There are various ways of dying the concrete.
Iron Oxide powder dyes are most common and they are mixed through the whole batch. This type of dye can also be applied to the mix in liquid form.
Concrete can also be dyed using a powder which is applied to the surface only and is trowelled into it as the concrete approaches the initial set but before it gets too hard.
This powder consists of concrete dyes and cements which has the added advantage of making the surface much harder than normal concrete would be.
This method is known as applying colour hardeners. Although it has obvious advantages not least the economy of its use and its durability qualities, the installers need to be experienced in its application.
Concrete can also be dyed after it has fully cured, about four weeks old. These dyes can be applied to the surface and will penetrate into the top layer of the slab and can be sealed using a proprietary sealer.
This dye is more suited to internal applications especially in this climate.