Process for the formation of fiber felt containing an additional product

A method for forming a fibrous felt hydroponic culture substrate, comprising:

• forming fresh mineral fibers from a molten melt in a formation zone, which fibers are entrained in a turbulent gaseous stream and deposited on one side of an advancing support and retained there by suction applied to the opposite side of said support, said fibers being uniformly sprayed with a binder comprising a thermosetting resin prior to deposit on said support and prior to exiting said formation zone,
• at least partially curing said binder downstream of said formation zone to set the felt formed by said fibers, said felt having two exterior edges, applying a surface active agent to the portions of said felt adjacent to said exterior edges downstream of said formation zone, said surface active agent rendering said fibers hydrophilic,
• trimming said surface active agent treated fiber material from said felt, and
• recycling said trimmed fiber material into said turbulent gaseous stream in said formation zone whereby said surface active agent treated fiber material is distributed throughout a felt formed from said recycled fibers and additional fibers introduced into said turbulent gas stream, said felt comprising said recycled fibers being substantially similar to that from which said excess fiber was trimmed, said recycled fiber being present in said felt in amounts no greater than 20%, by weight, of said felt.