DESCRIPTION TECHNICAL FIELD This invention relates generally to building construction techniques, and more specifically to an improved method for constructing curvilinear structures. BACKGROUND ART

Traditionally, buildings have been erected in generally rectangular configurations with the use of lumber, bricks, blocks and the like. These are rigid materials and may be most easily shaped with straight sides and square corners, which tends to require that structures built with such materials also have the same straight sides and square corners of rectangular configurations. Structures built from these materials have relatively low energy efficiency and require a high level of maintenance. They also tend to be fragile, and are more susceptible to storms, earthquakes, and fire than are other building shapes and other construction materials.

It is well known that curvilinear structures (such as domes) provide numerous benefits in structural integrity, longevity, and design flexibility. Structures with curved walls resist earthquakes, high winds, snow loads, leaks, and the like, and are extremely energy efficient. However, the construction of curvilinear structures has been problematic.

Materials such as reinforced concrete can be molded into curved shapes, but forms are required to shape

and support such materials in their initial fluid or plastic state. Since concrete forms have been generally constructed of lumber, it has been simpler and more economical to maintain the inherent rectilinear shape in the fabrication of forms and hence rectilinear concrete structures. Construction of wooden (or other material) forms in complex curved shapes requires a great expenditure of materials, cost, time, and effort. In addition, building construction using concrete has necessitated the erection of two structures: first, wooden, foam, or other forms are built; and second, the concrete is poured, pumped, or sprayed and is temporarily held in place by the forms, then the forms are removed and recycled or discarded. Previous curvilinear structure construction utilized prefabricated components or standardized parts limiting design flexibility and strength, and thus did not allow for modifications or adjustments during the construction process. Also, previous inventions primarily required the use of off-standard utilities because the resultant structures had no flat walls. For example:

1. GEODESIC DOMES are usually made of wood; lack design flexibility; may constitute a fire hazard; use prefabricated panel kits or hub systems, which create waste from endeavoring to construct triangular elements from rectangular materials; result in a conventional home built in a round space; have off- standard utilities because there are few flat walls; and the building technique does not allow modifications during

the construction process.

2. AIRFORM-CAST CONCRETE STRUCTURES are ecologically dangerous because they primarily use fluorocarbons that are damaging the ozone layer and are being outlawed; lack design flexibility; have virtually no flat walls; require specially trained workers to build; are a complex construction; and require specialized equipment and materials. The inflatable membrane method lacks control of height uniformity. 3. STRUCTURAL FORM-CAST CONCRETE

STRUCTURES such as those described in Pearcey et al. U.S. Patent Number 4,352,260 provide a pre-fabricated system consisting of a steel skeleton which serves both as the forming system and as structural members in the finished structural shell, but these lack design flexibility and have architectural limitations, are more costly than curvilinear structures, have limited openings, and the building technique does not allow modifications during the construction process.

DISCLOSURE OF INVENTION

The method of constructing curvilinear structures of this invention utilizes a precision armature system including a central armature mast portion, which accepts one or more armature booms, each comprising a vertically and horizontally rotatable arm terminating in a reinforcing rod (rebar) tying guide member, and associated hardware. The armature boom end may also accept a multiplicity of other end attachments serving a variety of

functions in the construction process.

The tying guide member is aligned with and engages a piece of generally vertical (or vertically- tending) rebar (e.g., from the foundation slab), and a first separate piece of generally horizontal (or horizontally-tending) rebar is placed adjacent and generally perpendicular to the vertical rebar for securing thereto. Alternatively, the order of alignment may be reversed, with the horizontal rebar placed against the tying guide first, followed by the vertical rebar. The armature boom and tying guide may then be rotated generally horizontally to engage the next adjacent piece of vertical rebar, and the first separate horizontal piece is bent inward or outward (or a combination of inward and outward) according to the specifications of the design, and eventually is bent towards the tying guide for securing to the vertical rebar. These steps are then repeated with the same or successive separate pieces of horizontal rebar. As the armature boom is rotated about the mast and progressively raised relative to the foundation, further vertical and horizontal pieces of rebar can be positioned in every portion of their extent at very accurately and precisely defined coordinates in three dimensional space, and can also be brought into juxtaposition at very accurately and precisely defined coordinates in three dimensional space and secured together, thus generating a generally non-planar (e.g., spherical or other curving) grid of rebar. This grid can be based on perpendicularly intersecting rebar members (a

rectangular grid), triangular grid patterns, spiral grid patterns, or other desired grid patterns.

