Natural Seasoning. Continued
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This section is from the book "Elementary Principles Carpentry", by Thomas Tredgold. Also available from Amazon: Elementary Principles Of Carpentry.
Natural Seasoning. Continued
447. In order to compare the times required to season and to dry timber when the sizes of the pieces remain the same, it will be necessary to consider the progress of evaporation from the same quantity of surface.
Let the whole time be conceived to be divided into equal parts, then if the quantity evaporated during any one of these parts of the time be n W, the whole quantity of sap being W; then as the time increases, the quantity of moisture decreases; and the force of evaporation being proportional to the excess of moisture, the quantity evaporated must decrease as the time increases, and the time is expressed by the equation
W ( 1-1/n)t = w, when w is the quantity of moisture the wood retains.†
But for calculation we must employ logarithms, and then if W/w = m, the equation becomes log.m = t the
log. n - log. (n - 1) time.
When timber is dry m = 12; and in seasoning in the open air n = 20 nearly; the timber losing one-third of its weight; but in seasoned timber m = 2.5, and n = 15; the time being expressed in months.
* Barlow's 'Essay on Timber.'
† The investigation is given in the author's ' Treatise on Warming and Ventilating Buildings, etc.'
Hence it appears how slowly the process of drying goes on; and the preceding equations showing that it proceeds most rapidly in small pieces, the importance of reducing timber to its proper scantlings for use is obvious. For however dry a piece of timber may be, when it is cut to a smaller scantling it will still shrink and lose weight, being always less dry in the centre than at the surface; and the more rapidly the drying has been carried on, the greater will be the difference. Nevertheless, in the first stages of seasoning it is best that it should proceed slowly; otherwise the external pores would shrink so close as not to permit the free evaporation of the internal moisture, and the piece would split from unequal shrinking; and, lastly, it should be reduced nearly to the proper scantling some time before it be framed.
448. The following Table gives the relative time of seasoning pieces of timber in the open air calculated according to the foregoing Rule.
Length in feet. | Breadth in inches. | Thickness in inches | Time of Seasoning in months. | Time of Drying in months. |
10 | 6 | 6 | 6 1/2 | 29 |
10 | 8 | 8 | 8 1/2 | 39 |
12 | 10 | 10 | 10 | 48 |
12 | 12 | 12 | 12 | 57 |
12 | 14 | 14 | 14 | 66 |
12 | 16 | 16 | 17 | 76 |
18 | 18 | 18 | 19 | 86 |
20 | 20 | 20 | 21 | 96 |
The time required to season timber under cover is reduced in the proportion of 5 to 7.
449. The following Table shows the Shrinkage and Loss of Weight in Seasoning of the principal Timbers used in Ship-building. The period of seasoning was ten years.*
