Abstract:
An edge lock is provided for use in a flooring system having a plurality of floor panels. The edge lock mechanically and releasably locks together adjacent edges of pairs of adjacent floor panels during assembly of the flooring system, and when said adjacent floor panels are laying flat on a subfloor with upper corner portions of said adjacent edges being mutually spaced apart, the edge lock includes a lock for forming a first mechanical connection for locking the adjacent edges to each other in a vertical direction, and for forming a second mechanical connection for locking the adjacent edges to each other in a horizontal direction at right angles to the edges. The lock includes a locking groove extending parallel to and spaced from a first one of the adjacent edges of one of the adjacent floor panels and being open at a rear side of the one adjacent floor panel, and a flexible and resilient locking strip integrated with another of the adjacent floor panels.

Description:
This application is a continuation of application Ser. No. 09/193,687, filed Nov. 18, 1999 now U.S. Pat. No. 6,023,907, which is a continuation of application Ser. No. 09/003,499 filed on Jan. 6, 1998 now U.S. Pat. No. 5,860,267 which is a divisional of application Ser. No. 08/436,244 filed on May 17, 1995 now abandoned, which is a 371 of PCT/SE94/00386 filed Apr. 29, 1994. 
    
    
     TECHNICAL FIELD 
     The invention generally relates to a system for providing a joint along adjacent joint edges of two building panels, especially floor panels. 
     More specifically, the joint is of the type where the adjacent joint edges together form a first mechanical connection locking the joint edges to each other in a first direction at right angles to the principal plane of the panels, and where a locking device forms a second mechanical connection locking the panels to each other in a second direction parallel to the principal plane and at right angles to the joint edges, the locking device comprising a locking groove which extends parallel to and spaced from the joint edge of one of the panels, and said locking groove being open at the rear side of this one panel. 
     The invention is especially well suited for use in joining floor panels, especially thin laminated floors. Thus, the following description of the prior art and of the objects and features of the invention will be focused on this field of use. It should however be emphasised that the invention is useful also for joining ordinary wooden floors as well as other types of building panels such as wall panels and roof slabs. 
     BACKGROUND OF THE INVENTION 
     A joint of the aforementioned type is known e.g. from SE 450,141. The first mechanical connection is achieved by means of joint edges having tongues and grooves. The locking device for the second mechanical connection comprises two oblique locking grooves, one in the rear side of each panel, and a plurality of spaced-apart spring clips which are distributed along the joint and the legs of which are pressed into the grooves, and which are biased so as to tightly clamp the floor panels together. Such a joining technique is especially useful for joining thick floor panels to form surfaces of a considerable expanse. 
     Thin floor panels of a thickness of about 7-10 mm, especially laminated floors, have in a short time taken a substantial share of the market. All thin floor panels employed are laid as “floating floors” without being attached to the supporting structure. As a rule, the dimension of the floor panels is 200×1200 mm, and their long and short sides are formed with tongues and grooves. Traditionally, the floor is assembled by applying glue in the groove and forcing the floor panels together. The tongue is then glued in the groove of the other panel. As a rule, a laminated floor consists of an upper decorative wear layer of laminate having a thickness of about 1 mm, an intermediate core of particle board or other board, and a base layer to balance the construction. The core has essentially poorer properties than the laminate, e.g. in respect of hardness and water resistance, but it is nonetheless needed primarily for providing a groove and tongue for assemblage. This means that the overall thickness must be at least about 7 mm. These known laminated floors using glued tongue-and-groove joints however suffer from several inconveniences. 
     First, the requirement of an overall thickness of at least about 7 mm entails an undesirable restraint in connection with the laying of the floor, since it is easier to cope with low thresholds when using thin floor panels, and doors must often be adjusted in height to come clear of the floor laid. Moreover, manufacturing costs are directly linked with the consumption of material. 
     Second, the core must be made of moisture-absorbent material to permit using water-based glues when laying the floor. Therefore, it is not possible to make the floors thinner using so-called compact laminate, because of the absence of suitable gluing methods for such non-moisture-absorbent core materials. 
     Third, since the laminate layer of the laminated floors is highly wear-resistant, tool wear is a major problem when working the surface in connection with the formation of the tongue. 
