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How to Waterproof Paper Mache Props

If there’s one question I get 20 times a day, this is two of them.

The simple answer is spar urethane. There. I just saved you a long read that covers way more thought and analysis than I ever intended upon starting this article. So, if you’re satisfied, then I’m satisfied. Otherwise …

Step one to the long-version of the answer is another question: How much protection do you really need? If your haunt is one-night-only and gets packed back into the garage by 10:00, then all you’re going to encounter is a little dew. In haunts where zombies and scarecrows spring up in September and are your drinking buddies on St. Patrick’s Day, the elements become more of a concern. The subtly different terms waterproof and weatherproof demand a little clarity.

Waterproof is defined as “impervious to water”, while weatherproof means “can withstand exposure to weather without damage”. This is essentially the difference between zombies melting in the rain and suffering acute sunburn. On the list of things that hate Halloween props and want to destroy them, sunlight is number three, preceded by dirty rotten vandals, with moisture at the top.

It’s inevitable that your graveyard dwellers will soak up a certain amount of sunlight. If this is limited to just a few days each October, it could be years before the results of accumulated UV radiation exposure become noticeable. For longer periods, what would it hurt to line them up for a Coppertone spritz every so often?

With sunspots out of the way (dirty rotten vandals are a topic for another day), we’re down to public enemy number one: Water.

In addition to the amount of exposure your props are going to encounter, choosing the best protection has a lot to do with the type of glue that you use. I’m not a fan of traditional flour-based paste recipes because a little moisture can quickly turn a zombie into a rancid biscuit. (From direct observation of an incident in which Spookyblue-co-founder-and-brother Joe was forced to chuck a malodorous biscuit skeleton over the fence along with 100 million fruit flies.) Even with the addition of salt, oils, and other mold mitigators, it must be completely and utterly sealed against moisture or it will turn bad and eventually fall apart. White glue is much more forgiving. It may soften when wet, but it remains adhesive, so it’s not a tragedy if some moisture seeps in.

Having covered the relevant provisos, choose the scenario that best fits you.

  • “My paper mache monsters are only outside for a few hours on Halloween night.”
    • You probably don’t need to bother, especially if you used white PVA (Elmer’s) in your paper mache glue recipe.
    • Elmer’s glue, by itself, makes a poor sealer. However, it is resilient in that if your critter does absorb some moisture overnight, just set him in front of a fan for a couple of hours. He’ll be good as new.
  • We put our Halloween props out about a week before Trick or Treat.
    • Here is a gray area where we need to look at waterproof versus water-resistant. Any oil-based sealer will generally outperform its water-based counterpart, which bumps up the cost. Cheaper, water-based deck sealer does a fair job repelling moisture. A rain shower may cause some softening, but even dew can accumulate overnight and squishify a prop.
    • If your props feel squishy in the morning, then they are absorbing moisture. They’ll dry out in the sun, and if this is all they’re subjected to for one week out of the year, there shouldn’t be any permanent damage. Repeated over a greater number of days, however, and this cycle will eventually take its toll.
  • Our pumpkins and zombies are on duty for the whole month of October.
    • Consider stepping up to an acrylic sealer like Polycrilic. It’s a touch more expensive, but does a decent job repelling moisture.
    • Note that we’re still in the water repellant area, not “also good for fixing cracks in your submarine”. A heavy dew, or a rainstorm can still lead to mushiness. Incidentally, you may also notice some hazy, white discoloration from Polycrilc after a shower. It will disappear once it’s dry.
  • I ain’t got time to bleed, so I ain’t got time to worry about this #&*%!
    • If you think there’s ever a chance you’ll fall down a waterfall to evade a Predator, and maybe a zombie would make a great floatation device, then you’re going to want to try a spar urethane.
    • Specifically formulated to block moisture, Spar urethane will not only waterproof paper mache, but also contains UV blockers that put it in the weatherproofing category.
  • Some other tips that can improve your prop’s chances of surviving the winds and rains of October:

    1. Steer clear of traditional water and flour mixtures. I use white PVA (Elmer’s) glue almost exclusively. It doesn’t totally give up the farm if it gets wet, and it’s not considered a delectable food source by most microorganisms.
    2. After your paper mache creation is finished, apply a coat of sealer before painting. If any internal surfaces will be exposed (a Jackolantern, for example), coat them as well.
    3. Any sharp corner or edge is a potential wick. Exposed edges, like the face cut into a pumpkin, will absorb lots of moisture and are difficult to seal. Cover these exposed edges with strip mache to reduce this threat.
    4. Outdoor acrylic paints are designed to withstand moisture as well as the hard stare of the sun. Latex paints are usually less expensive, but tend to allow in more moisture. I have far too many gallons of the latter to justify experimenting with the former, so I’m willing to expect less than perfect performance.
    5. After painting, apply a final coat (or more) of sealer. This will often lend a certain sheen to the surface, so if your witch/zombie/franken-critter is too shiny for your tastes, then rub on some talcum powder. Alternatively, a very light misting of flat black spray paint will knock down the shine and won’t need to be reapplied.
    6. Avoid situations where a paper mache prop comes into prolonged contact with the ground. Use some kind of base or stand. Giant Jackolanterns with an open bottom are especially vulnerable and look particularly pitiful after they’ve collapsed.

