Claims : 1. A mineral fibre element, totally or partly covered with a layer of a primer layer, said primer layer containing at least 50 % by dry weight, and preferably at least 80 % by dry weight, and more preferably, at least 90 % by dry weight of polyvinyl acetate. 2. A mineral fibre element according to claim 1, wherein said primer layer containing at least 50 % by dry weight, and preferably at least 80 % by dry weight, and more preferably, at least 90 % by dry weight of chlorinated polyvinyl acetate. 3. A mineral fibre element according to claims 1 and 2, wherein the primer layer contains up to 50 % by weight of filler material, said filler material preferably includes up to 10 % by weight of organic and/or inorganic fire retardants . 4. A mineral fibre element according to claim 3, wherein filler material essentially consists of inorganic material having an average grain size less than 0.2 mm, preferably up to 0.1 mm, said inorganic material preferably includes talcum powder, and ground fibre material. 5. A mineral fibre element according to any of the preceding claims, in the form of an insulating board, said insulating board having an average density of 50-1100 kg/m3, preferably having an average density of 50-300 kg/m3. 6. A mineral fibre element according to claim 5, wherein said insulating board comprises two or more layers with different densities. 7. A mineral fibre element according to claims 5 or 6, said insulating board is shaped as a parallelepiped having a first and a second side opposite each other, and four-edged side, wherein at least one of said sides comprises a primer layer. 8. A mineral fibre element according to claim 7, wherein said primer layer on said at least one side, covers at least 50 % of said side, preferably in a pattern. 9. A mineral fibre element according to any of the preceding claims, wherein said primer layer has a thickness corresponding to an applied amount of between 25 and 375 g dry primer/nr, preferably between 50 and 60 g dry primer/nr. 10. A mineral fibre element according to any of the preceding claims, wherein said primer layer provides a mooring in the mineral fibre body.Claims: 1. A mineral fiber element, totally or partially covered with a layer of a primer layer, said primer layer containing at least 50% by dry weight, and preferably at least 80% by dry weight, and more preferably, at least 90 % by dry weight of polyvinyl acetate. A mineral fiber element according to claim 1, wherein said primer layer contains at least 50% by dry weight, and preferably at least 80% by dry weight, and more preferably, at least 90% by dry weight of chlorinated polyvinyl acetate. A mineral fiber element according to claims 1 and 2, wherein the primer layer contains up to 50% by weight of filler material, said filler material preferably includes up to 10% by weight of organic and / or inorganic fire retardants. A mineral fiber element according to claim 3, said filler material essentially consists of inorganic material having an average grain size of less than 0.2 mm, preferably up to 0.1 mm, said inorganic material preferably includes talcum powder, and ground fiber material. A mineral fiber element according to any of the preceding claims, in the form of an insulating board, said insulating board having an average density of 50-1100 kg / m3, preferably having an average density of 50-300 kg / m3. A mineral fiber element according to claim 5, wherein said insulating board comprises two or more layers with different densities. A mineral fiber element according to claims 5 or 6, said insulating board is shaped like a parallelepiped having a first and a second side opposite each other, and four-edged side, comprising at least one of said sides comprising a primer layer. A mineral fiber element according to claim 7, wherein said primer layer on said at least one side, covers at least 50% of said side, preferably in a pattern. A mineral fiber element according to any of the preceding claims, said primer layer has a thickness corresponding to an applied amount of between 25 and 375 g dry primer / nr, preferably between 50 and 60 g dry primer / nr. 10. A mineral fiber element according to any of the preceding claims, said primer layer provides a mooring in the mineral fiber body.