Why Acid Etching is No Longer Recommended for Concrete Preparation
The durability of a floor coating largely depends on how well it adheres to the concrete surface. Achieving the best adhesion requires a thoroughly cleaned floor, free of laitance and contaminants. Laitance is a weak, milky accumulation of fine particles of cement dust, lime, and sand on the surface of freshly laid concrete, often caused by an excess of water bleeding to the surface.
Understanding Acid Etching for Concrete
Acid etching involves applying hydrochloric/muriatic or buffered phosphoric acid to a concrete slab, then rinsing it off with water. For many years, this was a common method of concrete preparation used by industrial, commercial, and institutional floor coating installers, depending on the size of the floor and the system to be installed.
The Acid Etching Process
The process of acid etching a concrete floor typically involves six steps:
- Prepare, Clean, and Degrease the Concrete: Ensure the concrete is free of dirt, grease, and other contaminants.
- Dampen the Area: Hose down or dampen the entire surface to be etched.
- Apply the Acid: Use a sprayer or watering container to distribute the acid, scrubbing it in as needed.
- Wait for the Reaction: Allow the acid to react with the surface of the concrete.
- Rinse Thoroughly: Rinse the floor thoroughly, squeegee away puddles, and allow the floor to dry.
- Apply Sealant or Epoxy: After etching, treat the concrete with a sealant or epoxy coating.
Why Acid Etching is No Longer Recommended
Inconsistent Results
While acid etching removes laitance, it cannot remove curing compounds or many contaminants found in industrial settings, such as oily deposits and water-insoluble materials. These contaminants can interfere with the adhesion of the coating. Additionally, every concrete slab is different, making the results of acid etching unpredictable and unreliable. Even when performed by experienced professionals, the surface can end up uneven, over-etched, or under-etched.
Minimal Surface Profile
Concrete Surface Profile (CSP) is a standardized measure of the 'roughness' of a concrete surface, as defined by the International Concrete Repair Institute (ICRI). CSP ranges from CSP-1 (smoothest) to CSP-10 (roughest). Acid etching typically produces a CSP-1 to CSP-2 profile, which is suitable only for very thin systems, such as the low solids, solvent-based coatings of the past. Modern ultra-high solids and solvent-free industrial, commercial, and institutional resinous flooring systems are much thicker and require a CSP-3 to CSP-9 for optimal bonding and performance. As a result, contractors now prefer mechanical preparation methods, such as diamond grinding, shot-blasting, and scabbling, to achieve the necessary surface profile.
Potential Damage to the Slab
The chemical reaction between the acid solution and the concrete surface is difficult to predict and control. Over-etching can occur, making the surface more porous. When the acid is rinsed away, the water can penetrate the porous slab, potentially leading to the corrosion of metal rebar and weakening the entire slab structure.
Health and Environmental Concerns
Physical contact with certain acids can cause chemical burns or other injuries. Inhaling fumes from concentrated muriatic acid is extremely dangerous, as it can turn the moisture in the respiratory tract into an acid solution. Even with safety equipment, the risks remain significant. Additionally, the rinse water used to neutralize the acid solution can pose environmental risks. Many local and federal agencies have imposed restrictions on disposing of this water down the drain due to the potential harm to waterways and the environment.
Increased Time and Cost
Handling and shipping high-concentration acids involves multiple safety measures and extensive paperwork, increasing the cost of acid etching products. Additionally, acid etching introduces water to the concrete, which can be problematic for many of today's zero VOC and ultra-high solids coatings. Once the substrate is saturated, contractors must either wait several days for the slab to dry completely or use a moisture-tolerant primer, adding to the project's cost. Mechanical preparation methods, by contrast, are faster and more economical.
DIY Concrete Preparation: Renting Equipment for Diamond GrindingFor do-it-yourself enthusiasts looking to prepare their concrete floor for an epoxy coating, renting equipment for diamond grinding is an efficient and cost-effective option. Diamond grinding is a mechanical preparation method that ensures a clean, rough surface, ideal for the adhesion of epoxy coatings. While professional services are available, taking on the task yourself can save money and provide a sense of accomplishment.
Renting Diamond Grinding Equipment
Many equipment rental stores offer diamond grinders at affordable rates, making it accessible for homeowners to undertake this crucial step. Before renting, it's essential to understand the types of diamond grinders available. Walk-behind grinders are commonly used for larger areas, while hand-held grinders are suitable for smaller, more intricate spaces. Rental rates can vary based on the machine's size and capabilities, but many DIYers find the daily or weekly rates manageable within their budget.
Preparing for the Job
Once you have secured your rental equipment, it's crucial to prepare adequately for the grinding process. Start by clearing the area of any furniture, debris, or loose materials. Ensure you have the necessary safety gear, including eye protection, a dust mask or respirator, ear protection, and sturdy gloves. Proper ventilation is also essential, so open windows and doors if you are working indoors.
Grinding the Concrete
Begin the grinding process by familiarizing yourself with the equipment. Most rental stores provide a brief tutorial or instructions on how to operate the grinder. Start with a coarse-grit diamond grinding wheel to remove any existing coatings or sealants and to roughen the surface. Move the grinder in a systematic pattern, overlapping each pass to ensure even coverage.
Finishing Up
After completing the grinding process, thoroughly clean the surface to remove any dust or debris. Vacuuming and washing the floor with a mild detergent can help ensure the surface is free of contaminants. Once the floor is clean and dry, it is ready for the epoxy application. By renting diamond grinding equipment and preparing the floor yourself, you can save on costs while ensuring a high-quality result for your epoxy coating project.
By following these steps and using rented equipment, DIYers can effectively prepare their concrete floors for a durable and long-lasting epoxy coating, achieving professional results at a fraction of the cost.
Contact Us
If you have any questions or need a flooring evaluation, give us a call. Our network of technical experts is here to help you achieve the best flooring value and performance. With a little patience, you can trust that your floor will be prepared and coated to the highest standards, ensuring a durable, beautiful finish that will stand the test of time.