Plaster building foam


Do-it-yourselfers often ask themselves whether they can plaster construction foam as well. The plastering of PU foam has been a standard combination for many years. How to plaster construction foam and special features can be found here.

Where construction foam can be used under plaster

Construction foam can be plastered like any other substrate. Due to the application areas of assembly or PU foam, the most different conditions arise:

  • PU foam when sealing construction joints (eg window to soffit)
  • for filling cavities
  • as an insulating layer
  • for filling holes (opened walls, etc.)

The foaming of PU foam during window installation is also widespread when proceeding according to the RAL guidelines. But also cavities and especially large wall openings can also be filled with foam. For example, it may be necessary to break up the wall during modernization, but in any case during initial installation of a heating system.

Consistency of mounting foam for plastering

The pipes laid here can not only be optimally insulated with insulating foam. Likewise, the PU foam, this wall openings completely refilled and then plastered. However, the peculiarities of PU foam should be considered. For example, foamy foam trees in their hardened consistency are rather soft, so they can yield.

Expansion of the mounting foam

On the other hand, foams that barely expand (less than 1 percent) can become very hard. This difference is important, for example, when a bath or shower tray is to be underfilled with construction foam. With respect to open walls, which are initially filled with construction foam, this is particularly important because of the size of the area.

Foaming and plastering of larger surfaces

The larger the surface to be foamed, the more elastic the plaster will be applied later and thus tend to crack. The larger the area to be filled and later plastered, the sooner it should be used to hard PU foams. The PU foam is then applied so far that it reaches the level of the wall or wall on which the unbroken plaster still rests. Also for this reason, low foaming foams are to be preferred.

Drying time before plastering

Please also note the drying time of Bauschaum. This differs significantly. 2-component foam usually dries up within 15 minutes, for 1-component PU foam this depends on other factors, which we explain in more detail in the linked guidebook. Otherwise, to fill the cavity or open wall, follow only the instructions of the manufacturer of the construction foam.

Construction foam not suitable for every surface

Also important is the subsoil itself. So foam should not be applied to any surface. These include glass, plaster, various plastics (PE, PP), ceramics, silicone and other materials. In outdoor areas, it should be noted that the PU foam is not UV resistant. So the plastering of the construction foam is even advisable.

Tips & Tricks

Some craftsmen and do-it-yourself embed a reinforcing net in the building foam when filling. This makes the area filled with PU foam even more resistant.


Video Board: Foam and Plaster Prop Tutorial (part one)