Patent Description:
Ceiling boards have been on the market for decades for providing a covering of a substructure of a ceiling. The ceiling boards may typically be of a rectangular shape in an X- and Y-direction. Typical visual dimensions of such ceiling boards in a position of use may for example be <NUM> meters in an X-direction and <NUM> meters in a Y-direction. To inter alia facilitate mounting such ceiling boards, a periphery of the ceiling boards may be provided with mating coupling means, such as a tongue-and-groove arrangement allowing a plurality of ceiling boards to be interconnected.

A transition zone between abutting edges of the ceiling boards is typically bevelled and may be filled up with a filler. To prevent subsequent cracking of the filler, a textile strip may be applied to the transition zone. This is a cumbersome process to arrive at a visually attractive end-result. Alternatively, the ceiling boards may be manufactured with a coating or wallpaper wherein the bevelled transition zones provide a groove remaining visible in a position of use.

Publication <CIT> discloses a board for use in interior construction, especially for producing new walls in a room or for panelling wall, ceiling or roof surfaces of a room. The board is provided on at least two opposite ends, a first and a second end, with connecting means, especially having a groove-and-tongue design, for linking the board with other boards of the same kind. The connecting means facilitate a catch, snap-in or click-in connection with an adjoining board of the same kind. Additional fastening means are provided on the board itself or on two boards linked with each other for fastening the board on a support construction. <CIT> further discloses a method for producing new walls of a room or for panelling already existing wall, ceiling or roof surfaces of a room, wherein a first board is mounted, a second board is linked with the first board by establishing a catch, snap-in or click-in connection on the adjoining lateral edges of the two boards, and the second board is secured by additional fastening means.

Publication <CIT> discloses a ceiling system in configured for concealing joints between adjoining ceiling panels to provide a monolithic ceiling appearance. The system includes the support structure and ceiling panels each having a top surface, bottom surface, and peripheral edges. The peripheral edges of the panels have a hybrid edge detail including a first edge profile and a second edge profile different than the first. A facing material, bonded to the bottom surfaces of ceiling panels after securement to the support structure, has a continuous uninterrupted extent to cover and conceal multiple panels and joints. The facing may be adhesively bonded to the panels.

Publication <CIT> discloses covering panel comprising a plurality of lips, wherein each lip projecting from a corresponding edge of the panel and extending along at least a portion of said edge, each lip comprising: at least one flange projecting from the lip; and at least one groove being configurable for receiving the at least one flange of a separate lip, the at least one groove being substantially contiguous with the flange of a same lip.

Publications <CIT> and <CIT> disclose tools for a seamless joining of profiled boards. The tool is provided with a profiled section which corresponds to tongue and groove connection of a profiled board.

Publications <CIT> and <CIT> disclose elongate ceiling planks provided with engagement means such as a tongue-and-groove arrangement.

A ceiling board is typically made from a particle board, an MDF-board (medium density fiber board) or HDF-board (high density fiber board) provided with milled tongues and grooves in the side portion so that a plurality of ceiling boards can be interconnected in a two-dimensional plane, i.e. in an X- and Y-direction.

Document <CIT> discloses a panel installation support apparatus for allowing temporary attachment of a panel to a frame member. The support apparatus includes an adjustable support surface for accommodating various panel thicknesses, a sloped surface to support the leading edge of the panel when positioning in place, and an alignment support shelf to properly align an edge of the panel with the joist or stud while supporting the edge of the panel.

To provide an inconspicuous transition, it is imaginable that it would be sufficient to provide a lower part of the side portion facing an interior of the room with abutting faces being perpendicular with respect to a plane of the ceiling board. The inventor has found that it is not possible to provide an inconspicuous appearance of the transitions between adjacent boards by providing such perpendicularly abutting faces only.

In a first aspect of the invention there is provided a ceiling board for use in a ceiling wherein, in a position of use, a transition between the ceiling board and another ceiling board mating with the ceiling board appears inconspicuous, the ceiling board comprising:.

