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Paper Mache Polyurethane test #1

with one comment

Since I am still building a boat made of paper mache and because I have to wait until spring for a safe launch,  I chose this time to do some further testing of the waterproofing outer layer.

I used a simple shape (again a balloon) to create another cup shaped bowl of paper mache to act as a scale representation of a boat. I only coated the outside of the shell with polyurethane and left the inside uncoated. The goal was to see if the coated paper mache would withstand sitting in water for one hour without the inside coatings absorbing water.

The result was a positive sign: if you properly seal paper mache with polyurethane, you can keep water at bay for at least one hour. This isn’t rain, this isn’t humidity, this is keeping the paper product floating on the water. I chose the one hour mark for a very simple reason: within 30 minutes I will have enough time to turn the boat around and head back to shore before she would sink. This is a safety issue more than a design parameter. I would prefer if the boat stayed afloat the whole time and I am confident that she will stay afloat for hours. Since many people have asked me to not try building this and think there is a large amount of danger, I wanted to help calm their fears.

Here is a summary video showing the testing:


Written by Josecito

November 9, 2011 at 11:33 pm

Posted in Uncategorized

One Response

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  1. Is dangerous, like almost all the things we like to do, but ¡I like it! … I hope it works, but please don’t forget your lifejacket ;)
    Good luck with that my dear :)


    November 10, 2011 at 4:54 pm

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