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.)

Tools and Materials

Scale 25 g capacity ±0.1 g

25 g capacity ±0.1 g ShapeLock pellets (3 g)

(3 g) Silicon carbide grit (6 g) “coarse” 60-mesh

(6 g) “coarse” 60-mesh Silicone baking cups (2-3)

(2-3) Microwave oven or heat gun / hairdryer

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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.