Teak Log Characteristics

Teak timber has qualities as: durability, workability, beautiful figure and non-spliting. Some desirable features are: straight grain, knotless and defect free. Teak is exceptionally stable under changes of temperature and moisture: free from warping in drying. Four major teak color types are recognized in Myanmar:

1. Uniform Golden color, straight grained and even texture and with few markings. Such teak is found in BAGO     YOMA forests and the forest of Upper Myanmar. It is the best teak of the country and is much preferred by     foreign customers.
2. Darker in color and harder, mostly found in the dry forests of the country. It is a good teak apart from a higher     density and comparatively harder in working properties.
3. The color is uniform grey-brown and mostly cross-grained and found in the northern part of the country.     Sometimes bee holes are observed. This variety could be said to be the worst quality of the quality of the     country, but it may yet be better than the standard quality teak of other origins in the teak-bearing region.
4. Black stripe teak in Thayet and Taunndwungyi areas with a limited availability. It is a good ornamental timber     and previously a high price was obtained. It is said that black stripe teak also occurs in Java.

Quality of Teak
Durability, stability, workability and ease in pre-treatment are the major determining factors of good quality teak. Beautiful figure, color, density and rate of growth are other wanted qualities. Straight-grained, knotless and defect-free timbers are also desirable qualities.

Durability of Teak
Teak is one of the most durable timbers in the world. On some dry sites, it has lasted for more than seven hundred years. In contact with ground, it can remain serviceable for more than twenty-five years. Extractives present in the heartwood are believed to be responsible for its durability. Several studies of teak heartwood extractives and decay resistance showed that most teak heartwood extractives directly contribute to the natural durability of teak. Decay resistance increases from the pith to the sapwood and is also related to the age, rate of growth and extractive content. It is also found out that a wide range of variation exists in decay resistance both between tress and within a tree. These variations are largely dependent on genetic rather than environmental influences. The basal portion is said to be not very durable, while the most durable portion is about 12.5 feet from the base. The middle to outer heartwood is the durable part and also contains the highest concentration of extractives. A teak tree consists of more heartwood than sapwood. Normally, the sapwood has about 0.5 Inch thickness in old-aged large trees whereas it consists of about 0.6-1 Inch sapwood in young tress of age 20 years and below. Natural durability is one of the prerequisites that make teak a high quality timber.

Stability and Movement
Teak is an exceptionally stable timber under changes of temperature and moisture. It is free from warping in drying. Movement due to its low shrinkage is unrivalled among the timbers of the world.

Shrinkage
The shrinkage and the specific gravity of teak from different localities are given in Table 1. It consists of both natural and plantation-grown teak, as well as girdled and green-felled teak. The specific gravities are on the basis of oven dry weight and green volume. Shrinkage data are from green condition to the oven dry state. In Table 1 are presented data from other teak bearing countries and planted area.

Table 1: Specific gravity and shrinkage of teak

Locality	Condition	Specific Gravity	Shrinkage %:Green to Ovendry
			Radial	Tangential
Myanmar	Green	0.586	2.1	3.0
Myanmar	Girdled	0.594	2.2	3.0
Malabar, India	Natural	0.614	2.5	6.0
C. Provinces, India	Natural	0.526	2.2	4.0
Bihar/Orissa, India	Natural	0.536	1.8	4.0
Honduras(a)	Plantation	0.560	2.1	5.0
Philippines(a)	Plantation	0.490	2.2	4.0
Thailand	Plantation	0.640	2.5	5.0
Indonesia	Plantation	0.646	0-2.0	0 - 3.5
Nigera	Plantation	0.509	0-3.0	0 - 5.0
Papua New Guinea	Plantation	0.509	2.1 - 3.0	3.6 - 5.0
South Africa	Plantation	0.646	2.1 - 3.0	3.6 - 5.0

It is observed that wherever teak is grown, the specific gravity is quite comparable except that of the Philippines. Similarly the shrinkage of teak from natural habitat is rather consistent and shrinkage from teak outside the natural habitat are rather high. Teak is so classified as "low" in shrinkage.

