WO1997037821A1

WO1997037821A1 - Impregnated moisture-resitant laminated veneer lumber product and method

Info

Publication number: WO1997037821A1
Application number: PCT/CA1997/000223
Authority: WO
Inventors: I. Bruce Buchanan
Original assignee: Buchanan I Bruce
Priority date: 1996-04-10
Filing date: 1997-04-09
Publication date: 1997-10-16
Also published as: CA2178529A1; AU2282697A

Abstract

Moisture-resistant laminated veneer lumber is made by forming a laminated veneer lumber article and impregnating it under pressure with an aqueous solution of a preservative such as chromated copper arsenate or as boron-based preservative. Disclosed articles are decking boards, floorboards and structural lumber such as joists. The laminated veneer lumber can be impregnated with very high amounts of preservative, making it usable for wet environments.

Description

IMPREGNATED MOISTURE-RESISTANT UMINATED VENEER LUMBER PRODUCT AND METHOD

Field of the Invention

This invention relates to a novel piece of lumber for use in situations where dampness is encountered, and to a method of making it. The invention also relates to a novel flooring product for use on wood decks or porches and the like which are exposed to the elements, or for use in damp locations, such as in contact with the concrete floor of a basement or the like.

Background of the Invention Decking boards are a known type of lumber which is intended for use in exterior floor constructions, such as a wood deck or porch floor. Decking boards are made by sawing lumber from a log, kiln drying the lumber, then treating the lumber by forcing a preservative under pressure into its pores. Usually, the preservative is a chromium-containing compound, with one of the most common preservatives being chromated copper arsenate.

Decking boards typically have a rectangular cross-section. Often, there are one or more longitudinal grooves scored in the bottom face of the board, so that, if water does get into the board and it begins to warp, stresses can be released, thereby reducing warping of the upper surface. Decking boards are usually made in a standard size which is 1 Vi" thick and 5 Vi" wide. Various lengths are provided.

Typically, when a deck is to be constructed, posts or uprights are set into the ground, to extend upwardly. On top of these posts or uprights a frame is assembled of joists. The joists are usually placed on edge on the top of the uprights or posts, and are assembled into a rectangular frame, or other shape of frame as desired. The decking boards are then assembled by nailing them onto the joists with parallel spaces between adjacent boards so that water can fall through.

Where flooring is to be laid on a potentially damp surface, such as a concrete basement floor, a frame of joists is also made to space the flooring from the floor. A subfloor, which is usually plywood, is then nailed onto the joists, and a flooring surface, such as tongue and groove lumber, is nailed onto the subfloor. The purpose of using joists in this case is to space the subfloor and flooring from the damp concrete, to reduce the likelihood of rotting of the floor and subfloor.

Joists and decking boards made of sawn lumber are sometimes treated with a wood preservative to inhibit rotting, if the decking boards or joists are to be used in damp environments. However, it is frequently difficult to get good and uniform penetration of the preservative into the wood, with the result that sometimes some portions of the wood are less well protected than others.

Besides sawn lumber, another type of lumber is known. This is called laminated veneer lumber, or LVL. In LVL, veneers of wood are laid together, usually with their grain all going in the same direction, although it is known sometimes to put in one or more layers of the grain at right angles as well. LVL is typically made in long lengths of rectangular cross-section. Typically, the cross section is made to be the same as common sizes of structural sawn lumber. LVL tends to be stronger and more uniform in its properties than sawn lumber of the same cross-sectional dimensions.

Brief Description of the invention

The invention comprises in one embodiment a piece of laminated veneer lumber impregnated with an anti-rotting wood preservative. The lumber comprises a top outer veneer, at least two interior veneers and a bottom outer veneer. Preferably, there are at least three and not more than thirteen inner veneers, so that the total number of veneers making up the piece of lumber is from five to fifteen. Preferably, the interior layers are all veneers which have their grains aligned in the longitudinal direction of the lumber. The lumber is treated with a wood preservative to inhibit rotting. Optionally, it is also treated with a paraffin wax to fill pores and to make it more water resistant. In one embodiment, the lumber is dimensioned as a decking board. In another embodiment, the lumber is dimensioned so as to be suitable as a joist or beam for use in damp environments. In a third embodiment, the lumber is formed as a floorboard with complementary interlocking shapes on its longitudinal edges. The preferred such floorboard has on one side of its transverse profile a tongue, and on the other side a groove to mate with the tongue, so that adjacent boards can be assembled together in a tongue and groove relationship. In other embodiments, the lumber is formed as a floorboard with non tongue and groove complementary interlocking shapes.

