The EN 13501 grades range from A, which is non-combustible and includes materials such as brick, to E, which is flammable with a substantial contribution to a fire. Brick, stone, and mineral wool insulation are examples of A1 materials. Plasterboard and fiber cement board are examples of A2 materials. Bricks that are dry when they are used in construction and adequately protected from heat and flame can be used in place of other A1 material. Dry-laid ceramic tile and concrete with no more than 10% moisture are examples of A3 materials. Brick and stone are very durable materials that will not need to be replaced often. However, they can become weathered with use or due to environmental conditions (e.g., salt air for brick) and should be maintained by cleaning with a stiff brush and warm water to remove dirt and dust or ice during the winter months. If clean enough, you could probably use your finger to trace around the outside of the material to check for any cracks or breaks. If it is not clean, then it won't burn! Mineral wool has many advantages for thermal insulation because it is lightweight, does not melt, and does not emit toxic substances when burned. It also has the ability to absorb sound which makes it suitable for use in walls and floors. Mineral wool comes in varying degrees of fineness from coarse to fine, with the coarser grades being less expensive but also less effective.