This PPT on seasoning of wood is prepared by Dr.E.Sreenivasan of WIPL,Kannur.

1. WOOD SEASONINGWOOD SEASONING
Dr.E.SREENIVASANDr.E.SREENIVASAN
Technical Manager, R&DTechnical Manager, R&D
THE WESTERN INDIA PLYWOODS LTDTHE WESTERN INDIA PLYWOODS LTD
BALIAPATAM,BALIAPATAM,
KANNUR-670010KANNUR-670010
Ph:8289865990Ph:8289865990
E-Mail: dr.sreeniettammal@gmail.comE-Mail: dr.sreeniettammal@gmail.com

2. INTRODUCTIONINTRODUCTION
 Seasoning means partial drying of wood.Seasoning means partial drying of wood.
 Wood from freshly felled trees contains a large quantity ofWood from freshly felled trees contains a large quantity of
moisture(100 to200 per cent). This has to be removed beforemoisture(100 to200 per cent). This has to be removed before
the timber becomes fit for servicethe timber becomes fit for service
 Water contained in wood is held in two forms: 1)as free water,Water contained in wood is held in two forms: 1)as free water,
in cavities of cells and space around cells 2) as absorbedin cavities of cells and space around cells 2) as absorbed
water, held in cell walls.water, held in cell walls.
 "Free moisture" is the name given to the water in the cell
cavities in timber, and the moisture saturating the cell walls is
termed the "bound" or "combined“ moisture. Although the
moisture is exactly the samein either position, its effect on the
timber is quite different.

3. OBJECTIVES
 The objectives of any seasoning process are to dry the material
to a low uniform moisture content with a minimum amount of
degrade in a minimum amount of time with a minimum cost
for operating expenses and equipment These objectives are not
all compatible with one another, and one must often be
sacrificed to satisfy another. The conditions of each situation
must necessarily determine the relative emphasis placed on
each objective Thus rate of drying must often be retarded to
allow the wood to dry with a minimum of degrade.

4. ADVANTAGESADVANTAGES
 Seasoning reduces gross weight and thereby subsequent
shipping and handling costs,
 imparts dimensional stability,
 increases most strength properties,
 increases fastener holding power and thereby joint strength,
increases electrical resistance,
 improves paintability and glueability,
 improves the thermal properties of wood.
 In addition to these advantages, drying wood below the fiber
saturation point renders it impervious to biological
 degradation so long as it is not re-wetted.
 Attack by wood destroying fungi is prevented.

5. METHODSMETHODS
 Seasoning aims at drying a set quantity of
timber uniformly to the equilibrium moisture
content required with a minimum of degrade in
the shortest possible time.
 There are many ways of seasoning or drying
timber, but only two methods have been found
satisfactory, principally for economic reasons.
 They are air drying and kiln drying.

6. AIR SEASONINGAIR SEASONING
 It is the simplest method pf drying woodIt is the simplest method pf drying wood
 Important points to be noted and taken care of:Important points to be noted and taken care of:
1.proper piling or stacking of the timber1.proper piling or stacking of the timber
2.protection of stack from hot winds, blazing2.protection of stack from hot winds, blazing
sun and rainsun and rain

7. VERTICAL STACKINGVERTICAL STACKING
 Usually in use for light timbers such as semulUsually in use for light timbers such as semul
((SalamaliaSalamalia) and salai () and salai (BosweliaBoswelia) used for) used for
packing casespacking cases
 Sawn planks are made to stand in open airSawn planks are made to stand in open air
against a wall or a framework of wood oragainst a wall or a framework of wood or
bamboosbamboos
 The surface of planks dries rapidly therebyThe surface of planks dries rapidly thereby
avoiding mould-attacks and sap stainavoiding mould-attacks and sap stain

8. HORIZONTAL STACKINGHORIZONTAL STACKING
 Most common practice and is suitable for allMost common practice and is suitable for all
kinds of sawn materialkinds of sawn material
 Stacking with the help of battens or crossesStacking with the help of battens or crosses
 Different species and different thicknessesDifferent species and different thicknesses
should be stacked separatelyshould be stacked separately

