White On Concrete
Sealer delaminating from concrete below
White or cloudy areas on a decorative concrete patio can be caused by a few different things. The most common cause is the use of incompatible sealer. When most professionals seal decorative concrete we use a solvent based sealer. Due to VOC laws, hazmat rules, and costs, these can be hard to obtain unless you're in the trade, but they are best. When you purchase a concrete sealer from Home Depot or Lowes you are most likely buying a latex (water based) sealer. When these two different sealers are put on the same slab the will not agree and will cause the finish to appear white and hollow. The material can even begin to flake off the concrete. The only way to correct this it to remove all of the sealer and start over. Unfortunately, there is not an easy way to remove sealer.
The second cause of whitening is over sealing. Assuming you have never used an incompatible product, but you still see a whitening or flake appearance, it is usually a result of the sealer becoming too thick and lifting off the concrete surface. This is known as delaminating. The first step is to stop sealing so much. We recommend sealing every other year to 30 months. This is usually the right balance of concrete protection, appropriate sheen, and natural wear off.
Kennedy Space Center fountain – With Scale
A contributing cause to delaminating can be sealing when the slab is not adequately dry. If you seal when there is moisture in the concrete, this can also cause the sealer to delaminate from the slab causing the 'white' appearance. To resolve this delamination, the slab can be treated with a xylene mix and rolled out. In most cases this will allow the sealer to adhere to the slab again and help the whitening appearance.
Though there are others, the last more common cause of whitening on concrete is scaling. Whether from an irrigation system or a water feature from the pool itself splashing on the concrete, if water is regularly splashing or spraying on the slab it can scale. The scale is a variety of minerals falling out of solution and depositing on the concrete. The solution is to stop allowing water to sit or spray onto the slab as able, and then apply a light acid solution to remove the mineral deposits.