ADDING COLOUR OXIDE TO BRICKS
Adding colour to bricks is done by adding coloured oxide to the mixture. This tints the concrete dry mix (or wet mix) to the colour desired. Typically, one would add 3% of the total weight to achieve a rich level of colour. The oxide, however, is not cheap & that means that each brick can cost an extra 20-25% ! This additional cost is usually carried onto the customer with interest. To reduce the cost, less oxide can be used - 1% for example. This would unfortunately also reduce the richness of the colour. A red oxide would instead make the bricks pink in colour. If you wanted a slight colouring then this is the way to go. There is a very sneaky cost-saving method that will let you be very competitive in price! We'll get to that before the end.
THE PROCESS
Take your aggregate mixture you will be using for your Doubell brick machine; Make sure you have not added the water yet!
Sprinkle your measured oxide around on the mixture (or premix it with the cement)
Mix the oxide into the dry mix thoroughly - it is important that the oxide be uniformly distributed.
Add your measured water to the mixture (NB do not pour into one location! Sprinkle the water over the mixture while mixing)
Once the mixture is evenly coloured, you can use the mix in the machine.
EVEN COLOURING
To achieve a uniform colour it is advisable to use a Doubell Panmixer - this will evenly mix the aggregate, cement & oxide quickly (6 minutes total!) to produce a good mixture for good paving bricks. When producing to SABS standards, a panmixer will also ensure that all your bricks are made in the same way, minimising human error. The mixer is also not like a concrete mixer - the pan is stationary & the paddles turn!
COST SAVING TRICK FOR PAVERS
Here's a great way to bring the oxide costs down to a mere 10% ! Why colour the whole paving brick when people only ever see the top?
Mix TWO batches of mixture: your cost-effective mixture for the brick & your expensive oxide + building sand mixture. What you do is fill the mould of your Doubell machine as normal. Then take your stamper & press down on the mixture (as if you were about to compact). Now instead of compacting, raise the stamper again.
You will notice that you have created about 10mm or space for more mixture. Some brick makers use this space to fill more mixture (depends on the mixture - not a necessary step for most aggregate types).
Take your expensive colour mixture & "top up" the mould box. Once levelled off, proceed normally.
You will produce a brick that has a coloured "cap" on top. This will still be as strong if not more; but it will also be a much cheaper method to offer coloured paving to customers.
Take note that this process will take some getting used to because you now have to mix two separate batches. Consider a Doubell Hyperstat for this purpose - a machine with two separate entrances to the same mould! Keep the mixtures separated with ease.