Actually I'm gonna talk about waterproofing your papier mache props.
Waterproofing is probably the biggest concern for anyone considering working with papier mache. Who wants to spend countless hours putting your all into projects only to have it end up as a pile of soggy mush? There are a few things that can be done to insure that your papier mache (or monster mud) masterpiece survives the elements to see the next Halloween.
First there is a great article by Jackie Hall, the owner of The Papier Mache Resource website. Jackie’s article “Waterproofing Papier Mache” chronicles the effectiveness of different sealants on papier mache. The results are interesting and impressive, especially the piece sealed with yacht varnish (marine varnish).
My 2007 Halloween display was set-up for six days and five nights and unfortunately it rained and was very damp for the majority of that time. The good news is that all the props survived intact without any damage. My method for waterproofing /weatherproofing is as follows:
Once the papier mache prop is completely dry, a coat of Spar Urethane is brushed onto all exposed surfaces. Spar Urethane is about $30 per gallon at home improvement stores such as Lowes or Home Depot. The yacht varnish or marine varnish that was used in above mentioned article runs about $90 per gallon.
Once the Spar Urethane has completely dried exterior latex paint is used for the base coat. Latex paint adds extra protection and is also an economical solution to painting props, especially the base coat. For dry brush techniques, black latex paint is used. For airbrushing or sections of props that require bright colors I used exterior white primer, then use small bottles of appropriate color acrylics and an airbrush.
After all the painting is complete and dry, a matte polyurethane sealant is applied (brushed or sprayed).
These techniques offer three layers of protection. The Spar Urethane protects the papier mache prop. The latex paint also helps protect the prop but more importantly eliminates the high gloss of the urethane. The final coat of sealant protects the paint, especially if you are using water based paints such as acrylics.
A few things to remember about papier mache and waterproofing.
If the sealant used does not protect the prop and it gets soft or damp don’t freak out. Place the prop in front of a box fan and it will dry, harden and can be resealed.
As a rule of thumb. The more toxic and nasty the sealant, the more effective. Use caution when working with urethanes, varnishes or shellacs. Fumes can be very toxic and flammable.
Water based sealants I have found are not very effective.
Make time in your production schedule to thoroughly seal your papier mache and don’t skimp on the quality of sealant. Properly sealed props can last for years, actually much longer than latex props.
Use common sense and caution when working with these materials, read the labels and follow the manufacturers guidelines.