     Fourth, the strength of the joint, based on a glued tongue-and-groove connection, is restricted by the properties of the core and of the glue as well as by the depth and height of the groove. The laying quality is entirely dependent on the gluing. In the event of poor gluing, the joint will open as a result of the tensile stresses which occur e.g. in connection with a change in air humidity. 
     Fifth, laying a floor with glued tongue-and-groove joints is time-consuming, in that glue must be applied to every panel on both the long and short sides thereof. 
     Sixth, it is not possible to disassemble a glued floor once laid, without having to break up the joints. Floor panels that have been taken up cannot therefore be used again. This is a drawback particularly in rental houses where the flat concerned must be put back into the initial state of occupancy. Nor can damaged or worn-out panels be replaced without extensive efforts, which would be particularly desirable on public premises and other areas where parts of the floor are subjected to great wear. 
     Seventh, known laminated floors are not suited for such use as involves a considerable risk of moisture penetrating down into the moisture-sensitive core. 
     Eighth, present-day hard, floating floors require, prior to laying the floor panels on hard subfloors, the laying of a separate underlay of floor board, felt, foam or the like, which is to damp impact sounds and to make the floor more pleasant to walk on. The placement of the underlay is a complicated operation, since the underlay must be placed in edge-to-edge fashion. Different underlays affect the properties of the floor. 
     There is thus a strongly-felt need to overcome the above-mentioned drawbacks of the prior art. It is however not possible simply to use the known joining technique with glued tongues and grooves for very thin floors, e.g. with floor thicknesses of about 3 mm, since a joint based on a tongue-and-groove connection would not be sufficiently strong and practically impossible to produce for such thin floors. Nor are any other known joining techniques usable for such thin floors. Another reason why the making of thin floors from e.g. compact laminate involves problems is the thickness tolerances of the panels, being about 0.2-0.3 mm for a panel thickness of about 3 mm. A 3-mm compact laminate panel having such a thickness tolerance would have, in ground to uniform thickness on its rear side, an unsymmetrical design, entailing the risk of bulging. Moreover, if the panels have different thicknesses, this also means that the joint will be subjected to excessive load. 
     Nor is it possible to overcome the above-mentioned problems by using double-adhesive tape or the like on the undersides of the panels, since such a connection catches directly and does not allow for subsequent adjustment of the panels as is the case with ordinary gluing. 
     Using U-shaped clips of the type disclosed in the above-mentioned SE 450,141, or similar techniques to overcome the drawbacks discussed above is no viable alternative either. Especially, biased clips of this type cannot be used for joining panels of such a small thickness as 3 mm. Normally, it is not possible to disassemble the floor panels without having access to their undersides. This known technology relying on clips suffers from the additional drawbacks: 
     Subsequent adjustment of the panels in their longitudinal direction is a complicated operation in connection with laying, since the clips urge the panels tightly against each other. 
     Floor laying using clips is time-consuming. 
     This technique is usable only in those cases where the floor panels are resting on underlying joists with the clips placed therebetween. For thin floors to be laid on a continuous, flat supporting structure, such clips cannot be used. 
     The floor panels can be joined together only at their long sides. No clip connection is provided on the short sides. 
     TECHNICAL PROBLEMS AND OBJECTS OF THE INVENTION 
     A main object of the invention therefore is to provide a system for joining together building panels, especially floor panels for hard, floating floors, which allows using floor panels of a smaller overall thickness than present-day floor panels. 
     A particular object of the invention is to provide a panel-joining system which 
     makes it possible in a simple, cheap and rational way to provide a joint between floor panels without requiring the use of a glue, especially a joint based primarily only on mechanical connections between the panels; 
     can be used for joining floor panels which have a smaller thickness than present-day laminated floors and which have, because of the use of a different core material, superior properties than present-day floors even at a thickness of 3 mm; 
     makes it possible between thin floor panels to provide a joint that eliminates any unevennesses in the joint because of thickness tolerances of the panels; 
     allows joining all the edges of the panels; 
     reduces tool wear when manufacturing floor panels with hard surface layers; 
     allows repeated disassembly and reassembly of a floor previously laid, without causing damage to the panels, while ensuring high laying quality; 
     makes it possible to provide moisture-proof floors; 
     makes it possible to obviate the need of accurate, separate placement of an underlay before laying the floor panels; and 
     considerably cuts the time for joining the panels. 
