I met up with a remodeling contractor on a project that was installed about a year prior to my arrival. The contractor wanted to speak with me about a solution to an efflorescence problem. They informed me that shortly after the remodel, efflorescence began in the bathroom. The efflorescence was not in the shower area, as is usually the case in a bathroom, but just outside of it.

They lifted the toilet and discovered the toilet flange was cracked and speculated that this may have been the water source to initiate the efflorescence process.  They replaced the flange, removed the efflorescence and re-installed the toilet. One month later, the efflorescence was back.

 With no evidence showing that the problem was coming from the homes interior plumbing or from the shower itself, I inspected the area outside the home near the bathroom. Everything outside looked fine, nothing to speak of. But I noticed that the home had no roof gutters in the corner near the bathroom. I never saw this home receive rain, but I was sure that when it did, a tremendous amount of water would wind up in this corner with no efficient way to evacuate. I told the remodeler that if they removed the dirt under the slab in that corner, they may find water.

They found a lot of water and a tremendous amount of efflorescence in a cavity below the slab. There was a rocky bottom that held water in a small pool, and with nowhere to go, the moisture began to escape in the form of moisture vapor through the slab above. Mineral deposits in the slab along with a tremendous water supply replenished every time it rained means this problem could have lasted years.

 The contractor installed a vapor barrier, filled the cavity and installed roof gutters. The efflorescence never came back.

What steps can be taken to reduce the likelihood of efflorescence forming?

Efflorescence is a deposit of soluble salts usually found on grout joints in showers, balconies, swimming pools and anywhere else that a tile installation receives water. The white powder is sometimes accompanied with small amounts of water.

  • Have the installer build your shower to method TCNA B422. This method utilizes a bonded waterproofing which effectively seals out unrefined mortars that may be used in constructing the mortar slope for the shower receptor.
  • When installing exterior tile incorporate an uncoupling membrane or liquid applied waterproofing on the sub floor as part of a water management system.
  • When moisture vapor is detected in a slab use a vapor barrier such as an epoxy coating or an un-coupling membrane.
  • Use high quality grouts and highly refined thin-set mortars.
  • Avoid installing river rock in your shower, unless you’re willing to take that risk. While the risk is low, the potential is there.
  • Hire a contractor that is a member of the NTCA!

How can efflorescence be avoided in my shower?

What efflorescence is, how to deal with it, and how to avoid it

 Written by Michael Weaver

The best way to avoid efflorescence in a shower is to have the shower installed utilizing TCNA method B422. This method is a bonded waterproofing type and effectively seals out most building mortars that may sometimes contain soluble salts. The drain is improved over a traditional system and has no weep holes to clog which could contribute to efflorescence.

This will eliminate the chance of the mortar slope contaminating the shower with efflorescence but not thin-set mortar or grout. However, thin-set mortar, especially modified premium mortars, have a substantially lower risk of producing efflorescence. This also goes for high quality grouts. But at this point in time, manufacturers of cement products cannot guarantee their products free of this mineral.

The bottom line is efflorescence is part of working with natural materials. With the right system in place we have a great chance of it being avoided

Testing should be performed by a licensed contractor specializing in moisture mitigation. A tile contractor is not licensed or responsible to carry out this test. A tile contractor may recommend that a test be done if they suspect a moisture issue, but more often than not they have no way of knowing.

What is the best way to avoid efflorescence at the start of my floor tile installation?


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Efflorescence is easily removed. However, it is just the symptom. There are only two scenarios that stop efflorescence.

  • The mineral is eventually depleted naturally. After 400 showers it may stop, it could also stop after 10, you have no way of knowing how long it will take.
  • The area no longer receives water. Remember, water is the switch that activates the chemical reaction. If there is no water or moisture vapor transmission, there is no efflorescence.

 Efflorescence is one of those unfortunate things that sometimes cannot be avoided. There are methods that reduce the likelihood, but it cannot be eliminated with absolute certainty. Most mortar manufacturers do not guarantee their products to be free of soluble salts

The tile industry designates efflorescence as a naturally occurring condition and not a defect.

Ok, so how do you remove it? With acid. The best acid to use is Sulfamic acid. That’s SULFAMIC, not sulfuric. This acid is available in crystal form and is mixed with water. It can be made extremely weak, moderate or strong. Typically the acid is applied directly to the efflorescence and then gently brushed loose. Then it’s just a matter of rinsing it away with plenty of fresh water. Keep in mind, the salt will return. A bad case of efflorescence can take years to deplete.

I know I harp on this a lot, but a legitimate contractor should know the best method for your project. There are so many facets in construction that one method simply cannot be the best solution for all.

The first line of defense is to incorporate a barrier between cementitious building products and the tile installation itself. This includes the concrete sub-floor. If a floor displays signs of moisture such as sweating concrete or after being tested displays high relative humidity, this is a clear indicator that water is a problem.

When installing tile on a concrete floor it is recommended that an uncoupling membrane is incorporated. This membrane is not a requirement in tile installation assemblies but it solves more than moisture problems.

Uncoupling membranes have an empty space that allow the moisture vapor to pass through. As it does, the vapor equalizes with the slab below and an equilibrium is reached. Part of the problem without a membrane is that the drier air above is helping to pull the wet vapor out of the slab. With the membrane in place you effectively eliminated efflorescence on your floor installation.

These membranes make it impossible for a settlement crack in your concrete slab transfer to the tile work above. They may increase the strength of your floor to an Extra Heavy service rating. Extra Heavy is the rating for floors in dealerships and airports. That is durable!

As you will see in this article, efflorescence can also be found in areas where no water source seems to exist. While it may not be permanent, the length of time you will deal with it is unpredictable.

This harmless but unsightly white powder begins as a trapped mineral. This mineral is either in the mortar, grout, concrete sub floor or stone at the time of installation. It is there unbeknownst to the distributor or the installation contractor. The mineral trapped in the material could be considered part A, and by itself, part A simply exists, waiting for part B.

 Part B is moisture. After your installation receives water from rain, the shower head, or any other type of moisture intrusion it will eventually begin to dry out. As it dries through evaporation these salts are driven to the top of your installation. Efflorescence usually accumulate in corners, on grout, and on the surface of stone. Water, and subsequent water vapor, is a necessary component to produce efflorescence.  If water did not interact with the mineral, efflorescence would not be able to migrate to the surface. Cement mortar building material and natural stone that is rich with soluble salts will show itself in the form of efflorescence as water interacts with it.

High quality grouts and thin-set mortars are refined to eliminate these salts. They are usually not the culprit, and when installed correctly they may reduce the transmission of efflorescence to the tiled surface. Concrete mix, stucco and sand mix are not refined as thoroughly, often they are the source. Mortar mix is also used much thicker than thin-set, and as such, may have an abundance of salt relative to the amount of mortar used. Some river rock used in shower pan installations may also contain this mineral.