* Fincham's ' Outlines of Ship-building,' 3rd edition.
Species of Timber | Seasoned. | Weight of a cubic toot. | |||||||||||
Size. | Weight. | Size. | Weight | Green. | Seasoned. | ||||||||
in. | in. | lbs. | ozs. | in. | in. | lbs. | ozs. | lbs. | lbs. | ||||
English Oak | butt | 6 | by | 6 | 7 | 8 | 6 | by | 5 14/16 | 6 | 7 | 60 | 51 1/2 |
top | " | 7 | 10 | 5 14/16 | " | 5 15/16 | 6 | 6 | 61 | 51 | |||
butt | " | 8 | 0 | 5 15/16 | " | 5 14/16 | 6 | 5 | 64 | 50 1/2 | |||
top | " | 7 | 4 | 5 15/16 | " | 5 15/16 | 6 | 0 | 58 | 48 | |||
Dantzic Oak | butt | " | 7 | 2 | 5 14/16 | " | 5 15/16 | 5 | 12 | 57 | 46 | ||
top | " | 7 | 0 | 5 14/16 | " | 6 | 5 | 15 | 56 | 47 1/2 | |||
butt | " | 6 | 7 1/2 | 5 13/16 | " | 5 14/16 | 5 | 4 | 51 3/4 | 42 | |||
top | " | 6 | 9 | 5 14/16 | " | 5 14/16 | 5 | 2 1/2 | 52 1/2 | 41 1/4 | |||
butt | " | 9 | 2 | 5 12/16 | " | 5 12/16 | 8 | 0 | 73 | 64 | |||
top | " | 8 | 6 | 5 13/16 | " | 5 13/16 | 7 | 2 | 67 | 57 | |||
butt | " | 7 | 12 | 5 13/16 | " | 5 14/16 | 7 | 2 | 62 | 57 | |||
top | " | 7 | 4 | 5 14/16 | " | 5 15/16 | 6 | 10 | 58 | 53 | |||
Cowrie .... | butt | " | 4 | 14 1/2 | 5 14/16 | " | 6 | 4 | 6 1/4 | 38 1/2 | 35 1/4 | ||
top | " | 4 | 9 | 5 14/16 | " | 5 14/16 | 4 | 0 | 36 1/2 | 32 | |||
butt | " | 4 | 10 | 5 14/16 | " | 5 14/16 | 4 | 2 1/2 | 35 | 33 1/4 | |||
top | " | 4 | 7 1/2 | 5 14/16 | " | 5 14/16 | 4 | 1 3/4 | 35 3/4 | 32 3/4 | |||
Italian Larch | butt | " | 4 | 15 | 5 15/16 | " | 5 14/16 | 4 | 8 | 39 1/2 | 36 | ||
top | " | 4 | 15 | 5 14/16 | " | 5 14/16 | 4 | 9 | 39 1/2 | 36 1/2 | |||
butt | " | 5 | 0 | 5 14/16 | " | 5 14/16 | 4 | 9 1/2 | 40 | 36 3/4 | |||
top | " | 5 | 1 | 5 15/16 | " | 5 14/16 | 4 | 11 | 40 1/2 | 37 1/2 | |||
Scotch Larch | butt | " | 4 | 8 | 5 14/16 | " | 5 14/16 | 4 | 2 1/2 | 36 | 33 1/4 | ||
top | " | 4 | 10 | 5 15/16 | " | 5 15/16 | 4 | 1 | 37 | 32 1/2 | |||
butt | " | 4 | 5 | 5 15/16 | " | 5 14/16 | 4 | 0 | 34 1/2 | 32 | |||
top | " | 3 | 12 | 5 14/16 | " | 5 14/16 | 3 | 7 | 30 | 27 1/2 | |||
Hackmetack Larch .... | butt | " | 5 | 14 | 5 12/16 | " | 5 12/16 | 4 | 13 | 47 | 38 1/2 | ||
top | " | 5 | 6 | 5 13/16 | " | 5 12/16 | 4 | 3 | 43 | 33 1/2 | |||
butt | " | 5 | 7 | 5 14/16 | 5 12/16 | 4 | 8 | 43 1/2 | 36 | ||||
top | " | 4 | 15 | 5 13/16 | " | 5 14/16 | 4 | 6 | 39 1/2 | 35 | |||
English Elm | butt | " | 5 | 9 1/2 | 5 13/16 | " | 5 12/16 | 4 | 10 1/2 | 64 3/4 | 37 1/4 | ||
top | " | 5 | 11 1/4 | 5 14/16 | " | 5 13/16 | 4 | 9 | 59 3/4 | 36 1/2 | |||
butt | " | 6 | 4 | 5 14/16 | " | 5 13/16 | 4 | 11 3/4 | 60 | 39 3/4 | |||
top | " | 5 | 7 | 5 12/16 | " | 5 12/16 | 4 | 3 1/2 | 53 1/4 | 33 3/4 | |||
Canada Elm | butt | " | 7 | 10 | 5 12/16 | " | 5 12/16 | 7 | 2 | 61 | 57 | ||
top | " | 6 | 9 | 5 11/16 | " | 5 12/16 | 5 | 5 | 52 1/2 | 42 1/2 | |||
butt | " | 7 | 1 | 5 11/16 | " | 5 12/16 | 6 | 8 | 56 1/2 | 52 | |||
top | " | 6 | 2 | 5 12/16 | " | 5 14/16 | 4 | 13 | 49 | 38 1/2 | |||
Table - corntinued.