9. HORIZONTAL STACKINGHORIZONTAL STACKING

10. PROTECTION OF STACKPROTECTION OF STACK
 The amount of protection required depends on:The amount of protection required depends on:
a. the species of timber,a. the species of timber,
b. thickness of the material, andb. thickness of the material, and
c. climatic conditions. Therefore, the provision of anc. climatic conditions. Therefore, the provision of an
air-seasoning shed is desirable as otherwise it is notair-seasoning shed is desirable as otherwise it is not
possible to regulate the factors affecting the rate ofpossible to regulate the factors affecting the rate of
drying (temperature, humidity, air circulation)drying (temperature, humidity, air circulation)
 Three seasoning sheds by FRI: Shed type1,2 and 3Three seasoning sheds by FRI: Shed type1,2 and 3

11. SHED TYPE 1SHED TYPE 1
 For refractory species ie, those species which are veryFor refractory species ie, those species which are very
liable to crack, split and warp. Eg.liable to crack, split and warp. Eg. AnogeissusAnogeissus
latifolialatifolia (Axle wood),(Axle wood), Madhuca indicaMadhuca indica (Mahua),(Mahua),
Diospyros melanoxylonDiospyros melanoxylon (Ebony),(Ebony),Syzygium cuminiSyzygium cumini
(Jamun),(Jamun), Lagerstroemia lanceolataLagerstroemia lanceolata (Benteak),(Benteak),
Terminalia paniculataTerminalia paniculata (Kindal),(Kindal), Xylia xylocarpaXylia xylocarpa
(Irul) and(Irul) and Palaquium ellipticumPalaquium ellipticum (Pali)(Pali)
 A closed shed provided with open space forA closed shed provided with open space for
ventilation in walls just below the roof and above theventilation in walls just below the roof and above the
groundground
 It should have a central passage for loading andIt should have a central passage for loading and
unloading or removable side wallsunloading or removable side walls

12. SHED TYPE 2SHED TYPE 2
 For medium refractory species Eg.For medium refractory species Eg.AcaciaAcacia arabicaarabica
(Babul),(Babul), Adina cordifoliaAdina cordifolia (Haldu),(Haldu), Albizia lebbekAlbizia lebbek
(Kokko),(Kokko), CedrelaCedrela toonatoona(Toon),(Toon), Dalbergia latifoliaDalbergia latifolia
(Rosewood),(Rosewood), Dalbergia sissoDalbergia sisso(Sisso),(Sisso), DipterocarpusDipterocarpus
spsp.(Gurjan),.(Gurjan), Pterocarpus marsupiumPterocarpus marsupium (Bijasal),(Bijasal),
Tectona grandisTectona grandis (Teak)(Teak)
 Shed open on one side and closed on three sidesShed open on one side and closed on three sides
 Open side should have sufficient overhang of the roofOpen side should have sufficient overhang of the roof
to protect the stack from direct sun and rainto protect the stack from direct sun and rain

13. SHED TYPE 3SHED TYPE 3
 For non-refractory species ie, for timbers which canFor non-refractory species ie, for timbers which can
stand rapid seasoningstand rapid seasoning
 Also recommended for species liable to staining,Also recommended for species liable to staining,
mould and decay during seasoningmould and decay during seasoning
 A simple shed open on all sides and provided with aA simple shed open on all sides and provided with a
roof sufficiently overhanging for protection againstroof sufficiently overhanging for protection against
rain and direct sunrain and direct sun
 Eg.Abies pindrow(Eg.Abies pindrow(Fir),Fir), Salamalia malabaricaSalamalia malabarica
(Semul),(Semul), Boswellia serrata(Boswellia serrata(Salai),Salai), Cedrus deodaraCedrus deodara
(Deodar),(Deodar), Mangifera indica(Mangifera indica(Mango),Mango), Morus albaMorus alba
(Mulberry),(Mulberry), Picea smithiana(Picea smithiana(Spruce),Spruce), PinusPinus
roxburghiiroxburghii (Chir) and(Chir) and Vateria indica(Vateria indica(VellapineVellapine))

