Thermally Modified Wood Products

Thermo Ash

What is Thermally Modified Wood?

Thermal Modification is the process of gradually heating any species of lumber to temperatures of 410 - 450º F in a special chamber that has had the oxygen completely removed from the system. These conditions are needed to prevent the wood from combusting, which takes place at temperatures over 300º F.

Why Use Thermally Modified Wood?



  • Durability: 25 year life span can be expected for exterior applications
  • Moisture Repulsion: The process seals the cellular structure of the wood making it impervious to water and moisture
  • Stabilizaton: Swelling and shrinkage is reduced as well as cracking and checking
  • Color: Consistent brown color all the way through to the very center of the board
  • Chemical Free: Chemicals are not used in the thermal modification process which makes this product an environmentally friendly alternative.

  • Milling

    Sawing: Sawing does not differ much from sawing untreated wood. Because of the stabilization from the heat treatment, distortion of the wood is greatly reduced after sawing. Since the heat treatment eliminates the resins in the wood, machines require little cleaning after milling.

    Planing: Machines well using all normal methods. Sharp Cutters provide the best results, as with all woods.

    Milling: Blades must be sharp, otherwise tearout may occur. Milling across the grain may increase tear out. Tearout is most likely to take place at the end of a board where there is a thick piece of wood behind the blade. Careful planning should be taken into consideration.

    Sanding: Material sands generally the same as untreated wood. Due to the absence of resins in the wood that has been crystalized in the process, the sand paper does not load up like it does with untreated woods.

    Surface treatment: Use surface treatment that will protect against Ultra Violet radiation in order to prevent color changes and surface shakes. Take into account that thermally modified wood has lower water absorption than normal wood and needs a longer time to penetrate the wood. Oil-based substances work just as well as they would with normal wood.

    Gluing: Longer Processing time is needed for the glue to be absorbed by the thermally modified wood, especially when using water based glues. Because the thermally modified wood has a low moisture absorption, penetration and drying time of the glue is increased.

    Screwing: Heat treatment reduces the splitting strength of the wood. The use of self-tapping or predrilling hardware is recommended. Also, the use of stainless steel screws with less threads and countersunk heads is recommended for external use and in humid environments. We recommend not using galvanized fasteners as they tend to leave bleed marks on the woods surface over time.

    Nailing: It is recommended to use a compressed air gun with depth control since hammer contact with the wood promotes splitting. To reduce the risk of discoloration from metal nails, the use of stainless steel nails is recommended. Small oval head nails help to reduce the risk of splitting as well.

    For more information on Thermally Modified Woods, please visit this website.

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