There are several uses for coir bricks, and choosing the best brick really involves knowing what its eventual use will be. Some bricks are coated in latex to preserve their shape or have been treated to accelerate decomposition and are not good in some situations. Similarly, the processing used to make some bricks could cause elevated levels of chemicals that could kill plants to which they are exposed, although such bricks could be perfectly acceptable as a decorative element or floor covering. Finally, the condition of coir bricks and their appearance can sometimes help to determine whether the bricks are still usable or have been stored incorrectly.
Coir bricks are generally compressed very tightly into bricks so they can be transported and have a minimal risk of exposure to moisture. Occasionally, the outside of the bricks are coated in water-based latex or other materials to hold the shape of the brick and to stop any unintended moisture from penetrating it. This coating might normally wash away in a garden when exposed to the elements, but if the coir is being used for starting seeds or vermiculture, then the coating could present problems and cause seeds to not grow and worms to die.
To avoid unnecessary expense, the features of the coir bricks should match the job they are expected to do. There is no reason to pay for coir bricks that have been treated with growing or rooting hormones if they are going to be used as compost carbon. Some bricks also might have salt or chlorine in them from the manufacturing process, meaning they will have to be thoroughly soaked and drained before use. There are available coir bricks, however, that have not been treated in any way.
Size is another consideration, and buying coir bricks that are large enough to do the job without being too large is advisable. Depending on how it was packed, it can be very difficult — if not impossible — to cut a coir brick into pieces. Leftover coir can be stored in a dry place in a container, but it does decompose over time.
Coir bricks that are old or improperly packaged might have been exposed to too much moisture from the air. This means that, when the brick is soaked, it will either not expand at all or will take a week or more to reconstitute. Bricks that look excessively frayed or have irregularities in the surface might have expired and should be avoided.