When concrete ends up being discoloured, that is a testament to the “quality” of installation, and the contractors you have hired. Needless to say, it is a disappointment to everyone involved.
Make no mistake; the contractor worked hard to deliver a product that is of high quality. However, far too many people look forward to an attractive driveway, but end up with something that is far from that, leaving many wondering why their concrete appears ‘spotted.’
The simple answer for that is discoloration, caused by poor installation technique. But bear in mind, concrete can fade with time as well. Discoloration is a tricky subject, and one that cannot be solved without taking contributory causes into account.
There are many factors that contribute to the problem. However, discolouration is mainly caused by one key culprit: inconsistency. That means inconsistency in materials, or in standards of workmanship.
Below we will discuss some of the causes for discolouration in concrete. But we will also check on the natural colour of concrete, and some far more preferable alternatives. Therefore, you will no longer need to ask the question ‘why is my concrete spotted’…
What is the Natural Colour of Concrete?
Before we answer the question why is my concrete spotted, let’s talk about the natural colour of the material. The most popular colour, and the most common one, is the natural grey colour of concrete.
This is the basic concrete colour. In the past several years, companies offer colouring of concrete, so that it matches your style, and gives you far more flexibility in terms of the options on offer.
But concrete is naturally a grey product, and that is the result of using grey cement for creating concrete. Cement is manufactured through a closely controlled chemical combination of calcium, silicon, iron, aluminium and other ingredients.
Concrete Discolouration: Common Causes
The natural colour of concrete is grey, but it can sometimes turn into another colour. In addition to spots, concrete can also change colour because of improper installation, and a number of different reasons, including:
– Inconsistent materials: In order for concrete to have a smooth finish, without any spotting occurring, the mix proportion should be the same from one batch to another. If deliveries are different, it makes it decidedly difficult to achieve a uniform, concrete surface. This is the responsibility of your concrete contractor
– Water at job site: Contractors adjust batches with inconsistent moisture content at the job site, to make finishing operations practically possible, and easier to achieve. But sometimes, this can lead to small variations in concrete moisture, which invariably lead to a blotchy appearance, and inefficient mixing
– Change in the colour of the cement: Since concrete is made out of cement, a change in cement colour will result in discolouration of the concrete. There is also a trend to use recycled products as partial cement replacements, that also product colour variations. This depends on the percentage of recycled material used in the mix
– Adding calcium chloride to the mix: This is one of the common causes for why your concrete takes on a ‘spotted’ appearance. The addition of calcium chloride will speed up the setting time of concrete. However, inadequate mixing after the addition of calcium chloride will make the colour even more irregular
– Last, but not least, poor workmanship, or inconsistent workmanship, is another reason for spotting. How your contractor reacts to variables during installation has a huge effect on the finished product. For example, the weather conditions can change from morning to afternoon, or from day to day.
They have a huge impact on the final results, and how your contractor adjusts to them, is also important in determining the final result. For example, in a dry environment, wetting down a subgrade prior to a slab placement is a common practice. But this is not always the case.