Why is my concrete turning white? 

The article aims to answer the question “Why is my concrete turning white?”. It will also highlight why the moisture is dangerous for your concrete and how you can take care of it.

Why is my concrete turning white?

Efflorescence can make your concrete turn white. White salty residue known as Efflorescence is formed when too much moisture seeps into the concrete. During curing, the moisture from the concrete seeps higher and transports salts embedded in the concrete to its surface. 

Concrete takes around 28 days to be completely dehydrated, and it starts turning white. 

Efflorescence, despite how sweet it sounds, is unappealing. Efflorescence appears in various ways depending on whether or not the floor has been completed. After staining, it might leave a white powdery coating on the concrete’s surface before sealing. 

This “blush” will appear on the concrete if the Efflorescence is trapped behind a sealer and certain stains. As indicated below, Efflorescence may cause various stain and sealer failures.

Non-reactive stains, on the other hand, do not change the colour of the concrete in any noticeable manner and so do not show signs of moisture damage. Colour fluctuation is the most common issue with reactive stains.

The acid in reactive stains includes metallic ions that react with the free lime in the concrete, resulting in undesirable color changes. 

When there is too much moisture, the salts or acids in certain blue and green stains may become brown or black. This reaction creates the stain colour. Oxidation or a fungus are two of the most common causes of colour change, which may occur with excess moisture.

Excess moisture in the presence of Efflorescing salts retards stain penetration, causing a lighter or uneven hue to appear on a concrete surface.

Several concerns arise if non-reactive stains are used in the presence of excessive moisture. 

Flaking, peeling, blistering, and black spots are common moisture-related issues with non-reactive stains because they fill the pores of the concrete or create a film that rests on top of the concrete surface.

Due to high wetness, the stain could not adhere to the concrete, resulting in flaking and peeling.

It’s scorching or bubbling because of moisture that can’t be expelled

A symptom of retained moisture that can’t be evaporated is the appearance of dark patches.

Water-based and solvent-based sealers are available.

The use of sealers might be complicated by difficulties caused by excessive moisture. In the case of the water-based sealer, the first one is likely to occur. When solvent-based sealers are applied in excessive moisture, the rest may occur.

When there is too much humidity, the sealing agent evaporates quicker than the water, so they never bind together, leaving behind this powdery or white residue.

Moisture may raise the sealer from the concrete, causing light to diffuse below the sealer (also known as “sealer diffusion”), resulting in the appearance of discoloration on the surface of the concrete.

There is too much moisture on a surface, so the sealer floats on the surface instead of bonding. Another result of moisture that can’t be expelled is cracking, chipping, peeling, or flaking. As soon as you add too much water to the two-part solvent sealer, you get a frothy material.

What is efflorescence and how does it occur?

The most common salt behind efflorescence is calcium hydroxide, called lime.  It’s almost impossible to pin down the source of lime in concrete because it can be found in the sand, water, or gravel used to make concrete. 

And it can even arise as a natural byproduct of the hydration process of Portland cement. So, it’s pretty much inevitable for any concrete to turn white at some point.  But as long as the salt is buried deep inside the concrete, efflorescence cannot exist. 

The only thing that can carry these salts to the surface is moisture.  Any source of moisture may induce efflorescence, ranging from deliberate splashing to rainwater. The water will dissolve all the concrete’s internal salts as it seeps through the microscopic pores. 

Then, when the water rises back to the surface to evaporate, the salt precipitates and interacts with the air, producing solid deposits that may be challenging to remove.  There are two types of concrete efflorescence: primary and secondary.

The secondary type I explained earlier — doesn’t happen unless the concrete suffers from water exposure. On the other hand, primary efflorescence can occur soon after a slab is poured, even in the absence of external moisture. But how does this happen?

As you probably know, water is essential for mixing concrete. But if there’s too much water in the mixture, it’ll gradually flow to the surface within a few weeks after the concrete hardens.

And again, it’ll carry the salt to the surface to precipitate the same white deposits.  

Efflorescence doesn’t have anything to do with the structural integrity of the concrete. As I said earlier, primary efflorescence can happen in freshly poured concrete, even in the absence of cracking, crumbling, or any other signs of degradation. 

However, it’s important to note that severe efflorescence may indicate moisture levels sufficient to support mould, which might cause some health issues depending on the type of grown mould. 

Besides, if you notice efflorescence in concrete ceilings, you must track down the underlying moisture source to avoid future cracking and potential collapse.

How moisture is ruining my concrete?

As water evaporates, it carries your design along. Moisture testing before applying stains and sealers might help protect your design and the concrete.

Decorative concrete combines the best of both worlds: beauty and strength. In the same way, acid stains fuse to form a lasting, appealing floor; they do the same for your home. 

A lot of criteria must be considered when selecting a stain and sealer combination to get the d0esired outcome. 

The moisture level of the concrete at the time of stain and sealer application is one of the most critical factors. One of the most common causes of moisture in concrete is a lack of proper ventilation. 