     These and other objects of the invention are achieved by means of a panel-joining system having the features recited in the appended claims. 
     Thus, the invention provides a system for making a joint along adjacent joint edges of two building panels, especially floor panels, in which joint: 
     the adjacent joint edges together form a first mechanical connection locking the joint edges to each other in a first direction at right angles to the principal plane of the panels, and 
     a locking device arranged on the rear side of the panels forms a second mechanical connection locking the panels to each other in a second direction parallel to the principal plane and at right angles to the joint edges, said locking device comprising a locking groove which extends parallel to and spaced from the joint edge of one of said panels, termed groove panel, and which is open at the rear side of the groove panel, said system being characterised in 
     that the locking device further comprises a strip integrated with the other of said panels, termed strip panel, said strip extending throughout substantially the entire length of the joint edge of the strip panel and being provided with a locking element projecting from the strip, such that when the panels are joined together, the strip projects on the rear side of the groove panel with its locking element received in the locking groove of the groove panel. 
     that the panels, when joined together, can occupy a relative position in said second direction where a play exists between the locking groove and a locking surface on the locking element that is facing the joint edges and is operative in said second mechanical connection, 
     that the first and the second mechanical connection both allow mutual displacement of the panels in the direction of the joint edges, and 
     that the second mechanical connection is so conceived as to allow the locking element to leave the locking groove if the groove panel is turned about its joint edge angularly away from the strip. 
     The term “rear side” as used above should be considered to comprise any side of the panel located behind underneath the front side of the panel. The opening plane of the locking groove of the groove panel can thus be located at a distance from the rear surface of the panel resting on the supporting structure. Moreover, the strip, which in the invention extends throughout substantially the entire length of the joint edge of the strip panel, should be considered to encompass both the case where the strip is a continuous, uninterrupted element, and the case where the “strip” consists in its longitudinal direction of several parts, together covering the main portion of the joint edge. 
     It should also be noted (i) that it is the first and the second mechanical connection as such that permit mutual displacement of the panels in the direction of the joint edges, and that (ii) it is the second mechanical connection as such that permits the locking element to leave the locking groove if the groove panel is turned about its joint edge angularly away from the strip. Within the scope of the invention, there may thus exist means, such as glue and mechanical devices, that can counteract or prevent such displacement and/or upward angling. 
     The system according to the invention makes it possible to provide concealed, precise locking of both the short and long sides of the panels in hard, thin floors. The floor panels can be quickly and conveniently disassembled in the reverse order of laying without any risk of damage to the panels, ensuring at the same time a high laying quality. The panels can be assembled and disassembled much faster than in present-day systems, and any damaged or worn-out panels can be replaced by taking up and re-laying parts of the floor. 
     According to an especially preferred embodiment of the invention, a system is provided which permits precise joining of thin floor panels having, for example, a thickness of the order of 3 mm and which at the same time provides a tolerance-independent smooth top face at the joint. To this end, the strip is mounted in an equalising groove which is countersunk in the rear side of the strip panel and which exhibits an exact, predetermined distance from its bottom to the front side of the strip panel. The part of the strip projecting behind the groove panel engages a corresponding equalising groove, which is countersunk in the rear side of the groove panel and which exhibits the same exact, predetermined distance from its bottom to the front side of the groove panel. The thickness of the strip when is at least so great that the rear side of the strip is flush with, and preferably projects slightly below the rear side of the panels. In this embodiment, the panels will always rest, in the joint, with their equalising grooves on a strip. This levels out the tolerance and imparts the necessary strength to the joint. The strip transmits horizontal and upwardly-directed forces to the panels and downwardly-directed forces to the existing subfloor. 
     Preferably, the strip may consist of a material which is flexible, resilient and strong, and can be sawn. A preferred strip material is sheet aluminium. In an aluminium strip, sufficient strength can be achieved with a strip thickness of the order of 0.5 mm. 