The invention also relates to a method for making moisture-resistant laminated veneer lumber, which comprises selecting at least four veneer sheets, drying said veneer sheets if necessary, gluing them together in face-to-face relationship to make a billet, sawing the billet into boards and treating the boards with a wood preservative. The invention also includes a method for making a floorboard, which comprises following the method for making moisture -resistant laminated veneer lumber as given above, and additionally profiling the lumber, before treatment with said wood preservative, so that it has complementary shapes on opposed longitudinal edges, whereby adjacent like boards can be assembled together tightly. A preferred arrangement has a tongue on one longitudinal edge and a groove on the opposing longitudinal edge, said tongue and groove being sized for mating, such that adjacent boards having the same profile can be assembled in tongue and groove relation. The invention also comprises a wood deck, which has upright members supporting a substantially horizontal frame of joists, with decking boards made as aforesaid nailed to the joists. Preferably, the joists are also made as aforesaid from LVL which has been treated with a wood preservative agent.

Description of the Drawings The invention will be further illustrated with reference to the drawings in which:

FIGURE 1 (which comprises SUBFIGURES 1A to 1G) is a schematic diagram of a process for making structural lumber, deck boards or floorboards according to the invention. FIGURE 2 is a perspective view of a decking board according to the invention.

FIGURE 3 is a perspective view of a deck made according to the invention, with some boards removed to show structure.

FIGURE 4 is a perspective view of a floorboard according to the invention

FIGURE 5 is a perspective view of a floor made with the floorboards according to the invention

FIGURE 6 is a detail of Figure 5 along the lines 5 - 5 FIGURES 7 and 8 are end views of two other embodiments of floorboards according to the invention

Detailed Description of the Invention

According to the invention, a piece of structural lumber, a decking board or a floorboard is assembled from veneers, with optional other layers as described below The veneers are made in known fashion by peeling logs For example, veneers can be made using machinery supplied by Durand - Raute Industries Ltd of New Westminster, B.C Such equipment includes debarking machinery for removing the bark from logs, lathes or spindleless lathes for turning the logs and peeling a veneer of substantially constant thickness from the logs, and veneer drying equipment for drying the veneers

The veneers are dried in a veneer drier if necessary to ensure that they are sufficiently dry so that the glues used for assembling the veneers together will bond Typically, most glues used for assembling veneers do not bond well when more than about 10% water content is in the veneers Therefore, it is usually desired to dry the veneers to a water content of below 10%, preferably about 7 - 8%

After drying, veneer sheets are chosen for assembly At least four veneer sheets are chosen These will be glued together in face-to-face relationship The number of sheets chosen to be assembled to form the product will depend on what its ultimate use will be, and also to some extent on aesthetic factors The sheets, once glued together, are known as plies A minimum of four plies is needed to give the product strength Generally, strength increases with the number of plies, if all plies are of the same species and wood quality The quality and the species of the wood also affect strength as is well known in the LVL art

Usually, there is not much advantage to having more than 15 plies, particularly as it becomes harder with increasing numbers of plies to apply heat and pressure evenly to bond the adhesive, It is generally preferred to have from 5 to 12 plies, depending on the intended use Floorboards which are to be laid on a subfloor need no more than 4 or 5 plies Floorboards which are to be laid directly onto joists with no subfloor preferably have 5 to 12 plies, depending on the intended distance to be spanned and the wood used Structural lumber such as joists, beams or posts preferably have from 6 to 12 plies depending on the weight they are to bear For aesthetic and customer acceptance reasons, it is often preferred to use a number of plies which gives rise to a thickness dimension equivalent to that of sawn lumber for the same application. Customers are reassured about the strength of the product when it is as thick as a product they have already used, and the same thickness permits it to be used interchangeably with sawn lumber products

