As it is widely known, there are sub-floors formed by a sub- structure of wooden bars, on which wooden boards are nailed forming the floor covering. Under another technology, there are sub-floors formed by concrete flagstones which are covered by small solid wooden plates, by boards made of massive wood or plywood, or by other coverings that form the floor itself.

These small solid wooden plates usually are applied on the concrete sub-floor by using pitch, and the boards made of massive wood or plywood are nailed or glued thereon.

A more modern technique of floor covering is represented by internationally so called"floating floor coverings", which are neither glued nor nailed to any substructure but instead comprise panels formed by boards of massive wood or plywood, or high density wood, each of the panels has side edges with tongue and groove type fittings. For the formation and laying of the floating floor, glue is applied to the side edges and/or onto the tongue and into the groove of the side edges of the panel. In the next step, as many panels as are necessary to cover a room are assembled to each other by inserting the tongue into the groove and drying and hardening of the glue, turning the set of panels into a single, integral floor covering; this floor is called"floating"as it remains just supported on the concrete sub-floor which gives the advantage that the floating floor may expand and move due to changes in humidity and temperature.

However, an intermediate material serving as a lagging is placed between the"floating floor"and the sub-floor in order to minimize unevenness existing on sub-floors made of concrete, and in order to further reduce the noise caused when walking on them, which still is the main disadvantage of the "floating floors". Said intermediate material may consist of felt, rubber, cork, polyester foam, plastic with bubbles or the like, wherein the choice of material should take into account that the application of such intermediate material must be easy, as it is normally only spread on the sub-floor before laying the floor covering. Nevertheless, none of the above mentioned intermediate materials represent an appropriate or ideal economical solution, as the most effective materials cost nearly as much as the floor itself, thus overpricing the product in the consumer market.

A reduction of noise during walking could also be achieved by applying glue on the whole surface of the sub-floor instead of or in addition to applying glue on the side edges of the panels. The main disadvantage of this alternative solution is that glue always contains a high percentage of humidity, and as the glue is applied on the whole surface of the sub-floor, that humidity will certainly be transferred to the lower surface of the panels or floor covering, consequently causing an excessive warping of several panels, their boards or any substructure of the floor.

Latest developments of flooring panels have introduced panels with groove and tongue fittings, which may be assembled without the necessity of glue and which are fixed to each other against movement in the horizontal plane of the panels by corresponding protuberances and indentations formed on protruding parts of the groove and tongue fittings. The upper and lower side of tongue and groove each are tapered and two adjacent panels are assembled by an arching movement, i. e. the tongue of one panel is introduced into the groove by inclination of nearly 10° and then slide along a slip-point on the upper side of a lower protruding projection of the other panel until its tip reaches the groove base. As the profile of groove and tongue of these panels is quiet detailed and complicated, special tools for manufacturing of these new flooring panels are needed leading to excessive manufacturing costs as well as low production rates per hour.

Object of the present invention is to provide flooring panels and a method of laying flooring panels on sub-floors which minimize the inconveniences mentioned with respect to the prior art. The flooring panels should be easily assembled while their manufacturing costs are low. The method shall be performed without time consuming steps and without excessive costs for material and man power.

SUMMARY OF THE INVENTION These objects are achieved according to the invention with a flooring panel having a rectangular shape with four side edges, one long side edge and one transverse side edge having one central, rectangular and longitudinally extending strip- like tongue element with one single ledge in its lower part, while the opposite long side edge and the opposite transverse side edge has one central, rectangular and longitudinally extending groove element with one single retaining recess in its lower part adapted for insertion of the tongue element and ledge to enable the coupling of adjacent panels both in parallel and perpendicularly with the plane of the panels.

Adjacent panels are preferably assembled by simply pushing the tongue element into the groove horizontally, thereby locking the ledge into the recess so that the panels are coupled and locked in parallel and perpendicularly with the plane of the panels. With regard to the prior art, it must be said that wood panels for floor coverings with conventional tongue and groove type fitting were fixed by glue to each other, thus it was necessary to use pressure belts or adhesive tapes to keep tongue and groove linked up to the consolidation of the glue, resulting in an increase of manpower and cost of material. If belts or tapes are not used in the systems of the prior art during hardening of the glue, the groove and tongue fitting inevitably will stick away from each other, forming unacceptable gaps that damage the finishing quality of the wooden floor covering.

A further advantage of the inventive solution is that the ledge in the underside of the tongue element may serve as a barrier for glue, if used, to fix adjacent panels to each other. In the wooden flooring panels according to the invention, the ledges and retaining recesses form couplings that keep tongue and groove linked up to the consolidation of any glue, if used for coupling the panels, and especially for keeping tongue and groove linked up to the consolidation of glue lines which are used to fix the floor covering to the sub-floor, eliminating the necessity of pressure belts or adhesive tapes, and in this way there will be no need for the additional manpower and cost related to the mentioned materials.

