Three quarters of the productions at Dorset Theatre Festival this summer have been architecturally-real box sets (not atypical for this company). One fairly standard feature for these kinds of sets is the oversized crown molding: typically the profile for molding like this is something like nine inches to a foot tall by six to nine inches wide, and features a couple of different curves and breaks to create shadow lines. Our three architecturally-real sets are no exception, all three have sported large crown molding--our last show, Clybourne Park, has some 120 linear feet of it.
Large crown molding like this is typically able to be constructed of built-up, off-the-shelf molding shapes. You take a piece of five-inch crown, for example, attach it to some 1x material, add a half round, maybe an interesting picture rail profile, then a cove or an ogee shape, and voila! Big crown molding.
A nice five-inch crown can run you something on the order of $3 per linear foot. Less if you go for less detail. You can probably pick up the half round and picture rail for about $1 per linear foot, the 1x for about the same. In other words, you can easily end up paying $6-$8 per linear foot for this stuff, depending on profiles and level of detail.
I can't pretend that that doesn't break my heart, every time.
Additionally, these built-up shapes weigh a lot--there's a lot of material in each linear foot, and not a few fasteners. I've never seen this stuff fall off a wall. But I've also never felt great about it hanging off a Lauan-covered flat with just a handful of fasteners between a beautiful piece of trim becoming a really heavy and loud crash.
We've been fortunate to have been able to work with an architectural shapes manufacturer who is local here in Vermont (I've used these folks before, for a production of Death of a Salesmen at the Weston Playhouse in 2010). They are able to make--usually within 24-48 hours--an exact version of the molding profile drawn by our designers out of expanded polystyrene foam. The advantage of this product is three-fold:
1) it weighs next to nothing: I could easily carry (provided I could get my arms around it!) the 15 8' lengths that will make up our 120 linear feet of crown molding, and not break a sweat,
2) it saves me time on the floor; if this firm is making my crown molding, I've got at least one more body back on the floor building something else instead of piecing the crown together out of various shapes,
3) it is pretty cheap: the crown for Clybourne Park is a mere $1.56 a linear foot; for that price I'm getting the exact shape my designer specified AND I'm getting an additional body back in the shop.
In other words, it's a no-brainer.
Expanded polystyrene is more commonly known as "bead-board"; this isn't the colored insulation foam you can pick up at the lumber yard, but rather the big brother to those inexpensive white beach coolers. I say big brother because the density of the foam is typically much higher than in those throw-away coolers, making the product stiffer and more resistant to dents and dings. However, expanded foam does present a few challenges to consider.
First, it's not a pretty paint surface. It has small voids and dimples. In the past, I've worked with charges who have applied various coatings to address this, including flex glue, scuplt-or-coat, a white-glue dope, and others. The charge at Dorset this year has used Aqua Resin in the past, so we are going with that product this time. This stuff isn't inexpensive, but only adds about $1 per linear foot to the total cost of the molding--still far less than a built-up shape would cost.
The coating serves another pretty useful purpose: expanded polystyrene, when used in building applications, typically needs to be enclosed in a more-fire-retardant barrier. These coatings encapsulate the foam, providing a layer of flame protection to the product as well as a sandable, paintable surface.
Expanded polystyrene foams also give off gasses that shouldn't be breathed when they are heated, so care must be given to work in well-ventilated areas and wear proper protection when working with these products--particularly when using power saws to cut them.
These risks, however, are manageable, and certainly, in my mind, don't outweigh the significant savings in time and labor that subcontracting out these large moldings provides. So far, we've been really happy with the results, and I don't expect things to be any different on Clybourne Park!