Waterproofing Paper Mâché Experiment Results

After the ball was cut off the Styrofoam ball and put back together.

Last week I started an experiment to see if a product could help waterproof paper mâché.  Many of us who work in paper mâché want to make items that can be used outside.  Paper mâché objects do not fare well in outdoor conditions since it is made from paper, flour paste, and water.  Painting and sealing with an exterior sealer help, but even that has its limitations. Items left outside overlong can be subject to water getting into the paper mâché and collapsing.  Last week I started an experiment to see if a product could help waterproof paper mâché. Today, I am reporting the results of the experiment.

The ball soaking in a tub of water.  It floated.

I will recap the experiment briefly.  I covered a Styrofoam ball with masking tape and then covered the tape with a layer of Press and Seal, a product available in grocery stores to cover food.  I covered the Press and Seal with three layers of newsprint soaked in a flour and water paste with some thin set mortar admix added at roughly a one to one to the amount of water. (I will describe my paper mâché methods in more detail below.)  After three layers, I used a craft knife to cut the dried paper mâché layer from the ball.  I cut it into four sections to remove the ball because I wanted to use the ball in other projects.  Using hot glue, I glued the sections back into a ball.  After the ball was back together, I covered it with three more layers of paper mâché.  The paper mâché ball had no other paint or sealers to protect the ball.  At that point, I was ready to see just how well a wet ball would hold up if it was placed in a container of water and left to sit for an extended period of time. 

Water infiltration above the waterline.

I put the ball in a container of water, making sure the ball was well soaked with water all over.  The ball floated.  I checked the ball at five minutes, ten minutes, half an hour, one hour, one and a half hours and two hours.  The ball floated the whole time.  After an hour, the section of the ball above the waterline had dried completely.  At an hour and a half, I began to see a few places where water seemed to be infiltrating in a few small places above the waterline.  I was unsure whether the water infiltration was caused by the ball moving around as it floated in the container.  At two hours, there was a definite line where the water was creeping above the water line. 

Completely dry again.  No edges came loose.

At two hours, I pulled the ball out of the water to see how badly the water had damaged the integrity of the ball.  The outer layer felt slimy, but the ball still felt solid.  I decided to end the soaking part of the experiment and see what happened to the ball as it dried.  After a few hours, the ball felt dry. 

By the next morning the ball was completely dry.  It is solid with no collapsed areas from having been wet.  None of the strips of the paper had come loose or pulled up on the edges.  Everything was as well glued down as when it went into the water.

I guess my conclusion is that by adding the thin set mortar admix that it did help to some extent in waterproofing the   paper mâché.  I will now be testing to see how well paint will work over this type of mixture.  If it holds paint well, and with additional sealer on top of the paint, it will add another step to making paper mâché be more outside friendly.  I will be reporting on this as things go along.

I am kind of annoyed with myself in one aspect.  If I had taken the time to make a extra ball with a standard  paper mâché mix, I could have compared the difference between the two mixtures and how it affected the ball.  I would also have liked to tried this experiment with the penetrating sealer I wrote about when making my last pumpkin.  Unfortunately, I did not have any more, or at least not enough for the project.

The method I used to make the  paper mâché ball. 

Please note:  I used eye protection and gloves while making and applying the mixture. When working with paper mâché you need to protect your work surface and flooring with plastic or some type of drop cloth.

I have worked with paper mâché for so long that I don't measure ingredients anymore.  The amounts would change depending on the size of whatever I was working on at the moment.  My basic method of making a basic paper mâché slurry would be to put flour into a container and add water a little at a time and stirring between additions.  I stir until the lumps have disappeared and the mixture is a smooth paste.  For this mixture, I modified the approach a little bit.

I mixed the flour with water only until it formed a stiff, slimy dough.  I wanted the action between the flour and the water to start setting up the gluten reaction.  Then, I added about an equal amount of the thin set mortar admix to the dough.  I kept adding the admix a little at a time and stirring between additions until the mixture formed a smooth, thick slurry.  If you have worked with paper mâché for a while, you will recognize the appropriate texture of the mix.  If you haven't the general rule of thumb is that if it is hard to spread and forms lumps, it is too dry.  Add more water (or admix in this case)  If the paper gets overly soaked and does not stick well it needs more flour. 

For the paper part, I used torn strips of newspaper.  I spread the paper mâché mixture on the strips of paper with a disposable foam brush.  I like this method because it is less messy than dipping the strips in the mixture.  Also, if there are small flour lumps, I can brush them off the strip easily.  That means fewer lumps on your project, which means less sanding.  (If you are inclined to sand that is.)  I add a single layer of paper mâché and let it dry overnight before adding the next layer.  If you do multiple layers, there is more potential for mold to develop.  This takes longer than doing multiple layers, but overall I have found it more successful than adding more layers at one time.

Future Blog Posts:  I have been working on another pumpkin and I will have photos of the new one in about a week.  I may post one other post in between on another subject (to be determined).  I am trying to get back into posting twice a week, but there is not much to write about when stuck at home trying to wait out the Covid-19.  However, a few humorous things have occurred that may be worth writing about just to keep things from being so quiet between posts.