What’s the White Stuff on Our Driveway?
- March 21, 2012
- Posted by: Lynn Donohue
- Category: News and Info
Are You Familiar With Efflorescence?
Las Vegas homes have some unique idiosyncrasies. One of these idiosyncrasies is rampant efflorescence. Efflorescence is the white stuff on the edge of the driveway or on the adjacent masonry fence. While this is a very common phenomena in Las Vegas it is not something that is often observed in other areas of the country. Chance are very good that if you own a home in Las Vegas you already have this condition occurring somewhere on your property. The photographs below demonstrate what I am talking about.
So what is this white stuff and should you be concerned about it? Yes, you should be concerned. I can tell you
- What it is;
- How it got there;
- How to make it stop and;
- How to make it go away once it forms.
It’s not as simple as you may think but it’s not difficult either. Many people assume this white build-up is/are mineral deposits and to a degree that is true. These deposits generally contain small amounts of both calcium and magnesium. But these deposits are primarily salt.
99.4 percent of the time the white build-up visible on Las Vegas Valley home site components is caused by improperly adjusted lawn irrigation sprinklers.
Lawn irrigation systems cause more damage to Las Vegas Valley homes than anything else.
The University of Nevada, Reno Cooperative Extension published a report in 2001 that was titled Fact Sheet 01-18 “CONCRETE PROBLEMS WITH DESERT SOILS”. It is a fascinating study with some extremely interesting facts.
Essentially, before the development of the hundreds of thousands of homes in our valley this was the desert. Even with hundreds of thousands of home on top of the soil beneath it all it is still desert soil. Our soil has a high salt content. Saline soils are common with most arid regions around the world because of the low amount of natural precipitation.
When we talk about salt be aware that the term “salt” is a very broad term because there are many different types of salts such as chlorides, sodium, and sulfates to name a few. These types of salts are known as “soluble salts” because they are easily dissolved in water. Our soil has a naturally high salt content and we have a large amount of soluble salt in our soil.
Salt is the Culprit but Water is The Problem
In addition to the high amount of salt existing in our soil we also bring in salt in the potable water we use to irrigate our lawns. The potable (or drinking) water in Las Vegas originates primarily from the Colorado River. The Colorado River water in our area contains about a ton of salt per acre foot of water (326,000 gallons). Tall fescue grass is typically irrigated in the 7 to 10-acre foot range. That means 7 to 10 tons of salt are applied each year to one acre of tall fescue grass. Granted there are not many homes in Las Vegas that have one acre lawns but for the average sized Las Vegas home several hundred pounds of salt are applied through the irrigation systems each year. That’s right, several hundred pounds of salt are added to the average lawn every year!
Ask anyone who has ever tried to plant something in their yard in Las Vegas; once you dig down about six to twelve inches the soil is extremely hard. Our desert soil does not percolate well. The term “percolate” refers to the ability of the soil to absorb or allow the water to pass through. For the majority of homes in Las Vegas the percolation characteristics of the soil change dramatically only 6 – 12 inches below the surface. That’s where water meets a barrier that is for the most part impermeable. Once the top 6 – 12 inches of soil is saturated with water it stays there unless it is taken up into the root systems of the vegetation; or runs off through drainage, or evaporates by way of the sun. More often than not excess water on site is removed via evaporation by the sun.
Quite often the vast majority of homeowners tend to over-water their lawns. When the vegetation begins to yellow from the salt they assume the vegetation is not getting enough water so they increase the frequency or duration of their sprinkler settings. More often than not they are applying more water than the vegetation can absorb. Usually the upper layer of soil becomes completely saturated. This cause soluble salts in the soil to dissolve and these salts are not conducive or beneficial for plant growth for many types of vegetation.
Inadequate site drainage is a huge problem in Las Vegas. Once the soil it saturated it often has no where to go. Under our hot Las Vegas sun much of the excess water evaporates. As it does it pulls salt from the lower areas of soil to the surface through capillary action. This additional salt will cause most types of grass to yellow further. To combat the yellowing of the lawn many homeowners further adjust their irrigation sprinkler setting to provide even more salt laden Colorado River water to the lawn. A good number of homeowners who are particularly interested in keeping their lawn looking good will also run down to the local nursery to buy a bag of Ironite plant food to “green-up” the lawn. By the end of the summer the lawn is still yellow and the water bill is astronomical.
Not many people realize it but concrete is a porous product that absorbs water. There are many different types of concrete and some types absorb water easier than other types. For example the brick walls surrounding many of the properties in Las Vegas are what we call “masonry fences” and they are constructed with CMU (Concrete Masonry Unit) blocks. People from the mid-west and east coast tend to refer to them as “cinder blocks”. CMU concrete absorbs water much easier than the typical driveway or walkway.
When excessive irrigation water is applied to lawns the water is also absorbed by the concrete components that border the lawn. This is not limited to masonry fences, driveways, and walkways but to our monolithic slab concrete foundations that are prevalent in Las Vegas. In the summer the water in the concrete that is exposed to direct sunlight gets very hot. The water evaporates and draws the salt into the concrete, again through capillary action, and this salt is high corrosive and damaging to the concrete. Although the water evaporates salt does not and the salt is deposited on the surface of the concrete product. The term for this process is called “efflorescence.”
Here’s home inspection trivia item for you: Did you know that one of the indicators that a home that is surrounded by a lawn that has been over-watered for an extended period of time is floor tiles that have lost adhesion to the substrate? One of the most common reasons for a home to contain an excessive amount of “hollow floor tiles” is because the property has been over-watered.
To recap briefly: We now know what the white deposits are; salt. We now know how they got there; prolonged excessive water to the site from the irrigation system. How do we stop it and how do we remove it once it forms on concrete products?
The way to stop it is by observing the settings promulgated by the Southern Nevada Water Authority (SNWA). Many people mistakenly believe that the focus point of the water settings recommended by the SNWA is conservation and that the settings are insufficient for maintaining a healthy lawn; they’re not. Over-watering will not only cause damage to your vegetation and all the concrete products on your property but you will pay more for the excess water without achieving your intended results.
If you do not know what your irrigation system settings are you can find them here.
How to remove salt build-up.
Salt cannot be removed from concrete with water alone. It requires an additional cleaning substance to release it from the surface. There are a variety of commercial products you could use to remove the salt but chances are you have all you need in your pantry already.
Spray the affected area with a hose and make sure it is saturated. Add a generous amount white vinegar to a bucket of hot water and dip a stiff nylon bristle brush into the solution and scrub the affected area vigorously. Allow the solution to soak on the concrete for several minutes to further break up the salt and then rinse thoroughly with a hose. It would be prudent to repeat these steps again and then allow the concrete to dry.
If this fails to fully and completely remove the salt you can repeat the procedure again or you may want to opt for a commercial salt removal product. Most commercial salt removal products were developed to remove salt from marine surfaces. Some are dangerous and should only be handled by a professional. As a retired US Navy engineering Chief one product I can recommend is Salt-Away which is not hazardous or toxic and it’s 100% biodegradable. It’s available in a 16 ounce spray bottle for light jobs and they have increasingly larger sizes all the way up to a 55 gallon drum.
I hope this answers your questions about the white build-up that is so prevalent on the concrete components in the Las Vegas Valley.