     In order to permit raking up previously laid, joined floor panels in a simple way, a preferred embodiment of the invention is characterised in that when the groove panel is pressed against the strip panel in the second direction and is turned anglularly away from the strip, the maximum distance between the axis of rotation of the groove panel and the locking surface of the locking groove closest to the joint edges is such that the locking element can leave the locking groove without contacting the locking surface of the locking groove. Such a disassembly can be achieved even if the aforementioned play between the locking groove and the locking surface is not greater than 0.2 mm. 
     According to the invention, the locking surface of the locking element is able to provide a sufficient locking function even with very small heights of the locking surface. Efficient locking of 3-mm floor panels can be achieved with a locking surface that is as low as 2 mm. Even a 0.5-mm-high locking surface may provide sufficient locking. The term “locking surface” as used herein relates to the part of the locking element engaging the locking groove to form the second mechanical connection. 
     For optimal function of the invention, the strip and the locking element should be formed on the strip panel with high precision. Especially, the locking surface of the locking element should be located at an exact distance from the joint edge of the strip panel. 
     Furthermore, the extent of the engagement in the floor panels should be minimised, since it reduces the floor strength. 
     By known manufacturing methods, it is possible to produce a strip with a locking pin, for example by extruding aluminium or plastics into a suitable section, which is thereafter glued to the floor panel or is inserted in special grooves. These and all other traditional methods do however not ensure optimum function and an optimum level of economy. To produce the joint system according to the invention, the strip is suitably formed from sheet aluminium, and is mechanically fixed to the strip panel. 
     The laying of the panels can be performed by first placing the strip panel on the subfloor and then moving the groove panel with its long side up to the long side of the strip panel, at an angle between the principal plane of the groove panel and the subfloor. When the joint edges have been brought into engagement with each other to form the first mechanical connection, the groove panel is angled down so as to accommodate the locking element in the locking groove. 
     Laying can also be performed by first placing both the strip panel and the groove panel flat on the subfloor and then joining the panels parallel to their principal planes while bending the strip downwards until the locking element snaps up into the locking groove. This laying technique enables in particular mechanical locking of both the short and long sides of the floor panels. For example, the long sides can be joined together by using the first laying technique with downward angling of the groove panel, while the short sides are subsequently joined together by displacing the groove panel in its longitudinal direction until its short side is pressed on and locked to the short side of an adjacent panel in the same row. 
     In connection with their manufacture, the floor panels can be provided with an underlay of e.g. floor board, foam or felt. The underlay should preferably cover the strip such that the joint between the underlays is offset in relation to the joint between the floor panels. 
     The above and other features and advantages of the invention will appear from the appended claims and the following description of embodiments of the invention. 
    
    
     The invention will now be described in more detail hereinbelow with reference to the accompanying drawing Figures. 
     DESCRIPTION OF DRAWING FIGURES 
     FIGS. 1 a  and  1   b  schematically show in two stages how two floor panels of different thickness are joined together in floating fashion according to a first embodiment of the invention. 
     FIGS. 2 a-c  show in three stages a method for mechanically joining two floor panels according to a second embodiment of the invention. 
     FIGS. 3 a-c  show in three stages another method for mechanically joining the floor panels of FIGS. 2 a-c.    
     FIGS. 4 a  and  4   b  show a floor panel according to FIGS. 2 a-c  as seen from below and from above, respectively. 
     FIG. 5 illustrates in perspective a method for laying and joining floor panels according to a third embodiment of the invention. 
     FIG. 6 shows in perspective and from below a first variant for mounting a strip on a floor panel. 
     FIG. 7 shows in section a second variant for mounting a strip on a floor panel. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 a  and  1   b,  to which reference is now made, illustrate a first floor panel  1 , hereinafter termed strip panel, and a second floor panel  2 , hereinafter termed groove panel. The terms “strip panel” and “groove panel” are merely intended to facilitate the description of the invention, the panels  1 ,  2  normally being identical in practice. The panels  1  and  2  may be made from compact laminate and may have a thickness of about 3 mm with a thickness tolerance of about ±0.2 mm. Considering this thickness tolerance, the panels  1 ,  2  are illustrated with different thicknesses (FIG. 1 b ), the strip panel  1  having a maximum thickness (3.2 mm) and the groove panel  2  having a minimum thickness (2.8 mm). 
