Directions for Foam Hard Coating

Written by larry simmons
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Directions for Foam Hard Coating
Cover foam with a hard coating to add strength and prevent breaks. (Hemera Technologies/ Images)

Modelling with foam allows you to create anything from theatre props to model railroad platforms with a lightweight easy to shape material suitable for painting. Unfortunately, the material is a weak one structurally, breaking under even a moderate amount of force. To add some strength to the foam, you can cover the material with a hard coating consisting of water-based polystyrene. The coating brushes over the foam smoothly and then hardens in place creating a protective shell around the foam that accepts paint as easily as the foam itself. The strength of the covering is dependent on the number of coatings placed onto the foam.

Skill level:
Moderately Easy

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Things you need

  • Foam
  • Dust sheet or newspaper
  • Polystyrene hard coating
  • Paintbrush
  • Acrylic paint

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  1. 1

    Place the foam onto a dust sheet or a pile of newspaper to protect your work surface. Mix the hard coat thoroughly with a wooden stir stick before use.

  2. 2

    Mix the coating material thoroughly in a pail using a wooden stir stick. If the mix is a 2-part component formula, mix both components individually before combining them in the ratio directed by the manufacturer. Place a base coat of the hard coating over the foam using a paintbrush to spread the hard coat evenly. Use a moderate amount of the coating as it needs to penetrate the surface of the foam to fill in the surface voids in the material. Allow the base coat eight hours drying time after application.

  3. 3

    Apply a second coat of the hard coat material after drying the first. Use the same application process, spreading the material across the surface evenly with a brush. Use a thicker coat of the material for the second application to provide a solid protective surface over the foam core. Allow the coat two to three hours drying time until it's dry to the touch.

  4. 4

    Brush on a third and fourth coat of the mixture with the same thickness as the second coat, allowing each the same two to three hours to dry to the touch in order to build up the hard coating on the foam. Apply two additional heavy coats if the foam object will be handled often, such as with war-gaming scenery.

  5. 5

    Allow the final coat to dry overnight before apply acrylic paint to the surface, or two to three days before applying oil-based paints, lacquers or any other substance that can seal the material. After painting allow the coating to dry for five days before use. Complete drying to maximum hardness occurs after two to three weeks.

Tips and warnings

  • Apply the hard coat in a work area that is well ventilated. Apply while the room is between 65 to 85 degrees Fahrenheit for best results.
  • Clean brushes immediately using soap and water to avoid ruining them with dried on hard coating.
  • Wear a respirator and safety goggles if you ever sand the hard coating to avoid inhalation of hazardous dust.
  • Foam coating may fill in small details in miniature applications, obscuring them in the process.

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