» October 20, 2023

What Causes Efflorescence in Concrete and How Do You Get Rid of It?

Efflorescence in concrete segmental retaining wall

Efflorescence in concrete is a common problem that occurs in precast concrete pavers, walls, steps and even in mortars, particularly as a result of wet weather exposure. This unsightly white powdery substance can diminish the appearance of landscape elements and even indicate conditions that might cause damage over time such as excessive moisture from poor drainage. In this blog post, we’ll explore what efflorescence is, why it occurs, and how to prevent and remove it.

What is Efflorescence?

Efflorescence is a naturally occurring phenomenon that happens when water seeps into the pores of concrete products and dissolves the naturally occurring salts within the concrete. These salts are then carried to the surface of the concrete, where they dry out and form a white, powdery substance.

Why Does Efflorescence Happen?

Efflorescence is the result of exposure to water, it can occur due to the curing process or concrete mix during manufacturing in addition to conditions during and after installation.

As newly poured concrete products harden or “cure”, the water in the concrete mixture evaporates. A denser mix of concrete will create a less porous finished product, essentially making fewer pathways for water to travel through the concrete once cured. With less water moving through the concrete in wet conditions, this decreases the chances for efflorescence to occur. If the concrete mix creates a more porous finished product, or is not allowed to cure properly, this can lead to higher porosity and therefore increase the chances of efflorescence happening.

In addition to the type of concrete, installation techniques, like not using open-graded base (base aggregates that allow water to drain through them) can lead to excess moisture becoming trapped under pavers and behind wall stones. With more water in contact with the concrete products for greater amounts of time, it increases the risk that efflorescence could occur.

A photo of a modular concrete retaining wall with stones that have efflorescence

How to Prevent Efflorescence

Preventing efflorescence requires careful attention during the manufacturing and installation processes. Here are a few tips to help decrease the chances of efflorescence in products used for your landscape project, or address it if it occurs:

Use high-quality products from industry manufacturers

While we don’t have any control over the manufacturing process, we can take steps to lessen the likelihood of choosing a product that might be susceptible. Pick a manufacturer that uses high-quality concrete with a proven mix design to ensure that the pavers or wall stones are durable and resistant to efflorescence. Source your products from a landscape supply store. Sales staff will be able to give recommendations based on feedback from their professional landscaping customers and you’ll be able to see a wide range of options in displays and catalogues.

Install interlocking pavers, walls, and steps with an open-graded base

An open-graded base uses aggregates with uniform sized, jagged stones. The shape of the stones allows them to lock together well for compaction and structural integrity while the spaces between the stones let water flow through them back into the ground. This prevents excess water uptake in the concrete products and improves drainage for the project.

Consider a permeable jointing material for pavers where applicable

Jointing products are installed in the spaces between interlocking pavers. Traditionally, a uniform sand would be used, but with no way to “glue” it in place, the sand required upkeep and replacing over time. Polymeric sand is a more modern option that includes a polymer glue, activated by water, which adheres the sand to the sides of the pavers, holding it in place for years without additional maintenance. While this is a great product that offers different colour options and longevity, it makes the entire paved surface impenetrable, so all water needs to flow off the paved area, and can create areas of standing water if the project isn’t graded properly. A permeable jointing material both adheres to the pavers and sets with spaces between the particles allowing water to flow through every joint. Permeable jointing can be used in any patio or walkway project, and advancements with this product mean some options can be used for driveways as well.

Do not use a sealant for at least 2-3 months after installation

Because efflorescence occurs with exposure to wet conditions, it’s best to let any newly installed concrete products go through several wet-to-dry weather cycles before sealing them. This will allow any moisture that might be able to move through the concrete do so, and the minerals to wick to the top of the concrete. That way you can address any efflorescence if it occurs without it being trapped under a sealer, which creates additional difficulty to correct the issue.

How to Remove Efflorescence

If you already have efflorescence, there are a few ways to remove it:

Pressure washing

A high-pressure water jet can help remove the efflorescence from the surface of the pavers. Be sure to use a pressure washer with a low-pressure setting to avoid damaging the surface of the pavers. Using a hot water pressure washer will help release the mineral layer more effectively and speed up the process.

Acid washing

Acid washing is a more aggressive method of removing stubborn efflorescence. It should only be used as a last resort. Be sure to follow the manufacturer’s instructions carefully, as acid can be dangerous if not handled properly.

Use a specialized cleaner

There are a variety of cleaners on the market that are specifically designed to remove efflorescence from concrete pavers and wall stones. Be sure to choose a cleaner that is safe for use on your particular type of pavers and follow the manufacturer’s instructions carefully

While efflorescence can be unsightly, it is not typically harmful to the pavers themselves. Preventing conditions for efflorescence to occur requires some planning for the installation process, and removing it can be accomplished through a variety of methods. By taking the necessary precautions, you can ensure that your concrete pavers and walls remain beautiful and durable for years to come.

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