture content is high, this helps speed up the heat treat process. Wet wood tends to conduct heat better to its center than dry wood.

In packaging there are hard requirements for the use of heat treated material. For domestic shipments this will be dictated by either the freight carrier, but most often it is the receiving company that sets the standards. For international shipments, it is the port of entry that will set these standards. There are international standards that are more or less universally applied. There are some countries where the local standards have broken down and specific requirements must be met to ensure safe passage. If the requirements are not met, the crate or pallet will not be allowed out of the port.

The rules are in general that solid wood must be heat treated and stamped. This stamp is similar to the one mentioned earlier, but this specifically marks the wood as being good for international shipment. There are specific locations where the crate must be stamped, two stamps total on opposite sides as a minimum. Best practice requires the stamping of all four sides and both ends of any large runners on the bottom of the crate.

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A generic stamp found on heat-treated wood. “000000” would be replaced by your own specific code.

This stamping only applies to dimensional wood. Plywood and sheet goods in general are exempt from these regulations. They are often stamped anyway to help ensure ease of travel through customs. If you are looking for a shipping crate, typically you will want it either totally made from sheet goods, or you will want heat treated wood pieces. This will ensure that your crate will travel without restrictions domestially.