TECHNICAL FIELD OF THE INVENTION The invention is related to civil engineering field, that is related to finishing works on buildings, for covering level surfaces, specially floors, and can be classified in E 04 F 15/00-Flooring, according to the International Patent Classification-seventh edition (IPC7).

TECHNICAL PROBLEM In practice, slab-like floor coverings must be installed in a way that they are mutually well connected, with minimum interspace, forming together perfect level surface. This surface must be able to support, in places, static and dynamic load, without raise and lowering down, in places, of one or more slabs, especially in relation to neighboring slabs in mutually opposite direction. The objective is to design level slab-like floor covering, which firmness and elasticity is lasting, but it can be, if desired, taken to pieces without destroying slabs. Technical problem to be solved is the construction of connecting elements that must link all slab-like elements (hereinafter slabs), with no remaining free edges, with the possibility of mutual additional taking slabs to pieces for partial substitution or removal.

An average skillful person must be able to install connecting elements in a simple way, without using special tool. After assembling, connecting elements must not be visible. The base on which slabs are installed, by means of such connecting elements, has not to be significantly leveled and smooth, while filling up of uneven spots that form holes between slab covering and supporting base, is not the issue this invention. Nevertheless, connecting elements should insure good mutual connection of slabs, even when such uneven spots appear.

STATE OF THE ART Contemporary solution for connecting floor slab elements anticipate variants with connecting elements but also various designs of slabs that are mutually connectable without connecting elements. The edges of some slabs have grooves on one side and tongues on the other, so you can get joint mutual fitting of edges into neighboring slabs, for example, with parquetry laths (FR 2746127 Al) and laminates (e. g. with hollow, longish elements as in EP 0783064 A).

Most of the connecting elements are designed for installment under the crossing-the place where 4 neighboring slabs are joined. In some cases their primary function is floor cover leveling that is made of slab-like elements (e. g. FR 2761095), like ceramic slabs or floor stone slabs, so there is a mechanical regulation of the height of the particular connecting elements. In other cases connecting elements are individually permanently fixed to all 4 neighboring slabs, on their junctions (e. g. JP 11013203), or along whole connecting line of these slabs, in case that connecting element has a shape of a strip with holes. An interesting solution for installing and connecting slabs is a self- centered slab for production of prefabricated bearing surfaces with mosaic, ceramic slabs or framing glass (e. g. DE 3801805), where there is a net-like screen with compartments, where slabs are laid in precisely prepared hollows, and where they are arranged in such a way to be interconnected by glue.

None of the above mentioned solutions for connecting slabs into level surface for floor covering doesn't anticipate single connecting elements that would connect slabs all along edges, in this way preventing every possible shifting of a single slab in relation to neighboring ones. Also, many of these solutions don't make it possible, neither they predict additional separation of joints, without damaging slab edges on joining places, slabs in their entirely or connecting elements themselves.

DESCRIPTION OF THE INVENTION ESSENCE For installing level slab-like coverings specially for floors, the method of connecting elements by simple hand tools is chosen in this invention (rubber or plastic hammer), with a single sequenced installment of slabs (2) that have to be linked by connecting elements (1), so as to perform solid frontal connection of slabs, with possibility of additional separation, if necessary.

With this technical solution the use of specially designed solid, level and cross-shaped connecting elements, that are mutually connectable on"tongue-groove"principle, is anticipated. Arms of such a cross must be placed into grooves that are made all along the edges of the slabs to be mutually connected. Every arm of the cross-shaped connecting element (1) has a shape of level flat tape whose cross-section thickness (a) is equal to the groove width (3) and the length of cross-section tape (b) is equal to half depth (b/2) of the groove (3), in which arms are placed. The length of some arms of cross-shaped connecting element (1) is equal to half length side (s/2) of one slab, so the groove in it (3) is completely filled when arms of two cross shaped elements (1) are connected. In need of connecting square slabs, it is necessary to choose cross-shaped connecting element (1) with arms of equal length. If it is about connecting rectangular slabs, then it is necessary to choose cross-shaped element with adequate arms of different length. The cross-shaped connecting element can be made of metal, plastic or wood, but it is recommend to be of metal with necessary strength and elasticity, so that arms can properly stiffen two slabs to be connected. It is important that compatibility of arms and grooves in slabs is kept so as to get firm joint on inserting, as well as for mutual connecting cross shaped connecting arm elements on"tongue-groove"principle.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 Cross-shaped connecting element-spatial (3D) display and arms ending cross-section Fig. 2 Method of connecting square slabs by using cross-shaped connecting element.

Fig. 3 Presentation of accomplished joint of four slabs, and installing of next cross-shaped connecting element.

