Rubberwood (Parawood): Hevea Brasiliensis

In 1901 British planters introduced rubber trees into the Malay Peninsula, where the soils and climatic conditions were highly suited to rubber cultivation. In Thailand early government restrictions on foreign investment led to development of the industry by local smallholders, usually subsistence rice farmers who were able to start rubber tree stands on the relatively abundant free land in the area. Land under rubber cultivation expanded rapidly in the 1930s, consisting mainly of smallholdings controlled by Chinese, Thai, and Thai Malays rather than large, European-owned plantations, as in other Asian countries. Thailand had about 1.6 million hectares in rubber in the mid-1970s, of which about 10 percent were located in an area along the Gulf of Thailand southeast of Bangkok. Of the 500,000 holdings in the early 1980s, about 150,000 were under 2.5 hectares in size, and another 300,000 were under 10 hectares. The remaining larger holdings were operated more as expanded smallholdings than as plantations. Production was increasing in the early 1980s and had reached about 830,000 tons in 1987. An extensive replanting program, in which old tree stock was replaced with new high-yield varieties, had reportedly been carried out in about half the planted area by the mid-1980s, significantly increasing the potential for expanded production.
Tapping of rubber trees starts in the fifth to seventh year after planting and then continues for 25 to 30 years. A special knife is used to incise the bark so as to wound the resin canals without damaging the cambium. 
After 30 years a decline in latex production makes further tapping of the trees uneconomic. The trees are then removed and replaced with new seedlings. In the past, felled rubber trees were either burnt on the spot or used as fuel for locomotive engines, brick burning or latex curing. 
A 30-year old cultivated rubber tree is about 30 m tall with an average branch-free bole of 3 m. The diameter at breast height (dbh) may reach about 30 cm. The stem tends to taper. Young rubber trees have a smooth brown-green bark. The constantly tapped portions of the stem may develop, with age, a latex-smeared cortex. 
Rubberwood’s favourable woodworking and timber properties make this medium-dense timber suitable for a wide scope of applications. It can be easily steam-bent, or stained to resemble any other timber, depending on consumer demand. Its favourable qualities and light colour make it a good substitute for ramin, a timber known for its quality in furniture making and other applications. The natural colour of rubberwood is one of the principal reasons for its popularity in Japan, where it is increasingly used to replace more traditional timbers in a wide variety of applications.
Rubberwood has traditionally been used as a cheap source of woodfuel in most of the countries where rubber plantations are abundant, such as for industrial brick burning, tobacco curing, or for fuelling of locomotive engines. Due to lack of durability, rubberwood was rarely used as utility timber except in timber-scarce countries. After a number of problems had been overcome with the help of applied research, particularly in connection with wood seasoning and preservation but also related to the small size of logs, rubberwood developed as one of the most successful export timbers of Southeast Asia.

It is reported that 61 different products are made from rubberwood. The most important uses are: furniture and furniture parts, parquet, panelling, wood-based panels (particleboard, cement and gypsum-bonded panels, medium-density fibreboard (MDF), kitchen and novelty items, sawn timber for general utility and fuel. Rubberwood has certain advantages over conventional timbers from the natural forest. Because it is a plantation by-product, it is available at a relatively low cost. Thus in spite of its comparatively low recovery rate, the production cost per cubic meter of rubberwood is only about 30 percent of the production cost of Meranti. Rubberwood is also still used for charcoal manufacturing and woodfuel. Timber availability, extensive research and aggressive marketing have contributed towards making rubberwood one of the most important export timbers in Southeast Asia, a substitute for light tropical hardwoods and one of the major timbers for the production of furniture and indoor building components.

The main reasons for success are its favourable timber and woodworking properties and the relatively low cost of the raw material since rubberwood is an agricultural by-product. This factor makes the timber highly competitive in comparison with timber from forest species that have comparatively high raw material costs. An additional asset is its “green” aspect: rubber trees have to be removed and the areas replanted once the latex yield has declined to uneconomic levels. The acceptance of rubberwood as a sustainable, plantation-grown, “environmentally friendly” timber has contributed to its universal appeal. 
It can be safely assumed that market prospects for rubberwood will continue to be favourable. This is also reflected by the increased overseas investments in the Southeast Asian rubberwood industry. Rubberwood now has a position no other single tropical hardwood species can match in terms of available volume. If we assumed that all plantations would be available for wood production and that there was a ‘normal’ distribution of age classes, then the potential annual production could be up to 30 million m3 of rubberwood logs. 
With the increase in plantation area and research in improved hevea clones, which may yield both high-quality latex and timber, prospects for a continuous supply of rubberwood seem to be good. 

 
PHYSICAL PROPERTIES

  Colour : Pale cream to yellowish brown. Oxidative discolouration can be limited by rapid production sequence and vacuum drying.  
  Grain pattern : Mostly straight. A cross section of Rubberwood shows few concentric markings reminiscent of growth rings. These markings combined with the large vessels in structure give an attractive appearance with clear patterns on the longitudinal surface. Many characteristics of Rubberwood are similar to Ramin wood.  
  Structure : Uniform in structure with an excellent 'Timber' feel  
  Green Density : 800 kg/m2  
  Density at 12% m.c .: 600–620 kg/m2 (light)  
  Relative Density : 0.63–0.66 (moderately heavy timber)  
  Volume Shrinkage : Negligible and comparable to Dark Red Meranti Tangential 1.4%, Radial 1%  
  Compression Strength : Parallel to Grain 32 N/mm2
                                                Perpendicular to Grain 4.69 N/mm2  
  Bending Strength : Modulus of Rupture 66 N/mm2
  Sheer Parallel to Grain : 11 N/mm2
  Modulus of Elasticity :9240 N/mm2  
 
WORKING PROPERTIES

  Durability : Resistant to many fungal, bacterial and mould attacks can also be made resistant to other specific susceptibilities.  
  Gluing : Good and compatible with almost all industrial grade adhesives--its glue bond strength is high  
  Machining : Easy to saw, machine, plane, turn and bore. The resultant surfaces are fairly smooth  
  Nail holding : Average of Radial Tengential value
                            Average of end values 91 kg 53 kg  
  Screw holding : Average of Radial Tengential value
                                Average of end values 267 kg 164 kg