Foam 101

As I was working on updating some information on a few past shows, I ran into several shows where I used foam - different types and different coatings. I thought it would be of benefit to write down a few notes on the matter. However, it should be noted up front that this topic is a pretty large one, and 1 post will certainly miss alot of the finer details of working with foam.

Types of Foam
EPS (Expanded polystyrene) or bead foam. This foam is available in various densities.
A chart discussing each density and the relative strengths is at the following link:
http://www.achfoam.com/EPS/properties.asp
Generally speaking, if it will take abuse (such as being climbed on) or if it needs fine, detailed carving, a higher density will be needed. Of course, the higher density is more costly, and weighs more. In my latest show, I sandwiched thin sheets of commodity (the least dense) foam between 2 sheets of 1/4" luaun for great looking, odd shaped doubled sided flats.
While many densities can be manufactured, commodity board (the least dense), 1 and 2 are the most common.

Extruded Polystyrene foam (Dow is one manufacturer) is often sold in colors (blue, pink, yellow).
It uses a different blowing agent and a different manufacturing process. White molded EPS, unlike extruded, and is available in many different densities and thicknesses. Extruded foam seems to be closest to the no 2 EPS foam.

Then it gets more complicated:
AB foam, Spray foam, Handi-foam versus Great Stuff.....
Some you put on your self, some companies you will need to send your set pieces out to, and some will come in and spray it on your set while it is in the theatre.

Companies and products to watch for: Smooth On, Great Stuff, Handi-Foam, Moore products froth packs as well as many others.... In the phone book looking under plastic / foam should find a few places to start with locally.

Things to think about
Vertical or horizontal orientation
Result needed (some dry in beads, some are easier to carve)
Costs / labor for each
Available to truck out pieces, or to have time during load to have the set coated in place
Substructure (solid block of foam, frame with wire or muslin) I have had very good luck with large scenic pieces being very stable for a show, yet be movable for transitions being made out of large solid pieces of foam.

Adhesives:
3M Fastbond contact adhesive
White Glue
Spray or 2 part (ab) foam
Liquid Nails FRP in 1 gallon buckets

Methods for getting the foam paint ready. This is probably as problematic as choosing the method of using foam in the first place. Some foams will have a hard exterior and will not need anything more than a priming coat. Other foams will need to be sealed. Some inherently take paint, others like ethafoam (permaprep works very well on this material) inherently rejects paint. And on top of all of the ambiguity, it will depend on the show and the paint treatment on which method is ultimately best, as well as how the scenic element is used in the show (displayed versus abused for instance). Finally, the different coating have different flame retardant effects, so take care to test and confirm that your end product meets applicable codes. But the following are some basic ideas:

Foamcoat
Flexcoat
Sculpt or Coat
Super 88 (great food grade adhesive sold at http://www.aabbitt.com/)
Glue, paint and joint compound mixture (flex glue helps to keep it not brittle)
Wet blend tile mastic
Cheesecloth or muslin and glue
Elastometric roofing polymer
Perma Prep (a latex vapor barrier primer sealer)
Scrape coatings of drywall compound

While this entry is long, it is by no means a complete primer to using foam onstage. The capabilities of foam and its scenic uses are numerous, and subject to much debate over the best practices. However, as each scenic element has unique functions, all of these options can create a prop or set piece that performs well for almost any production budget.