The sheet which will form the top outer face of the product is preferably chosen to be one which is substantially free of blemishes and knots The reason that such a veneer is chosen is because a knot or blemish might be an entry point for water and it is therefore not desirable to have it on an exposed face It is also preferred that the sheet which will form the bottom face of the board also be substantially knot and blemish free if the product is structural lumber so that the top and bottom faces will be interchangeable. For decking boards and floorboards, it is especially preferred that the top veneer be knot and blemish free, as these are the surfaces that will be seen and walked on by users However for these uses, it is not as important that the bottom face be knot and blemish free, , as the sheet forming the bottom face will usually be facing downwards after assembly, so water will run off it, and it is not likely to be as visible in most uses

The veneers chosen preferably all have their grain running in the same direction, in the direction which will form the longitudinal direction of the finished product As is known in the art, each veneer has two different faces, known as the "tight" and "loose" face The "tight" face is the surface which was farther away from the centre of the log when the veneer was peeled from the log Wood fibres tend to be closer together on this face than on the opposite, or "loose", face It is preferred, as known in the LVL art, to arrange (or "lay up") the veneers so that loose faces are glued to loose faces, and tight faces are glued to tight faces, as this is found to reduce splitting, cracking or curling of the product and its external veneers.

Preferably, the veneers are of conventional thickness, being either 1/10",

1/8" or 1/6". Preferably also, all veneers are of the same thickness in any one board.

The veneers are not crushed appreciably during manufacture of the board product, so the finished product has plies of approximately the thickness of the veneers chosen.

It is possible to replace one or more of the veneer sheets with a sheet of some other suitable material. For example, a sheet of oriented wood strands glued together, such as is used in the making of oriented strand board (OSB) can be used.

However, if one or more OSB sheets replace one or more veneer layers, these sheets should be made with a substantially water resistant glue, and should have compounds which impart water resistance incorporated in them at the time of making of the sheet. Replacement of a veneer sheet with another material, or orienting veneer sheets so that they do not all have their grain oriented in the longitudinal direction of the boards to be made, are not usually preferred, as the boards exhibit sufficient strength for their purpose without the need of such expedients. Obviously, the OSB sheet should not replace the top veneer, particularly in decking and flooring uses, as it is desirable to have a hard wearing and aesthetically pleasing wood veneer surface for the floor.

Each of the interior veneers is coated on both faces with adhesive, and each of the top and bottom veneers is coated with adhesive on the face which will contact the face of an interior veneer. Alternately, it is possible to coat only one of each pair of mating faces. For example, the top face of each of the veneer sheets except the topmost one can be coated.

The adhesive should be one which is moisture resistant after it bonds. It is preferred to use a thermo-setting adhesive which is not sticky until heat activated, as this facilitates the handling and positioning of the sheets. Suitable adhesives are phenolic adhesives, such as phenolic PF20/20, manufactured by the Borden Chemical Company of Belleview, Washington, or phenol resorcinol adhesives, such as LT75 (trademark) manufactured by the Borden Chemical Company of Belleview, Washington. It is also possible to use isocyanate adhesives, but these are generally not preferred because they are more costly than the phenolics or phenol resourcinols. There are certain advantages to use of isocyanates, however, as they can cure faster under heat and pressure than the phenol resorcinol or phenol formaldehyde glues, and because they are moisture resistant. A suitable isocyanate glue is PMDI, manufactured by ICI Chemicals Ltd., which is a polymethyl di-isocyaπate glue.

The amount of adhesive coated on the faces of the veneers is as is known in the art of LVL manufacture, and follows the recommendations of adhesive manufacturers recommend how much of their particular adhesive should be applied. For example, when phenolic PF 20/20 (trademark) adhesive is used, the recommended coating is 30 to 34 pounds per 1000 square feet of surface to be bonded.

After the adhesive is coated onto the faces of the veneers, the veneers are assembled in face-to-face aligned relationship. They are then held together with heat and pressure to bond the adhesive. Suitable temperatures and pressures are those recommended by the adhesive manufacturer. For example, when phenolic adhesives are used, a pressure of about 180 psi is preferably applied to the sheets at a temperature of about 300°F. When phenol resorcinol adhesives are used, a pressure of about 180 psi is preferably applied to the sheets at a temperature of about 200 degrees F.

