Coating lumber to prevent end checking

Nov. 8, 1938. μ. gray 2,136,351

COATING LUMBER TO PREVENT END CHECKING

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INVENTOR.

Patented Nov. 8,1938

2,136,351

UNITED STATES PATENT OFFICE

2,136,351 COATING LUMBER TO PREVENT END CHECKING

Milton Gray, Memphis, Tenn., assignor to E. L. Bruce Company, Memphis, Tenn., a corporation of Delaware

Application June 14, 1937, Serial No. 148,152 1 Claim. (CL 91—68)

My invention relates to the treatment of lumber to prevent what is known as “end-checking”. This object is attained by coating or sealing the transverse end of the lumber with a suitable 5 composition, preferably an asphaltic plastic composition. Lumbermen have sought for a long time, for a suitable and effective material that would stop end-checking. This is because end checks develop into longitudinal splits and in 10 handling, a split tends to become longer and eventually depreciates the value of the piece of lumber.

Checking in wood, which means wood that has opened up or cracked, is caused by a tension 15 stress in the outer fibers when they dry faster and attempt to shrink more than the portion located more nearly in the center. If the drying process is sufficiently retarded, these stresses do not operate to such an extent that they will 20 be of sufficient force to open up the wood or split it. Accordingly, if a satisfactory way can be found that prevents the rapid loss of moisture from the wood and spreads it over a longer period of time, the drying out process is more uni25 form as to different parts of the wood.

Since lumber dries more rapidly through the ends than between the ends, this more rapid drying increases the tendency to checking at the ends. If the ends can be prevented from check30 Ing, this cuts down the longitudinal checks for a space back from the end surface sufficiently to keep such longitudinal checks from developing into end checks.

The material that I apply to the ends of the 35 lumber in order to prevent checking should be plastic, adhesive, not completely moisture proof, water repellent, have a reasonably high resistance to solar rays so that it will not soften and run under high atmospheric temperatures and 40 not crack or become brittle at low atmospheric temperatures. It should also expand and contract without cracking.

Various types of compositions having these physical characteristics, may be used for this 45 purpose, but one that I have found satisfactory , after extensive use is compounded as follows:

I melt together a mixture of three different types of Mexican asphalts, 99.7% soluble in CSs, and in the following proportions:

Percent

235-250° F.\(M. P.)______ 7

160-170° F. (Μ. P.);53

120-130° F. (Μ. P.)40

When so compounded, the base asphalt pro duced has a melting point of 135-150° F. and penetration at 77° F., 30 c. m„ minimum and 50 c. m. maximum.

The final composition contains 51% of the above asphalt mixture, 34% of XXXX asbestos 5 fibre and 15% of mineral spirits. The product is usually made by adding one half of the solvent to the asphalt mixture, then adding the fibre and after this has been thoroughly mixed, the balance of the solvent is added. The blend of 10 the different types of asphalt provide a base having the desired physical properties, especially after the solvent has evaporated. The asbestos fibre absorbs the liquefied asphalt to which the solvent has been added. The asphalt Itself ab- 15 sorbs and retains a large percentage of the solvent. The fibre absorbs the liquefied asphaltsolvent mixture, and in this manner it prevents this mixture from penetrating the fibrous structure of the wood. This mixture while sticky and 20 cementicious, is not liquid. Another function of the fibre is to make the mixture flexible and plastic after the solvent has evaporated! The fibre adds to the stability of the mixture and prevents any sag of the mixture. It also bridges 25 the cracks and pores, thus preventing the asphalt from “sinking” into the crevices and pores. It also increases the resistance to the heat of solar rays which would otherwise cause the material to run under intense solar heat. 30

This product is not moistureproof, but it is waterproof, and it is only waterproof to the extent that it will shed and not absorb during heavy rains. However, under pressure, water will transfer through the plastic layer. Through 35 this layer escape of moisture will be retarded but not prevented. The solvent makes the mass more workable and also causes the product to stick better to the end of the wood.

This composition is plastic when used and can 4C be applied to the transverse ends of the lumber by a putty knife or similar tool, in a layer of substantial thickness, running from about A of an inch to A of an inch.

The composition is effective to prevent end 45 checking in field or kiln drying of lumber and timber.

Referring to the drawing,

Fig. 1 is a perspective view of the end portion of a piece of lumber, with the layer of coating 50 broken away; and

Fig. 2 is a section on the line 2—2 of Fig. 1.

The piece of structural lumber I, has applied over the entire end, across the grain of the wood, the coating 2 which is sufficiently plastic, so as 55

2,136,361 to be spreadable and adhere to the wood. The coating 2 when applied is from A to A of an inch thick. After the solvent has evaporated, the dry coating is not sticky. While it has a certain δ amount of rigidity, it never gets real hard or brittle and is plastic enough so that it can be cut with any sharp edge cutting tool.

When dry, the composition has sufficient adherence to the wood and has sufficient tensile 10 strength, to prevent to a considerable degree, the growth of very small cracks into larger ones. This is true where the check is in the ends and is very small. The corresponding force required to hold the check together is also small. In this 15 respect, the asbestos fibres which are interlaced in the composition, serve to increase the tensile strength of the composition, when dry.