The present invention relates to a parquet structure, wherein the direction of wood grains constituting the parquet surface layer is perpendicular or at an acute angle relative to the level of a parquet surface.

The invention relates also to a method for manufacturing a parquet, said method comprising the following oper¬ ations:

- laying a parquet body with a surface layer of wood which is made of wood blocks, wherein the direction of wood grains is perpendicular or at an acute angle relative to the level of a parquet surface;

- effecting the smooth grinding of a surface and

- effecting the lacquer finish with a parquet lacquer.

The use of vertically grained wood as a surface layer offers several benefits. Wear resistance, hardness and compression strength in the direction of wood grains are clearly superior to the corresponding values in the direction perpendicular to wood grains.

However, the use of vertically grained wood as a par¬ quet surface layer involves several problems with no satisfactory solutions, which is why no commercial breakthrough has not be achieved thus far, either. One of the problems is the formation of seasoning cracks in and the after-living (dimensional variation) of vertical¬ ly grained wood as a result of moisture variations. Another problem is the porosity of a finished wood surf¬ ace. If a porous surface is conventionally laid with layers of parquet lacquer (e.g. UV-setting urethane lac¬ quers) , the thin lacquer film would quickly break in normal service. The film develops dot-like bursts with

moisture penetrating in wood therethrough to blacken the surface. In traditional horizontal-grain parquets, use is made of a primer lacquer which is non-absorbent in wood and builds a film-like seal between wood and coating lacquer layers. The total consumption of ex¬ pensive parquet lacquers remains relatively low, al-

2 together appr. 30 - 40 g/m . However, such a parquet lacquering or varnishing technique, wherein a primer lacquer seal is applied directly to a ground wood surf¬ ace, would lead in this invention to a disadvantageous and non-durable surface structure.

An object of the invention is to provide a parquet struc¬ ture and its manufacturing method, whereby even the otherwise good wear resistance and hardness of vertical- grain wood can yet be substantially improved while pro¬ viding for an effective additional protection against the penetration of moisture and an effective binding against the forces of remaining moisture induced movements while, at the same time, the amount of an expensive par¬ quet lacquer or varnish can be conventional.

This object is achieved by means of a parquet structure as set forth in the annexed claim 1 as well as by the application of a method as set forth in claim 8 for manufacturing a parquet.

A parquet structure of the invention will now be de¬ scribed in more detail with reference made to the ac¬ companying drawings, in which

Fig. 1 is a perspective view of a cross-sectioned parquet element having a structure of the invention.

Fig. 2 illustrates the use of hexagonal wood blocks in

the surface wood layer of a parquet.

Fig. 3 shows a cross-section of the sandwich structure of a parquet, and

fig. 4 is a larger-scale view showing a vertical sec¬ tion of the surface wood layer of a parquet with wood grains extending in vertical direction.

The manufacturing of parquet structure of the invention proceeds as follows. A polygonal balk of fresh wood is cut perpendicularly or at an acute angle to the wood grains into blocks of suitable thickness (e.g. 14 mm thick) . These wood blocks, a hexagonal example being shown in fig. 2, is impregnated with a water-soluble polyalcohol, e.g. polyethylene glycol (PEG) , which is allowed to absorb and take effect in wood blocks by replacing cell-wall water therein. Absorption can be intensified by a thermal treatment, wherein the wood blocks are heated in a microwave oven and the non- diluted, fluidization-heated PEG is applied as a film to a wood block whose internal vacuum accelerates the absorption of PEG into wood. The purpose is that the water-soluble impregnant replaces a sufficient amount of the cell-wall water in wood cells. This prevents the post-movements (dimensional variations) of wood material caused by seasoning cracks and moisture fluc¬ tuations. It is well known that the moisture-induced movements of wood result explicitly from the amount of water contained in cell walls and from the swelling and shrinking of a cell wall caused by the fluctuations thereof.