The first is the amount of water needed to make concrete. A vapour retarder may also be necessary to prevent water from migrating from the ground to the concrete slab. Both evaporating and pooling water might interfere with applying a stain or sealer on wood.

Depending on the quantity of extra moisture and the kind of stain or sealer used, the damage that excess water might do to your paint or sealer can seem different. Some of the most typical signs that the colour or sealer was applied too early will be discussed in this post.

Can moisture testing be useful?

Yes, Moisture testing is useful and is the only method to know whether the concrete can be completed before pouring. The calcium chloride test is a standard moisture test in the United States. A salt compound is run on the concrete’s surface to determine surplus moisture. 

This technique is flawed since it only monitors moisture on the surface. Moisture evaporates from the concrete as it cures. It is common to add a vapor retarder underneath internal concrete slab installations, which means that all water must travel up the slab.

It’s also possible for concrete to give out or absorb moisture based on its surroundings’ relative humidity (RH). Staining or sealing concrete depends on how much water evaporates and how quickly it evaporates.

Stains and sealers may be applied to the concrete slab when it is within an acceptable range of moisture content – one that considers the particular moisture tolerance for the intended finishes. 

Stain and sealer may be applied without trapping additional moisture if you wait until the concrete has fully cured.

For this reason, the calcium chloride test does not offer an accurate depiction of the natural moisture situation deeper inside the concrete slab, nor does this test predict the amount of moisture that will be visible on its surface as it advances toward equilibrium.

In situ RH testing is the best method for determining the concrete’s genuine moisture content. Since this test has been around for some time, it has been adopted as a standard in Europe and is now being used in the United States.

Probes for relative humidity (RH) were found to accurately reflect the RH in the concrete slab after sealing when put at a depth of 40% (the proper depth for testing while the slab is drying from the top alone). 

Tolerances for finishes may be exceeded if RH is too high. If this is the case, the finish may not meet aesthetic or performance standards.

An in situ RH test can only accurately measure a concrete slab’s moisture level. Still, it’s just as important to know what RH values are appropriate for putting a finish on your project.

Each Project’s Individuality necessitates a Customized Moisture Condition Assessment. It is essential to compare the findings of the RH moisture test to the manufacturer’s indicated moisture tolerance for that specific stain or sealant. 

Pay close attention to the finish’s “breathable” or porous properties. When the relative humidity (RH per cent) levels are higher than the manufacturer’s guidelines, epoxies are the least porous and, as a result, the most prone to cause damage.

Is there any additional element I need to know?

Your project’s stain and sealer manufacturers’ suggestions must be considered. However, there may be additional elements specific to your project that need to be considered.

When selecting the appropriate RH range for your flooring finishes, here are a few things to keep in mind:

Concrete drying conditions include the following variables:

• concrete age
• Thickness
• Slab grade
• materials used in the preparation
• The amount of water in each batch.
• Stain application and sealer application

It requires foresight and perseverance to wait for the concrete to cure before staining and sealing it. However, the additional work is well worth the reward. A high-quality ornamental concrete that will last a long time and look beautiful is what you’ll get from this process.

Conclusion

To summarize, concrete may become white if exposed to moisture for an extended period. The salts in the water will be dissolved and carried to the surface, where they will form white crystals as the water evaporates.

Keep the concrete’s surface free of any moisture if at all feasible. Additionally, you may direct garden sprinklers away from your driveway or garden walls.” However, your efforts will be in vain if you live somewhere where it often rains.

Applying a silicate-based concrete sealant is the best technique to avoid efflorescence. For best results, adhere to the manufacturer’s instructions.

Frequently asked questions (FAQS): Why is my concrete turning white?

What Happens to Efflorescence in winters?

In chilly, wet conditions, both primary and secondary efflorescence is more likely to develop.

Slower evaporation means more time for salts to ascend to the top and settle, allowing them to accumulate.

In contrast, in dry areas, the water that soaks into concrete is quickly drained away, preventing salt from finding its way to the surface. 

Can You Prevent Concrete Efflorescence?

• It is possible to coat the surface using a silicate-based concrete sealer to prevent salts from reaching the surface.
• As a general rule, this is how the sealant is applied:
• Remove any traces of filth, grease, oil, and dust from the concrete surface.
• Peel off any old coatings.
• To prepare the concrete for the new sealant, use an appropriate acid to etch it.
• Give the first coat of sealant a few hours to cure fully before applying the second.
• Apply a second coat in the opposite direction of the first one.
• I wouldn’t advocate doing this on your own, even if it seems to be straightforward. It’s preferable to select a contractor that is familiar with all the chemicals involved.

Bibliography 

Brocken, H., & Nijland, T. G. (2004). White efflorescence on brick masonry and concrete masonry blocks, with special emphasis on sulfate efflorescence on concrete blocks. Construction and Building Materials, 18(5), 315-323.

Dow, C., & Glasser, F. P. (2003). Calcium carbonate efflorescence on Portland cement and building materials. Cement and Concrete Research, 33(1), 147-154.

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