The force fit is a so-called snap-in or click-connection.

The effect of the wallpaper being bevelled from an outer, visual portion of the wallpaper towards a contact face between the wallpaper and the first surface of the ceiling board is that the protrusion of the fibers at the periphery is prevented from protruding upwards, and any fibers of the wallpaper is prevented from being trapped between the abutting faces of the plate material itself. Thereby, a tight fit of abutting faces may be achieved.

In one embodiment, the groove of the tongue-and-groove arrangement arranged at the first side portion and the third side portion of the ceiling board, is defined by a lip forming part of the first surface of the board, and a cheek forming part of the second surface of the board, wherein an end portion of the cheek is provided with a cheek protrusion extending towards the first surface of the ceiling board, wherein the cheek protrusion of the third side portion is smaller than the cheek protrusion of the first side portion.

Measured from a bottom of a cavity of the groove, a length of the cheek forming part of the first side portion may be the same as a length of the cheek forming part of the third side portion. This has the effect that a common tool may be used for applying a force towards the grooves, as will be discussed below.

In a second aspect there is provided a method for mounting a plurality of ceiling boards according to any one of the previous claims, to a supporting structure of a ceiling extending in an X- and Y-direction to provide a ceiling substantially with inconspicuous transitions between the ceiling boards, the method comprising:.

After step f), the method may further comprise the steps of:.

Preferably, the force in step j) is applied by means of an impact block provided with a tongue profile complementary fitting with the grooves of the ceiling board so that the impact block interlocks with said grooves by means of a force fit, thereby being self-supported in a position of use. This has the effect that the impact block after being connected with the groove is in exact position while at the same time an operator mounting the ceiling boards does not have to hold the impact block in place. An impact block being in exact position eliminates a possibility of damaging the transition zone between abutting ceiling boards when a force is applied to the impact block for example by means of a hammer.

The method may further comprise the additional step of applying in at least some of the steps c), g) and i) an adhesive to a portion of the tongue of groove abutting in a position of use against the cheek of the secured ceiling board.

In a third aspect of the present disclosure, which is not part of the invention and is present for illustration purposes only, there is provided a kit of tools for use in the method according to the second aspect of the invention, the kit of tools comprising:.

an impact block having a tongue profile fitting with the grooves of the ceiling board.

The tongue profile of the impact block may be complementary fitting with the grooves of the ceiling board so that the impact block is configured for interlocking with said grooves by means of a force fit, thereby being self-supported in a position of use.

Preferably, the mounting rail has a tongue profile complementary fitting with the groove of the ceiling board so that the mounting rail is configured for interlocking with said grooves by means of a force fit, thereby being self-supported in a position of use.

In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:.

Positional specification, such as upper, lower, right, left, refer to positions shown in the figures.

In the figures, same or corresponding elements are indicated by same reference numerals. For clarity, some elements may in some of the figures be without reference numerals.

For illustrative reasons, the relative proportions of some of the elements may be somewhat distorted.

In the figures, reference numeral <NUM> denotes a ceiling board according to the invention.

The ceiling board <NUM> comprises a first surface <NUM> which in a position of use faces an interior of a room. The first surface <NUM> of the ceiling board <NUM> comprises, in the embodiment shown, a facing in the form of a fiber fabric or "wallpaper" <NUM> that are adhered to the first surface <NUM> in a thermo combining and laminating process. Thus, the wallpaper <NUM> adhered to the first surface <NUM> is the only surface being visible when a plurality of ceiling boards have been interconnected, i.e. in a position of use. A paint (not shown) may be applied on the wallpaper <NUM>.

Opposite the first surface <NUM> is a second surface <NUM> for abutting against a supporting structure as indicated in <FIG> wherein the supporting structure comprises a plurality of furring strips FS.

