White Portland Cement – Concrete
White Portland cement is a type of cement that is known for its characteristic whiteness and is typically used for decorative work and prestige projects. The process of making the cement white involves significant changes to the manufacturing process, but it is desirable because the whiteness will never fade or crack like regular cement that has been painted. This is because, unlike painted cement, the whole of the material is white, so there is no thin layer that can flake away, revealing non-white material behind it.
White Portland cement often takes the form of pre-cast cladding panels, as it is more expensive to manufacture, and thus not practical to use in the same manner that regular cement is used. White Portland cement can also be pigmented during the mixing process to give it colour, and some manufacturers even offer pre-blended pigmented cement so you can be sure you are getting the same tones, as ensuring the correct amount of pigment consistently across different batches of cement is an extremely challenging prospect.
Ingredients, Properties, and Health Concerns
There are certain health risks associated with Portland cement of any colour, such as inhaling the hazardous ingredients that make up the cement. Enough exposure to the powder can even cause lung cancer, so proper safety precautions must be taken when working with Portland cement.
While White Portland cement is relatively expensive due to the pigment, the basic Portland cement ingredients are readily available and in abundance—ingredients like limestone and shales. This makes Portland cement one of the cheapest construction materials available, which is a significant part of why it has been so widely used in recent history.
Unlike other construction materials, like brick and mortar, or wood, cement can be poured, making it an extremely versatile option. Framing of any shape can be constructed, and the cement poured in, where it will eventually cure in the shape of the mould.
For additional strength, reinforcements can be worked into the cement, or constructed in the space where the cement will be poured. This provides additional tensile strength to the cured concrete, addressing one of its main weaknesses as a construction material. Where it is not weak, however, is the fact that it is incompressible. While it would be possible to “snap” a concrete beam with relatively low force, it would be considerably more difficult to “crush” that concrete beam. It is this high resistance to compression that makes concrete so suitable for construction, as the weight of any sufficiently large building would destroy its own foundations if they were made from a less suitable material.
What is the Difference Between White Cement and Grey Portland Cement?
Outwardly, the only real difference between White Portland cement and Grey Portland cement is the colour. The differences become more apparent when you get into the manufacturing process, however. The raw materials that makeup Grey Portland cement are obtained through mines, quarries, and other means, and it is the natural colour of these ingredients when mixed that give the cement its grey hue. They include limestone, seashells, clay, and even iron ore.
In order to make white cement, you must reduce the amount of certain ingredients—specifically the ones that contribute to this grey colour. On top of that, aggregates like marble are added. The combined effect of reducing the number of ingredients that turn the cement grey and adding other ingredients that do not add any colour is what makes the cement white.
After that, both white and grey cement go through the same grinding, heating, and grinding again process that produces the fine powder that is cement. From there, it can be mixed with water to create pourable concrete.
Which is Stronger – White Cement or Grey Cement?
There is no real difference in strength between white and grey cement, despite the different ingredients and manufacturing process. It is certainly possible to make a stronger or weaker cement by tweaking the ingredients, but it would not be an inherent difference in strength.
It is often thought that white cement must be weaker due to the fact that it is not used in structural work, and is often limited to decorative features. However, as we mentioned above, this is down to the increased expense of white cement. It is not practical to make entire structures out of white cement when the bulk of the structure can be made for considerably less money with grey cement and then clad with white cement.
Indeed, the manufacturing process of making white cement can require almost half again as much energy as regular grey cement, not to mention the added cost of obtaining the necessary ingredients—it is much easier and cheaper to get clay than it is to get marble.
Of course, grey cement is often used to make concrete, which is mixed with aggregates such as sand, and that can be less strong than white cement. But then, on a similar note, concrete can also be reinforced with fibres or rebar frames, which would make it more durable than white cement.
Is White Portland Cement Waterproof?
Portland cement—and, by extension, White Portland cement—is not inherently waterproof. However, it can be made to be waterproof by adding a water-repellent agent. It’s important to note that, when we say cement is not waterproof, we do not mean that if you have a wall made of cement, it will let rain through. Rather, cement—and concrete in particular—can absorb water. This should not come as a surprise, since water is required to make cement in the first place.
Why is White Portland Cement More Expensive?
Simply put, the considerably more involved manufacturing process is what makes White Portland cement more expensive than its grey sibling. For one thing, the ingredients themselves are harder to obtain. As we mentioned above; clay is cheaper than marble. But even the more expensive ingredients do not make up the bulk of the extra expense.
The process of making White Portland cement is considerably more expensive, requiring almost twice as much energy to undertake than grey cement.
Part of this is due to the fact that white cement powder is considerably finer than grey cement and requires more grinding down—which is part of what makes it so suitable for decorative uses—but a more significant factor is the difficulty of keeping contaminants out of the mix. If any ingredients that could add colour to the mixture manage to find their way into the mixing process, it reduces the whiteness of the concrete. Given that the primary reason for all the added expense in the manufacturing process is to make the cement white, you can understand why keeping contaminants out of the mix is so crucial—a batch of white cement that comes out off-white is virtually worthless as white cement, but will have cost too much to manufacture to sell as grey cement.
Of course, this only applies in situations where the desired end result is white cement. White cement is also used to create other colours of cement, which involves adding pigmentation during the manufacturing process. This can be done with grey cement as well; however, the colours created using grey cement tend to be dull, whereas the colours created using white cement are bright and vibrant. For that reason, it is just as important to keep the mixing process contaminant-free, even if the cement is to be coloured eventually.
How Can White Portland Cement be Used Artistically?
One of the main reasons that White Portland cement can be used artistically is the much more delicate powder it is made from compared to grey cement. This allows for the creation of a much smoother surface than would be possible with the coarser grey cement, which results in generally more aesthetically pleasing surfaces.
The smoothness of white cement can be enhanced with a variety of post-curing techniques, such as sanding and polishing. Sanding, in particular, can be used to refine further the design of the cement, which a positive when talking about artistic uses of cement.
The same techniques can be used for grey cement, of course, but the nature of the cement means you will not be able to achieve as smooth a finish as white cement, no matter how much you sand.
And, of course, there is the colour of the cement. Creating artistic structural elements generally works better when the natural colour of the material is on display. We mentioned above about paint flaking off over time, and that is basically what we are talking about here. Applying a finishing coat that changes the appearance of the cement can—and usually will—flake off over time, and that can look fake and cheap, which is certainly not what you want if you are going to the trouble of having artistic elements made out of cement. With white cement, the finish the can’t flake off because the whole of the material consists of the same colour. It may still be prone to structural problems, such as cracking, but you won’t have to worry about the exterior peeling away to reveal an entirely different colour.