Coffin lids and the sweet smell of spray adhesive death

Coffin LidMinion “Pip” writes …

” I love the styroform coffin prop – just wondering when cutting the side walls, did you angle the edges so they fit together better, or did you not worry about that? Thanks for the great idea, I’m an American living in Australia and trying to come up with good Halloween props here is hard – they don’t really celebrate it but some of us are trying to change that. :)”

Hi, Pip!

Angling the walls is one way to keep your coffin lid from sliding down into the coffin. I went a different direction, mainly because angles and I don’t always see eye to eye. Study any roof I ever had a hand in building; it either looks like a church steeple or devolved into a Quonset hut.

In any case, yours is a good idea. Another option that doesn’t involve a protractor is to glue some foam blocks to the inside walls just below the “lip” of the opening. Then, if you attached your walls to the outside of the bottom of your coffin, and if your lid has the same dimensions as the bottom, it should slip right in and sit pretty resting on the blocks.

Spray adhesive is excellent for attaching bits of foam to each other. I like 3M brand. It does an outstanding job bonding foam to itself, to walls, your fingers, almost anything. However, do *NOT* spray directly on the foam unless a melted hole is really what you had in mind for that spot. Instead, spray onto a sheet of cardboard, or into a paper cup, and wait a few seconds for it to stop bubbling. If the adhesive you’re using contains Acetone, then stir well with a popsicle stick. This will help to evaporate the foam-devouring Acetone. Once it is dissipated, it is perfectly safe to apply to the foam. (Not with your fingers. You should be wearing gloves at this point.)

A few notes about spray adhesive …

1. Only use in a well-ventilated area, preferably outdoors. I’m not kidding. This stuff is killer. It smells sweet, but that’s the sweet smell of death and it’ll mess you up. *

2. Apply to both surfaces. Wait a few minutes before putting the pieces together to allow the glue to set up. The instructions usually recommend 15 minutes, but stirring it can speed up the process. Either way, it’s worth the wait. You don’t need to use clamps, and you get a strong bond almost immediately instead of four to 8 hours later using PVA glue.

3. Don’t let it dry on your fingers unless removing the top layer of skin with a belt sander is something you enjoy.

Good luck, show that prehistoric biatch how we do things downtown -I mean- how we Yanks do Halloween, and have a great haunt!

* According to the Material Data Sheet 3M provides for their “Super 77 Multipurpose Adhesive”, death is not in the ingredient list. However, it does contain Acetone, Propane, Cyclohexane, Petroleum distillates, and Hexane. It’s a great product that I use regularly. I just don’t ever want to wake up with a splitting headache from a spaghetti/unicorn dream wondering how long I’ve been sprawled on the floor of the shop, so I treat it with respect.

How thick should a paper mache pumpkin be?

Alternate title: How many licks does it take
to get to the pumpkin roll center of a Grumble top?

Horde of Pumpkins“Horde of pumpkins” by our friend Valerie

Minion TSchroder writes (to Grumble, by accident):

“Hey was wondering how many layers it takes to make a grumble pumpkin head. I tried your idea to use a plastic bag and fill it with paper. Hope it works really excited about how it is turning out.”

Dear tschroder,

Grumble say what mean, “how many layers make Grumble head”? Not know what talk about! Not do puny Spook Man mashy paper stuff!

Oops, Spook here. I’ll take this one.

Sorry, Grumble gets agitated when people ask him prop questions. He’s been on this “Dear Abby” kick, and wants questions like “Is my roommate an alien?” or “When is the best time to plant birdseed?” He’s really sensitive, in his own way, and I think he feels neglected because I get way more mail than he does.

Anyway, regarding your pumpkin question, lots.

The more layers you use to build a Stolloween-style pumpkin, the better. You want it to be strong enough to survive the de-gizzarding process (when you cut a hole in the bottom and pull out the insides). If you choose clay for detail work, you’ll need a nice thick shell to hold up the extra weight. Paper clay, when you pile it on, can get heavy. But it’s great for building up all those neat pumpkiny ridges and things. And boils. Some of the best pumpkins have boils.

If you’re lucky enough to have some really thick material, like brown paper shopping bags, then you may only need two or three layers. For newspaper, recycled phone books, and other thinner material, you may want to add up to five layers. The type and thickness of your glue plays a part, too. Try a 3:1 mixture of Elmer’s glue and water. That is, three parts glue to one part water.

You can test your (fully dried) pumpkin head’s tensile strength by pressing down with your thumb in various spots. This will give you a measure of its “Yield strength”, or the amount of stress a material can withstand without becoming permanently deformed. If it gives too easily, or if you push through and accidentally pop yourself in the eye, then you might consider adding a few more layers.

This is a very subjective test, so a dent here or there doesn’t necessarily mean your pumpkin isn’t plenty strong overall. But if it worries you, then add an extra layer. Another trick used by some large-scale model builders is to “harden” the piece with a coat of glue. Just paint on the 3:1 Elmer’s mixture and let it dry. Repeat as many times as you like.

Thanks for writing, and have a great haunt!


Further reading
Grumble’s paper mache pumpkin head
Stolloween – Gourd guru and professional patriarch of paper mache