Wednesday, 8 August 2012

Waterproofing paper mache

UPDATE: here is what the skull chalice looks like now it's been painted and epoxied.

"Waterproof" and "paper mache" aren't the most natural word associations ever, so one of the most important things to consider when making a paper mache drinking vessel is how I'm going to prevent it from disintegrating when it's in use.  As I mentioned, there are ways around that.

This post is all about how I treated paper mache to turn it into a drinking vessel suitable for everyday use.  For starters, the actual paper mache is moulded around a ceramic liner.  The liquid itself will be in the liner, which can be removed for washing (because no one likes to use a dirty cup).  Ceramic is a much better insulator than glass or metal, so it won't develop any condensation that could get into the paper skull and damage it.

The type of glue I used is important too.  This is Selleys' Aquadhere PVA, and unlike some other PVA formulations it's water resistant when dry.  When wet it is water-soluble, so I've mixed it with water and used it as the paste for my paper mache.


That's a good start so far and would have given me a nicely water-resistant skull.  But that's not all.  I'm bringing out the big guns on this one: epoxy sealant. 

Yeah baby!

This stuff is intended for use on boats, and it absorbs right into the surface for high-performance sealing.  You can get it or something similar from marine supply stores, or TradeMe (for readers outside NZ, that would be Ebay).  Be aware, however, that it isn't cheap.  You will need to shop around to get a good deal on it.

This particular sealant is a translucent amber colour, because it's designed for use with wood.  That's fine for my skull, but it would be a problem for some projects.  You can get clear sealants and marine varnishes, or you could probably get away with using exterior polyurethane.