After the sheets have been bonded together, they are sawn into strips, suitable for the intended final use. If the intended final use is a decking plank, it is desirable to have a plank which is generally as thick as the planks commonly used, so that users will not be concerned about the strength of the plank by reason of its thinness. Thus, where 1/8" veneers are used, 9 or 10 of such veneers are preferably glued together, so that the resulting product will have a thickness of between 1 1/8" and 1 1/4". This is approximately the same thickness as normal decking boards. Therefore, users will tend to believe that the boards are capable of carrying their weight. Where the board is to be a joist, the thickness is determined by the weight which the joist is to support, and by the distance apart of the upright supporting the joists. Typically, 1/8" veneers are used, from 6 to 8 veneers would be used for a joist, and upright supporting joists would be spaced about 3' apart.

The width of the strips into which the billet is sawn depends upon the ultimate use. As it is common to have 5 1/2" wide decking boards, boards intended for this purpose are conveniently sawn to a width of 5 1/2". If the product is to be a joist, post or beam, different widths may be used such as, for example, nominal 6" or nominal 8" widths (which are actually 5 1/2" and 7 1/2" respectively). If the board is to become a floorboard, it is sawn to a desired width for flooring, which would typically be between 1" and 4". The width to which it is sawn is slightly greater than the desired width of the finished floor board, to provide some extra material for the making of the tongue in a subsequent step. This subsequent step is carried out immediately after, using a moulder or profiling saw. The strips are passed tnrough this saw, so that a tongue is placed in one longitudinal edge of the strips, and a matching groove in the opposite longitudinal edge of the strip.

Once they have been sawn to the desired sizes, the strips are dried if necessary to a desired humidity level. The desired humidity will depend on the climate in which the flooring is to be used. It is generally desirable that wood products have a humidity level which is not greater than that of the surrounding air, to prevent them from drying out and cracking. For most climates, a humidity level of 15% to 18% is satisfactory. Humidity levels can be determined by taking a small sample of the product, weighing it, heating it until all water is driven off, and weighing it again. The loss in weight is equivalent to the weight of water in the original sample, and from this the % moisture content of the original sample can be calculated. In some cases, the humidity level of the wood is already at an acceptable level, and drying is not necessary.

Where drying is appropriate, this can be done in a drying kiln if desired, but it is usually quicker to remove moisture by applying a vacuum. To do this, the strips are loaded into a pressure vessei. In the pressure vessel, a vacuum is created to remove moisture from the wood. The exact amount of vacuum is not critical.

Generally, a vacuum treatment of from 15 to 50 minutes at an air pressure of 15 to 20 inches of mercury is found suitable, depending on the moisture content of the wood.

After the vacuum has been maintained for a sufficient time to reduce the humidity in the wood to a desired level, the preservative is added as a water solution, at ambient temperature (usually about 40° to 70° F depending upon the time of year.)

The chamber is pressurized to aid absorption of the preservative. Suitably the pressure is raised to more than 75 psi, and preferably to about than 200 psi. A particularly preferred procedure is to start addition of the preservative solution while there is still a vacuum in the chamber, and gradually to add air along with the preservative solution until the desired pressure is reached. A particularly preferred preservative is chromated copper arsenate, which is sold as a solution of 50% chromated copper arsenate in water by the Hicksoπ Company of Atlanta Georgia, U.S under the trademark WOLMANAC. This is diluted with water to a solution of about 2-3% chromated copper arsenate before use. Another suitable preservative is a boron based preservative sold under the name ACQ by the Chemical Specialties Company. Treatment with preservative is conveniently carried out at ambient above-freezing temperatures.

During the treatment with the wood preservative, optionally a paraffin wax may also be added in the treatment water. The paraffin wax enters any voids or cracks in the wood, to reduce the likelihood of water penetration into the finished product. Suitably, therefore, the solution for treating the product with preservative contains 2% to 3% of preservative and 1 % to 2% of paraffin wax. The paraffin wax must be one which is soluble in water in these percentages, if it is to be applied as part of the preservative treatment step. If a harder, less soluble paraffin wax is used, the paraffin- wax mixture may be heated slightly so that the wax is soluble in it, or the paraffin wax can be applied as a separate, subsequent treatment, by a spray of the wax dissolved in an organic solvent.

Optionally, a wood stain can be introduced into the wood at the time of the pressure treatment as well.

