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Working with Exterior Foam Coat

Step-by-Step Progression of a Foam Coat ball to be covered with tile.

First, a 6" round styrofoam shape was selected for the "armature". Then Foam Coat was mixed to an oatmeal (on the dry side) consistency. The Foam Coat was applied to the styro ball with a spatula, pictured here, in as thin a layer as I could make it because additional layers were to follow.

Next a fiberglass mesh layer was added for strength. The mesh was cut into little pieces to better conform to the roundness of the ball, and overlapped slightly. (Adding fiberglass mesh in this manner is also recommended when using Winterstone and AquaResin.)

I added the fiberglass pieces two or three at a time and then covered them with thin layer of Foam Coat. During this process care was taken to make sure there were no high or low areas, and that the ball was nice and round.


After the first layer of mesh was coated, I added one more layer with mesh. I left it very thin so I could see the mesh and be sure that the mesh covered the entire piece. I rolled the ball around on a flat surface to further smooth it. At this point the ball is ready to dry and then mosaic. The manufacturers instructions (see below) state the "maximum bond and hardness in 1 to 2 days."

After one day of drying the Foam Coat turned a lighter color. This 6in diameter ball with about 1/8in of foam coat and fiberglass mesh weighs exactly 1lb. (Exactly 1lb. I was impressed by this. I don't think I could have made it exactly 1 lb if I was trying. Sadly, no one else in the store thinks this is as amazing as I do.) Before adding mosaic tile, make sure to brush off any loose dust and sand from the surface of your piece.
  • This product is a cement-based foam coat and works pretty easily. It differs from Winterstone in that Winterstone is white and has a very low particle size. Therefore it is more easily pigmented and stained as well as sculpted, finished and smoothed . If you are coating a piece has little detail, such as this ball, or are not concerned with finely sculpted elements, this Foam Coat is a great material.
  • We recommend (although the instructions do not include it) reinforcing every foam coating. In an exterior environment this helps prevent cracking. Reinforced indoor pieces sustain less damage if dropped or hit. (The theory being that a crack is easier to fix than a shattered piece. If dropped on a hard surface, while it may crack even though the piece is reinforced, it may break into pieces if not reinforced). For cement based products such as Exterior Foam Coat and Winterstone, use a reinforcement that is alkali resistant such as A/R fiberglass mesh, A/R Fiberglass Matt and A/R Chopped Strand Fiberglass. These can also be used with AquaResin, Magic-Sculp and Magic-Smooth.
Last Updated 05/17/04
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Exterior Foam Coat Manufacturers Instructions

  • Instructions
    Mix in clean container with clean water. Add powder to water and mix until smooth. Do not over mix.
  • Applying
    Apply to a clean surface with a brush or trowel. May be applies as thick as 3/8 inch. Cover with plastic wrap to create a smooth polished surface. Try other texturing methods before coating sets.
  • Set Time
    About 90 minutes, Maximum bond and hardness in 1 to 2 days.
  • Finishing
    Remove dust before painting. This product has a natural rough finish and is not sandable.
  • Painting
    Works well with acrylic based paints. Experiment with a small sample before applying paint to your finished surface. Can be smooth coated with Interior Foam Coat when used indoors.
  • Clean-up
    Clean tools and brushes with clean soapy water.

This material contains Portland cement and is alkaline on contact with water. May be irritating to eyes and skin. Wear dust, skin and eye protection. In case of eye contact, flush immediately with water, consult a physician. Wash hands with soap and water after use an before eating. Keep out of reach of children.