The generally vertical rebar (e.g., from the foundation slab) may be other than truly vertical and instead have only a vertical component (i.e., angled to the foundation) . Collectively, this orientation may be referred to as "vertically-tending". For example, the rebar disposed about the foundation periphery may have a common angle of intersection with the foundation, such as to facilitate some non-rectangular rebar framing pattern (e.g., a triangular grid). Similarly, the generally horizontal rebar used to secure to the generally vertical rebar may be other than truly horizontal and instead have only a horizontal component. Collectively, this orientation may be referred to as "horizontally-tending". Thus the vertically-tending and horizontally-tending rebar elements may intersect at right angles or other than right angles, yielding a variety of patterns or grids, all within the method of this invention. The radial extension of the re--atable arm, and thus the tying guide, is preferably adjustable at any point in the process, thereby enabling the generation of a spherical or non-spherical grid. In addition, the armature boom is preferably vertically adjustable in height relative to the armature mast. The mast and armature boom system determines the accurate and precise placement, in three dimensional space, of the structural reinforcement bar (rebar) and precisely holds and secures the structural rebar in the accurate and precise

location(s) and/or crossing points in three dimensional space which are determined by the structural design requirements. The mast and armature boom system will weave different sizes of rebar and will create virtually any combination of rebar weaves, including rectangular, triangular, spiral, etc. The mast and armature boom system may be used to construct curvilinear and/or free- form structures whose designs may include rebar frameworks within rebar frameworks if desired. The rebar frame thus created is very strong and capable of supporting workers who can stand and climb upon and move about on the woven rebar frame during the construction process. The rebar frame may be adjusted during the construction process at any point prior to spraying of concrete or other material. The mast and armature boom system can be used to check the accuracy of rebar placement at any point during the construction process, including just prior to the spraying of concrete or other material.

A layer of burlap or wire mesh or other generally impermeable material is placed over the rebar grid, and air-entrained concrete (shotcrete) or other suitable hardening-type material is applied to form a rigid shell. Further outside and inside base layers may be applied, and further outside and inside surface layers (such as insulating, acoustic, decorative, or other layers) may also be applied.

Thus, the method of constructing curvilinear structures of this invention provides a simple, fast, and economical construction technique for constructing a

superior one-piece building that is cost-effective and long-lasting. The method provides a much easier and much faster means of precisely placing the rebar which forms the skeleton, or shaping, of the walls, ceilings, and all the structure's surfaces in a very quick manner and which also allows for diversity of design including, but not limited to, domes, elongated structures, domes with open ends and/or open sides, as well as free-form and multi¬ story structures. The method improves the construction process; it creates a building out of a suitably hardening-type material such as air-entrained shotcrete without using disposable wooden forms or foam forms, greatly simplifying the construction process by completely eliminating forms and molds. The method can be used to create structures that are much stronger than traditional structures, using standardized materials such as shotcrete, burlap or wire mesh, and rebar, which together create a very strong, permanent, self-supporting structure. The curvilinear design readily lends itself to a wide variety of decors and styles, e.g., elliptical, semi- elliptical, parabolic, semi-parabolic, conical, hyperbolic, semi-hyperbolic, or free-form, and makes the addition of rooms fast, easy, and cost-effective. The rebar assembly system proves extremely fast and inexpensive to construct and provides tremendous design flexibility for wall shapes before the shotcrete is sprayed. This enables the simple and rapid creation of tremendously complex curvatures, which may also

incorporate conventional right angles, conventional flat walls, shotcrete walls, or hollow block walls. The curvilinear design and construction methods of this invention easily integrates with other structures and can be built with and/or around an existing structure. Any item of virtually any geometry can be integrated into the design and even into the structure itself using the method of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a side elevation view of a simplified precision armature system that may be used in the method of constructing curvilinear structures of this invention, this view illustrating a central armature mast portion, a vertically adjustable and vertically and horizontally rotatable armature boom portion having a boom sleeve and an extendable arm terminating in a reinforcing rod (rebar) tying guide member, and associated hardware;

Fig. 2 is a modified precision armature system that may be used in the method of constructing curvilinear structures of this invention, having a plurality of armature booms laterally supporting a flexible vertical rebar receiving track;

