Efflorescence on Concrete: Where Does It Come From and How Do I Get It to Go Away?

Your brand-new patio is finally installed, and you’re all ready to roll out the barbeque and invite everyone over — until you notice the white, powdery dust emerging from its surface.

This emergent residue is known in the landscaping industry as efflorescence, and while it doesn’t affect the integrity or the usability of a hardscape, it can be a real eyesore. It is common on all types of concrete, and is a result of moisture interacting with minerals inside the concrete. The good news is, removing efflorescence on concrete can take some elbow grease and a few seasons, but it is possible!

What is Efflorescence (a.k.a. efflo)?

First of all, let’s look more closely at what efflo really is. This will actually help us better understand how its removal works.

Concrete contains minerals and salts that are water-soluble, including calcium carbonate and calcium hydroxide. In humid or wet conditions, water can penetrate the interior of concrete and dissolve these salts. Then, when the water is evaporated out of the concrete, the salts are left behind on the outer surface, where they react to the oxygen in the air by turning white.

All concrete will be subject to some amount of efflo, and different types of concrete will show different levels. Extra moisture such as humidity, rain, sprinkler overspray, poor drainage, or dew, all contribute to efflorescence, since more water will draw more salts out from the interior of the concrete.

In landscaping, we frequently see efflo on concrete products like pavers and retaining walls. Sometimes efflo makes itself known after an installation is complete, but it can also happen while these products are on pallets or even during the manufacturing process. This makes it difficult to predict and impossible to totally prevent. But thankfully, efflorescence doesn’t last forever, and there are things you can do to make it less noticeable now.

Removing Efflorescence on Concrete

When it comes to removing efflorescence on concrete, think of it as a marathon, not a sprint. Especially because Minnesota is humid in the summers and wet in the winters, it can take two to three full seasons for the water-soluble salts within the concrete to diminish to negligible levels.

When you do see efflo on your pavers or blocks, here are three ways to remove that season’s unsightly white cast:

Dry Brushing

All you need for dry brushing is a broom with stiff bristles. Push brooms work well for this, as well as small hand brushes or old-school whisk brooms.

Vigorously sweep the area where the efflorescence has appeared. This will loosen the salt deposits and move them off the surface of the concrete. Make sure to totally remove whatever salts that you loosen from the area, otherwise they will soak back into the pavers the next time they are exposed to moisture.

Wet Brushing

You can combine your stiff-bristled brush with water to remove more stubborn salt deposits. Scrub the concrete while it is dry, then use a strong stream of water to wash the surface. Continue to scrub and rinse until you see the desired results.

Regularly wetting your new concrete will also help move any mineral salts from the interior of the concrete to the exterior. This will result in more efflorescence at once, but will also help exhaust the supply of these salts within the concrete so that it stops producing efflo sooner.

Muriatic Acid

For the most entrenched efflo encrustments, you’ll need to break out some kind of efflorescence cleaner. There are a few of these on the market, but we recommend muriatic acid, a strong cleaner that must be handled with caution, but is super effective at clearing away efflo.

What is Muriatic Acid?

Muriatic acid is a form of hydrochloric acid. It is less concentrated than pure hydrochloric acid, but still fairly caustic. Hydrochloric acid contains only HCI molecules and is used primarily in laboratory settings with strict safety measures in place. Muriatic acid contains HCI molecules plus impurities such as iron, giving it a yellowish tint and a lower safety hazard. Muriatic acid is widely available in hardware stores because it has a plethora of uses, from dissolving oil stains to killing mold in basements to descaling surfaces.

That descaling power, plus its ability to neutralize alkaline salts like the ones that cause efflo, is why we like it.

Be Safe!

Muriatic acid is safe to use at home as long as you follow some basic safety procedures:

• Don’t get it on your skin or on your face. Acid-resistant gloves and long-sleeved pants and shirts are recommended.
• Never mix muriatic acid with other acids.
• Always pour muriatic acid into water, not the other way around. Adding water to acid can create a small exothermic reaction, pushing the acid out and onto you.
• Only mix muriatic acid in a glass or acid-resistant plastic container.
• Always store muriatic acid in the container it came in.
• Keep a neutralizing agent on hand nearby, such as a 1:16 ammonia-water neutralizing solution in a sealed spray bottle.

How to Use Muriatic Acid on Efflorescence

First, create your mixture. The ratio of acid to water should be 1:10, or one gallon of water per ten ounces of acid. Measure the water first, then add the acid, pouring slowly. You’ll also want to mix up the 1:16 ammonia-water neutralizing solution now, which you will use at the end of this process.

Spray the mixture across the area with efflo. While the mixture is safe to use on concrete, remove any yard furniture, pots, etc. from the area. Let the acid sit atop the efflo for a few minutes.

After the acid has had a chance to work, use a brush to scrape at the efflo. It should lift away easily.

Spray down the surface with the ammonia-water solution. This will neutralize the acid in the original mixture and keep it from affecting lawns or plants as it is washed away.

Finally, rinse your concrete with water to flush away the scraped-off salts. It may take a few seasons and a few applications of muriatic acid, but soon enough the efflo on your concrete will be a thing of the past!

Trust the Professionals

If all this talk about acid hasn’t scared you off your dreams of a new patio, or your dreams to renovate an old patio, then Rock Solid can make it happen — with a minimum of efflo! Our hardscape installations can help you enjoy your outdoor space in a whole new way with beautiful, functional design and high-quality components.

For an estimate, free consultation, or just some expert advice on efflo, call Rock Solid at 763-398-0739 or send us a message today!