As part of my job, I look at problem concrete every day. On nearly every job I troubleshoot, the issues I encounter involve one of three mistakes that are completely preventable. Contractors are either adding too much water to concrete, improperly antiquing it, or incorrectly applying sealer.
These three errors cause at least 90% of the problems I see, including sealer flaking, whitening, bubbling, and shortened sealer life span. They also cause blotchy, streaked, incorrect, or mismatched colors and surface scaling issues. We’ll take a look at these mistakes so you can avoid them in your own projects.
Too much water
Too much water in concrete is possibly the biggest culprit in a bad job. Whether the concrete was mixed, poured, and finished too wet, or whether the concrete finishers added water to the surface while finishing, the color suffers as a result. More water yields a weaker, more porous surface that cracks more easily and bleaches out lighter than intended.
For instance, if you sprinkle water on top of a slab while finishing, you’ll create a high water-to-cement ratio at the surface that results in weak cement paste. It won’t withstand freezing temperatures for long without exhibiting damage.
Even something as simple as dampening the brush while applying a broom finish can create light or discolored streaks on the surface.
If your concrete’s color turns out much lighter than you expected, first look at how wet it was poured and finished. Even the timing of the finishing operations can affect color. When two poured slabs abut each other and do not match color-wise, it is often because one was finished at an earlier stage of set than the other. Finishing concrete while it is still wet causes it to cure lighter, whereas finishing harder concrete allows it to cure darker. If the slab’s edges are finished at a different time than the field, they will be different colors as well.