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Wrapping or poultice method for thick plank stock.
Chemical dips.

Steam-box treatment, Kraetzer cured.

HANDLING AFTER SEASONING

Avoid unpiling or transporting in rain or snow.
Keep free of dirt.

Canvas covers for truck loads exposed to weather.

Adequate roofing over transportation channels from yard to planer, to storage shed, to shipping dock.

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FIGURE 33.-An example of one of the many ways in which methods of piling in the yard may favor the development of sap stain. In this pile the spaces between boards in the same course are irregular and at the top the circulation is cut off by the overlapping of the two top boards. Note the sap stain on the ends of the sap gum boards

Sanitation of storage sheds.

Foundation timbers and floors must be dry.
Ventilation needed to remove moisture in shed.

Prevent leaky roofs.

Do not store damp lumber.

Loading of freight cars.

Thoroughly clean the car.

Add layer of clean sawdust.

Add a number of clean wood strips.

Protect lumber from rain, snow, and condensation of moisture within car. (Even kiln-dried stock, though sterilized by heat, must be protected from moisture to prevent reinfection. Inclose a placard with each shipment, telling dealer how best to care for the stock in order to avoid staining, warping, checking, etc.)

There are two special methods used in the seasoning of lumber which have not been previously described in this bulletin and which need a word or two of explanation on account of their uniqueness. These methods are the end racking of green hardwood lumber practiced in the Southern States and the wrapping or poultice method of piling thick plank stock used to a limited extent in the Western States.

END-RACKING

This method consists of piling hardwood lumber on edge in racks in the form of the letter X. Sometimes this method of piling is called pole-piling and is used principally as a preliminary step in regular air-seasoning practice. The rate of drying is greatly increased under normal conditions by this method, and sap stain is prevented. After the boards have remained in these racks for several days they are placed in regular piles to complete the seasoning. The disadvantages of this method are the large amount of space needed for piling, additional handling costs, and a considerable amount of cup and warp. End checks frequently develop at the upper ends of the boards, and this is sometimes prevented by crossing the boards at the top instead of some distance down from the top. Care must also be exercised to keep the bottoms of the boards off the ground in order to prevent decay and stain. Due to the exposure of the stock to the weather, end-racking must be carefully watched and adjusted to local weather conditions. This practice is used in drying yellow poplar, basswood, cottonwood, sap maple and sap gum.

POULTICE-PILING

The poultice or wrapping method of piling lumber for seasoning is used to a limited extent in drying thick plank stock of the higher grades cut from pine sapwood. Pattern stock cut from western white pine is handled by this method, which consists of wrapping the two faces of each plank with 4/4 western red cedar heartwood. The planks and their layers of cedar boards are separated from each other by crossers. (Fig. 34.) The pile is often boarded up at front and rear to reduce end-checking. In some cases each plank has both ends coated with a layer of paraffin to reduce end-checking. The paraffin is applied hot by means of a special spraying apparatus and serves as a very effective end coating.

A study made of this method of piling indicated that the cedar boards not only aided in slowing down the drying rate and thus prevented the formation of center checks but the toxic water soluble or volatile constituents of these boards were found to be effective in preventing sap stain from developing in the thick sapwood planks. The use of unseasoned stock of species other than cedar for wrapping material was observed to have resulted in severe staining of the planks. Old cedar boards previously used for crossers or carrying considerable blue-stain infection are not as effective as new thoroughly dried boards.

More recently cedar boards have been used successfully in wrapping thick sapwood stock undergoing seasoning in the kiln. The

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drying schedule used with thick stock is usually a mild one, and with low temperatures sap stain and mold may appear on the plank. The cedar boards help to prevent this and also tend to slow down the rate of evaporation of moisture from the plank stock.

THE UTILIZATION OF BLUE-STAINED LUMBER

Blue stain in sap lumber is not a stage of decay. Although it is the work of fungi, it leaves the strength of the wood practically unimpaired for ordinary purposes. Nevertheless it is an object of natural suspicion and a source of large degrade losses. Proper kiln1 drying is the only completely effective method now known of preventing blue stain. In spite of years of experience with chemical

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FIGURE 34. A pile of 10/4-inch western white pine plank undergoing seasoning by the poultice method. Note the layers of inch cedar boards on the upper and lower faces of the planks. The front and rear ends of the pile are boarded up to prevent end checking

dips, nothing has yet been found which will give consistent results during the warm rainy season. Until a practicable, effective method of prevention is found for cases where kiln-drying is not feasible, proper utilization of blued stock will remain the only way of reducing the loss from this source.

The utilization of blue-stained wood must, however, be undertaken intelligently. In the first place, kiln-dried material should be chosen in preference to air-dried, for the reason that decay-producing organisms, as well as stain fungi, are more likely to be killed in the former. Secondly, before recommending the use of blued lumber, whether air-dried or kiln-dried, the holder of such stock should assure himself that it has not become infected with decay-producing fungi in addition to the blue stain. The recognition of decay associ

ated with sap stains is difficult, particularly when decay is in the early stages or when the staining is very heavy.55

Since wood destroyers thrive under conditions which favor the bluing of wood (fig. 35), heavily stained material should be examined carefully for signs of decay. If this is done and specific uses are suggested by the dealer, a greater confidence in decay-free blued stock will result.

Blue stain is freely accepted in rough lumber, lath, scantling, plank, and some of the larger sizes of dimension. More could well

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FIGURE 35.-Drawing of a section of Sitka spruce sapwood as seen under the microscope showing the large threads a of a blue-stain fungus and the smaller threads b of a wood-rot fungus in the wood cells. Conditions for the growth of both types of fungi were present in this material. Note how the blue-stain threads pass through the natural openings in the cell wall at c, while the rot-producing threads bore their way through the walls

be used, where sapwood is not objectionable, in the manufacture of frames, sash, doors, trim, finish, millwork, and other products, when the discolored wood is to be painted or otherwise hidden from view.

As blemish in any degree would destroy the beauty of the grain of the wood, bright, stain-free stock is highly desirable for a large variety of uses requiring a natural finish. But for many purposes where the wood is to be covered, stained, or painted, and where conditions of exposure permit the use of sapwood, there is no reason for

Forest Products Laboratory Technical Note No. 184.

discriminating against blued stock if it is free of decay. The following list of present or suggested uses for blue-stained material is to be applied under the restrictions stated above and according to best judgment in each case:

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While the utilization of blued stock is recommended with certain limitations, it must be remembered that the practical solution of the problem lies in finding efficient methods of preventing the blemishes caused by these mold organisms rather than in allowing the blemishes to appear and later finding uses for stained wood.

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