The wood blocks, thus impregnated with a water-soluble polyalcohol (e.g. PEG), are stored for 1 to 3 days at

a temperature of 50 - 80 C for a sufficient penetration and diffusion of polyalcohol, whereafter the blocks are dried and, thus, the polyalcohol concentrates upon the removal of water. The block surfaces are ground and the outlines are worked to precise measures. There¬ after, the blocks are glued into blanks of board par¬ quet, i.e. fitted between two body layers 4. Attach¬ ment to the body layer 4 of a parquet element can be ef¬ fected by using a resin or wood adhesive 5 (e.g. a poly¬ ester resin or a pol inyl acetate glue) . The body 4 can preferably be made of plywood having a thickness of e.g. 9 mm. The body 4 may also include one or a plural¬ ity of reinforced plastic layers. The blank is sawn in two parts in the middle of wood blocks 1 and the result¬ ing boards are provided with but ents and the sawn surf¬ aces are ground. Following the sawing and grinding, the vertical-grained surface layer 1 has a thickness of e.g. 3,0 - 3,5 mm.

To the surface of a finished wood parquet element is applied some filling resin or varnish which is allowed to impregnate inside wood grains and in interstices therebetween. The impregnation of filling resin is accelerated basically the same way as described above in relation to the impregnation of PEG. Thus, the boards are pre-heated and, upon cooling, they absorb the resin to a sufficient depth inside wood grains and in the interstices therebetween. The employed filling resin or varnish is preferably some inexpensive poly¬ ester resin to maintain the parquet manufacturing costs reasonable despite the fact that, due to the porosity of the surface, the required amount of resin will be more than

100 g/m ² , typically 100 - 300 g/m ² , preferably 150 -

2 200 g/m . Thus, the filling resin or varnish impreg¬ nates locally to the depth of up to 0,5 mm and over

most of the surface area to the depth of more than 0,2 mm. Thus, the thickness of a filling resin or varnish layer 2 varies according to the porosity and absorbing capacity of wood but remains typically with¬ in the above range. The process preferably involves the use of a UV-setting polyester resin but also a conventional extra heat activated (accelerated) curing reaction is possible. The layer built by filling resin or varnish 2 improves substantially the wear resistance and hardness of vertical-grained wood. The surface filling layer also provides an extra barrier against the penetration of moisture and at the same time braces the structure against the forces created by the remain¬ ing moisture-induced movements.

By virtue of filling layer 2 the consumption of expen¬ sive parquet lacquers, such as UV-setting polyurethane lacquers, remains on the same level as or lower than in conventional board parquets, i.e. it is typically

2 20 - 50 g/m . Thus, the amount of wood-impregnating filling resin or varnish is appr. 4 - 5 times that of a parquet lacquer. The filling resin may also be one of the following alternatives: acrylic resin, epoxy resin, urea formaldehyde and phenolic resin. A clear, colourless polyester resin is preferable as it is capable of well bringing out the inherent hues and natural beauty of wood. If necessary, the filling resin can be admixed with whitening pigments, such as titanium white or resin-soluble colourants.

A method of the invention can also be used for manu¬ facturing high-quality parquet from soft grades of wood. For example, tests have been made with alder to manufacture a vertical-grained wood parquet having about a double hardness and a multiple wear resistance

compared with normal oakwood parquet. Also aspen can be used to manufacture a parquet competitive with cur¬ rent grades of parquet in terms of its wear resistance and hardness. The same applies also to the relatives of aspen, e.g. poplar. In fact, one discovery and ad¬ vantage of the invention relates to the very use of soft grades of wood. Since the compression strength of soft grades of wood in the transverse direction of grains is low, also the cross-grain directed forces, which the grain structure is able to transmit, remain low and this is another reason why the contact-induced movements of parquet remain quite negligible.

An individual parquet element can be made relatively wide {e.g. 278 mm) whereby, when using wood blocks dif¬ ferent from each other in terms of colour tones and sizes/shapes, it is possible to create an extensive selection of designs by varying their lay-down patterns. A possibility of using inexpensive timber materials, such as alder and aspen, renders a parquet structure of the invention competitive also in terms of price.

This method can be applied for manufacturing a ready- made parquet or board parquet but it can also be applied as a genuine parquet, which is directly laid down on the floor and corresponds to a traditional block parquet with the blocks glued directly to the floor, ground and varnished with parquet lacquers.