It is found that the side and end edges of the veneers absorb the preservative and wax very readily. The top and bottom faces of the veneers (being whole sheets, and being cut radially to the tree) do not absorb as readily, but, since the whole face is exposed to the solution, there is appreciable absorption. The net result is that larger amounts of preservative are absorbed than would typically be absorbed by sawn wood at the same temperature, pressure and preservative concentration. For example, a treatment for 50 minutes at 200 psig and 50 °F with WOLMANAC (trademark) chromated copper arsenate at a 3% concentration has been found to impregnate a 9 veneer decking board of lodgepole pine with an amount of approximately 65 pounds of preservative per 1000 cubic feet of decking board., This amount meets or exceeds the standards issued by the preservative manufacturer for preservative recommended to be incorporated in sawn lumber to be used in wet exterior environments.

Shorter treatment times can of course be used if the intended use of the product does not warrant impregnating the wood to this concentration. Thus, flooring on a basement floor, which might be subject to occasional dampness, need not have preservative concentrations which are this high, whereas exterior deck flooring, which is exposed to rain, snow and ice, preferably has a somewhat greater preservative concentration than the basement flooring. Generally, it is desirable to impregnate with a preservative amount at least as great as that recommended by the preservative manufacturer for sawn lumber in the intended use. Particularly preferable amounts of chromated copper arsenate (dry weight) are at least 30 pounds per thousand cubic feet of lumber where the lumber is to be subjected to occasional dampness, or 60 pounds per thousand cubic feet of lumber where the lumber is to be subjected to large amounts of moisture, such as uses involving contact with moist ground or rain and/or snow. The preferred amount of ACQ (trademark) boron preservative is at least 0.25 pound (dry weight) of preservative incorporated per cubic foot of lumber. After the pressure treatment, it is preferred to remove air from the pressure vessel until a slight vacuum, such as an absolute pressure of 20-25 inches of mercury, ensues. This is convenient because it causes the preservative solution which is on the surface of the product to evaporate, thereby reducing dripping as the product is handled. After several minutes of slight vacuum, the pressure vessel can be returned to atmospheric pressure, and the treated product can be removed for use or storage.

Figure 1 shows the process of the invention in a diagrammatic form. Prior to carrying out the process of the invention, a veneer sheet 10 is made in known fashion, as by peeling a log 12 using a lathe knife 14 to peel off the veneer (Figure 1 A). This may be done on several types of equipment, such as spindled or spindleless lathes, and does not form a part of this invention. The prevailing grain of the wood is shown schematically at 16. The veneer is split into sheets of suitable size 18 by a suitable knife blade 20. The sheets 18 are then dried in a veneer drier 22 (Figure 1B) if necessary to reduce the moisture level to one at which bonding with a suitable adhesive can take place. As mentioned previously, this is 10% moisture or less for most commercially available adhesives.

Suitable veneers are then assembled for the product which is to be made. This is known as "laying up " the product. In a high speed veneer mill, the lay up is a continuous process, and veneers are joined together end-to-end to make continuous sheets which are run together in an assembly line with the subsequent steps to make very long billets of veneer, which are then cut to size at the end of the assembly line. In smaller, discontinuous, processes, the laying up is done by manually selecting and orienting sheets, As Figure 1 is intended to be diagrammatic of the process, not to show particular apparatus for continuous or discontinuous operation, the illustration will show sheets of discrete size rather than continuous sheets for ease of illustration.

In Figure 1 C, the veneers for a particular product are chosen and "laid up". There is a top veneer 24. As mentioned, this is generally selected as a veneer which does not have many knots or other imperfections. If the product is a flooring product, for interior flooring, the top veneer may also be of a wood which is prized for floor boards, such as birch or maple. Otherwise, the veneer may be any of the species which are usually used in the making of plywood or LVL. As is common in LVL, the grain of at least the majority of the sheets (preferably all of the sheets, as in the illustration) run in the same direction, as shown by grain lines 16. This direction will become the longitudinal direction of the product to be made, In the embodiment shown in Figure 1 , the product is to have a 5 veneer thickness. The bottom veneer 32 is also chosen as being one with few knots or other surface imperfections. T the veneers which will form the interior layers, 26, 27 and 30, need not be of such good quality and for example, in veneer 28 there are several knots 38 shown. In the drawing of veneer sheet 30, it is illustrated that the veneer need not be one single piece. Veneer 30 is actually two veneers 40 and 42 which have been joined together by joint 44. Joint 44 is what is known as a scarf joint, which means that it is cut at an angle to thickness of the wood. Such joints are known in the arts of laminated veneer lumber and plywood manufacture for joining the ends of veneers. Adhesive is sprayed onto the upper surface of sheet 32 by adhesive sprayer 46. It is possible to spray adhesive on only the upper surface of each of the sheets 32, 30, 28 and 26. Alternately, it is possible to spray adhesive onto the upper surface of the sheets 32, 30, 28 and 26 and to have another adhesive sprayer or roller coater (not shown) apply adhesive onto the bottom of sheets 30, 28, 26 and 24.

