Gypsum block for Soil Moisture Sensor

Based on the previous experiences of Reinier Van der Lee related in his blog I have made my own version of the gypsum block.

I made my firsts blocks in a very similar way that Reinier made before, but I started to think how to improve them, not really improve, because Reinier’s blocks works perfect, but I wanted to made them in an easier and methodic way.

So, this is the way my gypsum blocks are made:

I have found a very cheap and easy to find matrix: Hair Curlers

Once you take off the “skin” you get a nice matrix for the gypsum block:

These curlers have approx 35mm of diameter. To complete the structure of the block I have designed and printed two pieces (can be found here) in openScad that fits into the curler:

The final step is to cut 2 pieces of 7cm. stainless steel m3 threaded rod (all the metal pieces are stainless steel quality) and put all together as can be seen in the first photo.

To fill the matrix I cover the matrix with plastic film (the cooking one) and I pour the 50% plaster of paris 50% water (in volume) mix inside. This gypsum solidificates very quick and depending on temperature you can manipulate it in a couple of minutes.

Finally just attach two cables and use it with the Reinier’s sketch or similar.

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