This paper deals with dry mixing process of composites, whose components are natural fibres and soil based granulates like clay and sand. Such composites can be used for structural elements like bricks or can be spread to surfaces as a plaster. In comparison to the common soil reinforcements like wood chips, straw, hemp or lax, certain seed carrying fibres, as the ones in cattail (typha latitia), have a stellar acrchitecture, which binds the mineral components symmetrically in all directions producing an isotropic strength property. The problem is now how to manage the fibre treatment process softly enough to keep fibre structure undamaged during different process phases. Fibre processing starts with defibering the fibres from the inflorescence and separation of seeds from the fibres. The original purpose of the fibres is to carry seeds long distances under the influence of wind lift. After loosing the seeds the fibres are extremely lightweight. The next manipulation is to blow separate fibers to mixer. This unit has a circular chamber, inside which a set of mixing foils are fixed onto a shaft rotating co-axially with the chamber. The mixer is filled with soil and fibre components by means of a set of feeding inlets, the purpose of which is to dose the components in desired amounts. The mixing process of clay, sand, and natural fibres is very demanding process due to the large difference of the components with respect to the specific weight. The main difficulty is to keep the lightweight fibres inside the mixer, because the air flow generated by the fast motion of mixing foils easily lifts the fibres just to circulate at the upper part of the mixer chamber. As a consequence of the free flow of fibres the mixing process takes up to 500…1000 seconds, which is ten times more than needed for pure sand-clay composites. Disadvantage of too long mixing time is not only the inefficiency in the process itself but also the increase of energy consumption and the damage of the branched structure of the fibres. As this is decreasing the tensile strength of the end product, too long mixing time is avoidable. The mixing process can be accelerated by a fog bed consisting of large number of very small water drops. Such thin fog can be produced by commercial ultrasonic actuators as a concequence of cavitation of water on the surface of a thin fast vibrating circular plate. A set of such actuators is placed inside a water container and the fog is blown into the mixer through a connection pipe by means of an electrically powered fan. Washing of fibres by water fog increases their weight and adhesion with the clay dust particles. This relates to the natural purpose of the seed carrying fibre to anchore effectively to wet clay-type soil. This effect can be utilized by filling the mixer first by the fine fraction (clay) and by letting the clay dust then interact with the fog. The free fall and penetration of such clay particle-loaded fibres into the clay bed becomes much faster than in purely dry mixing conditions. The process is completed by filling and by mixing the large particle size component (sand) to the bed. Essential is that only short sand mixing time is needed in order to protect the fibres from damages.