Abstract: To apply hot grit particles to a continuous thermoplastic web such as a geonet, the web is brought to the upper part of the surface of a roller which is rotating in a container containing grit particles. A controlled layer of grit particles is carried up over the upper part of the roller, and the particles are heated by halogen emitters and are pressed into the web, causing local melting of the web so that the grit particles are embedded and firmly retained. Grit particles are added to a hopper and the top surface of the mass of grit particles adjacent the ascending part of the roller surface is kept at a controlled level below the uppermost part of the roller. Surplus grit particles not taken up by the web are recirculated by interaction with the roller surface.