The first and second surfaces <NUM>, <NUM> are defined by four side portions <NUM>, <NUM>, <NUM>, <NUM> wherein a first side portion <NUM> and a second side portion <NUM> complementary to and opposite the first side portion <NUM>, and a third side portion <NUM> and fourth side portion <NUM> complementary to and opposite the third side portion <NUM>. The sides portions <NUM>, <NUM>, <NUM>, <NUM> are provided with a force fit coupling means in the form of a tongue-and-groove arrangement for allowing a plurality of boards to be lockingly interconnected.

The ceiling board <NUM> has typically a rectangular shape but may alternatively have a square shape. For practical reasons, the following discussion is related to a rectangular ceiling board <NUM> as shown for example in <FIG>, wherein the first side portion <NUM> and the corresponding second side portion <NUM> are longer than the third side portion <NUM> and the corresponding fourth side portion <NUM>. The side portions <NUM>, <NUM> will hereinafter therefore be denoted "longitudinal edges" while the third and fourth side portions <NUM>, <NUM> will be denoted "end edges".

<FIG> shows a cross-sectional view through B-B in <FIG>. The first side portion <NUM> of the ceiling board <NUM> is provided with a groove <NUM> defined by a lip <NUM> forming part of the first surface <NUM>, and a cheek <NUM> forming part of the second surface <NUM> of the board. A cavity <NUM> is formed between the lip <NUM> and a portion of the cheek <NUM>.

An end portion of the cheek <NUM> is provided with a protrusion or rib <NUM> extending, in a position of use of the ceiling board <NUM>, downwardly from the cheek <NUM> along the first side portion <NUM>.

The second side portion <NUM> on the opposite side of the first side portion <NUM> is provided with a tongue <NUM> for engaging the groove <NUM> of an adjacent ceiling board <NUM>' as shown in <FIG>.

In <FIG>, the protrusion or rib <NUM> of the ceiling board <NUM> is accommodated in a retaining channel or recess <NUM> of the adjacent ceiling board <NUM>. A side portion <NUM> of the recess <NUM> abuts against a slanted side wall <NUM> of the rib <NUM> to form a contact face <NUM> between the two ceiling boards <NUM>, <NUM>'. The contact face <NUM> prevents the two boards from separating against forces acting transversely to the rib <NUM> and the recess <NUM>. Thus, the contact face <NUM> forms part of a force fit securing against disengagement of the two interconnected ceiling boards <NUM>, <NUM>'.

To keep the ceiling boards <NUM>, <NUM>' co-planar in a position of use, a height or thickness TT of the tongue <NUM> is identical to a height CT between a lower surface of the cheek <NUM> and an upper surface of the lip <NUM>, as shown in <FIG>. Thus, the tongue <NUM> accommodated in the groove secures the two ceiling boards <NUM>, <NUM>' against forces which act transversely relative to a plane (first and second surfaces <NUM>, <NUM>) of the ceiling boards <NUM>, <NUM>'.

From the above, it should be clear that the tongue-and-groove arrangement forms a force fit in the form of a snap-in or click-in coupling.

The lip <NUM> of the groove <NUM> is provided with an end face <NUM> having a lower portion being perpendicular to the plane of the ceiling board <NUM>. Similarly, a lower end face <NUM> of the tongue <NUM> is perpendicular to the plane of the ceiling board <NUM>. When coupled together, said end faces <NUM>, <NUM> abut against each other and provide a transition zone <NUM> between two adjacent ceiling boards <NUM>, <NUM>'.

One condition for achieving the desired inconspicuous transition between adjacent ceiling boards is that the milling tolerances are extremely narrow. In a prototype of a ceiling board made from particle board, the tolerances of the tongue and the mating portion of the cavity <NUM> of the groove <NUM>, is as narrow as <NUM>/<NUM>. Further, the slanted side wall <NUM> of the rib <NUM>, the side portion <NUM> of the recess <NUM> and the end faces <NUM>, <NUM> are also milled with extremely narrow tolerances so that when the rib <NUM> abuts against the side portion <NUM>, the end faces <NUM>, <NUM> abut exactly against each other and form the transition zone <NUM>. In said prototype the milling of said items are produced with tolerances as narrow as <NUM>/<NUM>.

