Manufacture of bricks

Manufacture of bricks

To minimize breakages in cold weather, increase the cement content of the mix or the curing period before moving blocks.

Ordering and stockpiling materials

Aggregates and cement should be ordered in good time. Stocks should be sufficient to prevent stoppages due to lack of material.

As a rough guide, using an aggregate: cement ratio of 8:1 by loose volumes, three and a half bags of cement and a cubic meter of aggregate will be enough to make about 400 bricks. The number of blocks produced from the same quantity of material will depend on block size and whether they are solid or hollow.

Aggregates must be stockpiled in such a way that contamination is prevented and mixing of different types is prevented.

Cement must be stored in such a manner that it is kept dry. Cement in bags should be used within one month of being delivered.

Batching

Cement, if supplied in bags, should preferably be batched by the full bag. Cement supplied in bulk may be weighed (preferable) or batched by loose volume (not recommended).

It is important to batch all materials accurately. Batching containers, e.g. wheelbarrows, buckets, drums and wooden boxes, should be loosely filled to the brim and struck off flush with it. To avoid errors, there should be enough containers for a full batch to be made without using any container more than once. Dented or broken containers must not be used. The amount of water to be added to the mix is judged by eye and by doing some simple tests

Water content

Water content is critical. The mixture must be wet enough to bind together when compacted, but it should not be so wet that the blocks slump (sag) when the mould is removed. A common mistake is the use of mixes that are too dry, resulting in incomplete compaction. The moisture content should be as high as possible as this allows better compaction and thus gives the best strength.

Mixing

Hand mixing with the use of shovels should be done on a level concrete slab or steel plate.

First spread the sand out 50 to 100 mm thick. Then distribute the cement, and stone if any, evenly over the sand. Mix aggregate and cement until the color is uniform. Spread the mixture out,

sprinkle water over the surface and mix. Continue with this process until the right amount of water has been mixed in.

Molding

Hand operated machines should be used as instructed by the manufacturer.

The mould of a powered machine should be filled until approximately six to eight cycles of compaction are required to bring the compacting head to its stops. Too little or poor compaction should be avoided as it results in greatly reduced strengths.

Curing

Curing is the process of maintaining a satisfactory moisture content and a favorable temperature in the blocks to ensure hydration of the cement and development of optimum strength.