How to test your soil when making construction blocks

Did you know that there are 2 different ways to test your soil?

Before any block making starts, the soil used must be tested to determine its sustainability and the amount of stabilizer to be used.

The 2 basic field tests that must be carried out on every soil are:

  1. Bottle Test
  2. Box Test (Linear Shrinkage Test)

The Bottle Test

Ever had a hard time differentiating between silt and clay? You are not alone!

Through this test, you will be able to determine the amount of clay, silt, sand and gravel in the soil you are testing.

The Box Test (Linear Shrinking Test)

This test is used to determine the amount of cement or lime stabilizer to be used in a particular soil. To perform the test, you will need a box with internal dimensions of 600m*40mm*40mm.


  • First oil the inside of the themould box.
  • Some sieved soil is mixed with water until it cannot hold more. i.e it gets saturated
  • The box is now filled with wet soil. The excess soil is removed by leveling the top. The box is then left in a protected area where the soil will be left to dry.
  • After drying, the soil will have shrunk and probably cracked as well. It should now be pushed to the end of the box,¬†leaving a gap on the other end. The gap left should be measured. This indicates the overall shrinkage of the soil.

To determine the cement soil ratio to be used, use a 15-litre bucket as a measuring/batching unit as follows:

ShrinkageCementSoilNo. of Blocks Straight & Curved Interlocking Per Bag of CementNo. of Blocks wide interlock & standard blocks Per Bag of Cement
Less than 12mm1 bucket18 buckets150 blocks110 blocks
12mm-24mm1 bucket16 buckets130 blocks90 blocks
25mm-39mm1 bucket14 buckets115 blocks85 blocks
40mm-50mm1 bucket12 buckets100 blocks75 blocks

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