In a prototype of the ceiling board <NUM>, the side wall <NUM> of the rib <NUM> and the side portion <NUM> of the recess are slanted <NUM>° with respect to the first surface <NUM> of the ceiling board.

In an embodiment, very good results were achieved by means of a wallpaper <NUM> being composed of a basic material comprising about <NUM> - <NUM>% cellulose and <NUM> - <NUM>% syn-thetical, non-woven fibers, and a binding agent. The basic material constituted about <NUM>% of the wallpaper material. The rest of the wallpaper material comprised about <NUM>% inorganic filler, acrylic polymers and <NUM> - <NUM>% additives. The wallpaper <NUM> had a density in the range of <NUM> - <NUM> grams/m<NUM>.

The fiber fabric or wallpaper <NUM> is applied to the ceiling board prior to forming the side portions <NUM>, <NUM>, <NUM>, <NUM>, i.e. the tongues and grooves, of the ceiling board material itself in a milling machine. While milling the tongues and grooves, the wallpaper is also milled at the periphery thereof by means of a cutting tool adapted for cutting some, but not all, of the fibers of the wallpaper. One would imagine that a wallpaper being cut to be flush with the end faces <NUM>, <NUM> would provide a substantially invisible transition zone. However, the inventor has found that by doing so, it is not possible to provide a transition zone <NUM> fulfilling the applicant's desired inconspicuousness between the ceiling boards <NUM>, <NUM>'.

Turning now to <FIG> showing in greater detail A of <FIG>. In an embodiment, the inventor has surprisingly found that it is an advantage with respect to the desired inconspicuousness of the transition zone <NUM> between two adjacent ceiling boards <NUM>, <NUM>' to cut the wallpaper <NUM>, <NUM>' so that at least some of the fibers <NUM>, <NUM>' at a periphery of the wallpaper <NUM>, <NUM>' protrude beyond each one of the four side portions of the first surface <NUM> of the ceiling board <NUM> so that, in a position of use, fibers <NUM>, <NUM>' of two adjoining ceiling boards <NUM>, <NUM>' interdigitate. Interdigitating fibers <NUM>, <NUM>' seems to provide a reinforcement or "binder" of any paint applied to the wallpaper <NUM>, <NUM>' after the ceiling boards <NUM>, <NUM>' have been interconnected.

To prevent any fibers <NUM>, <NUM>' from protruding upwards at the border area between the wallpaper <NUM>, <NUM>' and the ceiling board material itself, and thereby possibly preventing a tight fit between the end faces <NUM>, <NUM>, a fiber cutting is bevelled from an outer, visual portion of the wallpaper <NUM>, <NUM>' towards a contact face between the wallpaper <NUM>, <NUM>' and the first surface of the ceiling boards themselves. In <FIG>, a cutting line for the fibers <NUM>, <NUM>' protruding from the left wallpaper <NUM> is indicated by bevelled line <NUM>, while a cutting line for the fibers <NUM>' protruding from the right wallpaper <NUM>' is indicated by bevelled line <NUM>'.

In a prototype of the ceiling board <NUM>, an angle of the bevelled lines <NUM>, <NUM>' is approximately -<NUM>° and <NUM>° with respect to an end face of the wallpaper <NUM> being coplanar with the end faces <NUM>, <NUM> forming part of the transition zone <NUM>.

The protrusion of the longest fibers <NUM>, <NUM>' at a lower, visible surface of the wallpaper <NUM>, <NUM>' is very small, typically less than <NUM>, preferably in the range of <NUM> - <NUM>.

