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Why Acid Etching Is No Longer Recommended For Concrete Prep

There are numerous components that must be considered when installing epoxy coating systems on concrete floors to achieve this stunning finish. The truth is that you don’t need to be an expert to epoxy coat a concrete floor. However, using high-quality commercial-grade epoxy coating products, some DIY skills, and understanding the proper surface prep methods will ensure that your epoxy coating application is a success.

Acid etching is a well-known and was once a widely used method for prepping concrete slabs. It is also one of the industry’s oldest methods. So, is acid etching still regarded as a good preparation method for applying epoxy to concrete?

In this article, we will look at the acid etching process and explain why it is no longer recommended by coating manufacturers for concrete surface preparation.

Surface Preparation: The Secret Formula

It is critical to prepare the concrete surface before applying an epoxy coating system so that the coating will mechanically bond to the concrete. To prevent failed adhesion, a solid bond between the concrete slab and epoxy coating is required. The degree to which an epoxy coating adheres to the concrete determines its durability.

The surface must be free of laitance and contamination for good adhesion. Laitance is a weak, milky build-up that occurs when water accumulates on the surface of concrete slabs. This usually results in an accumulation of tiny particles containing cement dust, lime, and sand fines. Previously, the process of acid etching was used to resolve such issues.

What is acid etching?

Acid etching is a treatment method that involves applying hydrochloric (muriatic) or phosphoric acid to a concrete slab and then washing it away with water. Apart from certain types of plastics, hydrochloric and muriatic acid eat through anything they come into contact with, including clothing, metal, and skin. As a result, modern concrete prep methods are thought to be far safer, more environmentally friendly, and far more consistent than acid etching concrete. For a variety of reasons, most coating manufacturers no longer recommend acid etching.

1. Acid Etching Results Are Not Consistent

While acid etching can remove laitance, it cannot remove curing compounds or a variety of other contaminants found in industrial settings, such as oily deposits and water-insoluble materials, all of which can impair coating adhesion.

2. Concrete Acid Etching Produces Only a Minimal Profile

According to the International Concrete Repair Institute (ICRI), Concrete Surface Profile, Or CSP, is a standard measure for assessing the ‘roughness’ of concrete surfaces. CSPs range from CSP-1 (the smoothest) to CSP-9 (the roughest). Acid etching produces a CSP-1 to CSP-2 profile, which is only suitable for coating systems with extremely thin layers, such as low-solid systems and solvent-based coatings.

Resinous flooring systems used in industrial, commercial, and institutional applications are now much thicker, emit less pollution, and do not contain solvents. They also need CSP-3 to CSP-9 for optimal bonding and performance, making acid etching obsolete. Contractors use mechanical concrete preparation methods such as diamond grinding and shot blasting to achieve a higher concrete strength percentage.

3. Acid Etching Can Damage Concrete Slabs

After being applied, acid etching solutions react chemically with concrete; however, this reaction is difficult to predict and control. When a concrete slab is acid etched, the acid solution disrupts the balance between alkaline pH and the other materials that contribute to the hardness and durability of the concrete. Eventually, the concrete will begin to crumble, and cracking and peeling may occur. When acid is applied to a concrete slab, it can cause over-etching, resulting in a very porous surface. After the acid solution has been washed away from the surface, water can more easily enter the porous slab. The potential outcome is corrosion, which weakens the entire slab structure over time.

4. Acid Etching Has a Negative Effect on Humans and the Environment

Chemical burns or other injuries can result from any physical contact with certain acids. When working with acid-based products, there is a significant risk of inhaling harmful fumes. This can happen even when using safety gear and equipment. After the acid etching process is completed, the concrete slab is rinsed with water to neutralise the acid solution. Nonetheless, many local and federal agencies have imposed restrictions on washing acid solutions, whether “neutralised” or not, down any drains due to the significant risk posed to waterways and the environment as a whole.

5. Acid Etching Likely Adds Time and Cost to Your Project

It only takes one minor setback for the possibility of acid etching to add time and cost to your project. If even one of the previously mentioned issues arises, you will be forced to scrape the surface and reapply the solution until you achieve success. This could result in additional spending on products and materials, as well as a delay in completing any time-sensitive projects you may be working on. Furthermore, because the slab will be saturated as a result of the acid etching process, epoxy coating systems cannot be applied to the surface until the moisture has completely dried. This automatically means that the surface preparation process will take longer, and as we all know, time is money.

Safer Alternatives to Acid Etching Concrete

Mechanical grinding is the best option for preparing a concrete slab for an epoxy coating application. Concrete grinding is the process of removing the smooth top layer of a concrete slab using concrete equipment equipped with grinding tools (or discs). Concrete grinding makes controlling the surface profile easier, as well as ensuring a consistent result for the desired texture. Concrete grinding is the most effective method for producing a rough surface profile to which the epoxy coating can mechanically adhere.

Concrete grinding can be accomplished with industrial equipment such as concrete floor grinders or hand-held angle grinders for smaller projects. The flooring equipment and concrete machinery available from Xtreme Polishing Systems Europe are ideal for any project, whether residential, commercial, or industrial.

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