Advantageously, the shape both of the tongue element with ledge and of the groove element with recess may be constant over the entire length of the corresponding side edge of the panel. Further, the ledge may comprise a leading front face angled almost 55° with respect to the front side of the tongue, a flat lower side angled perpendicular to the front side and a rear side angled perpendicular to the leading front face and/or the retaining recess has front and rear surfaces angled 90° to each other. Due to this configuration, the tongue may easily slide into the groove obtaining the locking of the panels with the rear side of the ledge and the recess and thus preventing disassembling of adjacent panels.

In one embodiment, the upper side of the tongue element and the inner side of the groove facing down are flat and rectangular with respect to the groove base and tongue element front side, respectively. Further, the front flange between upper panel finishing surface and tongue element and the opposite front flange between panel surface and groove may be angled backwards to leave a free space inside assembled panels. Particles, such as dust, glue, sawdust or the like may be pressed into this free space when assembling adjacent panels, thus avoiding gaps and providing a good finishing quality of the floor covering. As the profile of ledge and recess is simple, has flattened faces and constant angles, ledge and recess may be manufactured with revolving tools, thus reducing producing costs and providing good accuracy of manufacture and high production rate.

The above mentioned objects are also achieved with a method for laying floor coverings with flooring panels on sub-floors made of concrete or other materials, comprising flooring panels formed by boards of massive wood or plywood, or of high density wood, each panel having side edges with tongue and groove type fittings, wherein the method is characterized by the steps of distributing flexible guides spaced from each other in longitudinal parallel sequences on the sub-floor made of concrete or other material, applying glue lines with a glue of high viscosity between the guides, the glue lines having a height higher than the guides, and laying and coupling of the flooring panels, whereby such guides are levelling the panels, separating the panels from the sub-floor during laying and are forming initially longitudinal air passage between the panels and the sub-floor by the longitudinal open spaces existing between the glue lines and the separating and levelling flexible guides.

This method was developed in order to minimize the inconveniences mentioned in the prior art. By the proposed method it is possible to achieve a reduction to about eight per cent in the use of glue compared to the conventional methods, in which the glue is applied on the whole surface of the sub-floor. It should be emphasized that the proposed method eliminates completely the necessity of expensive and inefficient intermediate or lagging materials, such as felt, rubber, cork, polyester foam, plastic with bubbles and other.

Another very important point is the fact that in the proposed method, the wooden floor covering is just partially glued on the sub-floor, decreasing considerably the noise caused by walking and it must be pointed out that the mentioned reduction of noise is more efficient than the reduction caused by the intermediate materials mentioned before with respect to the known"floating floors".

Advantageously, the guides are removed after the drying of the glue from the gap between the formed floor and the sub-floor, only remaining between the sub-floor and the panels longitudinal separating rows of solidificated glue lines, now forming air ducts between each other, the flooring panels and the sub-floor. The air ducts allow the evaporation of the humidity, considerably decreasing the risk that a warping of the wooden floor covering may occur. In another embodiment, the guides may remain as loosing guides between the panels and the sub-floor during and after solidification and hardening of the glue, thus serving as additional lagging to reduce noise when walking on the floor covering. Flooring panels having a nut and groove type fitting with ledge and corresponding recess may be advantageously used with the inventive method as these panels may be coupled without the need of belts, tapes or the like and may be affixed by positive locking only.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and advantages of the method for laying wooden floor coverings and the structure of the flooring panels will be better understood from the following description of a preferred embodiment shown in the attached drawings, in which: Fig. 1 shows in perspective several panels of a floor covering laid on a sub-floor using the method according to the invention; Fig. 2 shows in a side view the floor covering with inserted guides; Fig. 3 shows in a side view the floor covering after removing of the guides; Fig. 4 shows a cross section of two adjacent panels before the process of joining; Fig. 5 shows a cross section of two adjacent panels after joining the groove and tongue type fitting; Fig. 6 shows in perspective a flooring panel; and Fig. 7 shows in detail the structure of the tongue profile and the groove profile of a preferred embodiment.