Fig. 4 Presentation of connecting two arms of cross shaped connecting element-spatial display

DESCRIPTION OF THE EMBODIMENT OF THE INVENTION This invention can be carried out in several ways, all of which have in common that connecting element is always cross shaped, with flat, long, thin lath arms. These arms should be inserted into grooves (3) all along slab edges (2) that are connected so as to get floor covering.

In fig. 1 cross-shaped connecting element (1) is presented with arms of the same length. Such connecting element is intended for connecting square like slabs, as shown in figures 2 and 3. The opposite arms of cross-shaped connecting element are of different shape endings: on one side there is a short tongue-"feather-edge element" (4) of reduced arm thickness, to approximately 1/3 of the width, shown in detail"A", and on the other side there is a hollow-"groove" (5) compatible with "tongue"thickness (d) and its length, as shown in detail"B".

The condition for using this invention comprising a cross-shaped connecting element (1) is that every slab (2) which has to be connected with the same such slab has grooves (3) made along the center of each of its 4 sides. The depth of this groove has to be equal to half arm width of cross- shaped connecting element (1). One cross-shaped connecting element should link 4 identical slabs that have to be installed one by one on arms of cross-shaped connecting element.

The assembling starts (phase 1, figure 2) with placing the first cross-shaped connecting element (1) into grooves at the angle of a slab (2). Slight manual blows can perform this with rubber hammer on the lateral sides of arms of connecting element (1). Both mutually vertical arms of connecting element (1) have to be placed into grooves (3) completely, whereby it is fixed exactly at the corner of a slab (2), while its arms are sticking out from the edge of the slab with the half of its width.

The next slab should lean against such a fixed cross-shaped connecting element (phase 2, figure 2) and it should be secured in the same way so that remaining width of one connecting arm (1) enters the groove (3) completely at the corner of the other slab. Now, both slabs lean against each other and one arm of connecting element is placed at the same time into groves of both slabs up to their half side, but it is not visible. The same procedure goes on until all four slabs are assembled on all 4 arms of cross-shaped element that connect them (fig. 3).

In the next phase (fig. 4) the other cross shaped connecting element (1) is taken that shall be on "tongue-groove"principle linked by one of its arms, with the already fixed first cross shaped element (1) with one of its 4 sides (fig. 3). This procedure, with in this way connected slabs, is repeated until level covering is formed, and until net of connecting cross elements is formed.

Although this is not visible, in fact, 4 cross-like connecting elements (1) encircle every slab (2) along all of its sides, filling completely grooves (3) made in slab edges. Therewith, the mutual connection of arms, on"tongue-groove"principle is placed exactly on the half length of the lateral edge of a slab. This place is chosen as being the most favorable in terms of load supporting, as distinguished from corners, for which it was experimentally proved that they represent the most unfavorable point in terms of load suppor, where 4 slabs are connected on their corners. That's why solid cross-shaped connecting element, whose strongest point is the intersection of arms, is placed as a support exactly on this the most unfavorably loaded place.

Net obtained from joined cross-shaped connecting elements should represent design solution by which increased solidity of slab-like covering is obtained, e. g. on the floor. Therewith, joint leveling of 4 slabs is surely obtained. Existing uneven spots under such formed covering don't represent major problem any longer as the covering in its entirely is now solid whole. Its elasticity depends only of material elasticity from which connecting elements are made.

UTILIZATION OF THE INVENTION The invention can be applied without special conditions, on the part of an average skillful person using common manual tools. Connecting element is equally suitable for installing slabs indoor and outdoor. The base on which the slabs are installed by use of cross-shaped connecting elements, must be level. After the base is covered with slabs, it is possible to use such slab surface immediately, since no materials that need to dry up or stiffen are used.

Since connecting elements are not visible from upper finished level surface, as they are hidden in grooves of slab edges, their esthetic effect is not relevant, so they can be made of the cheapest material in any color. It is important that arms of cross-shaped connecting elements are undamaged

and without additional protuberances, especially on their ends. That is important so as to achieve firm joint on"tongue-groove"principle, so that thin lath shaped arms could have suitable place in the grooves of slab edges.

In cases of required reconstruction of slab-like floor covering or replacing damaged slabs, it is possible to take to pieces the floor covering by taking out single slabs so that mutual connection of arms is taken to pieces on"tongue-groove"principle, and by separating slabs from arms. It is possible to use the same connecting elements for additional connecting, that is, for separated settings of new slabs or combination of new slabs with the old ones.

Shortening of single arms by cutting, chopping or sawing off, should not to be a problem, and this need may appear in case of leveling slabs on floor covering ends, e. g. on the meeting places of floor covering and walls. It is important that all grooves on side edges of slabs are filled up with arms of connecting elements, even with those shortened ones to insure solidity of the slab edges.

Duration of connecting elements need to be at least equal to slab coverings duration, but it is desirable that it is even longer, so to use them repeatedly on the same place or other places.