Ask the Builder: Fluffy salt crystals are not mold

Sun., July 31, 2022

I routinely presume that people know all about efflorescence, but in fact many don’t. I’m referring to the fluffy white deposits you might find on your concrete floors, brick walls or basement walls. It’s harmless salt, but people often mistake it for mold.

A few years ago, in early spring, I recorded a video in my garage titled “Efflorescence Tips and Tricks.” You can find it on AsktheBuilder.com or on YouTube. The video continues to get comments regularly. Most surprise me, because the viewer is relieved to discover that efflorescence is not deadly mold.

I remember doing an experiment in high school chemistry class that demonstrated the mechanics of what causes this white powder to appear and how to get rid of it. But in my everyday life today, I mostly come into contact with efflorescence thanks to the rock salt used on the roads in central New Hampshire during ice and snow storms.

The rock salt, once it comes into contact with the ice or snow, dissolves and turns the frozen precipitation into brine. This salt water then drips off my car when I park it in my garage. The brine soaks into the concrete floor. With the garage temperature close to freezing and no wind in the garage, the evaporation of the water in the concrete happens very slowly. And each time I drive back into the garage, I add more brine into the concrete.

When spring arrives with warmer temperatures, the brine starts to come to the surface of the concrete like the hosta shoots that peek up from the soil next to our front sidewalk. The first place the efflorescence appears is along the tiny hairline cracks where the brine entered the concrete with ease. Soon, patches of fluffy white crystals surround the parking area of the car.

I can see why you might think these harmless salt deposits are some sort of scary mold. They do look strange and they can appear in a short amount of time. But you might make a big mistake trying to get rid of them.

You might, for example, get out your hose and try to wash the deposits away. But this just dissolves the salt into brine again and allows it to soak back into the concrete, only to return to the surface of the concrete later, leaving efflorescence after the water evaporates.

The best way to get rid of efflorescence is to just brush the salt off the concrete or brick and blow it away. You may need to use a stiff scrub brush in some instances. Never use a steel wire brush, as that will harm any masonry surface, including concrete.

The salt deposits can and do happen in places that don’t get snow and ice. Many soils and sand deposits contain the invisible salts that can create efflorescence. The salt can be an ingredient in concrete paving brick you may use for a patio. The salt can be part of the sand used to make brick mortar.

The salt can be in soil behind a retaining wall. In all these cases, when water enters the masonry surface, it dissolves the salt just like you might have done that day in your high school chemistry lab. Now you have the brine in the masonry. Wind and warmth pull this liquid to the surface where the water in the brine evaporates, leaving the salt behind.

This is the exact same process with normal hard-water deposits you might see in your kitchen or bathroom. The salts are already dissolved in your drinking water. When this water gets on a dark countertop or on the bright metal finish of a faucet, you can see the white salts in a few hours after the water droplets evaporate.

You can often buff the surface with an old towel and remove them. If the deposits are allowed to accumulate on a shower door, faucet, or counter, you can remove them with ease using a paper towel saturated with white vinegar. Vinegar is a mild acid and it can dissolve light amounts of hard-water deposits with ease if you’re patient.

Don’t rub the deposits with the paper towel. Just drape the saturated towel over the area that has the deposits and walk away. Let the vinegar work on its own for a few hours. In almost all cases when you come back and rub the surface with the paper towel, rinse with clear water, and dry with a clean rag, the deposits will be gone.

Don’t use the vinegar on polished or burnished marble surfaces. Or, if you do, test it with a small drop applied with a cotton swab. Put one single drop of vinegar on the marble and come back in a few hours.

You want to see if the vinegar alters the polish of the marble. You may not realize it, but the marble has a chemical makeup very similar to the salt. Strong acids will etch marble. It’s just a matter of seeing if the low-grade vinegar acid will harm your marble.

Local journalism is essential.

Give directly to The Spokesman-Review's Northwest Passages community forums series -- which helps to offset the costs of several reporter and editor positions at the newspaper -- by using the easy options below. Gifts processed in this system are not tax deductible, but are predominately used to help meet the local financial requirements needed to receive national matching-grant funds.

Get breaking news delivered to your inbox as it happens.