Fig. 3 is a top plan view in partial cross- section of an armature boom end rebar tying guide member used in the method of this invention, illustrating the tying guide member alignment with and engagement of a piece of vertical rebar, with a separate piece of horizontal rebar being placed adjacent and generally

perpendicular to the vertical rebar for securing thereto;

Fig. 4 is a front elevation view of the armature boom end tying guide of Fig. 3, illustrating a vertical rebar receiving channel, horizontal rebar receiving channel, and wire access channel;

Fig. 5 is an end elevation view of a portion of the flexible vertical rebar track of Fig. 2, bearing a vertically arranged plurality of tying guide members for simultaneously securing a plurality of horizontal rebar elements to a single vertical rebar element;

Fig. 6 is a side elevation cross-sectional view of a portion of a curvilinear structure constructed with the method of this invention, and illustrating a foundation slab with a plurality of circumferential rebar elements surrounding a single vertical rebar element; a series of horizontal rebar elements having been attached to the vertical rebar element in accordance with the method of this invention; a burlap or wire mesh layer over the rebar grid; outside and inside base shotcrete layers; and outside and inside surface layers; and

Fig. 7 is a side elevation view in partial cross-section of a curvilinear structure constructed by the method of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Fig. 1 is a side elevation view of a simplified precision armature system 10 that may be used in the method of constructing curvilinear structures of this invention, this view illustrating a central armature mast

portion 12, a vertically adjustable and vertically and horizontally rotatable armature boom portion 14 having a boom sleeve 16 and an extendable arm 18 terminating in a reinforcing rod (rebar) tying guide member 20. Alternatively, the boom portion may terminate in any of the many other boom end attachments which are used in. the construction process.

Armature mast 12 may be secured to foundation slab 22 by tripod base 24 and nails or bolts 26, and may be designed to telescope or otherwise be adjustable in height. Armature boom 14 may be selectively secured at any point on mast 12 and in a given vertical angular relationship relative to mast 12 via pivot (or rotation point) 28 and locking lever 30, which may comprise a cam- type lock, screw lock, recessed pins, or any other known securing method. Similarly, extendable arm 18 may be selectively secured in a given length relative to boom sleeve 16 by locking lever 32. Boom end 34 may be further supported by support cable 36, secured to mast top 38 via pulley 40 and cleat 42. Armature boom 14 is enabled to rotate about the vertical axis of armature mast 12 by any of numerous methods, including rotating of the entire mast structure within the tripod base, providing a rotating collar 44, or the like. Tying guide 20 is placed against and aligned with a piece of vertical rebar 50 previously placed in foundation slab 22, so that a separate piece of horizontal rebar may be placed against and secured to the vertical rebar, as described below. It can be seen that the entire

apparatus of the present invention is of a size and dimensional extent that it is readily portable and transportable to and from and within each construction site, with a minimum of effort. Fig. 2 is a modified precision armature system

52 that may be used in the method of constructing curvilinear structures of this invention, having a plurality of armature booms 54a, 54b, and 54c laterally supporting a flexible vertical rebar track 56, which extends past and is slidingly captured by mast top 58.

Use of this arrangement may significantly reduce or even eliminate the vertical rotating adjustments normally required with only one armature boom. Here, a piece of vertical rebar 59 may be bent against flexible track 56, for simultaneous tying to separate pieces of horizontal rebar.

Each of these armature booms can have as attachments, additional armature booms, each of which can have additional armature booms attached as necessary. This enables the determination of reference points in three dimensional space very accurately and very precisely back to the coordinates or location of the central mast of the original armature boom, thereby allowing for the construction of additional separate or connected rooms and spaces by the method of this invention. Each room or space so constructed has a known accurate and precise spatial relationship to the overall design of the structure, which is centered on or referenced to the central mast of the original armature boom, thus allowing

all additional portions of the structure to be accurately referenced in relationship to each other.

