Seal polystyrene afterwards


Styrofoam is also popular because of its ease of processing. However, there are limits when recesses and individual trimming are required. The crumbling "blown up" polystyrene quickly creates cavities and joints in insulating layers. With incorporated foam or a coating is sealing possible.

Three sealing methods

Styrofoam insulation often requires cutouts for pipes or other installations. The consistency of the material leads to unclean and brittle edges when cutting and drilling. When attaching the polystyrene therefore creates cavities and spaces.

To seal these cavities or barrier joints, three approaches are possible:

1. The Styrofoam edges are coated with adhesive and sealing compounds before fitting and fixing.

2. After assembly, the cavities are sprayed with sealing foams.

3. Especially when joints forming the seal can be done by a coating or cladding such as a plaster layer. The insulating effect remains restricted at these points.

Means for sealing

For foamed plastic Styrofoam fit other plastic foams as a sealant. Polyurethane as a PU foam is well suited in various designs, as it remains elastic after drying and compensates for any possible settling forces. PU foam is available for connections between styrofoam and:

  • aluminum
  • fiberglass
  • Wood
  • plastics
  • stole
  • Styrofoam

Flame behavior and alternatives

Like styrofoam itself, polyurethane is not flame resistant. Styrofoam specially prepared for insulation can have a somewhat stronger flame resistance. When sealing, the filler used must always be checked for compliance with the building regulations fire protection regulations.

Depending on the cavity shape to be sealed, alternative methods may help. The filling with polystyrene foam as bulk material is possible with horizontal seals. Insulating tapes can create impermeability, but leave potential thermal bridges in the insulation. It is also possible to insert wedge-shaped pieces of styrofoam, which were previously provided with adhesive.

Keep moisture away

Styrofoam reacts to moisture with decreasing adhesive power and sinking insulation effect. Therefore, care should always be taken when sealing between styrofoam and any sources of moisture. If required, PU films can also be applied as vapor barriers on both sides.

Tips & Tricks

Straight edges and corners in styrofoam can be made cleaner with a hot cutting device such as a blade or a wire than with pure mechanical sawing. Wear a respirator.

Artikelbild: ALPA PROD / Shutterstock


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