14. SHEDSSHEDS

15. PROTECTION OF ENDS OFPROTECTION OF ENDS OF
TIMBERTIMBER
 A common problem during air seasoning is theA common problem during air seasoning is the
checking or splitting at the ends of boards or plankschecking or splitting at the ends of boards or planks
 The best way to protect is to coat the ends with any ofThe best way to protect is to coat the ends with any of
the following moisture proof compositions up to athe following moisture proof compositions up to a
distance of about 8cm for the ends:distance of about 8cm for the ends:
1.Thick coal tar or bituminous paint1.Thick coal tar or bituminous paint
2.Rosin and lamp black(10:1),melted,mixed and2.Rosin and lamp black(10:1),melted,mixed and
applied hotapplied hot
3.Hardened gloss oil3.Hardened gloss oil
4.Molasses and lime(3:1)4.Molasses and lime(3:1)

16. PREVENTION OF DRYING OFPREVENTION OF DRYING OF
LOGSLOGS
 If logs cannot be cut immediately, their drying shouldIf logs cannot be cut immediately, their drying should
be reduced by storing them under waterbe reduced by storing them under water
 Barks on the logs should be removed before they areBarks on the logs should be removed before they are
stored in waterstored in water
 When storage under water is not possible,logs shouldWhen storage under water is not possible,logs should
be stored on land preferably under shade overbe stored on land preferably under shade over
foundations which are slightly raised above groundfoundations which are slightly raised above ground
 Apply one of the compositions for moisture-proofApply one of the compositions for moisture-proof
coatingcoating

17. MOISTURE CONTENTMOISTURE CONTENT
FOR DIFFERENT USESFOR DIFFERENT USES
 The final moisture content to which timber shall beThe final moisture content to which timber shall be
seasoned before use depends upon the serviceseasoned before use depends upon the service
requirements of the finished articles and the climaticrequirements of the finished articles and the climatic
conditions of the locality where it is to be usedconditions of the locality where it is to be used
 For this purpose, India has been divided into 4 zones:For this purpose, India has been divided into 4 zones:
Zone I: less than 40% average annual RHZone I: less than 40% average annual RH
Zone II: ,, ,, 40-50% ,, ,, ,,Zone II: ,, ,, 40-50% ,, ,, ,,
Zone III: ,, ,, 50-67% ,, ,, ,,Zone III: ,, ,, 50-67% ,, ,, ,,
Zone IV: ,, ,, above 67% ,, ,, ,,Zone IV: ,, ,, above 67% ,, ,, ,,

18. MOISTURE CONTENTMOISTURE CONTENT
MAXIMUM PERMISSIBLE (%)MAXIMUM PERMISSIBLE (%)
No.No.
ProductsProducts ZoneZone
II
ZoneZone
IIII
ZoneZone
IIIIII
ZoneZone
IVIV
11 Beams& raftersBeams& rafters 1212 1414 1717 2020
22 Doors& windowsDoors& windows
i. less than 50mmi. less than 50mm
in thicknessin thickness
ii.50mm&aboveii.50mm&above
88
1010
1010
1212
1212
1414
1414
1616
33 FurnitureFurniture 1010 1212 1414 1515

19. KILN SEASONINGKILN SEASONING
 Kiln drying of lumber is perhaps the most effective and economical
method available Drying rates in a kiln can be carefully controlled and
defect losses reduced to a minimum. Length of drying time is also greatly
reduced and is predictable so that dry lumber inventories can often be
reduced. Where staining is a problem, kiln drying is one n the only
reasonable method that can be used unless chemical dips are employed
 Kilns are usually divided into two classes-progressive and compartment.
 In the progressive kiln, timber enters one end and moves progressively
through the kiln much as a car moves through a tunnel Temperature and
humidity differentials are maintained throughout the length of the kiln so
that the lumber charge is progressively dried as it moves from one end to
the other. Progressive kilns may be further subdivided into natural draft
kilns in which heated air is allowed to rise through the material by natural
convection, and forced draft kilns in which fans are employed to force the
air through the wood