Fig. 3 is a top plan view in partial cross- section of an armature boom end rebar tying guide member 20 used in the method of this invention, illustrating the tying guide member alignment with and engagement of a piece of vertical rebar 50 from the foundation slab, with a separate piece of horizontal rebar 60 being placed adjacent and generally perpendicular to the vertical rebar. Vertical rebar 50 generally fits within vertical (or vertically-tending) rebar receiving channel 51, while horizontal rebar 60 generally fits over vertical rebar 50 and into horizontal (or horizontally-tending) rebar receiving channel 61. Alternatively, the relative depth of these receiving channels may be reversed, with the horizontal rebar being placed into the tying guide first, and the vertical rebar placed over it for tying. Heavy tie wire 62 can be threaded behind both of these pieces through wire access channel or depression (concavity) 63, and twisted together at the front (or behind or to the sides) to secure the rebar together. This system can accurately and precisely position rebar and can so securely attach rebar that the rebar frame can be stood upon and walked upon during the construction process. In addition, the rebar employed can be of different sizes, and even the crossing and intersecting rebar members of the weave can be of different sizes.

Fig. 4 is a front elevation view of the armature boom end tying guide 20 of Fig. 3, illustrating a vertical

rebar receiving channel 51, horizontal rebar receiving channel 61, and wire access channel or depression 63.

Fig. 5 is an end elevation view of a portion of the flexible vertical rebar track 56 of Fig. 2, bearing a vertically arranged plurality of tying guide members 64 for simultaneously securing a plurality of horizontal rebar elements to a single vertical rebar element. This flexible rebar track may be laterally supported by one or several armature booms and may serve to reduce the number of armature boom pivoting steps normally required to fully generate a rebar grid. Even after the rebar grid is fully generated and tied or clipped in place, the frame, in whole or in part, is modifiable and adjustable at any point prior to the spraying or other means of application of the concrete or other suitable material which initially has fluid-like properties and which can also harden into structural load bearing rigidity.

Fig. 6 is a side elevation cross-sectional view of a portion of a curvilinear structure 70 constructed with the method of this invention, and illustrating a foundation slab 72 with a plurality of circumferential rebar elements 74 surrounding a single vertical rebar element 76; a series of horizontal rebar elements 78a - d having been attached to the vertical rebar element 76 in accordance with the method of this invention; a burlap or wire mesh or other impermeable layer 80 over the rebar grid; outside and inside base shotcrete layers 82, 84; and outside and inside surface or texture layers 86, 88. Fig. 7 is a side elevation view in partial

cross-section of a curvilinear structure 90 constructed by the method of this invention. This view better illustrates one particular pattern of the rebar grid 92 (other patterns, e.g., triangular, spiral, etc., are of course possible and may be preferable), burlap layer 94, outside and inside base shotcrete layers 96, 98, and outside and inside surface layers 100, 102.

The method of this invention may be accomplished in the following manner. A foundation and floor slab are formed and poured in accordance with standard construction techniques. Water and sewer piping, raceways, ducting, etc., are placed under the foundation. The foundation and floor slab preferably include reinforcing rods or members. Further reinforcing rods (rebar) extend upwards from the outer edge of the foundation (recessed in from the outer edge about five inches or more depending upon engineering specifications) to a height of four feet or more, spaced equally at a distance of twelve inches, ultimately to become the wall of the structure. This peripheral border is preferably generally circular, but may be made in any shape. If footers are necessary for archways, they are constructed at the same time as the foundation.

A removable plastic plug of the same size as the armature mast is placed in the concrete area before pouring the slab to create a recessed concavity deep enough to support the armature mast, for later placement of the armature mast into this recessed concavity in the foundation; for example, if the determined shape is a hemisphere, it should be put in the exact center of the

structure. When the foundation is dry, the plastic plug should be removed from the foundation, resulting in a recessed concavity for the placement of the armature mast. The tripod is then placed over the recessed concavity, and the mast of the armature system is carefully inserted through the tripod into the recessed concavity in the . concrete. The tripod of the mast support system may be leveled with shims. Another option would be to shoot nails into the tripod, if desired. Adjust the proper height and the proper distance of the armature by loosening the locking levers (adjustment screws, pins, or their equivalent) on the armature boom and loosening the support cable. Carefully swing the boom over to the foundation and follow it around to ensure that it is positioned properly. If any adjustments need to be made in the height or length of the boom system, they are made at this step. When placing the armature system in the recessed concavity in the foundation, make sure that it is appropriately leveled. The mast should be at ninety degrees to the foundation; this should be checked with a square or level. However, other angles are possible and may be uniquely useful in certain applications. Swing the armature boom over to the edge of the wall to check that the boom is adjusted properly, which in one mechanical implementation would mean tightening the locks and cable. Carefully move the rebar into a suitable conformation in either a left or right horizontal direction, i.e., a perpendicularly intersecting weave generation system. Starting at the

base of the wall, tie in the first two levels of horizontal rebar at three to four inches apart. Each row after that will be at twelve to sixteen inches apart, depending upon engineering specifications. The top six to eight inches of the foundation

(or wall) serves as a tension ring, which means that it contains five or six times the density of rebar as the rest of the walling system. This prevents spreading under the weight of the structure. The rebar is placed in the foundation ring as required by engineering specifications of each design.

