The rockwools produced from diabase have a mineral balance that is inert and nonreactive. A few rockwools are produced from slag left over from smelting operations. These rockwools contain a high proportion of metals and may be somewhat reactive with the nutrient solution. The most important quality a high grade rockwool should have is uniform wetting. The rockwool should wet easily but not remain water-soaked.
Good drainage is important.
The wetting characteristics of rockwools vary considerably. In the highest quality rockwools the mineral oils are removed during the manufacturing process and mineral wetting agents are incorporated in the melt. This form of horticultural grade rockwool naturally attracts water and wets easily. While this is the highest quality process the actual quality of the rockwool will depend upon the care taken in manufacturing. The major drawback to this approach is that the wetting agent must be supplied regularly or it may wash out.