What Happens If You Don’t Etch Concrete Before Epoxy?

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If you have a new concrete floor, you may already know that you want to cover it with epoxy. Epoxy protects the concrete underneath from moisture, stains, and prevents cracks. The extra durability that epoxy provides is well worth it, as it provides savings in long-term maintenance and repairs. But first, you’ll have to etch the concrete, a step that most likely requires a professional. So what if you just skip it, and you don’t etch the concrete first? We’ve checked with contractors to find out – does new concrete really need etched before epoxy?
Concrete must be etched before any other material is applied. This includes both epoxy and paint. Epoxy cannot bond to the surface of unetched concrete. This leads to the peeling and stripping of the failed epoxy coating. Etching is often thought of as a solution of muriatic acid, but you should also consider diamond grinding or shot blasting alternative methods -both require professional application.
Keep reading to learn how to etch concrete. We’ll cover how to prepare the surface first, and how to etch the concrete. This article will also cover how to apply epoxy to sealed concrete. Finally, we’ll cover how long it takes epoxy to cure. Read on to learn everything you need for a great epoxy floor that will last without peeling or cracking.
Up close photo of a concrete wall, What Happens If You Don't Etch Concrete Before Epoxy?

Why Etch Concrete?

When the concrete surface is too smooth, nothing can adhere to it. Since the bond between the floor and epoxy is incomplete, it’s only a matter of time before the epoxy begins to lift and peel. This is, for the record, true for paint as well. No matter what you try to apply to concrete, it simply can’t stick to a perfectly smooth surface. This is why muriatic acid is used to roughen the surface.
Epoxy is a resin that needs to cure. Temperatures that fluctuate during the curing process can lead to peeling floors. Excessive humidity can also keep the floor from hardening properly.
The last reason that epoxy floors peel is that the surface wasn’t prepared properly. The floor must be thoroughly cleaned. Any grease, oil, or dirt left on the floor will prevent the epoxy resin from bonding with the concrete. Once clean, the floor must also be given enough time to dry. A damp floor, just like a dirty floor, creates a surface that the resin can’t adhere to.

How Clean Should Concrete Be Before Epoxy?

The surface needs to be cleaned well before you attempt to epoxy the floor. Begin, first, by repairing any cracks or damage to the floor.

Next, clean the floor with a degreaser. It’s essential that any grease or oil spills are taken care of. Otherwise, it will interfere with the epoxy’s ability to bind with the concrete. A good concrete degreaser or Trisodium Phosphate is essential.

Click here to see this cleaner on Amazon.

A good scrub brush is also key. Don’t try to use a push broom in place of a brush. They aren’t as effective at cleaning. A short bristled deck brush will give better results. Lastly, a pressure washer or a garden hose with a high-pressure nozzle will make your job easier.

If the floor has been dirty for a while, letting the cleaner soak into the concrete may help. Just don’t let it dry out altogether. As the pores of the concrete open, the dirt and other contaminants start to lift out. If you let them dry back into the concrete, this may undo much of your cleaning efforts. Keep using the pressure washer to lift away dirt and rinse it away. Don’t let the floor dry until the dirt is rinsed out.

After this, you can focus on any additional oil or grease stains that need to be scrubbed out. Wet the surface and then apply a good concrete degreaser for spot treating.

Click here to see this degreaser on Amazon.

If you’re still struggling to get the floor clean, just remember that it’s vital before applying the epoxy. An improperly cleaned floor won’t provide the right surface for the epoxy to bind, making your efforts a waste. Better to do the job right the first time, rather than have to do it all again. Renting a floor buffer may give your cleaning the extra boost it needs. Just be sure to specify that you need a buffer for cleaning concrete. A special nylon head on the buffer is necessary when dealing with concrete.

How Do You Etch Concrete Before Epoxy?

Most people think of muriatic acid when they think of etching concrete. This is a common method, especially where there’s only a small floor to etch. It’s cheap to do and can be accomplished without special tools. But you can also consider diamond grinding or shot blasting to etch the surface of the concrete.