In an alternative embodiment of the ceiling board <NUM>, which is not part of the invention and is present for illustration purposes only, the first surface <NUM> of the ceiling board <NUM> may be provided with a coating in the form of primer instead of a wallpaper <NUM> as discussed above. The primer should be applied to the first surface <NUM> of the ceiling board <NUM> prior to milling the grooves and tongues in the side portions <NUM>, <NUM> and <NUM>, <NUM>, respectively. This is important because any primer applied after said milling of the side portions would interfere with the tongues and grooves. The desired tolerances discussed above would not be achievable and the end-result would most likely be visible transition zones <NUM> between the interconnected ceiling boards <NUM>. To achieve inconspicuous transition zones <NUM> a substantive finishing process would then be necessary.

<FIG> show a groove-and-tongue arrangement of the third side portion <NUM> and fourth side portion <NUM> of the ceiling board <NUM>, respectively, i.e. a cut through C-C in <FIG>. The major difference between the side portions <NUM>, <NUM> or longitudinal edges shown in <FIG> and the side portions <NUM>, <NUM> or end edges shown in <FIG>, is that the cheek protrusion <NUM>' of the third side portion <NUM> is smaller than the cheek protrusion <NUM> of the first side portion <NUM>. In a prototype of the ceiling board <NUM>, the cheek protrusion <NUM>' of the third side portion <NUM> is in the range of <NUM> - <NUM>, while the cheek protrusion <NUM> of the first side portion <NUM> is in the range of <NUM>,<NUM> - <NUM>. The purpose of this difference will be appreciated in view of <FIG> illustrating a method for mounting a plurality of ceiling boards as discussed above.

To achieve the desired inconspicuous transitions between the boards <NUM>, the respective side portions <NUM>, <NUM> and <NUM>, <NUM> must be fitted exactly. This is achieved as follows:
The first ceiling board <NUM> shown in <FIG> forms the basis for the rest of the ceiling boards mounted in an X- and Y-direction as shown in <FIG>. In <FIG>, the X-direction is in parallel with the longitudinal edges, while the Y-direction is in parallel with the short edges. It should be emphasized that it is extremely important that all ceiling boards are interconnected without any deviations from the X-direction, and thus also the Y-direction determined by the first ceiling boards; any individual corrections of the ceiling boards succeeding the first ceiling board must be avoided.

In <FIG>, a first ceiling board <NUM> is brought adjacent to a corner of the ceiling so that the ceiling board is arranged with the groove portions <NUM> of the tongue-and-groove arrangement facing away from a corner of a ceiling. To avoid any excess and/or to adapt the ceiling board to the furring strips FS of the supporting structure, at least the tongues facing against walls defining the ceiling may be cut, as will be appreciated by a person skilled in the art.

The first ceiling board is aligned with respect to a predetermined guiding line G determining the X-direction. The guiding line G may typically be made by means of a chalk line applied against the second furring strip FS for supporting the groove portion <NUM> of the longitudinal edge of the ceiling board <NUM>. When the first ceiling board <NUM> is aligned with the guiding line, the ceiling board is secured to the furring strips FS of the ceiling supporting structure by mechanical fastening means, here in the form of screws (shown before penetrating the ceiling board), at least some of which penetrating the cheek of the grooves. In the portion of the plate facing against the periphery of the ceiling, the screw penetrates through the plates from the first surface as the screws will be covered by cornice.

In <FIG> the ceiling board <NUM> is temporarily supported by a supporting rod SR.

In <FIG>, a tongue of a subsequent ceiling board <NUM>' is brought towards and engaged with a groove of the first ceiling board <NUM>, i.e. the ceiling boards are connected in an X-direction of the ceiling.