The armature mast system gradually creates the desired curvature of the rebar by determining the proper placement which ultimately becomes the final shape of the finished wall, or ceiling, or any other surface of the structure. The mast and boom system accurately and precisely determine the placement, in three dimensional space, of all portions of the rebar, and also accurately and precisely holds and secures the rebar in the intended location(s), and at the intended crossing point(s) in three dimensional space, as determined by the structural, functional, and aesthetic requirements of each design. The armature system can also be adjusted at any point during construction. This feature is especially useful for the creation of a free-form structure. The mast and boom system can be used to check the accuracy of any rebar placement at any point during the construction process, including just prior to the spraying of concrete or other suitable material with an initially fluid-like nature

which later hardens into structural, weight-bearing rigidity.

The armature system consists of a mast and boom that is adjustable and rotatable horizontally as well as vertically. Once the proper curvature of a wall or other surface has been determined, the armature is adjusted to the desired length and height starting at the base of the foundation, and the three-eighths inch (or other suitable diameter) rebar is placed usually (but not necessarily) horizontally on, and securely affixed to, the rest of the structure. The armature is moved into place behind the vertical rebar, which is bent against the end of the armature system; then the horizontal rebar is held in place against the vertical rebar, crossing every twelve inches to create a weave from eight inches to sixteen inches, or any desired spacing as required (or sixteen by sixteen inches, depending upon engineering specifications), and may be tied twice from two different directions with heavy tie wire or a clip system. Be sure to tie or clip carefully. Then the arm is moved to the next vertical rebar and the cycle is repeated. The mast and boom system can be used to check the accuracy of rebar placement at any point during the construction process, including just prior to the spraying of concrete or other comparable and suitable material. This creates a framework of rebar, which can be rectangular, triangular, spiral, etc., gradually forming the developing design shape of the final curved walls.

The horizontal rebar that is tied should be laid

in such a way that it curves appropriately between the vertical rebar according to the specifications of the design, which may be a convex outward curve (smooth or otherwise) ; or which may be a straight line as part of a flat surface, which would be a chord rather than an arc, and which would give that portion of the structural frame the appearance of a facet; or which may be a concave inward curve (smooth or otherwise), which would give the structure a fluted surface. There can be a continuous variation and transition between any of the three styles

(convex, flat, concave) in any dimension of the surface of the structure.

The rebar weave is very forgiving of minor errors, but horizontal rebar members should be guided by suitable positioning and bending guides between each intersection with the vertical rebar members to ensure optimum conformation with the design specifications. This can be easily checked with the armature system, especially when the armature boom arm is equipped with a suitable rebar bending and curve forming guide attachment.

When tying one rebar to another, the vertical rebar must overlap down to about twenty-four inches to thirty-six inches below the top rebar, or as determined by engineering requirements. As the reinforcing rods rise during the assembly process, they will come closer together at the top. Assuming that the rebar rods used are ten to twenty feet long, the second lift of rebar rods should be overlapped about twenty-four to thirty-six inches below the tops of the first lift. This same

process is repeated for each bar until the top is reached.

Reinforcing for special openings or for extra strength is constructed as required. In any area where doors, windows, or other openings are planned, the concrete around these openings should be reinforced with additional rebar. It is a significant advantage of the present invention that the rebar frame is adjustable at any time during the construction process provided the concrete spraying (or other comparable and suitable materials) application process has not begun.

In the course of construction, if desired, large wall openings may be readily provided within the wall. This is accomplished simply by cutting out the rebar and reinforcing the edge surrounding the opening with extra rebar.