Diamond grinding uses a floor grinder with special attachments. If you’re not familiar with the equipment, this might not be an easy DIY project. It’s easy, without the right technique, to grind uneven rings or spots into the floor. Shot-blasting pelts the floor with metallic beads. It doesn’t leave the same dust and residue as diamond grinding. However, the machinery is complicated and requires skill. As a general rule, this is only used in large-scale jobs where there’s a lot of flooring to etch.

How To Acid Etch

Since acid etching is considered the DIY option, it’s the one we’ll cover in detail here. It’s important to note that muriatic acid can be hazardous. This should only be attempted by a DIYer who is experienced and able to work safely with chemicals.

The necessary mixture is 5:10 muriatic acid and water. Be sure to use proper safety gear, such as goggles, boots, and gloves. Use a one-gallon mixture for every 100 square feet. Be sure to apply the mixture evenly, avoiding puddles.

Scrub with a stiff bristle brush, allowing it to set on the concrete until it stops bubbling. Alternatively, you can use a sprayer to apply it across the floor. Then, rinse thoroughly with clean water. The solution should dry fairly evenly in a few hours – if it doesn’t, rinse again. You don’t want puddles to develop, as the acid will be more concentrated in those spots.

Click here to see muriatic acid on Amazon.

Finally, you need to neutralize any remaining acid. There are many methods for this. A simple one is to mix two pounds of baking soda in five gallons of water. Apply to the surface in the same way that you applied the acid. Keep wet for ten minutes while the mixture works, then rinse off.

This video that demonstrates the process may help.

How Long Does Concrete Need To Dry After Etching?

The concrete needs to dry thoroughly after etching. Damp concrete won’t bind correctly with epoxy, which can cause peeling. Too much humidity can also be problematic. A moisture level of 12% is ideal if you have a tool for measuring. Typically, you should leave the concrete for at least 48 hours to dry.

Click here to see this moisture meter on Amazon.

If you don’t have a way to measure, a useful test takes a square of polyethylene plastic. The plastic sheet must be at least 4 millimeters thick, and 18 inches both long and wide.  Tape the square down to the concrete with 2-inch wide duct tape. Leave the square for at least 16 hours. While this isn’t a fool-proof measurement, it does give an indication of how much moisture is in the concrete. If, after 16 hours, the plastic is still dry, then the moisture content of the concrete is likely low enough to not interfere with epoxy.

Can I Put Epoxy Over Sealed Concrete?

Sealed concrete is meant to protect the concrete. It’s a finishing surface, and anything placed on top of it cannot adhere. This goes for epoxy, as well. Epoxy won’t be able to break past the sealed surface to stick.

You can tell if the concrete is sealed by spilling a cup of water on it. If it absorbs into the concrete, then the surface is not sealed. It’s safe to use epoxy on this surface. If the water sits on top of the cement, then a sealer has been applied. Epoxy will be ineffective on this surface. If you’re determined to epoxy the concrete, you’ll have to remove the sealant first. However, acid etching as described above also works to remove sealant from concrete.

In Closing

New concrete must be etched before applying the epoxy. The smooth surface of unaltered concrete won’t bind with other materials, such as epoxy or paint. As a result, epoxy will peel and lift away, failing to adhere to the surface. The epoxy may also fail to bind due to the surface not being cleaned properly first, especially if oil or grease interfere. Other causes of failed epoxy include not letting the surface dry between etching and epoxy. A sealant will prevent the epoxy from adhering as well, though it can be removed by acid etching.

There are other methods available for etching concrete, but muriatic acid etching is the most popular DIY option. It is affordable and requires no special tools. Muriatic acid is a hazardous material, and proper safety precautions should always be followed. If you’re not comfortable handling hazardous chemicals, find a professional to perform the job for you.

For further reading, see:

How to remove paint from a concrete porch [7 methods to try]

How long does porch paint take to dry?

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