The five sheets are then assembled in face-to-face relationship, and are subjected to heat and pressure in a press 48. (Figure 1 D) This press 48 has platens 50 and 52 which press the sheets together and activate the thermo-setting adhesive, to form a block-like form 54 known as a billet. This billet is comprised of the glued together sheets (now known as plies).

The billet is then passed through a gang of saws 56, (Figure 1 E) which cut it into strips of the desired width. As mentioned, this width varies with respect to the desired product.

If the product is to be a floorboard, the strip illustrated at 60 goes through a separate profiling step to have a tongue and groove imparted to them (Figure 1 F). A tongue 62 is formed on one longitudinal edge of strip 60 by moulder blade 64 and a corresponding groove 66 is formed on the opposed longitudinal edge by moulder blade 68.

The strips 60 (whether or not a tongue and groove is imparted to them) are then placed in a pressure vessel 70 (Figure 1 G). This is placed under reduced pressure, as discussed previously, to get rid of moisture. Then, preservative is directed against the strips from nozzles 72 and the pressure is gradually raised to approximately 75 - 200 psi. The pressure is kept at this value for a sufficient time to ensure sufficient impregnation of preservative for the intended use. For example, if the strips are to be decking boards exposed to year-round weather conditions, impregnation of about 30-60 minutes at 150-200 psig is desirable, whereas tongue and groove floorboards, which are intended to withstand only occasional moisture, can be impregnated for about 20- 40 minutes at 100 - 150 psig. Suitably, the impregnation is for long enough, and at a high enough pressure, so that from 5 to 70 pounds of preservative (dry weight) per thousand cubic feet is added to the strips, with the amount being selected according to the preservative manufacturer's recommendations with respect to sawn lumber for the particular preservative and intended use. As noted, at least 30 pounds per thousand cubic feet is preferred, with at least 60 pounds per cubic feet if the product is to be exposed to rain, snow or damp ground. More than 70 pounds per thousand cubic feet could be impregnated into the lumber in many cases, but the added moisture resistance will seldom justify the increased time and cost.

As discussed, optionally the preservative solution can also contain a wax and a colorant.

After the treatment with preservative, the strips are stacked for drying, and are ready for their intended use.

Figure 2 shows a decking board according to the invention. In the embodiment illustrated, it has 9 plies. To show the plies of the board clearly, the thickness has been greatly over-emphasized with respect to the length and width.

Typically, such a board would be about 5 1/2" in width, 1 1/8" in thickness (i.e. nine times the ply thickness of 1/8") and would have a length of from 2 to 20'.

The board is shown at 100. There is a top ply 102, and 8 other plies, generally indicated as 104. In some cases, pieces of veneer have been joined end-to- end to make a ply by either a scarf joint, as shown at 106, or a butt joint (vertical to the surface of the ply) as shown at 108.

Figure 3 shows a deck made using decking boards of the invention. Into ground 150 are inserted posts 152, which can be ordinary treated wood posts or can be wood posts made of treated LVL according to the invention. Joists 154 are assembled to form a frame with crosspieces 156 and longitudinal pieces 158. The frame is shown as being rectangular, but can be of any convenient shape. This frame is covered with decking boards 100 to form a deck. For clarity, only part of the frame is shown as covered.

Because of the increased strength of the decking boards 100 over conventional decks, it is possible to space the joists farther apart than it is in most conventional decks, assuming that the decking boards are of approximately the same thickness as normal decking boards. Thus, in the deck shown here, the joists numbered 158 and 160 are spaced 30" apart, which would not be an acceptable spacing for conventional decking boards. However, a decking board of 1 1/8" thickness made of 9 plies according to the invention can accept this spacing, and can support without failure the weight of a reasonable number of persons walking on the deck.

