Concrete Etching – How to Acid Wash Concrete Surfaces Yourself

Do you plan on coating your garage floor? Before you start painting it is important to prepare the concrete floor or you might find the new coat begins to chip and peel. When preparing your surface concrete etching is a great option as it is not as labor-intensive as when you use a grinder or abrasive disc. It is of course necessary to take precautions if you will be handling harmful chemicals, this guide will assist you in using muriatic acid to acid etch your concrete.

Disclaimer when doing Acid Etching

This article has been well researched. However, craft-art.com will accept no liability for injuries to persons or damages to property that may occur. Choosing to work with the chemicals mentioned in this article is done so at your own risk. Always follow all safety guidelines and water protective gear. Always read the manufacturers manual and follow their guidelines.

What is Concrete Etching and Why Should I Do it?

When you apply a water and acid solution to a concrete floor with the desire to roughen up the surfaces, this is called concrete etching. The pores in the concrete are opened by the acid wash which allows for strong adhesion of any new coating applied to the surface. Concrete etching is a cost-effective method to prepare your concrete flooring.

The acid neutralizes the concrete’s alkalinity while also roughens up the texture, this further increases the coating and concrete’s bond. If you fail to prepare the concrete using either concrete etching or other mechanical methods will lead to poor paint bonding and the coating will not last. There are two distinct problems with fresh concrete, that concrete etching can help rectify; laitance and efflorescence.

Problem One: Concrete Laitance

A build-up of weak, powdery-type concrete particles on the surface of the concrete which has been newly installed is called laitance. It happens quite often and is caused by the concrete having too much water in it. The water rises to the surface during the curing process and fine particles are brought along with it which subsequently dry on the surface.

You can use acid etching to remove thin layers of laitance, which is a good idea to do before painting. If you simply just paint over the laitance there is a strong likelihood that the paint will peel off and bringing with it a layer of concrete laitance.

Problem Two: Concrete Efflorescence

Much like laitance, you can end up with a chalk-like build-up on concrete that has been newly installed. It contains salt, not concrete particles and sand. Efflorescence results in problems linked to the adhesion of a new coat but using muriatic acid to etch will remove the residue.

Concrete Etching Methods

There are two different approaches you can take to etch your concrete. The first is acid etching, and the second is grinding. Acid etching is quite easy to do and affordable, but it is advisable to rather hire a coating specialist if you can stretch your budget to afford it. A coating specialist will use mechanical means to prepare the surface like grinding, shot blasting, or dustless sanding. To achieve a uniform result these methods are perfect for surface profiling concrete. The machines are purpose-designed to collect a large amount of dust that is found during the process, but they do require heavy machinery and an expert to operate them. Both grinding or etching are called surface profiling. You can make or break the bond of a newly laid concrete coating by achieving the correct surface profile.

Grinding Etching

The grinding method of concrete etching is not as easy to do yourself as acid etching. You can try to prepare the concrete yourself using an abrasive disc and grinder but it can prove difficult to do properly. In all likelihood, you will have to hire a professional to complete the task. Hiring a professional can be quite expensive, and the process can also create a lot of dust which may not be ideal. The dust is non-toxic, however, which is a benefit.

Acid Etching

The best option is acid etching if you are planning on preparing and coating a concrete floor yourself and not hire a professional. There are products available that have been specifically designed for etching concrete, some contain mild non-toxic acids, and some are a blend of chemicals, which include phosphoric acid and muriatic acid. These specialized chemicals are a safe option than hydrochloric acid or muriatic acid as they emit fewer fumes, and the eco-friendly nature of certain products means they do not need neutralization. Keep in mind they can be less effective and are more expensive.

There are different types of acid that you can use for acid etching, including muriatic acid, hydrochloric acid, phosphoric acid, and citric acid.

Muriatic Acid

This is the most common and effective acid that you can use for etching concrete, it can be identified by its yellow hue and is an unrefined variant of hydrochloric acid. It can be used to clean masonry of excess mortar and rust and is a very powerful acid, but it can corrode certain metals and eat away at fabrics. Sadly, the fumes are noxious and can damage your nasal passage and lungs if inhaled and it can burn your skin, you, therefore, need to be very careful when working with it.

Hydrochloric Acid

This acid is used to treat swimming pools, process steel, and manufacturing batteries and is even found in gastric acid (stomach acid). It can be used for etching concrete, but keep in mind that it is just as strong as muriatic acid and you will need to take the same level of care when working with it.