     To enable mechanical joining of the panels  1 ,  2  at opposing joint edges, generally designated  3  and  4 , respectively, the panels are provided with grooves and strips as described in the following. 
     Reference is now made primarily to FIGS. 1 a  and  1   b,  and secondly to FIGS. 4 a  and  4   b  showing the basic design of the floor panels from below and from above, respectively. 
     From the joint edge  3  of the strip panel  1 , i.e. the one long side, projects horizontally a flat strip  6  mounted at the factory on the underside of the strip panel  1  and extending throughout the entire joint edge  3 . The strip  6 , which is made of flexible, resilient sheet aluminium, can be fixed mechanically, by means of glue or in any other suitable way. In FIGS. 1 a  and  1   b,  the strip  6  is glued, while in FIGS. 4 a  and  4   b  it is mounted by means of a mechanical connection, which will be described in more detail hereinbelow. 
     Other strip materials can be used, such as sheets of other metals, as well as aluminium or plastics sections. Alternatively, the strip  6  may be integrally formed with the strip panel  1 . At any rate, the strip  6  should be integrated with the strip panel  1 , i.e. it should not be mounted on the strip panel  1  in connection with laying. As a non-restrictive example, the strip  6  may have a width of about 30 mm and a thickness of about 0.5 mm. 
     As appears from FIGS. 4 a  and  4   b,  a similar, although shorter strip  6 ′ is provided also at one short side  3 ′ of the strip pane  1 . The shorter strip  6 ′ does however not extend throughout the entire short side  3 ′ but is otherwise identical with the strip  6  and, therefore, is not described in more detail here. 
     The edge of the strip  6  facing away from the joint edge  3  is formed with a locking element  8  extended throughout the entire strip  6 . The locking element  8  has a locking surface  10  facing the joint edge  3  and having a height of e.g. 0.5 mm. The locking element  8  is so designed that when the floor is being laid and the strip panel  2  of FIG. 1 a  is pressed with its joint edge  4  against the joint edge  3  of the strip panel  1  and is angled down against the subfloor  12  according to FIG. 1 b,  it enters a locking groove  14  formed in the underside  16  of the groove panel  2  and extending parallel to and spaced from the joint edge  4 . In FIG. 1 b,  the locking element  8  and the locking groove  14  together form a mechanical connection locking the panels  1 ,  2  to each other in the direction designated D 2 . More specifically, the locking surface  10  of the locking element  8  serves as a stop with respect to the surface of the locking groove  14  closest to the joint edge  4 . 
     When the panels  1  and  2  are joined together, they can however occupy such a relative position in the direction D 2  that there is a small play Δ between the locking surface  10  and the locking groove  14 . This mechanical connection in the direction D 2  allows mutual displacement of the panels  1 ,  2  in the direction of the joint, which considerably facilitates the laying and enables joining together the short sides by snap action. 
     As appears from FIGS. 4 a  and  4   b,  each panel in the system has a strip  6  at one long side  3  and a locking groove  14  at the other long side  4 , as well as a strip  6 ′ at one short side  3 ′ and a locking groove  14 ′ at the other short side  4 ′. 
     Furthermore, the joint edge  3  of the strip panel  1  has in its underside  18  a recess  20  extending throughout the entire joint edge  3  and forming together with the upper face  22  of the strip  6  a laterally open recess  24 . The joint edge  4  of the groove panel  2  has in its top side  26  a corresponding recess  28  forming a locking tongue  30  to be accommodated in the recess  24  so as to form a mechanical connection locking the joint edges  3 ,  4  to each other in the direction designated D 1 . This connection can be achieved with other designs of the joint edges  3 ,  4 , for example by a bevel thereof such that the joint edge  4  of the groove panel  2  passes obliquely in underneath the joint edge  3  of the strip panel  1  to be locked between that edge and the strip  6 . 
     The panels  1 ,  2  can be taken up in the reverse order of laying without causing any damage to the joint, and be laid again. 
