ANIL

Finishing studies on Poly urathene (PU) and Shellac coats on Teak (Tectona

grandis) and Deodar (Cedrus deodara) surfaces

Forest Research Institute, Dehradun

Under sincere guidance of :DR. KISHAN KUMAR V.S.

Scientist FWood Working and Finishing Discipline

Presented By :ANIL MUNDOTIYA

WST-13-04M.Sc. (WST)

Finishing wood refers to the final step in any woodworking project, or, more specifically, to applying one of many kinds of protective coating, usually clear, generically called "finish".

Numerous such finishes are available for use. The selection of a suitable finish for suitable end use is quiet important.

Sometimes a suitable finish may improve the surface look manifolds. Defects have to be covered for better look and inferior grade timbers can be correctly processed to look like superior grade timber.

INTRODUCTION

INTRODUCTION

While applying a finish many properties are to be taken into consideration such as density (specific gravity), growth rate, hardwood-softwood, heartwood–sapwood, earlywood–latewood, grain angle, vessels, and texture vary within and across wood spe cies.

the difference of softwood and hardwood is of major importance while applying a finish.

Similarly no coating is entirely moisture proof. As there is no way of completely keeping moisture out of wood that is exposed to prolonged periods of high RH.

Perfect application of a finish on the wood surface has to be a well-planned partnership of the finish manufacturer, the machine manufacturer and the end user.

Gloss

A measurement proportional to the amount of light reflected from a surface is gloss. A kind of paint that dries to a shiny finish.

Gloss is basically the specular reflection of light from the finished wood surface.

Gloss of the surface is measured by gloss meter.

Essence of finishing

Finishing wood for interior applications serves the functions of (1) protecting the wood (mostly from liquids) and (2) enhancing the appearance of the wood.

Selection of a finish will depend on the appearance and degree of protection desired and on the substrates used. Because different finishes give varying degrees of protection, the type of finish, its quality and quantity, and the method used to apply the finish.

Objectives To determine the behaviour of two finishes, i.e.,

spirit shellac and polyurethane in two wood species deodar and teak with respect to coat thickness.

To determine the effect on gloss in both the species.

To determine the difference in moisture intake capacity between the two species.

Materials and methods

A total of 30 sample planks of Teak and Deodar each were taken for the study with a dimension of 15 X 9 X 1 cm3 deodar, 15 X 7 X 1.5 cm3 teak.

The samples were then conditioned at 35°C and 30% RH until their weights became constant.

The samples were then sanded with 60, 80, 100, 120 grit size sandpapers.

Of the 30 samples of teak 10 samples were coated with polyurethane (PU), 10 samples); the same was done for deodar.


Preparation of polyurethane: The polyurethane applied was prepared by diluting

polyurethane with turpentine oil in the proportion of 10 ml of Turpentine oil for every 50 ml of polyurethane.

Application was done by spray gun.

Preparation of shellac: Shellac was prepared by mixing 60 gm of shellac in 1liter of

spirit and placing it in sun.


The samples are than placed in the humidity chamber again at elevated humidity levels, i.e., at 35°c and 85% R.H.

Weight were taken for all the samples continuously for

3 days after placing the samples at elevated relative humidity and then taken at a gap of 3 days.

Deodar Samples Teak Samples

Control Sample (uncoated)

PU coated Sample

Shellac coated Sample

Control Sample (uncoated)

PU coated Sample

Shellac coated Sample

Observation and analysisCoating material effect on coat thickness: For Teak samples, the thicknesses are almost similar in the case of both the

coatings(PU and shellac ). In case of deodar it is seen that there is a considerable difference on average thickness of coating.

the three coats of PU seem to be giving a much thicker coat on Deodar compared to the six coats of shellac used.

PU Shellac0

10

20

30

40

50

60

70

80

90

3531

81

54

Avg Thickness

TeakDeodar

Coat

Th

ick

nes

s

Observation and analysis

Coating material effect on gloss: The polyurethane coating gives considerably more gloss than

shellac coating. Only three coats of PU seems to be give a much higher gloss

on Deodar and a slightly higher gloss in teak were used whereas six coats of shellac were used to coat the samples.

Teak Deodar0

102030405060708090 79.5

86.7

32.727.6

Average Gloss

PUShellac

Species

Glo

ss (

GU

)


Moisture studies : From the data obtained the softwood samples had a higher initial MC, these

samples have taken up more moisture (25.67 %) as against that taken up by teak (16.09 %).

moisture gain is highest in the non-coated control samples in case of deodar.

when coated samples are compared with the control (non-coated samples) it is found that the MC increment is significantly lesser for the coated samples.

pu shellac non-coat0

10

20

30

% moisture gain

deodar teak

Coating Material

MC

in


Coat thickness studies: Both the species Teak and Deodar shellac coated samples

offer higher retention in coat thickness on exposure to adverse condition, i.e., 85% Rh for a prolonged period as compere to PU.

Teak Deodar0

5

10

15

20

25

30

3532.6

29.8

14.417.8

%change in coat thickness on exposure to adverse conditions at 85%R.H.

PUShellac

% C

hange


Change in gloss studies: Gloss in PU coating offers a greater resistance to adverse condition as

compared to Shellac coating.

The retention provided by PU is more than double the amount of retention provided by shellac coated samples.

Gloss reduction in shellac is very high in adverse climatic condition in both hardwood and softwood.

Teak Deodar0

10

20

30

40

50

60

70

21.2

26.6

54.7

60.3

% c h a n g e i n g l o ss o n e x p o su r e t o a d v e r se c o n d i t i o n s

PU

Shellac

Glo

ss (

GU

)

CONCLUSION The coating thickness is always higher on Deodar. The thicknesses formed by either coating on

Deodar were significantly higher than those on teak surface.

Three coats of PU seems to be give a much higher gloss on Deodar and a slightly higher gloss in teak were used whereas six coats of shellac were used to coat the samples.

Moisture gain is highest in the non-coated control samples in case of deodar. The MC increment is significantly lesser for the coated samples. Thus both shellac and PU (in thicknesses of 31 and 35 µm) are equally efficient in blocking moisture entry into teak.

Gloss in PU coating offers a greater resistance to adverse condition as compared to Shellac coating. The retention provided by PU is more than double the amount of retention provided by shellac coated samples.

In both the species Teak and Deodar shellac coated samples offer higher retention in coat thickness on exposure to adverse condition, i.e., 85% Rh for a prolonged period as compere to PU.

REFERENCES

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ANIL

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