Phosphoric Acid

This acid is quite weak and can be used in food additives and is found in many household cleaning detergents. It is a much safer option than hydrochloric or muriatic acid but it is less effective, more expensive, and not as widely available.

Citric Acid

This acid is used a lot in food manufacturing and is found in citrus fruits, that being said it is a weak acid so has a longer reaction time than the likes of hydrochloric or muriatic acid so will take much longer to etch the concrete’s surface.

It is safe to use, just like phosphoric acid, and you will not have to wear as much protective gear, but it is very expensive.

Here are the Pros and Cons for using acid wash to prepare your concrete surfaces:

A Step-by-Step Guide on Concrete Etching

It can seem overwhelming to have to etch concrete. You will need to begin by getting all your supplies and then you can follow the steps we have laid out. As long as you adhere to the safety precautions and have the necessary supplies you will be ready to use muriatic acid to etch your concrete. You will need the following equipment and safety supplies before attempting to acid wash concrete surfaces yourself.

• pH test strips
• Gloves (rubber)
• Baking soda to be used as a neutralizer
• Boots (rubber)
• Hose (spray nozzle) and water supply
• Safety goggles
• Plastic watering can with sprinkle head (2-gallon capacity)
• Approved respirator for use with fumes
• The wooden stick which will be used for stirring
• Broom (will be used to scrub the acid solution)
• Plastic bucket (5-gallon capacity)
• Muriatic acid

How to Acid Etch Concrete

You can begin etching your garage floor once you have gathered all your safety gear and supplies. We have also provided tips and tricks towards the end of the article that will assist you in achieving effective results.

Step One: Preparing the Concrete for Acid Etching

Remove any furniture, décor, and equipment from the room, and if there is anything left in the room that you are unable to remove you will need to cover it in plastic sheeting so that no acid splashes on it. Remove any dirt, dust, oils, or debris from the concrete’s surface before starting with the acid wash. Anything left behind such as some debris or oil can be acid-resistant that will stop the etching from working in that area and will result in an uneven surface.

If there is an old coat of concrete, a sealer, or a curing compound you will have to grind or sand to remove it from the surface first otherwise the acid will not be effective.

Start by sweeping the floor and then remove any oil, dirt, or grime from the concrete’s surface using an industrial degreaser. When your surface is cleaned use a hose to rinse the concrete thoroughly. To ensure the concrete is completely free from contaminants you might want to repeat the process. When applying the acid solution ensure that the concrete is damp but that there aren’t any puddles of water. You can take a large clean sponge to soak up any puddles which may have formed.

Step Two: Mixing the Acid Solution

At this stage, you should put on your goggles, rubber boots, respirator, and rubber gloves. It is imperative that the acid is added to the water and not the other way round as it would then result in a chemical reaction and you could be splashed with acid

The suggested ratio is one part acid to four parts water but if you have concrete that is highly polished or much harder you can use a stronger solution of three parts water to 1 part acid. If you are uncertain, you can always mix up a small batch of five parts water to one part acid and pour about half a cup onto a spot of concrete, you should see an immediate reaction. The solution is strong enough if you see bubbling or fizzing. If there is no reaction then try the 4:1 ratio and if you still do not get a reaction then resort to the 3:1 ratio and you should then get a reaction. Always mix the solution well using a wooden stick to gently stir it.

Step Three: Applying the Acid Solution

When you have mixed the acid solution you can start acid etching the concrete. Pour the solution into your watering can you will reduce any splashing using the sprinkle nozzle and the solution will be spread evenly. Using a broom, scrub the concrete with the acid solution. After 15 to 30 minutes the bubbling should stop, do not allow the concrete to dry during the etching process. The acid is no longer reacting when the bubbling has noticeably calmed down. The appearance of the concrete should now be similar to medium-grit sandpaper. If it appears smooth you should rinse down the concrete and apply the fresh acid solution.

A damp floor provides a buffer that stops an uneven etch if you allow the concrete to dry before you apply the acid solution.

Step Four: Neutralization

Certain etching acids will come with a neutralizer but if you do not receive one it is easy to mix your own. Mix a gallon of water with one cup of baking soda and evenly distribute the solution onto the concrete flooring using a watering can which will neutralize the acid, allow the neutralizer to sit for roughly 10 minutes before you rinse it off.

Step Five: Rinse

Use a hose to rinse the floor while scrubbing and sweeping away the water. Once the concrete dries the neutralizing solution will leave a white powder residue so rinsing the concrete is important, the white powder residue compromises the bonding of the coating. You may have to repeat the rinsing process a few times.

