The present invention relates to the joining of panel plate elements for the formation of wall or floor coverings, in particular the latter. It is well known that wooden floor- ings, besides of simple, spiked floor boards, may be made of parquet staves or plate elements with a more or less struc- tured surface, e. g. with a parquet stave pattern, which are joined by gluing edge to edge with an associated rib and groove engagement. However, there are quite noticeable prob- lems with respect to a correct gluing together, not least in the do-it-yourself-area, where both overdosage and underdos- age of glue is rather common.

It is customary practice to apply the glue from a nozzle spout of a compressible glue bootle and to thereby introduce the glue into the groove of the grooved edge portions. This is an unlucky practice, because the ribs and grooves fit rather closely together, whereby it can be difficult to press the edges entirely together. Even a very narrow slit between the edges makes the joint sensitive to intrusion of water, whereby the material may swell along the joint line. The same may happen even by an overdosing of the glue, already due to the water content of the glue itself. A swelling even at the underside will cause the edge areas to be slightly raised and thus make them susceptible to heavy wear.

Exaggerated glue dosage will incur a useless overconsump- tion of glue and even difficulties with respect to removal of the surplus of glue that will reveal itself as upstanding glue ridges along the joint lines; a corresponding surplus may similarly appear at the underside, where it is not even observed.

Underdosing of the glue presents a special problem, be- cause it is not only a perhaps attractive saving possibility for the customer, but also involves problems with respect to product responsability on the part of the manufacturer, since the flooring as a whole and not only the single elements should meet with certain quality standards.

For the invention it is a purpose to provide improvements in both of these respects.

As far as the glue application is concerned, the inven- tion is based on the consideration that it is of primary im- portance to establish the gluing together between the edge surface portions that are pressed together, rather than be- tween the interengaging surfaces of the rib and groove con- nections. On this basis it has been found possible to design a special applicator nozzle head for use on a compressible glue bottle, this head having two opposed nozzle openings separated by a plate portion adapted to be received in the groove of the grooved joining edge, such that the two nozzles will be located next to and shortly outside the opposed regu- lar edge surface portions when the bottle head is placed against and moved along the grooved side edge of the element.

Persons desirous of overdosing the glue should be satis- fied in being instructed that the limited dosage provided by the use of such a nozzle head will be sufficient for a fully qualified result, and persons desirous of underdosing can be correspondingly informed that the very limited dosage of the applicator head will be a preset condition for the required quality guarantee. It will be readily clear to any user that the dosage really is very limited.

An obvious alternative is that the opposed glue nozzles can be arranged on either side of a nozzle head, separated by a groove formation operable to receive the rib of a ribbed joining edge.

Some users will still be able to overdose, squeezing the glue bottle strongly and moving it slowly, which, however, will amount to the user's own problem with respect to the overconsumption of glue and difficulties in cancelling the traces of surplus glue.

A bigger problem is encountered with respect to users tending to underdose the glue, by squeezing the bottle too lightly or moving it too fast. Without further measures it will be very difficult to prove later on that the glue has been underdosed, but the invention provides for a remedy in proposing that a tracing agent is added to the glue, such

that in case of a later failure incident it will be possible, e. g. by ultraviolet irradiation of the broken edges, to as- certain whether or not the glue has been applied as pre- scribed from the beginning.

In the following the invention is described in more de- tail with reference to the drawing, in which Fig. 1 is a perspective view of three plate elements to be edgewise joined, Fig. 2 is a cross section of a joint, Fig. 3 is a perspective view of a glue bottle provided with a nozzle mouthing cap according to the invention, and Fig. 4 is a side view illustrating the use of the glue bottle, and Fig. 5 is a perspective view of a modified glue bottle cap.

The plate elements 2 shown in Fig. 1 are ordinary floor- ing plates with edge grooves 4 and ribs 6 for joining pur- poses, a joint being more clearly illustrated in Fig. 2. As mentioned, what matters in the joint is that a rather accu- rate, modest amount of glue is applied between the edge sur- face portions 8,8', outside the rib and groove area, before they are pressed together, and it is sufficient to apply the glue to one of these opposed surface portions.

Fig. 3 shows a compressible glue bottle 10 provided with a screw cap member 12 made in accordance with the present in- vention. At its front side this cap member is shaped with a protruding, narrower and cylindrical portion 14 having at its- outer end a diagonally arranged plate portion 16, at either side of which there is provided an outlet nozzle hole 18.

As shown in Fig. 4, the nozzle holes 18 are spaced a dis- tance D1 from the outer end of the plate portion 14 such that when the outer edge of this plate portion is brought to en- gage the bottom of the groove 4, the holes 18 will be spaced a short distance D2 from the surface portions 8. This dis- tance D2 is chosen so as to correspond to the recommended or required optimum thickness of the glue layer to be applied when the bottle is squeezed and drawn along the plate edge.

It will be appreciated that the plate portion 16, in ad- dition to ensuring a correct working orientation and posi- tioning of the nozzle head, will also serve the purpose of closing the groove 4 against intrusion of glue. Also, the nozzle holes 18 are located approximately midways of the re- spective surface portions 8 such that glue, when dosed cor- rectly, will not extend to the outer edges thereof, thus not giving rise to surplus ridge formations when the plate ele- ments are subsequently forced together. The applied glue strings will merely be distributed in a suitable thin layer all over these surfaces when the pressure is applied.

Fig. 5 shows a cap which is modified in that instead of the protruding plate portion 16 the cap is provided with a groove 16'for co-operating with the rib edges of the plates 2.