20. KILN SEASONINGKILN SEASONING
 Compartment kilns differ from progressive kilns in that the timber isCompartment kilns differ from progressive kilns in that the timber is
loaded into the kiln and remains in place throughout the drying processloaded into the kiln and remains in place throughout the drying process
These kilns are usually smaller than progressive kilns, and because of theirThese kilns are usually smaller than progressive kilns, and because of their
construction the temperature and humidity conditions within them can beconstruction the temperature and humidity conditions within them can be
closely controlled .Consequently, they are often used to dry expensiveclosely controlled .Consequently, they are often used to dry expensive
material or woods which are difficult to dry. It may be either forced ormaterial or woods which are difficult to dry. It may be either forced or
natural just as with progressive kilns.natural just as with progressive kilns.
 Drying conditions cannot be controlled as closely in natural draftDrying conditions cannot be controlled as closely in natural draft
compartment kilns, however, as in forced draft kilns, and the rate of dryingcompartment kilns, however, as in forced draft kilns, and the rate of drying
is also slower For these reasons kilns built today are of the forced draftis also slower For these reasons kilns built today are of the forced draft
type and many of the old natural draft types have been convertedtype and many of the old natural draft types have been converted

21. PILING OF TIMBER IN KILNPILING OF TIMBER IN KILN
 The mode of arrangement of sawn timber forThe mode of arrangement of sawn timber for
air seasoning is equally good for kilnair seasoning is equally good for kiln
seasoningseasoning
 The crossers should be placed at more frequentThe crossers should be placed at more frequent
intervals and in good alignment, in order tointervals and in good alignment, in order to
avoid greater stresses during dryingavoid greater stresses during drying
 The ends of planks should not be leftThe ends of planks should not be left
unsupportedunsupported

22. TYPES OF KILNSTYPES OF KILNS
 Internal fan, reversible circulation, steamInternal fan, reversible circulation, steam
heated kilnheated kiln
 Indirect heated, thermal circulation, furnaceIndirect heated, thermal circulation, furnace
kilnkiln
 Hor air kilnHor air kiln
 Electrically heated kilnElectrically heated kiln
 Special methodsSpecial methods

23. SEASONING DEFECTS&THEIRSEASONING DEFECTS&THEIR
CONTROLCONTROL
 Checks: Rupture of wood along the grain. There are two types: End checksChecks: Rupture of wood along the grain. There are two types: End checks
and surface checks. Control: In air seasoning, both kinds of checking canand surface checks. Control: In air seasoning, both kinds of checking can
be decreased by creating conditions which will cause evaporation ofbe decreased by creating conditions which will cause evaporation of
moisture at a slow uniform rate. Surface checking can be reduced bymoisture at a slow uniform rate. Surface checking can be reduced by
cutting down the speed of circulating air and end checking can becutting down the speed of circulating air and end checking can be
minimized by using moisture resistant coatings. In kin seasoning, it can beminimized by using moisture resistant coatings. In kin seasoning, it can be
retarded by regulating temperature, humidity and circulating airretarded by regulating temperature, humidity and circulating air
 Warping: a kind of deformation or distortion from the true plane in a pieceWarping: a kind of deformation or distortion from the true plane in a piece
of woodof wood
1.Bowing1.Bowing
2.Crooking or splitting2.Crooking or splitting
3.Cupping3.Cupping
4.Twisting4.Twisting
5.Diamonding5.Diamonding
 Case hardening: develops in wood on rapid dryingCase hardening: develops in wood on rapid drying
 Collapse: This is due to abnormal and irregular shrinkage.Collapse: This is due to abnormal and irregular shrinkage.

24. SPECIAL METHODS
 Chemical seasoning (McMillen, 1960)
 High frequency di-electric heating (McMillen& James, 1961)
 Resistance heating; emersion in hot liquid metal, boiling in
oily liquids (McMillen,1956)
 Infra-red radiation; vacuum drying and Vapour drying
 Solvent seasoning (McMillen,1956)
 High temperature drying by solar radiation
 Forced air drying with unheated (Stevens,1965)
 Heated air (Kimbal and Torgeson, 1959)
Note: A few of these methods are of commercial importance;
some are apparently impractical ; others at present are
uneconomical

25. THANK YOUTHANK YOU