Consult your local and national regulations and adhere to them when disposing of the solution. You may have to add additional baking soda into the water you have collected to ensure the acid has been sufficiently neutralized before disposing of it. When you have done the final rinse, you should pH test your wet floor, you can do this by dipping the pH test strip into the water collected from the final rinse, or by dabbing a pH test strip on the wet concrete flooring. You are looking for a pH of 0.7 which is perfect for maximum coating adhesion. Excess acid is indicated with a pH below 0.6 this means you will have to neutralize and rinse the concrete surface once again. Allow the floor to dry completely before coating the concrete floor, depending on the climate it can take a few days to dry completely.

Tips and Tricks for Etching Concrete Successfully

• Use a high-pressure hose. Using a high-pressure hose ensure that any loose dirt and stubborn grime is lifted from the concrete.
• Grease and oil are not broken down by muriatic acid. A good option for cleaning and degreasing the concrete is to use laundry detergent.
• Test a weaker acid solution. In doing so you can avoid wasting time and muriatic acid.
• Use Kleen Green or Simple Green’s to clean the concrete surface. When you have finished neutralizing the acid and rinsing you can use one of these cleaners to clean the concrete. Remember to rinse the concrete after using the cleaner as bonding can be impacted by the residual cleaner.

• Use a wet vacuum cleaner. This is a great option to remove the neutralized acid solution from the concrete floor.
• Before mixing the acid ensure you have a premixed neutralizer on hand. So, if you have any unwanted spills you are prepared with a neutralizer.
• You can damage the concrete if you use too much acid. You are aiming to get a texture similar to sandpaper of a medium-grit.
• Test to ensure you have a substantial profile when you have completed etching. You can do this by placing a small amount of water directly onto the dry concrete surface, it should be absorbed into the surface which will mean you have achieved a sufficient profile to the coating.

Important Safety Considerations

• Be aware of the exothermic reaction. This will happen if you pour water into the muriatic acid, what this means is that the acid will throw itself out of the container and could land on you. So, it is imperative to add the acid to the muriatic acid and not the other way round.
• Be careful when pouring acid. When pouring acid into an empty container there is always a risk that acid could splash upwards towards you.
• Do not combine acids. Do not mix any other acids with muriatic acids.
• Do not use a metal container. Never use a metal container to mix muriatic acid, always use an acid-resistant container.
• Always use safety Gear. Wear full-coverage clothing and full-face protection when working with muriatic acid.
• Keep your muriatic acid in the container you received it in.
• Keep water within reach. Keep water nearby so that if you accidentally get muriatic acid onto your skin, you can wash it off.
• Beware of the muriatic acid fumes. If you get muriatic acid in your eyes, you should flush it out with water immediately for at least 15 minutes and then consult a medical professional immediately. Should you inhale acid fumes you need to get fresh air immediately and then consult a doctor.

Concrete etching is an essential process to perform on freshly laid concrete. Etching your concrete with either acid, a ready-made product, or by grinding it, will ensure that the surface will adhere strongly to any sealers or paints. Following all the necessary safety precuations, you can easily acid wash your concrete surfaces at home!

Frequently Asked Questions

How Dangerous is Muriatic Acid?

If your skin is exposed to muriatic acid, it will be burnt badly. If it comes into contact with your eyes it can lead to blindness so you must wear the necessary safety gear when working with it. You should be using a respirator, goggles, gloves, and have long sleeves when working with muriatic acid.

How Soon Can I Etch My Freshly Installed Concrete Floor?

Before doing an acid wash you should wait at least 60 days, this is as poured concrete will cure in 30 days and then requires a further 30 days for any excess moisture to completely evaporate.

Instead of Acid Etching Can I Use a Grinder to Roughen the Surface of my Concrete?

Absolutely, it is a great option for surface profiling concrete but there is a risk you could end up damaging the concrete’s surface if you are inexperienced and it is very labor-intensive. If you are going to go the route of grinding, we recommend you get a professional to do it. The most cost-effective option remains using muriatic acid to etch your concrete.

If I do Not Prepare My Concrete Flooring Before Coating What Will Happen?

You create a rough surface which is great for the coating to bite onto by opening up the pores through sanding away the top layer or using a strong acid. The coating will not last if you do not do this step and will start to peel, chip, and lift right off the surface.

When Can I Begin Coating My Garage Floor?

Allow two or three days for the concrete to dry when you have finished the concrete etching process before you start coating. The coating will not bond if there is residue moisture on the concrete. Keep in mind in a cooler climate the drying may take longer.