Efflorescence: Preventing Efflorescence

ASTM C67 efflorescence test for brick.

The Understanding Efflorescence Tech Talk discussed several different types of efflorescence, their causes, and simple cleaning procedures. You can minimize the potential for efflorescence to occur in the first place if you pay special attention to the materials that are being used, jobsite procedures, and make sure the wall system is designed to manage moisture infiltration. Following are some simple recommendations to keep efflorescence from showing up on your project.

Brick and Block

• The requirement that all brick be tested for efflorescence was dropped from ASTM standards several years ago. Have the brick tested following the method of ASTM C67 and make sure they are rated as “no efflorescence” being detected during the test.
• If you see any type of staining or salt deposits on a pallet of bricks (before they are put in the wall), start asking questions. Brick rarely effloresce before they are placed in the wall.
• Water is less likely to move through high density normal weight concrete masonry units, reducing their efflorescence potential.
• Water penetration is also reduced by using integral water repellent (IWR) in concrete block and mortar. Efflorescence is less likely to form when IWR is used.

Poorly tooled joints (left) will let in water. Fill all joints and tool concave (right) for the best weather resistance.

Mortar and Grout

• Many efflorescing salts originate in cement, and you can reduce efflorescence potential by using Type N mortar, which has a lower cement content than Type S.
• Full, well-tooled joints and solid grout with no voids both keep water penetration to a minimum, reducing the moisture movement that drives the efflorescence process.
• Consider using low alkali cement (Type II or Type I/II) or white cement, both of which have lower concentrations of alkali salts than Type I cement.
• New efflorescence-curing admixtures react with chemical impurities, preventing them from causing efflorescence. Consider using these admixtures in mortar and grout.

Don't let your walls get wet as shown on the left. Efflorescence forms as wet walls dry out - cover tops of walls at the end of the day if rain or snow is coming.

Keeping It Dry

• Keep brick and block covered and off the ground. Efflorescence may form as wet units dry out once they are placed in the wall.
• Keep the sand pile high and dry. This will keep the pile from absorbing alkalis present in soils and reduce roadway runoff from contaminating the sand.
• Cover walls at the end of every day to keep them from being saturated with rainwater or snowmelt. Covers should extend 2 feet down the sides of walls.

Use flashing, weep holes, and a vapor barrier to move moisture out of the wall system and keep the drainage cavity separate from backup materials.

Check Your Details

• All masonry walls need caps to keep moisture from penetrating into walls. Metal coping, stone, and precast wall caps work best.
• Seal joints between stone and precast wall caps with flexible sealant, and install through-wall flashing beneath all wall caps to keep water from soaking down into walls.
• Install veneer with a clear drainage cavity to separate it from backup materials and prevent water from moving into the building.
• Masonry walls must be designed and constructed with flashing and weep holes to move any penetrating water out of the wall system. Use base flashing to prevent groundwater from rising up into masonry walls
• Avoid ledges, raked joints, and other details that collect water.

Install through-wall flashing under rowlock brick caps to minimize moisture penetration.

Cleaning

• Be careful with acids. When acid-based cleaning solutions soak into a wall, they dissolve salts that are then available to form efflorescence.
• Pre-wet the wall and apply cleaning solutions with low pressure.
• Rinse the wall thoroughly, from the top down, removing all traces of cleaners.
• Clean walls in warm, sunny weather, so they dry quickly.