To fully align the subsequent ceiling board <NUM>' with respect to the secured first (or previous) ceiling board <NUM>, a mounting rail <NUM> having at least a tongue profile <NUM> (see <FIG>) mating with the groove <NUM> of the ceiling boards, <NUM>, <NUM>', is provided. The tongue profile <NUM> of the mounting rail <NUM> is tailored to abut against a bottom portion of the cavity <NUM> (see <FIG>) of the groove <NUM> of the ceiling boards. As shown in <FIG>, the mounting rail <NUM> is engaged to overlap the transition <NUM> of the ceiling boards <NUM>, <NUM>', i.e. to overlap the interconnected tongue and groove of the short edges of the ceiling boards <NUM>, <NUM>'. To align the ceiling boards in the X-direction, the subsequent ceiling board <NUM>' is adjusted in a Y-direction with respect to the secured ceiling board <NUM> so that the tongue profile <NUM> of the mounting rail <NUM> fully abuts the bottom portion of the cavity <NUM> of the groove <NUM> of the connected ceiling boards <NUM>, <NUM>' throughout its length. When aligned by means of the mounting rail <NUM>, the subsequent ceiling board is secured to the supporting structure by means of screws, at least some of which protruding the cheek of the grooves as discussed above. In <FIG>, the adjustment of the subsequent ceiling board <NUM>' with respect to the already secured ceiling board <NUM>, is provided by means of an impact block <NUM> that is described in further detail below with respect to <FIG>. The impact block <NUM> is also used to apply a force against the end edge of the subsequent ceiling board <NUM>' prior to securing this to the supporting structure as discussed above.

Any further ceiling boards are connected to a previous ceiling board in the same way as described above, until a first row of ceiling boards is mounted in the X-direction. To secure a tight fit of the last ceiling board in the X-direction, a crowbar is used as shown in <FIG>.

<FIG> shows the start of mounting a second row of ceiling boards. The second row is mounted in parallel with the first row. In the embodiment shown the ceiling board of the second row has been cut to allow the transition of the end edges of the second row to be displaced with respect to the transition <NUM> (see <FIG>) of the end edges of the first row. However, it should be noted that such displacement is preferred but is not strictly required since the transition between the ceiling boards will be inconspicuous.

A tongue (not visible in the figure) of the first ceiling board <NUM> in the second row is interlocked with a portion of the continuous groove <NUM> provided by the aligned plurality of ceiling boards of the first row. This is achieved by abutting the tongue of the second row against the groove <NUM> of the first row while the second row ceiling board <NUM> is arranged obliquely (not shown), for example at an angle of <NUM>° with respect to a plane of the first row of ceiling boards that have been secured to furring strips FS of the supporting structure. Thereafter, each board in the second row is brought into the same plane as the first-row ceiling boards. To secure a complete interlocking, i.e. fully activating the force fit, between the second-row ceiling board with the first-row ceiling board, a force may be applied towards the groove <NUM> of the second-row ceiling board. To avoid any damage to said groove, an impact block <NUM> is connected to the groove and an impact force is applied against the impact block for example by means of a hammer H.

When the force fit has been fully activated, the first ceiling board <NUM> in the second row is secured to furring strips FS of the ceiling supporting structure by mechanical fastening means at least some of which penetrating the cheek of the grooves as for the first ceiling board in the first row.

When the second row's first ceiling board <NUM> has been secured to the ceiling supporting structure FS, a mounting process of a subsequent second-row ceiling board is commenced by interlocking a second side portion <NUM> tongue <NUM> of a subsequent second-row ceiling board with a portion of the continuous first side portion groove <NUM> of the previous row of ceiling boards, said interlocking taking place adjacent, but not in contact with a third side portion groove <NUM> of the previous ceiling board in the same row. When the subsequent second-row ceiling board is in the same plane as the secured ceiling boards, a force is applied in an X-direction of said subsequent ceiling board to engage a fourth side portion tongue <NUM> of the subsequent ceiling board with a third side portion groove <NUM> of the previous ceiling board in the same row to provide a force fit and securing the ceiling board in the row to the ceiling supporting structure by a mechanical fastening means that penetrates the cheek <NUM> of the third and first side portion grooves <NUM>.

