Features & Benefits of Our Hydro-Thermo Plants

What is Hydro-Thermo Modification of wood?

A newer treating process (about 15 years old) where we heat up the lumber under pressure to 170 – 220 degrees C (338-428F) under controlled conditions in an atmosphere of steam.

This result is the “burning off” of the hemi-cellulose in the lumber, giving us some new and desirable properties in many lumber species:

1. Exotic color
Turns ordinary species into a warm brownish color equivalent to the color of tropical hardwoods such as Merbau, Teak, etc. The brown color goes all the way through the timber so the timber can be machined and sanded without exposing untreated timber.

2. Upgrading of rustic grade
Many light-colored species such as poplar, ash, maple etc. are often downgraded to rustic grade in the flooring and component industry when they contain color defects such as brown and red heart, blue stain, etc. Many of these color defects disappear when the timber is modified, whereby the value of the wood is significantly increased.

Installation Pictures

Examples of Thermo modified Lumber

3. Environmentally sustainable
Makes it possible to use plantation and or regular grown wood instead of tropical hardwood for applications where the dark color and high dimensional stability of tropical hardwoods normally is preferred.

4. Equilibrium moisture content
Reduces the equilibrium moisture content of the timber by 30-50%.

5. Improved dimensional stability
Because of the reduced equilibrium moisture content and changes in the chemical composition of the lumber, the tangential and radial swelling/shrinkage of the timber is reduced 30-50%, making the lumber much more dimensional stable. This is important when the lumber is used for solid flooring and window components in areas with high fluctuation in the relative air humidity.

6. Using a closed system as well as our HYDRO-THERMO modification technology
Allow you a process where you do NOT NEED any inert gasses to prevent the lumber from burning and, most importantly, we do not bring the lumbers MC to 0 which causes lots of stress an internal cracking – contact us and our clients for more technical details.

Mostly lower density hardwoods are used for Thermo modification like Ash, Aspen, Poplar, Maples and Birch. You occasionally see Oaks and Beech being modified for special purposes. Radiata pine is often being modified, whereas Southern yellow pine with high pith content would be less desirable.


We offer turnkey plants in any size based upon your specifications. Our team has been involved in the Thermo modification business almost from the very beginning in the late 1990s. We have one of the largest client bases of any manufacturer and offer our industry the very best process available in this field.

Most plants for North America are designed based on our hardwood lumber length and are supplied in 6 ft. diameter x 30 ft. or 40 ft. length. This is for our system based on using 3/8” sticks, which equates to about 3,815 -4,660 b.ft. per charged or 1.2 – 1.6 MM b.ft. annually or more. We built plants to your specifications as well, should you have a different or unique set of needs.

The advantages of using our closed Hydro-Thermo modification plants are:

  • Faster cycle times ~ 12-18 hours per charge!
  • Least production cost per B.ft.!
  • Smallest investment cost per b.ft. produced!
  • Turnkey delivery – everything is included!
  • Best product quality result of any system!
  • Can operate easily with different load levels!
  • We can offer emission-free systems!


1. Better control and quality
The Moldrup process is carried out inside a pressure vessel using super-heated steam with a pressure between 14.5-175 psi. The steam pressure varies during the process according to a pre-programmed schedule and serves to ensure that the moisture content in the lumber never falls below 4% ideally. This is an important advantage compared to the traditional systems for thermal modification, where the process is carried out using steam, oil or inert gasses at atmospheric pressure. At 180 – 200 degrees C (350-390F).

The atmosphere is very dry when the pressure is at atmospheric pressure. The very dry conditions cause the moisture content to fall close to 0% and this results, very often, in many drying defects. By having pressurized steam in the chamber, it is possible to ensure that the moisture content does not fall below 4% or so. With the Moldrup system, the number of drying defects is therefore significantly lower compared to the traditional systems.

2. Short cycle time
The total process time is 12-18 hours compared to 1 – 2 days in the traditional systems. This naturally depending on specie, dimensions and desired treatment levels.

3. Lower costs
Operating costs are significantly lower compared to many of the traditional systems due to the shorter cycle time, reduction in drying defects and no use of chemicals or inert gas.

4. Easy operation
The system is very easy to operate and maintain.

5. Extensive experience
The Moldrup process has been used commercially in the flooring industry since 2001. The system is therefore well proven and a large amount of experience has been collected on the optimum schedules for the various timber species in the flooring ..and reg. hardwood industry. The long experience has also made it possible to select the best possible materials and designs for making the equipment as durable and long-lasting as possible.

6. Stainless steel
The high temperature used in Thermo treatment of timber causes the timber to produce acetic acid. This creates a very corrosive environment. To withstand the very corrosive environment and high temperatures, only top-quality components such as stainless steel and temperature resistant valves, bearings etc. are used in the construction of the plants. Moldrup systems can offer a 5-year guarantee on the pressure vessel and 1-year guarantee on all other parts.