DETAILED DESCRIPTION OF A PREFFERD EMBODIMENT Fig. 1-3 show the different sequences of the method for laying a floor covering on a sub-floor CP made of concrete or some other material. The floor covering comprises several panels R formed by massive wooden boards or plywood, or of high density wood, each panel having four side edges 7,8,9 11 with tongue and groove type fittings. In the inventive method there are used essentially separating and levelling flexible guides 1, which are distributed in a spaced way in longitudinal parallel sequences on the sub-floor CP, thus serving as parallel rulers for applying glue lines 2 of a glue with high viscosity, parallel to each other and spaced by the guides. The glue is applied such that its height is higher than the height of the guides 1, as symbolized in the right half of Fig. 1. The guides 1 may consist of bands, ropes, strips or the like of suitable material and the guides are preferably distributed and initially arranged perpendicular to the long side edges of the panels R.

As shown in Fig. 2, when laying adjacent panels R on the top side of the guides 1, the glue lines 2 will be flattened as far as the uniform height of the guides 1 be reached, forming initially longitudinal sequences of air passage between the wooden flooring panels R and the sub-floor CP. These air passages are formed by longitudinally open spaces 3 existing between the glue lines 2 and the separating and levelling flexible guides 1.

After drying and solidification of the glue, as shown in Fig.

3 with reference numeral 2A, the guides are removed from the inside of the floor, thus remaining between sub-floor CP and flooring panels R the longitudinal and separated rows of the solidified glue lines 2A only, which then form air ducts 3A between the flooring panels R, sub-floor CP and the solidified glue line rows 2A. These air ducts 3A allow the evaporation of humidity thus considerably decreasing the probability that a warping of the flooring panels or the laid floor may occur.

The glue lines 2 are shown as straight lines but they may also be applied with zig-zag profile or the like.

Fig. 4 to 7 show the structure of the panels and the inventive groove and tongue fitting in detail. Referring now to Fig. 4, showing in cross-section two adjacent and separated wooden panels having rectangular shape, each panel R comprises, at a first long side edge 11, one central rectangular and longitudinal tongue element 4 with a one and single ledge 4A in its underside 12, and there is at the opposite, rear long side edge 7 a central rectangular and longitudinal groove element 5 with one single retaining recess 5A in its lower half 13 facing upwards. Groove 5 and retaining recess 5A are adapted for insertion of the tongue element 4 and ledge 4A in order to lock adjacent panels after joining both in parallel and perpendicularly with the plane of the panels, as shown in Fig. 5. Glue is not needed for locking the tongue and groove fitting against disassembling.

As shown in Fig. 6, one transverse side edge 9 also has a central, rectangular and longitudinal groove element 5 with the same retaining recess 5A in its lower part 13, and the opposite transverse side edge 8 has a corresponding longitudinal tongue element 4 with one ledge 4A in its underside 12. The shape both of each tongue element 4 with ledge 4A and of each groove element 5 with recess 5A is constant over the entire length of the corresponding side edge of the panel R, as best seen in Fig. 6. Adjacent panels R thus may be assembled and linked at all side edges by simple fittings-without the use of glue at the bordering side edges - allowing a floor covering with plain upper surface.

As shown in Fig. 7, the profile of tongue element 4 and ledge 4A is almost simple and may be manufactured with revolving tools 30. The profile of groove 5 an recess 5A at the opposite side edge is as simple as the other, corresponding profile and may also be manufactured with revolving tools 31, so that high production rates are possible while tool costs are low. Each ledge 4A comprises a leading front face 15 angled between 50° and 60°, preferably 55° with respect to the front side 16 of the tongue 4, a flat lower side 18 angled perpendicular to the front side 16 and a rear side 17 angled perpendicular to the leading front face 15. The side edge 7 comprising the groove 5 has no protruding parts but almost a vertical contacting flange. The retaining recess 5A in the lower part 13 of groove 5 has front and rear surfaces 21,22 angled 90° to each other.

The upper side 19 of the tongue element 4 and the underside 23 of the groove 5 are flat and at right angle to the groove base 24 and tongue element front side 16, respectively. The lower part 13 of groove 5 is flat except for the recess 5A. The tongue element 4A may be inserted horizontally into the groove 5 i. e. by receiving an impact strike with a hammer or the like on the rear side edge 7 whereby the ledge 4A slips into the retaining recess 5A. Both adjacent panels are then locked, since the rear surface 21 prevents ledge 4A from being separated from the recess 5A.

If glue is used to additionally fix adjacent panels R to each other, the glue may advantageously be applied on the underside 12 of tongue element 4 into the cavity between the rear side 17 of ledge 4A and the lower, vertical front flange 26 of side edge 11. Ledge 4A thus forms a barrier, preventing glue from rising to the finishing surface 25 of the panels R. The front flange 27 between upper panel surface 25 and tongue element 4 and the opposite front flange 28 between panel surface 25 and groove 5 are angled backwards almost with 10° to leave a free space 29 (Fig. 5) inside assembled panels R. Upper front flange 27 and lower front flange 26 lie almost in the same vertical plane.