Harden the surface of Styrofoam with a coating

In some applications, such as model making and out-of-home advertising, polystyrene should be provided with a hard surface. To harden it with a coating, several means come into consideration. Often also great hardness must be combined with a light weight as possible. There are misused and specific solutions.

Waterproof and solvent-free coatings

A classic way to create hard surfaces on Styrofoam is by coating with plaster. What is well suited in stationary model making, such as landscaping around model trains, is too heavy for moving objects such as model vehicles, aircraft and ships. In addition, gypsum is water-soluble.

To waterproof surfaces made of styrofoam, hardening and solvent-free materials must be used. This also applies to outdoor advertising material such as letters and company signs. Sometimes mixtures of different coating agents are the ideal solution. As hardening sealants come into question:

  • polyester resins
  • Polyurthanlacke
  • Polyester fine putty
  • Waterproof wood glue
  • Parkettlack
  • Japanese paper
  • Synthetic resin paints
  • Gelcoat (boat and caravan construction)

Serve as supplementary and stabilizing aids or as a carrier layer:

  • Glass fiber fabrics
  • polyester fabric
  • Micro balloon
  • papier

Create smoothness

After the coating has dried out, smoothing the polystyrene surface by sanding is risky. Styrofoam balls break out immediately with every slight injury or tilting.

To create a smooth surface, the smoothing process should be performed when the styrofoam is applied and processed. Therefore, the application technique and the viscosity of the hard seal are crucial. In most cases, the best result can be obtained by a different viscous two-layer technique.

Better than with a brush, the coating can be spread smoothly with a sponge roller. If there is a possibility, always work the surfaces of the styrofoam horizontally. Paints and sealants can be adjusted well by adding water and microballoon in their flowability.

For outdoor use, crack resistance and UV resistance must be considered. Too much tension developing substances can lead to cracks at higher temperature differences from about forty degrees Celsius.

Tips & Tricks

In the art supplies trade you will find microballoon and other fillers to enrich the coatings. For example, for smaller objects, you can test modeling clay from epoxy and polyurethane resins.

Artikelbild: Maja Askraba / Shutterstock

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