Waterproof Paper Mache

Note: Dan Berg, the creator of this video, suggests using acetone to make a foam sculpture hollow. Read the comments below to see why using acetone for anything is very dangerous, and should only be used by people who are very aware of everything that can go wrong. I personally recommend not using it at all!

If you’ve been watching my blog for any length of time, you know one of the most common questions we ask is “how can I make my paper mache sculptures waterproof?”

I’ve experimented with several different methods and products for waterproofing paper mache, and all my experiments have been miserable failures. I know people say that marine varnish will work, but it didn’t work for me.

That’s why I was so excited when I got an email from a reader yesterday with a link to the video on this post. It was made by Dan Berg, of DIYeasycrafts.com. I haven’t tried this yet, but I watched the whole thing and I can’t find any reason why it wouldn’t work. Here’s why:

1. The inside of the sculpture is foam, not crumpled paper or any other organic material. That means that even if there’s a pinhole in the outside ‘skin,’ water leaking inside won’t cause any damage.
2. The ‘paper mache’ uses mortar mix with the paper strips, instead of paste. Ants, crickets, and mice should have no interest in chewing holes in the skin of the sculpture. (Do wear gloves. The mortar will dry out your skin.)
3. The mortar mix is covered with exterior paint.
4. The fellow who made the video actually did some tests, and he proved that the mortar mache is waterproof. It even holds its shape when he removes the foam and leaves the sculpture completely hollow.
5. The mortar mix is much cheaper than the commercial foam coatings that I’ve seen. The cost of the coatings is why I haven’t tried sculpting with foam until now.

The man in the video is using a particular brand of mortar, called Flexbond. You can find it at a Home Depot near you. And it looks like he’s using the blue rigid foam insulation sheets, which you can also find at a building supply store. The sheets would need to be glued together to make a piece big enough for a sculpture, and you’ll need special glue for that. The guy at the store should point you in the right direction.

You can use a bread knife to cut foam, but it leaves little nubbins of foam all over everything, and static causes the pieces to stick to your clothes, and they end up all over the house. I think I’ll grab a foam cutting knife before I start my project, to avoid some of the mess.

I really hope to try this soon. The hard part will be sculpting the foam. I like sculpting by addition, adding bits of clay or paper until I like what I see. Foam requires “subtraction,” taking away the excess material until you get the shape you want, like stone carvers do. Maybe if you take off more than you wanted to, you could repair the boo-boo with expanding foam.

I found some interesting sculpted foam projects out on Pinterest. If you try this, please let us know how your project turned out.