     The strip  6  is mounted in a tolerance-equalising groove  40  in the underside  18  of the strip panel  1  adjacent the joint edge  3 . In this embodiment, the width of the equalising groove  40  is approximately equal to half the width of the strip  6 , i.e. about 15 mm. By means of the equalising groove  40 , it is ensured that there will always exist between the top side  21  of the panel  1  and the bottom of the groove  40  an exact, predetermined distance E which is slightly smaller than the minimum thickness (2.8 mm) of the floor panels  1 ,  2 . The groove panel  2  has a corresponding tolerance-equalising surface or groove  42  in the underside  16  of the joint edge  4 . The distance between the equalising surface  42  and the top side  26  of the groove panel  2  is equal to the aforementioned exact distance E. Further, the thickness of the strip  6  is so chosen that the underside  44  of the strip is situated slightly below the undersides  18  and  16  of the floor panels  1  and  2 , respectively. In this manner, the entire joint will rest on the strip  6 , and all vertical downwardly-directed forces will be efficiently transmitted to the subfloor  12  without any stresses being exerted on the joint edges  3 ,  4 . Thanks to the provision of the equalising grooves  40 ,  42 , an entirely even joint will be achieved on the top side, despite the thickness tolerances or the panels  1 ,  2 , without having to perform any grinding or the like across the whole panels. Especially, this obviates the risk of damage to the bottom layer of the compact laminate, which might give rise to bulging of the panels. 
     Reference is now made to the embodiment of FIGS. 2 a-c  showing in a succession substantially the same laying method as in FIGS. 1 a  and  1   b.  The embodiment of FIGS. 2 a-c  primarily differs from the embodiment of FIGS. 1 a  and  1   b  in that the strip  6  is mounted on the strip panel  1  by means of a mechanical connection instead of glue. To provide this mechanical connection, illustrated in more detail in FIG. 6, a groove  50  is provided in the underside  18  of the strip panel  1  at a distance from the recess  24 . The groove  50  may be formed either as a continuous groove extending throughout the entire length of the panel  1 , or as a number of separate grooves. The groove  50  defines, together with the recess  24 , a dovetail gripping edge  52 , the underside of which exhibits an exact equalising distance E to the top side  21  of the strip panel  1 . The aluminium strip  6  has a number of punched and bent tongues  54 , as well as one or more lips  56  which are bent round opposite sides of the gripping edge  52  in clamping engagement therewith. This connection is shown in detail from below in the perspective view of FIG.  6 . 
     Alternatively, a mechanical connection between the strip  6  and the strip panel  1  can be provided as illustrated in FIG. 7 showing in section a cut-away part of the strip panel  1  turned upside down. In FIG. 7, the mechanical connection comprises a dovetail recess  58  in the underside  13  of the strip panel  1 , as well as tongues/lips  60  punched and bent from the strip  6  and clamping against opposing inner sides of the recess  58 . 
     The embodiment of FIGS. 2 a-c  is further characterised in that the locking element  3  of the strip  6  is designed as a component bent from the aluminium sheet and having an operative locking surface  10  extending at right angles up from the front side  22  of the strip  6  through a height of e.g. 0.5 mm, and a rounded guide surface  34  facilitating the insertion of the locking element  8  into the locking groove  14  when angling down the groove panel  2  towards the subfloor  12  (FIG. 2 b ), as well as a portion  36  which is inclined towards the subfloor  12  and which is not operative in the laying method illustrated in FIGS. 2 a-c.    
     Further, it can be seen from FIGS. 2 a-c  that the joint edge  3  of the strip panel  1  has a lower bevel  70  which cooperates during laying with a corresponding upper bevel  72  of the joint edge  4  of the groove panel  2 , such that the panels  1  and  2  are forced to move vertically towards each other when their joint edges  3 ,  4  are moved up to each other and the panels are pressed together horizontally. 
     Preferably, the locking surface  10  is so located relative to the joint edge  3  that when the groove panel  2 , starting from the joined position in FIG. 2 c,  is pressed horizontally in the direction D 2  against the strip panel  1  and is turned angularly up from the strip  6 , the maximum distance between the axis of rotation A of the groove panel  2  and the locking surface  10  of the locking groove is such that the locking element  8  can leave the locking groove  14  without coming into contact with it. 
