Thermally Modified Wood vs Ipe and other Imported Tropical Hardwoods. How do they compare!

Booth species fall under Class 1 for durability. Class 1 is the highest rating a species of wood can obtain within the various class rating categories. Sometimes wood does not live up to user expectations. In most cases this is not the fault of the material but rather as a result of a lack of understanding of the various species of wood, their suitability and their installation and maintenance.

Thermally modified wood is a process which is performed on the wood to make it Class 1 whereas Ipe is Class 1 durable in it’s natural state. There are some subtle differences. Generally speaking, thermally modified wood is a product that has been heat treated with water and steam to improve the heat treated wood’s resistance to attack by wood destroying fungi and wood destroying insects. In other words, the wood’ durability is enhanced to a level which is suitable for use in a variety of exterior uses such as decking and siding.

Ipe has long been used as the species of choice when it comes to exterior wood decking and siding but its a wood of extremes: extremely dense and durable, as well as extremely difficult to work. Its incredible hardness and strength make it well suited for decking and flooring applications. Overall, Ipe is a difficult wood to work, being extremely hard and dense, not favorable characteristic’s if you ask the woodworkers and decking contractors who have worked with the wood.

The main advantage of thermally modified wood is that some species of wood can now be used for applications that require high durability like Ipe and other imported hardwoods and can be made and produced right here in North America with North American wood species. The thermal modification process enables species such as North American Ash to be utilized into decking and siding products that the species could not have otherwise been utilized just a few years ago. Ash has long been considered a joinery wood which has been easy to work with while remaining very strong. It has been used in the baseball bat and hockey stick manufacturing industry for many years. Once this species has been “thermally modified” it rivals species such as Ipe and other imported tropical hardwoods for strength, durability and stability. In fact, tests have shown that Thermally Modified Ash falls into the highest portion of the Class 1 durability even above Ipe.

Some experts say that because of the “thermally modification” process to the Ash species it makes the wood fall within the top 1 percent of the Class 1 rating even above Ipe for durability and stability. Reasoning has it that because you remove the moisture and all living elements from the wood during the thermally modification process that the Ash becomes even more stable and durable and expansion and contraction are virtually eliminated.  Ipe and other tropical hardwood species would have higher moisture levels remaining in the wood which if not air dried properly can cause stability issues. Most Ipe and tropical hardwood species are air dried rather than kiln dried to achieve the desired moisture content levels because of the difficulty associated with kiln drying the species.

Thermally modified wood and tropical species such as Ipe can co-exist and both offer specific advantages over other wood species used in the wood decking and siding marketplace. Consumers must weight the advantages and disadvantages out before making their decision. However consumers must remember that “thermally modification” is a process that is performed on wood species to give added stability and durability while many other woods are simply left to mother nature and the natural characteristics of the species to achieve the desired stability and durability.

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Thermally modified wood siding made from pine.
Novawood and Cutek Extreme Deck Project 4
Thermally modified North American Ash decking.


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