Thus, each subsequent ceiling board in the second row (and subsequent rows) is interconnected with the previous board by means of a displacement in an X-direction, i.e. in a direction being in parallel with a plane of the secured ceiling boards. This is made possible by means of the very limited protrusion <NUM>' as shown in <FIG> and <FIG>.

To avoid any damage to the short edge groove <NUM>, i.e. groove <NUM> formed in the fourth side portion <NUM>, the impact block <NUM> as mentioned above is connected to the groove <NUM> and an impact force is applied against the impact block <NUM> for example by means of a hammer H. Subsequent ceiling boards are connected in the same manner until the row of ceiling boards is installed throughout the length of the ceiling in the X-direction and until the ceiling boards completely cover the ceiling in the X- and Y-direction. Since the first row is fully aligned by means of the mounting rail <NUM>, any alignment by means of the mounting rail <NUM> of the second and further rows is superfluous. Thus, the second and subsequent rows may be installed quickly, and the result is a ceiling without inconspicuous transitions both in an X-direction and a Y-direction.

Preferably, an adhesive such as a curable glue is applied to an upper surface of the tongues <NUM> immediately prior to interconnecting a ceiling board with a secured ceiling board. Such a glue prevents, when cured, any individual movements of the ceiling boards. Further, prior to curing, the glue provides a slip agent reducing friction between the tongue-and-groove arrangement thus establishing the force fit.

Turning now to <FIG> showing a mounting rail <NUM> forming part of a kit of tools for use when mounting the ceiling boards.

The mounting rail <NUM> is provided with a body <NUM> which forms a handle configured for being gripped by an operator. The handle <NUM> is provided with a protrusion <NUM> provided with a tongue profile <NUM> being tailored for abutting against at least a bottom portion of the cavity <NUM> of the longitudinal edge groove <NUM> of the ceiling boards <NUM>, <NUM>' disclosed herein. To fulfil its purpose of fully aligning two subsequent ceiling boards in the first row, a length of the mounting rail is at least <NUM>% of a length of the longitudinal edge of the ceiling board <NUM>. In a prototype of the mounting rail <NUM> tailored for mounting a ceiling board having a length of <NUM> meter, the length of the mounting rail <NUM> is <NUM> meter. In general, the longer mounting rail <NUM>, the better. However, for practical reasons it is considered unnecessary that a length of the mounting rail <NUM> exceeds twice the extension of the plate in an X-direction.

In <FIG>, the tongue profile <NUM> of the mounting rail <NUM> is configured for complementarily fitting the groove <NUM> of the longitudinal edge of the ceiling board <NUM> (see <FIG>) so that the mounting rail <NUM> is configured for interlocking with said groove <NUM> by means of a force fit, thereby being self-supported in a position of use. The mounting rail <NUM> shown in a position of use in <FIG> and <FIG> is further provided with a lip <NUM> configured for abutting against a first surface <NUM> of the ceiling board so that the mounting rail <NUM> is self-supported with respect to the ceiling board even without a tongue profile being configured for completely interlocking with said groove <NUM> of the ceiling board <NUM>.

A self-supported mounting rail <NUM> has the advantage that it can be left temporarily in place without being held by an operator.

