BRICKS FIELD TESTING AND IDENTIFICATION

However, there are some simple tests which can be done in the field. Firstly, when you handle a brick, see if it's soft. Can you pick off the edges? Can you scratch the surface with your fingernail? If so, the brick is probably under fired - one of the most common problems. Now, break a brick in half. Was it easy? Is there a 'core' of different colour material? If the brick breaks easily or has a core like this, then it's under fired. What about the cross section? Are there lumps or stones, internal cracks or holes? If so, the soil probably wasn't mixed well enough.

Soak bricks in cold water for 48 hours. If you weigh bricks before and after soaking, you can calculate the percentage of water they absorb. A good brick shouldn't absorb more than 15% of its dry mass. If bricks are too absorbent they suck moisture out of mortar and weaken the bond. You may find the brick dissolves altogether. In this case, it's definitely under fired - and dangerous to use in any building. The presence of lime may also be detected by soaking bricks. If lime is present as lumps, it may expand and cause fractures, exposing powdery white deposits. 

Laboratory tests

If bricks have to satisfy an official standard, they will probably have to be tested in a laboratory. These tests will need to be repeated periodically to maintain quality control. Tests normally specify the sizes for bricks and the acceptable compressive strength - how much weight they can bear before crushing.

 

Raw material tests

The quality of brick which can be made at a particular site is largely predetermined by the type of soil available. There are some simple soil tests which don't need very special equipment. In the sedimentation jar test, a sample of soil is dissolved in a transparent jar of water. When the soil settles you can get an idea of the fractions of clay, fine and coarse sand that are present. Another test is the linear shrinkage test. A sample column of wetted and mixed soil is pressed into a mould and allowed to dry. The shrinkage indicates how much clay there is in the soil and whether problems can be expected when drying bricks. Soil test are useful indicators, but you really only find out whether good bricks can be made by firing samples. Before investing in a full size kiln, however, it is possible to fire cubes or eggs of soil either in a laboratory kiln or a simple field oven.