Hinges in/on styrofoam

[Zooey]

I have a plant for Little Shop that needs to be hinged somehow. It has been hinged in the past and seems to have had chunks of foam eventually torn from it. A puppeteer control both the top and bottom of the plant by holding onto a crossbar embedded near the lips of the plant. It is designed to allow the puppeteer to stand up and manipulate both halves, but as I said, it is now broken.

Any ideas on how to bind together the two halves so it can withstand the movement required?

 

[ajb]

Do you know how it was hinged before? How thick is the foam, and is it expanded (white bead foam) or extruded (smooth pink, blue, or green foam) polystyrene? Two options come to mind: A fabric hinge--a strip of fabric thoroughly glued to both halves (maybe green glue), or hardware hinges through-bolted with large backer plates (could be 1/8" maso) sandwiching the styrofoam and preferably green glued to it.

 

[Zooey]

I think it has been hinged in multiple ways. The puppet was originally made of styrofoam sheets glued together and carved into shape. It appears that it has been repaired with cans of expanding spray foam. Inside the plant was a chunk of that foam that had a wooden dowel with a heavy canvas or nylon strap. So, I would guess that the last user of the puppet foamed around a loop that ran through both halves, and ultimately did not hold. The thing needed a metal "jaw" in its creation, but I can't do anything about that now.

I, too, am thinking that gluing fabric makes the most sense, but I don't know what kind of glue to use. I considered making a multi-layered dutchman painting only the fabric in direct contact with the shells, but don't know if that would hold. Got any glue suggestions?

 

[BrianWolfe]

3M 847 or spray 74 or 78 adhesive

 

[FatherMurphy]

I'd lean towards a fabric hinge too. I'd suggest using two strips of fabric seamed down the middle, so that you can glue one flap to both angles of each side of the mating line (think of the fabric strips in cross section as an X, with the upper jaw in the top quadrant of the X, and the lower jaw in the lower quad), so that the fabric has less chance of starting to peel and pulling free at the hinge line, plus it doubles your contact area. Make sure to use water-based glues, anything solvent based will just attack the foam and make matters worse. If the mating surfaces aren't flat, cut the fabric strips on the bias (diagonal), and then stretch the fabric to match the curves of the foam.

If you want to try mechanically anchoring the fabric as well as gluing it, drywall screws work disturbingly well in extruded foam. Numerous 3" screws and fender washers could help stabilize things.

I'd be careful with trying to use spray foam to build back missing foam. Some brands are solvent based, and all of them tend to keep expanding for a while after spraying, and could do as much harm as good if you're trying to fill a confined space.

As for glue, you'll have more problems getting the glue to grip the foam than the fabric. I'd look for something that's somewhat flexible when dry, rather than a brittle white or yellow glue. Tacky Glue comes to mind, as does water-based contact cement, or even just using unthinned latex paint.

I'm assuming your theater owns the puppet, since you're talking about repairing it yourself. Many theaters rent a set of Audreys, and any repairs or modifications would tend to make the rental house upset.

 

[ajb]

Also look at 3M Fastbond 30NF aka "Green Glue". I suspect that you'll want a liquid adhesive rather than aerosol to get better bonding with the fabric, although Spray 78 is great for fast foam-foam bonds. Just be aware that contact adhesives tend to be very unforgiving, so make sure you stick it together right the first time!

 

[Zooey]

Many thanks to you all.

I looked for the 3M and green glue products, and did not find them locally. I see our local Big Box place has a product called PL300 foamboard adhesive that claims to bond foam to most other surfaces, so perhaps that would be worth a shot.

I cannot do the X pattern because someone needs to lean inside the pod to use it, and an X would prevent that. I see the value in that construction, but it won't work on this project.

 

[venuetech]

I would embed a series of anchor points into the foam.
use a 3/4" dowel about 5" long
round one end with a sander
drill a pilot hole for your drywall screw in the center of other end
drill a 5/8" 4.5" deep hole into the foam
glue up the dowel and hole with foam adhesive
gently tap the dowel into the hole till it bottoms out leave the last half inch out
after glue cures sand dowel flush
repeat as needed.

practice this on similar materials before you try it on the puppet

 

[BrianWolfe]

You can get the 3M adhesives online at McMaster.com. They will have it to you the next day.