     FIGS. 3 a - 3   b  show another joining method for mechanically joining together the floor panels of FIGS. 2 a-c.  The method illustrated in FIGS. 3 a-c  relies on the fact that the strip  6  is resilient and is especially useful for joining together the short sides of floor panels which have already been joined along one long side as illustrated in FIGS. 2 a-c.  The method of FIGS. 3 a-c  is performed by first placing the two panels  1  and  2  flat on the subfloor  12  and then moving them horizontally towards each other according to FIG. 3 b.  The inclined portion  36  of the locking element  8  then serves as a guide surface which guides the joint edge  4  of the groove panel  2  up on to the upper side  22  of the strip  6 . The strip  6  will then be urged downwards while the locking element  8  is sliding on the equalising surface  42 . When the joint edges  3 ,  4  have been brought into complete engagement with each other horizontally, the locking element  8  will snap into the locking groove  14  (FIG. 3 c ), thereby providing the same locking as in FIG. 2 c.  The same locking method can also be used by placing, in the initial position, the joint edge  4  of the groove panel with the equalising groove  42  on the locking element  10  (FIG. 3 a ). The inclined portion  36  of the locking element  10  then is not operative. This technique thus makes it possible to lock the floor panels mechanically in all directions, and by repeating the laying operations the whole floor can be laid without using any glue. 
     The invention is not restricted to the preferred embodiments described above and illustrated in the drawings, but several variants and modifications thereof are conceivable within the scope of the appended claims. The strip  6  can be divided into small sections covering the major part of the joint length. Further, the thickness of the strip  6  may vary throughout its width. All strips, locking grooves, locking elements and recesses are so dimensioned as to enable laying the floor panels with flat top sides in a manner to rest on the strip  6  in the joint. If the floor panels consist of compact laminate and if silicone or any other sealing compound, a rubber strip or any other sealing device is applied prior to laying between the flat projecting part of the strip  6  and the groove panel  2  and/or in the recess  26 , a moisture-proof floor is obtained. 
     As appears from FIG. 6, an underlay  46 , e.g. of floor board, foam or felt, can be mounted on the underside of the panels during the manufacture thereof. In one embodiment, the underlay  46  covers the strip  6  up to the locking element  8 , such that the joint between the underlays  46  becomes offset in relation to the joint between the joint edges  3  and  4 . 
     In the embodiment of FIG. 5, the strip  6  and its locking element  8  are integrally formed with the strip panel  1 , the projecting part of the strip  6  thus forming an extension of the lower part of the joint edge  3 . The locking function is the same as in the embodiments described above. On he underside  18  of the strip panel  1 , there is provided a separate strip, band or the like  74  extending throughout the entire length of the joint and having, in this embodiment, a width covering approximately the same surface as the separate strip  6  of the previous embodiments. The strip  74  can be provided directly on the rear side  18  or in a recess formed therein (not shown), so that the distance from the front side  21 ,  26  of the floor to the rear side  76 , including the thickness of the strip  74 , always is at least equal to the corresponding distance in the panel having the greatest thickness tolerance. The panels  1 ,  2  will then rest, in the joint, on the strip  74  or only on the undersides  18 ,  16  of the panels, if these sides are made plane. 
     When using a material which does not permit downward bending of the strip  6  or the locking element  8 , laying can be performed in the way shown in FIG. 5. A floor panel  2   a  is moved angled upwardly with its long side  4   a  into engagement with the long side  3  of a previously laid floor panel  1  while at the same time a third floor panel  2   b  is moved with its short side  4   b ′ into engagement with the short side  3   a ′ of the upwardly-angled floor panel  2   a  and is fastened by angling the panel  2   b  downwards. The panel  2   b  is then pushed along the short side  3   a ′ of the upwardly-angled floor panel  2   a  until its long side  4   b  encounters the long side  3  of the initially-laid panel  1 . The two upwardly-angled panels  2   a  and  2   b  are therefore angled down on to the subfloor  12  so as to bring about locking. 
     By a reverse procedure the panels can be taken up in the reverse order of laying without causing any damage to the joint, and be laid again. 
     Several variants of preferred laying methods are conceivable. For example, the strip panel can be inserted under the groove panel, thus enabling the laying of panels in all four directions with respect to the initial position.