In the early days of cellulose insulation (in the 1900s), cellulose was also used as spray insulation for internal wall insulation. The C-profiles or timber frames required for the subsequent installation are positioned in front of the wall. The cellulose is then sprayed onto the wall whilst damp, and any excess material is brushed off using a rotating brush. The cellulose is moistened by a ring of nozzles arranged around the spray nozzle, from which a fine mist of water lightly moistens the cellulose. Thanks to the papier-mâché effect, the cellulose sticks to the wall and forms a seamless layer of insulation. The material brushed off by the rotating brush (‘overspray’) is collected and added to the new cellulose. This means that no waste is produced with this method either.
However, as relatively large quantities of water are introduced into the building, and the insulation layer can take several weeks to dry out – particularly in winter – this method has not become widely adopted and is hardly used at all these days. Furthermore, this method is quite labour-intensive (one person sprays the wall, one person brushes off the overspray, a third collects it and takes it to the blowing machine, and a fourth fills the blowing machine with a mixture of new and (damp) brushed-off material.

However, this method is of interest for soundproofing recording studios, where cellulose is sprayed onto the ceiling whilst damp – sometimes mixed with adhesive. Due to the very large surface area created in this way, the reverberation effects in the recording studio are significantly reduced. A final colour finish using spray paint is also possible.

Insulation thicknesses of up to 10 cm can be achieved in a single pass. If a greater thickness is required, the spraying process must be carried out several times – with a slight time lag between each application.