Species of Timber. | Green. | Seasoned. | Weight of a cubic foot. | ||||||||||
Size. | Weight. | Size. | Weight. | Green. | Seasoned. | ||||||||
in. | in. | lbs. | ozs. | in. | in. | lbs. | ozs. | lbs. | lbs. | ||||
Cuba Cedar | butt | 6 | by | 6 | 4 | 0 | 5 15/16 | by | 5 15/16 | 8 | 12 | 32 | 30 |
top | " | 4 | 3 | 5 15/16 | " | 5 14/16 | 3 | 12 1/2 | 33 1/2 | 30 1/4 | |||
butt | " | 3 | 14 | 6 | " | 6 | 3 | 0 | 31 | 24 | |||
top | " | 3 | 10 | 5 15/16 | " | 6 | 3 | 5 | 29 | 26 1/2 | |||
N. S. Wales Cedar... | butt | " | 4 | 0 1/2 | 5 15/16 | " | 5 14/16 | 3 | 10 | 32 1/4 | 29 | ||
top | " | 3 | 12 | 5 15/16 | " | 5 151/6 | 3 | 6 1/2 | 30 | 27 1/4 | |||
butt | " | 4 | 6 | 5 15/16 | " | 5 15/16 | 3 | 8 | 35 | 28 | |||
top | " | 4 | 5 | 5 14/16 | " | 5 14/16 | 3 | 9 | 34 1/2 | 28 1/2 | |||
Pencil Cedar | butt | " | 4 | 5 3/4 | 6 | " | 6 | 4 | 3 | 34 3/4 | 33 1/2 | ||
top | " | 4 | 5 | 6 | " | 6 | 4 | 3 | 34 1/2 | 33 1/2 | |||
butt | " | 3 | 10 1/2 | 6 | " | 5 14/16 | 3 | 8 | 29 1/4 | 28 | |||
top | " | 3 | 12 1/2 | 6 | " | 6 | 3 | 10 | 30 1/4 | 29 | |||
Pitch Pine | butt | " | 5 | 11 1/4 | 5 15/16 | " | 5 15/16 | 5 | 9 1/4 | 45 3/4 | 44 1/2 | ||
top | " | 4 | 12 1/4 | 5 14/16 | " | 5 15/16 | 4 | 11 | 38 1/4 | 37 1/2 | |||
butt | " | 5 | 12 | 5 13/16 | " | 5 15/16 | 5 | 10 | 46 | 45 | |||
top | " | 4 | 14 | 6 | " | 5 151/6 | 4 | 12 1/4 | 39 | 38 | |||
450. A Table of the transverse Shrinkage in Seasoning of Boards 12 inches square and 1/2 an inch thick. The period of seasoning was thirteen years.*
Species of Timber. | Shrunk in Seasoning. | |||
English Oak.. | butt | 1/12 | the | breadth |
top | 1/13 | ,, | ,, | |
African Oak.. | butt | 1/27 | ,, | ,, |
top | 1/32 | ,, | ,, | |
Riga Fir | butt | 1/32 | ,, | ,, |
top | 1/32 | ,, | ,, | |
Dantzic Fir .. | butt | 1/38 | ,, | ,, |
top | 1/38 | ,, | ,, | |
Virginia Fine | butt | 1/27 | ,, | ,, |
top | 1/38 | ,, | ,, | |
Species of Timber. | Shrunk in Seasoning. | |||
butt | 1/38 | the | breadth | |
top | 1/48 | ,, | ,, | |
Larch.. | butt | 1/27 | ,, | ,, |
top | 1/48 | ,, | ,, | |
English Elm | butt | 1/24 | ,, | ,, |
top | 1/27 | ,, | ,, | |
Canada Elm | butt | 1/16 | ,, | ,, |
top | 1/21 | ,, | ,, | |
Cowrie | butt | 1/64 | ,, | ,, |
top | 1/64 | ,, | ,, | |
* Fincham's ' Outlines of Ship-building,' 3rd edition.
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