What heat-treated wood means on a crate

What heat treatment is

Heat treatment is a process in which lumber is heated in a chamber until the centre of the thickest piece reaches a set temperature, then held there for a set time. The aim is to kill pests living in the wood, and the target is the wood core because the core is the last place to heat.

USDA APHIS states the requirement as a minimum wood core temperature of 56 °C for a minimum of 30 minutes. Those numbers are the standard, and a treatment that heats the surface but not the core does not meet it. The temperature is monitored with probes in sample pieces.

How it is verified and marked

In the United States, the American Lumber Standard Committee administers the heat treatment program. An accredited agency inspects the facility and its records, and wood that passes is stamped. APHIS says heat-treated packaging must carry the ISPM 15 official mark together with the quality mark of the accredited agency.

The HT code in the stamp is the buyer's proof. A crate with a clear HT mark can be inspected at a border without anyone needing to see the chamber records. A crate with a missing, smeared or painted-over mark can be held, whatever treatment it really had.

HT is not the same as kiln-dried

Kiln-dried lumber, marked KD, has been dried in a kiln to a target moisture content. The drying schedule may also heat the wood, but it is not set or checked against the 56 °C, 30-minute rule, and a KD stamp is a grade mark and not a phytosanitary mark. Kiln-dried lumber is not automatically heat-treated.

Ask for HT on the stamp. Some lumber is both: dried, then treated. The point for a crate buyer is that the phytosanitary claim lives in the mark, and not in the word dried on an invoice.

Pressure-treated and painted wood

NELMA states that pressure-treated wood meets ISPM 15 only if it was heat-treated and stamped HT before the preservative treatment. Wood that has been preservative-treated first, and heat-treated afterwards, or not at all, does not meet the standard on the strength of the preservative.

Painting is also a question. Paint can hide a stamp, and a crate with an unreadable stamp is a problem. Mark and finish are decided together: apply the stamp where it will stay visible, and keep any paint or stencil off it.

What to look for on delivery

Check each lumber member of the crate. The skid, the runners and the cleats should show the stamp, and the crate should show it on two opposite sides. Make sure the HT code is present, the number belongs to the producer you ordered from, and the agency mark sits beside it.

Record the stamp with a photograph before the crate leaves your dock. If a stamp is unclear on arrival, contact us before the crate ships, since we can identify the facility from the number and fix the problem while the crate is still at your location.

1. 01
   Find the stamp

   Look at the skid and the side faces. It is on two opposite sides of a finished crate.

2. 02
   Read the code

   Confirm the treatment code reads HT, with the country code and producer number beside the symbol.

3. 03
   Check the agency mark

   Find the accredited agency's mark next to the ISPM 15 symbol.

4. 04
   Photograph

   Take a clear photo of each stamped face and put them in the shipping file.

Why export crates are built HT by default

Heat treatment leaves no residue, needs no fumigation certificate and is accepted as an approved treatment. For a crate that may be inspected on arrival, it is the simplest path. We use HT lumber for export orders and put the treatment in the crate spec.

If your destination requires another approved treatment, tell us when you quote. The decision belongs to the importing authority, and we build to it.

Common questions at the receiving dock

Receivers and brokers ask the same few things. Does every board carry a mark, or only the skid? Is the stamp crisp enough to read from arm length? Does the crate come with paperwork from the treating facility? A stamp is the proof the standard asks for, but some importers also want a treatment certificate on file, and the producer can usually supply the details behind the number on the mark.

Keep a copy of the facility details with the shipping documents. If an inspector at the port questions a crate, a fast answer from the shipper, with the stamp number and agency named, usually settles the matter without a detention. Delays on a held crate cost far more than the lumber, so keeping the file complete is cheap insurance.

Heat treatment and the finished crate

Treatment happens to the lumber, usually before the crate is assembled, so a builder buys stamped stock and cuts it to size. Cutting a stamped member can remove its mark, and a cut piece with no mark is no longer proof of anything. We keep the stamp visible on each member or apply marks to finished assemblies through the program.

Moisture is worth a thought as well. Freshly treated boards that sit in the rain can swell, split and grow mould on a long haul, so stock is kept covered. A crate built from wet lumber and sealed into a barrier bag traps that moisture with the machine, which is another reason the desiccant and bag guides matter.