How-To: ShapeLock Sanding Blocks

How-To: ShapeLock Sanding Blocks

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Inspired by the Sandables concept that recently made the rounds, we’ve been experimenting with adding abrasive grit to polycaprolactone (aka ShapeLock) thermoplastic to make rigid sanding blocks that can be reformed, with mild heating, to fit into hard-to-reach nooks and crannies on your work.


If you’re not familiar with ShapeLock, it’s pretty cool stuff. Rigid at room temperature, it melts to a soft putty at 60 °C (140 °F), which is cool enough to shape with your fingers. (Still, always use caution when first picking up a piece of hot ShapeLock, because if you’re not using a temperature-controlled bath it can be easy to over-heat.)

Polycaprolactone line-angle structureTools and Materials

  • Scale 25 g capacity ±0.1 g
  • ShapeLock pellets (3 g)
  • Silicon carbide grit (6 g) “coarse” 60-mesh
  • Silicone baking cups (2-3)
  • Microwave oven or heat gun / hairdryer


Put one of the baking cups on your scale and note the weight. Add ShapeLock pellets, followed by grit. Transfer the cup to your microwave oven and heat on full power for 10 second intervals, until the ShapeLock turns clear. Remove the cup from the microwave, nest it inside one or two additional cups to protect your fingers, and knead the contents together slowly, rewarming if necessary, until grit and plastic are thoroughly mixed.

Cool the plastic to room temperature. ShapeLock seems to hold heat for a long time, but you can use water and/or ice to speed things up. Once it’s rigid, rewarm it 5 seconds, and form it to whatever shape you please. When it stiffens up again, it’s ready to use.

Used ShapeLock sanding blocks can be reheated and reformed as necessary, though it’s a good idea to clean the surface with an old toothbrush first. Use caution when reheating in the microwave: While the plastic and the grit are microwave-safe, whatever you’ve been sanding on may not be.  If you’d rather err on the side of caution, a heat gun or hairdryer works just as well.

8 thoughts on “How-To: ShapeLock Sanding Blocks

  1. andytanguay says:

    COOL!!! What a great Re:Make!

  2. brian says:

    wouldn’t the friction cause enough heat to make it lose shape?

  3. Ross says:

    I just tried this recipe and when even a little warm, this stuff sheds grit like crazy. I tried sanding painted wood and the remaining paint is now grey with loose grit. Also, as brian guessed, you can’t use it to make a sharp inside corner and then expect the corner to hold shape. The corner sags and distorts quite quickly during use.

    I was trying to sand a window frame moulding in one pass, but I’m going to have to retry. I think I’m going to clean the paint out of the block, reform it, refrigerate it until it’s good and cold, and then try again. Maybe I was simply too hasty and starting sanding when it feels firm and slightly warm to the touch is still too aggressive.

  4. juannavarro says:

    Meh, till this day my hands are the best thing for sanding. I could see maybe a very specific job using this, but really with all the work heating and adding grit, you could probably get the job done with some elbow grease. It’s cool that it does that though!

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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