Grodan is a subsidiary of the Rockwool Group, which started the commercial production of stone wool in Hedehusene, Denmark in 1937. In 1949, Rockwool opened a manufacturing plant in IJmuiden, the Netherlands, relocating this facility to Roermond in 1968. One year later, Rockwool in Denmark founded Grodan to focus on production of stone wool substrate for the horticulture sector.
At the end of the 1960s, environmental objections against the increasingly intensive land use in the horticultural sector mounted. One result of these objections was that the commonly used soil disinfectant methyl bromide was prohibited by law. Likewise, steaming the soil, which was very expensive and labour intensive, fell out of favour. In the search for an alternative, th parent company of Grodan, the Danish stone wool manufacturer Rockwool, in cooperation with a number of universities, investigated the possibilities of cultivation on stone wool substrate, eradicating the need for soil altogether. This was the solution the world had been waiting for: crops proved to grow extremely well on stone wool. The result was immediate increased production with less water and nutrients.
Stone wool is a natural product. It is made from basalt, congealed lava spewed from the innermost depths of the earth. In the mid-nineteenth century, American geologists on Hawaii discovered a “woolly” material consisting of stone threads, which the local inhabitants were using to insulate their huts. This was a volcanic material, the product of red hot steam being forced through liquid lava under high pressure.
To produce stone wool commercially, Grodan/Rockwool duplicated this natural process as closely as possible. Today, extracted basalt is re-liquefied in furnaces at a temperature of 1,500 degrees Celsius. The liquid basalt is then spun into threads in spinning chambers, and then congealed in a hardening kiln using hot air (230 degrees Celsius) and compressed into wool packets, which are then cut into slabs, blocks or plugs and packaged in film. With factory processing, one cubic metre of basalt can produce approximately ninety cubic metres of stone wool.
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