Why is Your Concrete Blotchy (and How to Fix it)

Have you ever walked past a home with discolored concrete in the driveway? It’s lighter here and darker there, creating a blotchy effect that you know couldn’t have been intentional. Looking at the chaotic design, you can’t help but wonder what went wrong,… and how you can avoid making a similar mistake with your own concrete projects in the future.

Concrete discoloration is not a rare event

Laying concrete isn’t an exact science, and there are a variety of factors that can contribute to concrete discoloration from the very beginning. These factors include:

• Variability in concrete mixtures
• The use of too much or not enough water
• The use of calcium chloride
• Improper concrete laying techniques
• Outside temperatures
• Exposure to water and salt

Many of these issues can be resolved by properly sealing the concrete after it has been poured. But what if you noticed discoloration even after sealing?

The culprits of blotchy concrete after sealing

When you find yourself staring at discolored concrete that has already been sealed, there are usually three potential sources of blame:

1. The sealer was applied poorly
2. Not enough sealer was applied
3. The concrete itself had varying absorption rates

Blotchy concrete after sealing has almost everything to do with the sealing techniques used and the very nature of concrete itself.

Concrete is a porous material, with some areas of concrete naturally being more porous than others. That’s why we use concrete sealers to begin with—to combat that permeability and protect our newly laid concrete from absorbing water and salts that could more quickly erode or stain it.

But if you combine that already variable porousness with a less than stellar sealer application, you’re almost asking for a blotchy finish.

Even if your concrete coloring initially looks uniform, improper sealing can open it up to discoloration in the future as the surface is permeated by water or deicing salts.

How to prevent blotchy concrete

The best way to save your concrete from discoloration is to seal it properly to begin with. If you were to look at a concrete slab under a microscope, you would find that it consists of an almost infinite number of hills and valleys. The final profile on the surface of the slab is directly related to the finish. A smoother finish will produce less hills and valleys, while a rushed or rough finish can resemble the Grand Canyon.

The whole point of applying a concrete sealer is to even out the hills and fill the valleys until you have a consistent surface. But we also have to realize that at least some sealer will be absorbed into the pores of the concrete, and how much absorbs where will depend entirely on the variability of the concrete itself. So if you fail to use enough coats of sealer, you will find you have some areas of concrete that appear to have been sealed perfectly, while others clearly have not been.

Thus contributing to a blotchy appearance.

What you want is a finished surface that is uniform and no longer full of variability. But if the sealer isn’t applied uniformly to begin with, or if not enough coats are used, the slab will appear blotchy upon drying. This is caused by the sealer filling in some of the valleys, but not all, and failing to remain on top of the hills.

W. R. MEADOWS sealers are specifically formulated to help produce the most uniform seal possible. Unfortunately, even a premium-grade sealer will not compensate for poor application techniques or insufficiently applied product.

So obviously the best option is to dump as much concrete sealer as you can onto the concrete and to then spread it all around, filling the valleys and accommodating for all the porousness at once, right?

Wrong. Heavy coats of sealer can cause the appearance of bubbles in your concrete. The coloring might be uniform, but the top finish will be so full of air displacement that all you’ll ever see from now to eternity is those bubbles in your concrete.

To avoid all of this, sealer needs to be applied in a uniform manner over multiple, light coats. You should allow two to three hours for drying in between each of your coats and watch for any blotchiness as the coats seal. When your last coat has dried and you don’t see any signs of concrete discoloration, you’ll know your job is done.

But this patience and willingness to go slow and steady with your sealing is the key to that consistent finish you’re looking for.

How to fix blotchy concrete

Let’s say the damage has already been done and you’re looking with agony at your discolored concrete. Knowing what you now know, it’s clear that enough sealer was applied in some areas, but not all.

Is breaking up the concrete and starting from scratch now your only option?

No! You can still rectify this situation, but you will have to put some work into the process.

Your first step should be flushing and scrubbing the concrete. This involves soaking the concrete in hot water and then scrubbing it forcefully with a hard brush. The goal here is to even out some of the variability in the concrete’s moisture and mineral build-up. You may have to do this several times, but as soon as the concrete dries without discoloration, you will want to seal it again with a new, light coat of concrete sealer to preserve the work you’ve done.

Alternatively, you could consider using a concrete stain top coat to even out the blotchiness you are seeing. Of course, this would involve having to first strip the sealer you’ve already used, leading to more work overall in the end.

The bottom line

Concrete sealers can go a long way in preventing concrete blotchiness, but only if they are used correctly to begin with. So take your time on your next concrete sealing project, saving yourself a lot of headaches in the future.

Of course, W. R. MEADOWS is happy to help in all cases.  If you have a specific question about application techniques, please contact your local sales office at (800) 342-5976 or email info@wrmeadows.com.

What is Concrete Curing and Sealing Video

Resources

• Sealer Maintenance Tips
• Concrete Curing and Sealing Compounds
• Concrete Curing Compounds

 

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