Bare concrete floors and walls are popular elements of brutalist and industrial architecture. It gives a natural aesthetic with depth and texture, creating a unique and well-designed space.
One of the challenges in constructing with bare concrete is efflorescence. Efflorescence is the salt depositions on concrete slabs and walls that are powdery and white. It’s commonly caused by several factors like salt in the concrete mixture, improper curing, slow evaporation, and imbalance of water content.
Avoiding efflorescence in concrete is challenging but doable. That said, here are seven ways to prevent it.
1. Use High-Quality Concrete Mix
Poor-quality concrete materials can cause efflorescence, especially if it includes sand and gravel retrieved near the sea, which contains high salt levels. Therefore, it’s best to use all high-quality materials in your concrete mix to prevent efflorescence. It’s also best to keep the water level balanced. Although high-quality materials cost more, ensuring the aesthetic and safety of the construction is worth spending. Plus, you won’t need to scrape salt from the walls and floors before proceeding to the next step.
If efflorescence is already present in your newly cured concrete walls or slabs, there’s still a solution. You can brush it off and clean it thoroughly before applying a sealant. For a detailed step-by-step process, you can learn more here.
2. Ensure The Concrete Mixture Is Salt-Free
One of the main culprits of efflorescence is salty water. In some areas, water may contain higher salt levels, which is unsuitable for a concrete mix.
If the concrete mixture contains salt, it will later permeate the surface as the water evaporates. Thus, efflorescence occurs. To prevent this issue, ensure the water you use for construction projects is entirely salt-free.
3. Cure Concrete Properly
Failure to properly cure concrete can cause efflorescence. Concrete is highly susceptible to its environment during the curing process, so it’s best to know the different methods that fit specific conditions.
One of the standard practices is water curing. It involves sprinkling or pouring water onto the surface to keep it moist. This process is required to harden and strengthen the concrete, preventing moisture penetration and surface salt deposition.
Curing concrete properly through hydration keeps the salt content below the surface. This way, small amounts of salt in the concrete mix or from the soil won’t appear and cause any issues.
4. Install Under-Slab Membrane
Concrete slabs are more prone to efflorescence since they’re exposed to soil on one side. However, you can prevent this problem by installing an under-slab membrane to protect it from liquid and moisture from the ground.
Soil naturally contains water-soluble salt that may penetrate your concrete mix. As the slab hardens, the water evaporates, and salt appears on the surface. An under-slab membrane serves as a barrier between the salt-rich soil and the concrete slab. In this case, no amount of moisture from under it will permeate.
For exterior concrete walls, it’s best to cover the outside part to control moisture levels. Doing so will prevent efflorescence and cracking, maintaining the beauty and structural integrity.
5. Install Vapor Barrier
Another concrete curing method that prevents efflorescence is placing a vapor barrier. Like water curing, it keeps the concrete hydrated to avoid dry products like salt from depositing on the surface.
A vapor barrier is a waterproof sheet, usually made of high-quality plastic. Thus, covering concrete slabs and walls with this protective membrane increases its strength and density, keeping the surface less porous.
Moreover, installing a vapor barrier prevents premature drying. Although concrete may look dry after 24 to 48 hours, it reaches its maximum strength after 28 days. Therefore, it’s best to keep it covered within this period.
6. Avoid Exposure To Liquid And Moisture When Hardened
After curing, it’s best to avoid liquid and moisture exposure. It remains porous and prone to efflorescence until properly coated and sealed on the surfaces.
For constructing slabs directly on the ground, moisture from the soil is inevitable. Placing a plastic membrane efficiently protects hardened concrete from unwanted water and the salt that comes with it.
In regions with extreme snow and rain in some parts of the year, installing a waterproof membrane below a concrete slab is required to ensure safety. Since the soil is expected to be moist all year round, placing a plastic membrane is an efficient solution.
7. Apply Sealants And Waterproof Coatings
Since concrete is naturally porous, applying coats of waterproofing agents is necessary to protect it. However, this process differs in concrete walls and slabs.
For concrete walls, applying a coat of liquid waterproofing material on the exterior is required to protect it from changing weather conditions. This sealant dries into a rubber-like texture, creating a protective barrier from liquid and moisture. Using an anti-efflorescent primer would also help seal the surface.
On the other hand, concrete floors need an acrylic or epoxy sealant as a layer of protection. These products sit on the concrete’s surface, preventing moisture, liquid, and oil from penetrating. Plus, they can keep your floors strong and shiny for years.
Preventing efflorescence in concrete is necessary for aesthetic and structural purposes. For your next construction project, consider the tips discussed above to ensure excellent results.