Thermoplastic sheets like Wonderflex and Worbla have a textured surface which can be rather annoying if you are planning to make something with a more smooth and shiny finish to it. In this tutorial, I will show you how to mask the bumpy texture .



  1. A paintbrush
  2. Gesso: I don’t think the brand really matters, but the thicker it is the better. I’ve been using Liquitex Gesso.
  3. Various grits of sandpaper: I use three different kinds of grit, 100, 220, and 400.



I’m going to be using some armor parts that I test-built based off of a character named Shun from Saint Seiya. It is made out of Wonderflex with craft foam inside of it. I am done building it and now I just need to paint it! NOT. Before painting anything, I have to apply multiple of layers of gesso on it if I want this armor to look smooth.

To do that, I applied a layer of gesso onto the armor. Each time it dried, I painted another layer of gesso. I repeated this process many, many times until I knew it was thick enough to withstand a whole lotta sanding that I’m about to do.

A good way to tell if you don’t have enough layers is to take a pen/marker and doodle something on the thermoplastic before applying gesso to it. If you still see your doodles through the gesso then it most likely means you don’t have enough layers. So keep on applying gesso until there are no traces of your pen markings.


Here’s what it looks like after it’s been gesso’d up but hasn’t been sanded yet. Pretty icky right? TO THE SAND PAPER WE GO!

I first started with 100 grit to get rid of the obvious bumps and ridges that the gesso made. I did this for about 5-10 minutes. I didn’t want to take too long because 100 grit is pretty rough so I didn’t want to over-do it.


Next, I moved up to 220 grit to smoothen out the surface. I did this for about 20 minutes.


Finally, I used 400 grit to smoothen out the surface even more. I did this for about 30 minutes. The time it takes to sand the armor greatly depends how smooth you want it to be and how patient you are.

After I was done with the sanding, I sprayed a coat of primer on it. When that dried, I used a glossy pink paint spray for the base color of the armor.

gessowonderflex bumpywondeflex

Applying layers upon layers of gesso and then sanding it for an hour doesn’t sound like fun but trust me, the result is absolutely worth it. Next, I will write a tutorial on how to paint the armor!