Measurement
Seasoned timber in services is liable to fluctuate dimensionally according to the Equilibrium Moisture Content of the locality. Some movement tests were carried out in the Forest Product Laboratory in Prince Risborough. Movement percvents of some selected species, including teak, are reproduced in Table 2.

Table 2: Movement of Teak and other species

Species		Movement %
Trade Name	Scientific Name	Tangential	Radial
Teak	Tectona grandis	1.2	0.7
Gurjan	Dipterocarpus spp	3.3	2.0
Kuruing	Dipterocarpus spp	2.5	1.5
Mahogany	Swietenia macrophylla	1.3	1.0
Oak	Quercus spp	2.5	1.5
Pyinkado	Xylia dolabriformis	2.1	1.7
Rhodesian Teak	Baikiaea plurijuga	1.0	0.7

It is noticeable that teak has a small movement. Rosewood has similarly small movement, whereas the so-called Rhodesian teak is a little higher in movement. Movement is an important index for fine works, cabinet making and parquet flooring.

Workability
Apart from the teak from drier areas of the country, the rest are quite easy to work in all aspects. The resulting surfaces of planing, boring and turning process are smooth. Resistance to spliting when nailed is rather good. Tools tend to become dull in machining process because of the presence of silica.

Silica is said to be present in the vessel elements. Silica content in teak varies up to 1.4%. Teak form the northern part of Myanmar has slight fiber pricking in planing, and due to some cross-grained nature, it is not a good quality teak compared to those from other parts of the country.

Pre-Treatment
Preservative treatment and the drying of timber are the two main pre-treatments to be considered.

Preservative treatment
As teak is a naturally durable timber, no preservative treatment is necessary. Even if treatment is carried out, it is rather hard to apply.

Timber drying
Teak is said to be moderately refractory and is not liable to check, split and warp.

(a) Air Drying
A slight spliting is said to occur but practically there is little or no Surface checking and warping. There are no signs of insect attack, Discoloration or decay. End coating to prevent spliting is Advisable.

(b) Kiln Drying
Different kiln schedules were tested in drying teak. Table 3 Show the most suitable schedules for minimising drying defects:

Table 3: Kiln Schedule for Teak

Moisture Content %	Temperature (F)	Relative Humidity
Initial	120	80
35	125	75
30	130	70
25	135	65
20	140	60
15	145	50
10	150	40

(c) Solar Drying
Drying of teak by solar means has been carried out by one local Researcher, who used a semi-green house type. It takes 26 days to reduce 1-Inch thick board of 39%.1 % initial moisture content to 12.2% moisture content. No drying defects were observed. It is thus observed that parquet blocks that are solar dried are quite satisfactory.

(d) Drying by Girdling
is a common practice in Myanmar, India and Thailand, the sapwood being removed and leaving the tree standing before felling, normally for three years. This is to allow the wood to float for water transportation and at the same time reduce the drying time with less drying defects. Girdled teak that stands for 27 months has a moisture content of 33.6% still left in the wood. It is still above the normal fiber saturation point and therefore it is only partially dry.

Rate of growth
Growth rings of 2-13 per inch are usual and yet up to 40 rings per inch have been found occasionally; plantation teak has wide growth rings. Teak Plantation in Thayawaddy showed an average growth ring of 4.3 per inch. In Thingan-Neenaung and Koloon area, the averages are 5.5 and 9.6 rings per inch. In the natural forests of Bago Yoma, the average growth ring was found to be 12 per inch. An optimum number of growth rings per inch is said to be six, which increase the strength properties. Beyond that the strength decrease in such a way that it is about the same as that of 15-20 rings per inch, which is extremely poor strength value or comparable to fast grown pieces of 2 rings per inch. On the other hand growth rate may not be of prime importance, if the timber is to be used for ornamental or other purposes apart from structural use.

In the early years of the tree life, the strength properties of wood are comparatively low, but under normal growth conditions, rise steadily for twenty years to a level at which thy remain more or less constant. It is rather obvious that slow grown and fast grown teak have different properties and one may be useful for one purpose but it may not be good for another purpose. From the research, it appears that for the same stem diameter, there is more sapwood if the growth rate is faster as is the case in the better quality areas. It also appeared that the sapwood increases with the height of the cross-section above the ground. Teakwood of very fast growth is weaker and spongy.

