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What are these white stains on my concrete or pavers?

One of the largest misconceptions when it comes to sealing concrete or pavers is that when white spots appear on the surface after being sealed, it is from the sealer failing. Now, in some cases, this may be true, but it isn’t true for every case.

The three main causes of white spots on concrete and pavers are:

  1. Mineral deposits on the surface
  2. Efflorescence
  3. Failing acrylic sealer

All three may look similar at times, making it very hard to determine the cause of the white spots on your concrete or pavers. In some cases, your concrete or pavers may be experiencing a combination of two, or even three, factors. To help shed some light on this topic, let’s dive a little deeper into each cause.

Mineral Deposits on The Surface

Mineral deposits on the surface are one of the most common causes of white spots on sealed and unsealed concrete and pavers. Mineral deposits are formed when mineral enriched water traveling on or over the surface evaporates and leaves mineral deposits on the surface. These minerals can be hard water from irrigation, poor drainage, and a variety of other sources. Mineral deposits can’t be removed with water and often need to be cleaned with a mineral remover and pressure washer (with filtered water). If the concrete is unsealed, the mineral deposits will bond to the concrete or pavers; if the concrete is sealed, the mineral deposits will bond to the surface of the sealer.

So, you may be wondering why you didn’t see the hard water stains before you sealed? There are usually signs, but they aren’t always obvious because some unsealed surfaces are very porous. Any water that travels over a porous surface is usually absorbed into the surface, and with it, the minerals the water carries. Most of the minerals deposited by water are left in the pores of the concrete or pavers instead of on the surface. Now in extreme cases, the minerals can build up enough to where they become visible on the surface, but more times than not, the minerals are carried into the pores of an unsealed surface.  Sealed surfaces perform differently. When you seal your concrete or pavers, water is forced to remain on the surface and that is why you may start to see mineral deposits on the surface after sealing.

Mineral deposits typically form where highly mineralized water puddles or travels, and these deposits can look similar to salt stains. They can be in small spots, droplets, or appear in a large area. It really depends on where the minerals are being transferred from, and where they settle.

Now, let’s take a minute to talk about new pavers. It is not uncommon for new pavers to be installed with mineral deposits on the surface. Many pavers are made with calcium lime and other minerals, which will leave white stains on the surface of the pavers. In addition to mineral deposits forming during manufacturing, they can also develop during cleaning, storage, or from the application of the joint sand. They can also form shortly after being laid, especially if they are laid over a stone or crush-crete type of base material. With new pavers it can be hard to determine if the white spots are strictly mineral deposits, or efflorescence, or a combination of both. Before cleaning or sealing new pavers, you should consult with the paver manufacturer to see what they recommend.

Efflorescence

Efflorescence may look similar to mineral deposit stains because they are essentially the same thing.  Efflorescence is a crystalline deposit of minerals that migrate up from the ground below to the surface of the concrete or pavers. It can be hard to tell the difference between mineral surface deposits and efflorescence. They can both be cleaned with the same cleaning methods, and they may both come back shortly after cleaning.

There is one large difference however – mineral deposits will form on the surface of the sealer, and efflorescence will form below the surface of the sealer. Now, in extreme circumstances, efflorescence can penetrate through the coating and form above and below the surface of the coating. Typically, to clean efflorescence below a sealer, you will have to remove the sealer first so that you can access the mineral deposits.

Failed Acrylic Sealer

When an acrylic sealer starts to fail or age, it can blush, and blushing can look very similar to mineral surface deposits and efflorescence. If a sealer gets to the point of blushing, it can turn white and look hazy. It may be in small spots, or a large area. For example, the photo below (left) shows a solvent based acrylic that blushed from age. Once it was verified that the acrylic sealer blushed, the Armor Blush Repair was applied to the entire area, and the patio was rejuvenated. One of the best qualities about solvent-based acrylic sealers is that they are very easy to repair, and can typically be repaired with a product like the Armor Blush Repair. Had this been a water-based acrylic sealer however, the repair process wouldn’t have been as easy. When a water-based acrylic sealer blushes, there is no way to repair the sealer, unfortunately. The severity of the blushing will determine the required action. If the water-based acrylic looks warn but shows signs of blushing in a couple small areas, you may be able to get away will removing the delaminated acrylic in those areas, pressure washing the entire surface, and resealing. If however the old water-based acrylic sealer continues to delaminate, it will take the new coat of the water-based acrylic sealer with it. If the water-based acrylic sealer shows severe signs of blushing in multiple areas, it is best to remove the old water-based acrylic sealer completely before reapplying.

It’s pretty normal for an acrylic sealer to blush or haze near the end of its life. While some acrylic sealers will just fade, others will start to turn white, peel and flake. However, if an acrylic sealer blushes shortly after application, or within the first several months, you’ll want to figure out the cause of the blushing.

There are several factors that can cause an acrylic to blush, other than age, including:

  • The presence of water or moisture before, during, or after application
  • Application over an incompatible sealer or coating
  • Premature application to pavers (most paver manufacturers suggest waiting at least 2-3 months, and some as long as 12 months, before sealing newly installed pavers)
  • Application over a surface that was not properly cleaned, or where cleaner residue was left on the surface
  • Application over a surface that was not properly prepped
  • A chemical reaction with something present on or within the concrete or pavers
  • The presence of excessive subsurface moisture
  • Issues arising from applying acrylics to pavers that were installed over a concrete slab
  • Issues arising from applications where moisture is trapped below the surface of the pavers
  • Exposure to high heat or extreme temperatures
  • Harsh winters and the use of de-icing salts

As mentioned above, solvent based acrylics can usually be repaired when blushing occurs, however, water-based acrylics may need to be fully removed. Depending on the cause of the blushing, it could return shortly after. It’s not always easy to determine the cause of blushing and often times the only way to determine the actual cause is through trial and error. If the blushing is repaired and the coating is restored, it’s safe to assume that the blushing was caused by something relating to the application, surface abrasion, or age. If the blushing is repaired, the coating is restored, and the blushing re-appears shortly after, that is a clear sign that there’s a larger factor contributing to the failure that would need to be dealt with before reapplying a sealer or coating of any kind.

Final Thoughts

It can be hard to determine what caused the white spots on the surface, and trial and error can be frustrating. Unfortunately, not all issues can be solved with a sealer, and in many cases, a sealer can bring attention to pre-existing issues that weren’t obvious before sealing. If you aren’t sure what is causing the white spots on your concrete or pavers, please don’t hesitate to reach out to a Foundation Armor technician. They can help walk you through how to test and determine the cause of your white spots.

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