Floor panel and method of producing such a floor panel

1. A floor panel or wall panel, comprising a laminate of:

a magnesium oxide based core layer comprising magnesium oxide and magnesium sulphate and/or magnesium chloride, wherein magnesium oxide and magnesium sulphate and/or magnesium chloride comprise 60-90% of the total mineral content of the core layer, wherein the core layer further comprises wood fibres;

at least one magnesium oxide based upper crust layer positioned on top of said core layer, said upper crust layer comprising wood fibres;

at least one magnesium oxide based lower crust layer positioned underneath the core layer;

at least one upper reinforcing layer situated in between said core layer and said at least one upper crust layer;

at least one backing layer situated on an underside of the lower crust layer; and

at least one decorative layer and at least one wear layer attached to a top surface of the upper crust layer;

wherein the density of said upper crust layer is at least 8% larger than the density of the core layer; and

wherein the weight content of wood fibres in the core layer is larger than the weight content of wood fibres in the upper crust layer.

2. The panel according to claim 1 , further comprising a first pair of opposite edges, said first pair of opposite edges comprising complementary coupling parts allowing to mutually couple of plurality of floor panels to each other.

3. The panel according to claim 2 , further comprising a second pair of opposite edges, wherein both pairs of opposite edges comprise coupling parts allowing to mutually couple a plurality of floor panels to each other.

4. The panel according to claim 1 , wherein the upper crust layer comprises magnesium sulphate and/or magnesium chloride.

5. The panel according to claim 1 , wherein both the core layer and the upper crust layer comprise water, and wherein the weight content of water in the core layer is larger than the weight content of water in the upper crust layer.

6. The panel according to claim 1 , wherein the upper reinforcing layer comprises a fiberglass mesh.

7. The panel according to claim 6 , wherein the fiberglass mesh has a mesh size of at least 5×5 mm.

8. The panel according to claim 6 , wherein the fiberglass mesh has an area weight of at least 90 g/m 2 .

9. The panel according to claim 6 , wherein the fiberglass mesh is provided with a coating.

10. The panel according to claim 1 , wherein the density of the core layer is between 1000 and 1800 kg/m 3 .

11. The panel according to claim 1 , wherein the density of the upper crust layer is between 1100 and 2000 kg/m 3 .

12. The panel according to claim 1 , wherein the density of said at least one lower crust layer is larger than the density of the core layer; and, the floor panel further comprises

at least one lower reinforcing layer situated in between said core layer and said at least one lower crust layer.

13. The panel according to claim 12 , wherein the laminate comprises a plurality of lower reinforcing layers stacked on top of each other.

14. The panel according to claim 13 , wherein the laminate comprises a plurality of lower crust layers, wherein at least one lower crust layer is positioned in between at least two lower reinforcing layers, and wherein at least one lower crust layer is positioned underneath a lowest, lower reinforcing layer.

15. The panel according to claim 12 , wherein the density of the lower crust layer is between 1100 and 2000 kg/m 3 .

16. The panel according to claim 12 , wherein the lower crust layer comprises magnesium sulphate and/or magnesium chloride.

17. The panel according to claim 12 , wherein the lower crust layer is free of wood fibres.

18. The panel according to claim 12 , wherein both the core layer and the lower crust layer comprise water, and wherein the weight content of water in the core layer is larger than the weight content of water in the lower crust layer.

19. The panel according to claim 12 , wherein the lower reinforcing layer comprises a fiberglass mesh.

20. The panel according to claim 19 , wherein the fiberglass mesh has a mesh size of at least 5×5 mm.

21. The panel according to claim 19 , wherein the fiberglass mesh has an area weight of at least 90 g/m 2 .

22. The panel according to claim 19 , wherein the fiberglass mesh is provided with a coating.

23. The panel according to claim 1 , wherein the laminate comprises a top structure attached to the upper crust layer comprising the decorative layer and the wear layer covering said decorative layer.

24. The panel according to claim 1 , wherein the laminate comprises a urea-formaldehyde impregnated, decorative paper layer, attached to the upper crust layer.