The method I use to waterproof paper mache has been working pretty good, so I thought I would use it for outdoor air-dry clay sculptures.
- Air dry clay
- Waterproof Wood Glue
- FlexBond Thin-set Mortar
- Exterior House Paint
- Acrylic paint
- Polyurethane Spray
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Step 1: Make Your Clay Piece
Simple star fish using Activa Air-Dry Clay. Let Dry 24 Hours.
Step 2: Waterproof Glue-Paint
Paint Top and bottom with h a mixture of waterproof wood glue and acrylic paint. Roughly equal amounts of each.
The paint thins down the glue a little and makes it easier to apply.
The color doesn’t matter at this point. Let Dry 24 hours.
Step 3: Flexbond Thin-Set Mortar
Mix up a bowl of roughly 4 parts mortar to 1 part water. Mix as you slowly ad water until you get a consistency you can paint with. It should slowly flow off your mixing spoon in a thick stream, something like pancake batter. If it runs off quickly , add more mortar. If it drops off in clumps, add more water.
Paint your piece with the mortar mix. It will destroy your paint brush after your done, so use an old one. The mortar doesn’t get absorbed into the red glue layer. It just kind of sits on top. Make sure you get full coverage.
There are two major disadvantages when using this-set mortar.
- You lose detail
- You will have a rough surface
This method is only good for certain kinds of sculptures. It’s great for anything made to look like concrete like garden statues or gargoyles. Also creatures with rough skin like dinosaurs, dragons, Godzilla and starfish!
Step 4: Paint With House Paint
Paint a layer of exterior house-paint to seal the mortar layer.
I use black Exterior Semi-Gloss Acrylic-Latex house paint. Here I’ve started painting with orange acrylic paint on top of the black house paint.
Step 5: Paint and Spray
Finish your paint job with acrylic paint, Then spray with polyurethane spay.
Just sealing the clay with polyurethane or varnish without the waterproof glue will make the clay water resistant but not waterproof. Eventually it will disintegrate.
Step 6: Give Your Starfish a Nice Wet Home
I don’t expect any of my outdoor sculptures to last forever, but this method seems to be working pretty good so far.
Dan at Gourmet Paper Mache has had success with his Waterproof Dragon outside in a tree using waterproof glue and exterior paint. Dan is in Seattle. I'm in Vancouver, Canada so we get similar weather.
After watching the waterproofing method recommended by DIY Easycraft, I started using Thin -Set Mortar for all my outdoor paper mache projects
Let me know in the comments your method of waterproofing air-dray clay.
Step 7: Outdoor Waterproof Sculptures
The keys to a waterproof outdoor sculptures are Waterproof Wood Glue, Thin-set mortar, and exterior house paint.
UPDATE: The starfish started to fall apart after 1 month of being fully submerged in water. This method is great for the rain and the summer heat, but it's not 100% waterproof.
Here are some outdoor paper-mache sculptures that have held up very well in the rain.
See more at Paper Mache Props