Concrete bricks and blocks can easily be made at home with only a few items. Making your own concrete bricks and blocks can save you money if you are looking to build a small structure at home. You can even start your own small business producing these cost-effective building materials.
These building blocks can be solid or hollow – it just depends on the builder’s preference. Making concrete bricks and blocks is quite easy, but they need to have a standard size and consistent quality if they are to be sold for a profit.
Make sure you have access to a flat piece of land big enough to store the equipment, materials and finished bricks. There should also be enough space to store the aggregates (crushed stone, gravel and sand) and cement. Do not store the aggregates or cement outside on bare ground or under trees as this can cause moisture damage and contamination.
Keep aggregates and cement dry and separate until you need to mix them. Ideally, bags of cement should be stored in a dry room. You’ll need space to produce and store the concrete bricks and blocks. A flat concrete slab will be perfect. You will be able to store 1000 bricks or 200 blocks for curing and drying on a space of about 50 square metres.
You’ll require a number of general-purpose tools, as well as a moulding machine. You get two types of moulding machine – a stationary block moulder that produces one brick at a time on a pallet, and an “egg-layer” machine that moulds bricks on a concrete slab.
Concrete mixers will make the process easier, but they are not essential. Mixing concrete by hand will save money but it is harder work. Concrete can be mixed with a shovel on a flat concrete slab or steel sheet. Don’t ever mix concrete directly on the earth – the soil will contaminate the concrete batch.
Only a pan mixer should be used if you are able to use a concrete mixer. Drum mixers will not work as they cannot mix the semi-dry concrete required to make bricks. Other equipment you will need includes hosepipes, wheelbarrows, shovels and plastic sheeting.
The cement used to make concrete bricks must be strength class 42,5N or higher, as the concrete needs to cure as fast as possible. Sand and stones will form the aggregates for the concrete bricks. You can use pit or fine river sand, coarse sand (up to 5mm in size) or stones that are no bigger than 10mm for hollow bricks or 13mm for solid bricks. Usually, you can make concrete bricks with just coarse sand, but a combination of aggregates can also be used.
When you make your first batch of bricks, try to use coarse sand only. Then replace some with fine river sand and stones to see what creates the strongest mix for your bricks. Try to use aggregate to cement ratios of 6:1, 8:1 and 10:1 (230 litres, 300 litres and 380 litres of aggregate per 50kg bag of cement).
For each ratio or combination, mix a batch of concrete with water and use the brick moulding machine to make some test bricks. This way, you can find the perfect mixture for your needs. The heavier the freshly moulded brick, the better. Knock the dried bricks together to test their strength. If you hear a hollow thud, it means the bricks may be weak. If you hear a ringing sound, it means that your bricks are strong.
Once you’ve found the “recipe” for the best mixture for the concrete bricks and blocks, you can start making them in larger quantities. Ensure you have enough cement and aggregates to make the number of bricks you need.
If you use an aggregate to cement ratio of 8:1 with three-and-a-half bags of cement and a cubic metre of aggregates, you will produce enough concrete mixture to make about 400 bricks. This number can vary depending on the size of the bricks and whether the bricks are hollow or solid. When the approximate amount of water needed per batch is known, measure about 90% of this amount and add it to future batches. The remaining 10% of the water can be added slowly, in order to get the right consistency of concrete.
It is important that the concrete mixture is wet enough to hold together when compacted. Yet it must not be so wet that the bricks sag and lose their shape when removed from the mould. If you notice ripple marks on the bricks once they are moulded, your mixture contains slightly too much water. If the concrete is too dry, bricks won’t bind properly and they will crumble when they are dry.
To mix the concrete you should spread the sand out on a concrete slab or a steel plate. The sand must be 5cm to 10cm thick. Spread the cement over the sand and add aggregates. Use a shovel to mix the sand and cement until a uniform colour is achieved. Sprinkle water over the surface of the mixture. Continue to mix until the correct consistency of concrete is reached.
Put the concrete in the moulding machine and compact it about six to eight times. This will ensure that the brick is properly formed. Carefully take the moulded brick out of the machine and set them somewhere to cure for seven days. Protect the bricks from rain and direct sunlight while they are curing.
To prevent moisture loss, you can cover the bricks with a plastic sheet. If it’s hot and windy, it may be necessary to lightly spray with water. This will enable the bricks to cure properly and not dry too quickly.
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