If conventional walls, or any other flat surfaces of the structure, are desired, they can be built in place under the archways, or the conventional flat walls can be built out of hollow block or other construction materials, and the armature system can be used to create the desired curved or flat walls, ceilings or roofs. Construction methods of the present invention allow for the easy and natural integration into the structure of pre-cast sections and/or molds of prefabrication which can have a nearly unlimited range of geometrical shapes, and can also be used to repair and/or build onto existing structures.

The burlap or wire mesh serves as a spraying surface for the shotcrete. Other reinforcing mesh may

also be used, such as chicken wire, hardware cloth, and the like.

The technique for applying the burlap or wire mesh on the rebar framework is as follows: start by placing the roll of burlap on top of the structure and tying it with the wire or other suitable means. Unroll it straight down the side with a twelve inch overlap along the edges of each layer of burlap or wire mesh, gently pulling the burlap or wire mesh tight enough to remove major wrinkles and tying it in place with heavy tie wire at twelve to twenty-four inch increments.

The technique for applying burlap or wire mesh on the high domed sections of the rebar structure; start at the base of the rebar framework, attaching the burlap or wire mesh horizontally to the rebar with tie wire, and unroll the burlap or wire mesh while walking around the structure, overlapping one foot as you proceed. Tie in place with tie wire at twelve to twenty-four inch increments. The shotcrete is sprayed on the same level all the way around the rebar-burlap (or wire mesh) frame, rather than all on one side, thereby preventing shifting of the frame. Depth gauges are tied onto the rebar-burlap (or wire mesh) layer prior to the shotcreting process to continually gauge the thickness. Small concrete blocks made of the same material as the wall (e.g., shotcrete) may be used as depth indicators for uniform thickness during the shotcrete spraying process. These depth gauges are tied with tie wire on the outside and inside surface

of the burlap-rebar or wire mesh frame to determine the proper wall thickness during shotcrete spraying. They should be applied over the entire surface of the building on a five foot grid, all the way around the structure. They become an integral part of the finished shotcrete wall.

After the depth indicators are in place, the electrical cables are tied to the rebar on the outside of the burlap or wire mesh frame. By means of the thickness gauges, the shotcrete operator judges the thickness of the layer as it is being sprayed on in the multi-layer system, and uniformly covers the burlap or wire mesh frame to the depth of the gauges. The shotcrete will harden quickly and will become integral with the depth gauge blocks to constitute the uniform layer progressing up the wall. The thickness of the shotcrete at the base of the wall is approximately eight inches. The rest of the wall should be a preferred minimum thickness of four inches, tapering from eight inches at the base to four inches at the top or other thicknesses as required. If exterior insulation is required, it can be sprayed on later in a similar manner (insulative shotcrete or pumicecrete process).

The shotcrete spraying operation should start at the base or lower portions of the structure; spraying is continued upward so that the spraying of the structure is completed at the top. Each additional sprayed area of the layer receives support from the previously sprayed areas which have hardened, and no undue strain will be placed

upon the rebar and burlap or wire mesh frame. For larger structures, the spraying operation may be done in successive layers, allowing for curing of each layer, with walls of adequate thickness and strength to support itself and additional layers of shotcrete without assistance.

Using temporary bracing poles may be desirable for the shotcrete layers when spans are substantial, until the shotcrete layers have cured and become completely self-supporting, or if there is a desire or a design requirement to ellipse or otherwise deform the structure, after the weaving of the rebar is completed. Have all necessary internal bracing poles in place before you start the shotcrete step.

Properly made air-entrained concrete (shotcrete) will never rot even though subjected to moisture. The thermal expansion coefficients of shotcrete and rebar are nearly identical, making them ideally matched construction materials.

The armature system may be removed by simply reversing the armature installation steps, after which removal, the entire system is easily portable and transportable. The exterior surface of the still-wet shotcrete may be smoothed out in a conventional manner with trowels, or with rollers, or both, or textured as desired. After twenty-eight to thirty days, the shotcrete has hardened sufficiently to be earth bermed if desired. Fill in the armature boom recessed concavity with concrete and trowel it smooth. A layer of concrete mixture may be plastered on or sprayed against the interior surface of

the wall after the shotcrete layer has been sprayed on the inside surface and allowed to cure.

While this invention has been described in connection with preferred embodiments thereof, it is obvious that modifications and changes therein may be made by those skilled in the art to which it pertains without departing from the spirit and scope of the invention. Accordingly, the scope of this invention is to be limited only by the appended claims.