Girdled and Green-Felled Teak
There is a tendency for girdled teak to be stronger and better than green-felled teak. Regarding the Bending Strength, the survey showed as per Table 4.

Table 4: Bending strength of girdled and green felled teak

Locality	Bending Strength (psi)
	Green-Felle	Girdled
Zigon, Bago Division	16, 397	17, 414
Tharyawaddy, Bago Division	11, 580	11, 670

The Table shows that there is a tendency of the timber from girdled trees to be a little bit stronger in both localities, but the difference is not significant. A similar subject was studied by Pearson and Brown(1932). The results of the test are given below as per Table 5.

Table 5: Strength Properties of Girdled and Green Felled Teak

Condition	Girdled	Green Felled
MC (%)	14.0	14.1
Density (Lb/Cft)	43.0	40.0
Static Bending (psi) FS@PL MOR MOEx1000	9145 14965 1913	9425 14465 1830
Compression Parallel to Grains (psi) FS@PL Max.Crush	5345 8525	5385 8350
Compression Parallel to Grains (psi)	1445	1280
Sher Parallel to Grains (psi)	1355	1140
Hardness End (Lb) Side (Lb)	1225 1240	975 860

Note:
MC = Moisture Content, FS@PL = Fibre Stress at the Proportion Limits
MOR=Modulus of rupture, MOE = Modulus of elasicty

In term of strength as a whole, the difference between girdled teak and green felled teak is not significant. On the other hand, there is a trend that the girdled teak has a slightly higher strength value, except in the Fibre Stree at the Proportion Limits. In hardness, it is quite obvious that girdled teak is harder. Although the girdled tree is stronger than the green felled tree, the magnitude of difference is not that great. However, great care should be taken in extracting green felled teak. Unless every precaution is taken in different stages of processing, green felled timber will naturally suffer various defects and be devalued. At the same time, timber volume loss could be greater. So, it is advisable to extract and process green teak efficiently to avoid loss. Otherwise green felling teak may not have the similar strength value to girdled teak.

According to the research, the shrinkage and swelling properties and other properties of wood are not altered by the length of the period during which the trees stand girdled. Sawing and seasoning of timber did not show difference girdled and green felled teak trees. After one year, green felled trees reduced their moisture contents to About 66% and girdled trees to about 64%. After two years, the respective moisture contents were found to be about 47% and 34%.

End User Requirements
Naturally, buyers like to get timber of good quality for the money they pay. The physical quality of wood normally required is defect free timber, straight and free from curvature or twists even exposed to weather. Spiral grain, large knots, sapwood, shakes of different types, too fast grown, bee holes, and springs, are the defects most undesirable by the buyers. Girdled Teak, free from visible defects, less sapwood, small tolerances in sawing, and having specified moisture content, is much preferred. Discoloration is an unwanted defect.

Apart from the physical quality, some of the qualities to be considered in the international trade consist of the following:

• In term of wood quality, traders prefer natural grown teak as it is harder and more stable than the fast grown plantation teak.
• Plantation teak is said to be lighter in colour.
• Natural grown teak is said to have a more oily nature and is better uniformity in colour. These characteristics are much preferred in the use of teak as a long lasting high quality timber.
• Outdoor living is becoming popular and garden furniture is in large-scale production, where durable and light teak timber is much admired.

The quality of Myanmar Teak is naturally already good. The stem is normally cylindrical and straight apart from the teak of the northern area, which is rather flatted and cross-grained. Teak being a light-demander competes among its associates and this naturally favours straight and clean holes. The branches in younger aged trees are naturally pruned in both the natural and plantation teak. Since the size of the trees harvested is rather large, the presence of knots is less pronounced.

Apart from naturally favoured qualities, some work on the collection of good and sound seeds from better mother trees is being carried out in forming plantations. Seeds orchards, selection of plus trees for seed collection, and the development of hybrids are in a state of research and development.

Normal timely silvicultural operations, namely thinning in plantations and improvement felling in the natural teak bearing area, are carried out for better timber quality. Correct selection of sites for plantations is of great importance.

Pre-Treatment in teak harvesting, accelerated transportation and processing, and the proper cutting season and drying are processes that may improve the wood quality in pre- and post harvesting operations.

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