Mineral wool, also known as mineral cotton, silicate cotton, stone wool, slag wool, rockwool, and rock wool, is an inorganic substance used for insulation and filtering.
Mineral wool is a furnace product of molten rock, at a temperature of about 1600°C, through which is blown a stream of air or steam. The final product is a mass of fine intertwined fibres with a typical diameter of 6 to 10 micrometres. Mineral wool may contain a binder and an oil to reduce dusting. It is a poor conductor of heat and sound, is fire-proof and insect-proof, and therefore is ideal as a building insulation. Other uses are in resin bonded panels, growth medium in hydroponics, and as a filtering medium.
Precautions need to be made when handling the fibre product as it can be absorbed into the body by inhalation. It can also irritate the eyes, skin and respiratory tract. Prolonged exposure could lead to long term effects and it is considered a possible carcinogen to humans. This effect may depend upon the fibre diameter and length, chemical composition and persistence within the body.
The EU risk and safety phrases associated with this material are:
R38 – Irritating to the skin
R39 – Danger of very serious irreversible effects
R40 – Possible risk of irreversible effects
S36/37 – Wear suitable protective clothing and gloves.
Use in Hydroponics
Mineral wool is used in hydroponics for its ability to hold large quantities of water and at the same time maintain a high percentage of air as well. This aids root growth and nutrient uptake. The fibrous nature of mineral wool also provides a good mechanical structure to hold the plant stable. Mineral wool has a high pH, which is not suitable to plant growth. This requires correcting or conditioning. Conditioned mineral wool has a stable pH over long periods of time.
In the highest quality rockwools the mineral oils are removed during the manufacturing process and mineral wetting agents are incorporated in the melt.
Rockwool slabs are placed in the rows, holes for plants are cut in the plastic surrounding the slabs and the drippers placed in the holes.
Rockwool is an inorganic substrate as are sand, gravel and perlite.
Rockwool cubes can be reused several times, and are premade to use for hydroponics.
Rockwool holds 10 times more water than soil, yet is impossible to over-water, because it always retains a high percentage of air.
Since rockwool is easily reused over and over, the cost is divided by 3 or 4 crops, and ends up costing no more than vermiculite and lava, which is much more difficult to reclaim, sterilize and reuse (repot) when compared to rockwool.
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