The joists 154 can also be made from strips produced according to the invention. As illustrated, the joists are laid on edge. Typically, they will be of a thickness of about 1 1/2" (nominal 2" thickness) and a width of 7 1/2" to 11 1/2" (nominal 8" to 12". Because they are treated with wood preservative according to the invention, they will be resistant to rot, even if water or snow builds up on their edges between the decking boards.

Figure 4 shows a floorboard according to the invention, with a tongue and groove profile. This board has 9 plies, although floorboards of as few as four plies could be used where lesser strength can be tolerated. To show the plies of the board, the thickness has been greatly over-emphasized with respect to the length and width. Typically, such a board would be about 2" in width, 1 1/8" in thickness and would have a length of from 2* to 20'.

The board is shown at 170. There is a top ply 172 of a wood having good wearing properties and good appearance, and 8 other plies, generally indicated as 174. In some cases, pieces of veneer have been joined end-to-end to make a ply by either a scarf joint, as shown at 176, or a butt joint (vertical to the surface of the ply) as shown at 178. A tongue 180 runs longitudinally along one side edge of the board, and a groove 182 runs along the other side edge. The tongue and groove are sized so that when two similar boards are placed side by side, the tongue of one fits into the groove of the other. The tongue is large enough so that it is formed of more than one ply (to improve its strength), and in the illustration it is formed of three plies.

Figure 5 shows flooring made according to the invention in place on a concrete floor 200. A frame of joists 254 comprising crosspieces 256 and longitudinal pieces 258 is laid directly on the concrete floor. As the joists have been treated by inclusion of the wood protector to be resistant to rotting,, they will not rot even if the floor is occasionally damp. Tongue and groove floorboards 170 made according to the invention are laid directly over the joists. The detail in Figure 5 shows how they are nailed to the joists by nails 204 which are nailed through the bottom of the grooves into the joists. One nail 206 is shown in position where the nailing has been commenced but not yet completed. This nailing technique is the same as is used in attaching tongue and groove floor boards to a subfloor. However, because of the strength of the floor boards made according to the invention, no subfloor is needed.

The flooring according to the invention can be of any thickness which is suitable for the spacing between joists 258. If the joists 258 are spaced on 16" centres from one another, a floor board of 5 plies of 1/8" veneer is suitable, making a thickness of 5/8", when the top veneer is birch and the remaining four are lodgepole pine. If wider spacings are preferred, such as 24", then 9 plies, for a total of 1 1/8" is preferred, if the top veneer is birch and the others lodgepole pine. Suitable numbers of plies will be obvious to one skilled in the art, having regard to the wood species available for making the veneers and the desired spacing of joists 258.

The flooring of the invention, having been treated with the wood preservative, need not be protected by a subfloor or vapour barrier from moisture which may arise from the concrete of the basement floor. Therefore, a much simpler construction technique can be used. It is also possible to assemble the tongue and groove flooring directly on the basement floor, without using joists 254, 256, 258 at all. In this case, the pieces of flooring are not nailed to the concrete, except where the edge of a floor occurs, to reduce the amount of concrete nailing required.

The flooring disclosed to this point in the disclosure has a conventional mating tongue and groove. This is preferred because it is a pattern which is familiar to flooring installers, and also because it lends itself to nailing as shown in Figure 4. However, other mating profiles can also be made according to the invention, by using a moulder of a different profile. For example, board 290 having a double tongue and groove arrangement as shown at 291 in Figure 7, or board 300 having an interlock arrangement 301 as shown in Figure 8, or any other desired longitudinal edge profile can be made, by using a moulder with the desired configuration. With these profiles, adjacent boards are joined by applying adhesive to their edges, or by nailing through the thickness of the boards as shown by the dotted nail at 292 in Figure 7, or by nailing through a portion of the interlock if the interlock design permits this, as shown by the dotted nail at 302 in Figure 8. Other interlocking shapes will be evident to persons skilled in the art in the light of this disclosure. The invention as it regards floorboards therefore comprises any LVL floorboards which have interlocking edges so that they can be assembled in side by side relationship, and which have been impregnated with a wood preservative.

It will be seen that the product of the present invention provides for the manufacture of decks and floors in damp environments which have both less material and less labour cost than conventional decks or floors.

