What Causes Patchy Colour in Concrete?

So you have poured your slab, added your colour, stepped back, and thought… hang on, why does it look like that? Bit darker here, lighter there, maybe a strange swirl or two. Do not worry. You are not the only one. Patchy colour in concrete is more common than people think, and the good news is it is usually easy to explain and even easier to avoid next time.

Let us get one thing clear from the start. If you want good even colour, you have got to get the mix right and do the prep properly. These two things will decide how your slab turns out. Get them right and the rest tends to fall into place.

First, the mix. When you are using dye, it needs to be blended through the concrete properly before the pour. If you are just tossing it in and hoping for the best, you are going to end up with streaks or patches. The colour has to be spread through the entire batch evenly. If one part of the slab gets more pigment than the other, it is going to show. Whether you are mixing by hand or using ready mix, make sure that dye is properly stirred through from the start.

Next is prep. And this is a big one. If you are staining older concrete, or working on a surface that has been sealed, oiled, or left to weather, it is not going to take colour evenly. Some parts will soak it up, others will barely touch it. That is where a good clean and a light surface etch come in. You want the surface open and ready to take the stain. Skipping this step is one of the most common reasons for patchy results.

Moisture can also play a part. If the ground underneath is wet in one spot and dry in another, or the slab gets sun on one end and shade on the other, the concrete will cure at different speeds. This can cause blotchy colour even if the mix was perfect. Same goes for when and how you seal it. If the sealer goes on heavy in one area and light in another, it will show through.

And do not forget your tools. Switching rollers or sprayers halfway through, missing a bit, or doubling up on overlap can all leave visible patches once it is dry. Keep your application steady and consistent from start to finish.

So if your concrete colour came out patchy, it is usually down to one of these things. Uneven mix. Poor surface prep. Moisture imbalance. Or inconsistent application. The good news is they are all avoidable.

Focus on a proper mix, prep your surface well, and apply with care. Do that and your slab will come out even, smooth, and just how you want it.