The kit of tools further comprises an impact block <NUM> as shown in <FIG>. The impact block <NUM> is provided with a tongue profile <NUM> complementarily fitting with the grooves of the first side portion <NUM> and second side portion <NUM> of the ceiling board <NUM>. The tongue profile <NUM> comprises a protrusion <NUM> configured for abutting in a position of use against a bottom portion of the cavity <NUM> in the grooves <NUM> of the ceiling board <NUM>, and a face <NUM> configured to abut against an end face of the cheek <NUM> of the grooves <NUM>. The impact block <NUM> is further provided with a lip <NUM> configured to abut against a portion of the first surface <NUM> of the ceiling board <NUM>. Between the protrusion <NUM> and the lip <NUM>, the impact block <NUM> comprises an indentation or gap <NUM> which in a position of use of the impact block <NUM> accommodates a portion of the lip <NUM> forming part of the first surface <NUM> of the ceiling board <NUM> so that the impact block <NUM> is self-supported with respect to the groove <NUM> of the ceiling board <NUM>. To avoid any damage to the end face <NUM> of the lip <NUM> of the ceiling board <NUM>, a depth of the gap <NUM> is larger than an extent of the lip <NUM> so that there is a clearance between a bottom portion of the gap <NUM> and the end face <NUM> of the lip <NUM>. Thus, when an impact force is applied against the impact block <NUM> for example by means of a hammer H (see <FIG>), the impact force is transferred to the bottom portion of the cavity <NUM> of the groove <NUM> and the end face of the cheek <NUM> of the groove, both of which are invisible when the ceiling boards have been mounted.

A self-supported impact block <NUM> has the advantage that it can be left temporarily in place without being held by an operator.

From the disclosure herein, it should be appreciated that the ceiling boards <NUM>, <NUM>' may be interconnected so that the transitions <NUM> of abutting the ceiling boards will be inconspicuous to a degree that hitherto has not been possible. After having aligned a first row of ceiling boards in an X-direction, subsequent boards may be easily and quickly mounted by one person.

Claim 1:
A ceiling board (<NUM>) for use in a ceiling wherein, in a position of use, a transition between the ceiling board (<NUM>) and another ceiling board (<NUM>') mating with the ceiling board (<NUM>) appears inconspicuous, the ceiling board (<NUM>) comprising:
a first surface (<NUM>) for facing an interior of a room, and a second surface (<NUM>) opposite the first surface (<NUM>) for abutting against a supporting structure (SF); and
four side portions (<NUM>, <NUM>, <NUM>, <NUM>) defining the first and second surfaces (<NUM>, <NUM>),
wherein the side portions comprise a first side portion (<NUM>) and a second side portion (<NUM>) complementary to and opposite the first side portion (<NUM>), and a third side portion (<NUM>) and fourth side (<NUM>) portion complementary to and opposite the third side portion (<NUM>),
wherein the side portions are in the form of a tongue (<NUM>) and groove (<NUM>) arrangement adapted to provide a force fit coupling means for allowing a plurality of boards (<NUM>, <NUM>') to be lockingly interconnected, wherein a lower end face (<NUM>) of the tongue (<NUM>), and a lower portion of an end face (<NUM>) of a lip (<NUM>) of the groove (<NUM>) are perpendicular to the first surface (<NUM>) of the ceiling board (<NUM>) wherein the first surface (<NUM>) of ceiling board (<NUM>) is further provided with a wallpaper (<NUM>) comprising non-woven fibers, the wallpaper (<NUM>) being adhered to said first surface (<NUM>),
characterized in that the tongue and groove arrangement of the four side portions (<NUM>,<NUM>, <NUM>, <NUM>) and a periphery of the wall paper (<NUM>) has been concurrently formed in a milling process wherein the periphery of the wallpaper (<NUM>) is bevelled with respect to the end face (<NUM>) of the lip (<NUM>) of the groove (<NUM>) and the end face (<NUM>) of the tongue (<NUM>), from a visual portion of the wall paper (<NUM>) towards a contact face between the wall paper (<NUM>) and the first surface (<NUM>), wherein at least some fibers (<NUM>) at a periphery of the wallpaper (<NUM>) protrude beyond the end faces (<NUM>, <NUM>) of the groove (<NUM>) and the tongue (<NUM>) of the ceiling board (<NUM>), so that, in a position of use of the ceiling board (<NUM>), the at least some fibers (<NUM>) interdigitate with at least some fibers (<NUM>') protruding from the another mating ceiling board (<NUM>').