While the foregoing has disclosed various embodiments of the invention, it is not desired that the invention be limited by the particular embodiments disclosed, but instead that it be limited as set out in the attached claims.

Claims

What is claimed is:

1. A piece of laminated veneer lumber impregnated with sufficient amount of a wood preservative to reduce rotting.

2. A piece of laminated veneer lumber as in claim 1 , in which the wood preservative is chromated copper arsenate.

3. A piece of laminated veneer lumber as claimed in claim 2, in which the chromated copper arsenate is present in an amount of at least 30 pounds per thousand cubic feet of lumber.

4. A piece of laminated veneer lumber as claimed in claim 2, in which the chromated copper arsenate is present in an amount of at least 60 pounds per thousand cubic feet of lumber.

5. A piece of laminated veneer lumber as claimed in claim 1 , in which the wood preservative is a boron based preservative.

6. A piece of laminated veneer lumber as claimed in claim 1 , additionally impregnated with a paraffin wax.

7. A piece of laminated veneer lumber as claimed in claim 1, said piece being dimensioned as a board, having an upper face, a lower face, two ends and two longitudinal edges, the faces being the faces of veneer layers and the width of the face being at least four times as great as the thickness of the board, and the veneer forming the uppermost face of said board being substantially free of knots and imperfections.

8. A piece of laminated veneer lumber as claimed in claim 1 , said piece of lumber being a floorboard having an upper face, a lower face and two longitudinal edges, said upper and lower faces being the faces of veneer layers, and complementary shapes on opposite longitudinal edges, said complementary shapes being shaped so that such shapes will matingly engage with the corresponding shapes of like floorboards laid alongside.

9. A piece of laminated veneer lumber as claimed in claim 1 , in which said complementary shapes are a tongue on one longitudinal edge and a groove on the other longitudinal edge, the groove being sized to mate with a like tongue.

10. A piece of laminated veneer lumber as claimed in claim 1 , comprising a top outer veneer, at least three and not more than eleven interior veneers and a bottom outer veneer, said veneers being joined together in face to face relationship with an adhesive which is resistant to moisture.

11. A piece of laminated veneer lumber as claimed in claim 10, in which all layers including the outer faces are wood veneers having their grain in the longitudinal direction of the piece of lumber.

12. A piece of laminated veneer lumber as in claim 10, in which the wood preservative is chromated copper arsenate.

13. A piece of laminated veneer lumber as claimed in claim 10, in which the chromated copper arsenate is present in an amount of at least 30 pounds per thousand cubic feet of lumber.

14. A process for making a laminated veneer lumber article, which comprises :

(a) selecting at least four veneer sheets

(b) gluing said veneer sheets together in face to face relationship to form a billet, using a glue which is moisture resistant when bonded, at least the majority of such sheets being oriented so that their grain runs in the same direction;

(c) sawing the billet in a direction parallel to the grain of said majority of said sheets to form linear veneer lumber,

(d) impregnating said linear veneer lumber with a wood preservative in a sufficient amount to reduce rotting induced by dampness.

15. A process as claimed in claim 14, including, prior to the step of impregnating, the step of profiling the linear veneer lumber to provide complementary shapes on the longitudinal edges thereof, whereby pieces of such lumber with complementary shapes can be assembled together tightly in side by side relationship.

16. A process as claimed in claim 15, in which the complementary shapes are a tongue on one longitudinal edge and a groove on the opposite longitudinal edge.

17. A process as claimed in claim 15, in which the uppermost of the veneer sheets is a wood commonly used for floor surfaces.

18. A process as claimed in claim 15, in which the uppermost veneer is substantially free of knots, holes and imperfections.

19. A process as claimed in claim 14 in which the wood preservative is chromated copper arsenate.

20. A process as claimed in claim 19, in which the chromated copper arsenate is impregnated into the laminated veneer lumber in an amount of at least 30 pounds per thousand cubic feet of lumber.

21. A process as claimed in claim 19, in which the chromated copper arsenate is impregnated into the laminated veneer lumber in an amount of at least 60 pounds per thousand cubic feet of lumber.

22. A process as claimed in claim 19, in which the wood preservative is a boron based preservative.

23. A process as claimed in claim 19, additionally comprising the step of impregnating said lumber with a paraffin wax, either simultaneously with or after impregnation with the wood preservative.