Once solidified, the concrete can be too hard and smooth to apply paint or sealant directly. An acid treatment will open pores in the surface, preparing it for painting. The surface can also be roughened by hand, with a grinding wheel, but with acid you will have less effort.
Steps
Part 1 of 4: Prepare the Solution
Step 1. Get muriatic acid or any other acid suitable for the purpose
Before you start, make sure you have enough to get the job done. Having to run to the store to buy more in the middle of work would be a problem. Muriatic acid (also called hydrochloric acid) is the most commonly used for this type of work. It is not possible to say precisely how much of it is needed for a particular project, because it is sold in different formulations. Usually, one liter of acid diluted adequately is enough to cover about 4.5-6.5 square meters.
- Phosphoric acid and sulphamic acid can also be used. The latter is especially suitable for beginners, being much less caustic and dangerous than the other acids.
- If you're not sure you have the right product, check the label on the package. Most products suitable for use on concrete will report this.
Step 2. Remove any obstacles
To begin with, remove all furniture, vehicles, and any other obstacles on the area you intend to treat. Acid can permanently damage items in no time, so it's best to move them before you start.
It would be better to wash the surface to remove dirt. The acid must make perfect contact with the surface to act, and even the smallest debris can interfere with the reaction, leading to an uneven result
Step 3. Use a degreaser for oil and fats
If you need to roughen the surface of your garage or driveway, there will likely be oil or grease stains from cars. The acid does not penetrate the grease, so it will not work properly at the spots. Try eliminating them with one of the degreasing products that are easily found in home improvement stores.
Alternatively, try using laundry detergent. Most laundry detergents are formulated to dissolve grease stains, so they will work well for the floor as well
Step 4. Water the area to be treated
After perfectly cleaning the surface, wet it with the water hose. Wet the area evenly, but without creating stagnation. Keep the concrete moist until you apply the acid.
If there are walls or other surfaces near the one to be treated, wet these too to prevent them from coming into direct contact with the acid
Part 2 of 4: Applying the Acid
Step 1. Mix water and acid in a ratio of 3: 1 or 4: 1
Pour clean water into a plastic bucket. Add the acid being very careful not to splash. Do not use a metal container, as the acid will corrode it.
- Always pour acid into the water, never the other way around. If acid splashes in your face, you risk being disfigured or blind.
- From this moment on, you must take the necessary precautions for your safety. Wear a long-sleeved shirt, gloves, safety glasses and, if necessary, a mask to protect yourself from the fumes. For more information, see the safety section below.
Step 2. Test the blend on a small area
Most mixes with an acid content of 20-25% will be fine for treating concrete. But before doing the job it is good to try the mixture on a smaller and less important surface, for example on a point that is usually covered by a piece of furniture. Pour half a cup of the mixture directly onto the floor. If it is strong enough it should immediately begin to react, producing bubbles.
If bubbles don't form right away, the mixture is probably not strong enough. Try adding more acid, being careful
Step 3. Apply the acid with a spray bottle
Pouring all the mixture in a single point you risk that the acid reaches the corners of the surface to be treated having already exhausted its reaction. With a sprayer, however, you will get a more uniform application. Then pass a brush or polisher to distribute the product even better.
The floor must remain wet during application. Do not let the acid dry on the floor; if necessary, water the areas that are drying out
Step 4. Wait the necessary time for the reaction
After applying the product, wait for the reaction to finish. It usually takes 2 to 15 minutes. By reacting with the surface, the acid will open pores in the concrete, preparing it for treatment with a sealant.
Inspect the surface while the reaction is underway. The acid must react uniformly over the entire area. If there are any points where the reaction is stopped, this may mean that there are dirt spots. In this case you may need to roughen the surface later with a mechanical process, for example with a grinding wheel
Step 5. Neutralize the surface
Check the acid label. Many of these require a solution to neutralize the reaction, while others deplete on their own. If your acid requires a neutralizing compound, mix this product with water and distribute it over the surface following the instructions on the package. Usually it is necessary to apply the neutralizer with a sprayer and distribute it evenly with a brush or a polisher.
A classic solution to neutralize acids is a cup of baking soda in 4 liters of water
Step 6. Rinse the floor
At this point your surface needs to be clean. Rinse with the water hose, then use a broom to collect the remaining water in one place and vacuum it with a wet vacuum. Read the instructions on the acid disposal package. Sometimes you need to add more baking soda before you flush the liquid down the drain.
Alternatively, you can rinse the treated surface directly by directing the water towards a manhole. Check your local regulations before doing this, you could break the law and cause damage to the environment
Part 3 of 4: Subsequent Treatments
Step 1. Apply the sealant
Acid is often used to make concrete porous for the application of a sealant. These products give the surface a professional look and make it resistant to water, grease, oil, making it easier to clean. You can also add an anti-slip additive to the sealant, guaranteeing your vehicles a good grip even in rain or snow.
Step 2. Add the color
You can add a pigment to the sealant to beautify the surface. In the interior spaces the colored concrete gives a modern, clean and elegant look to the room. But it will also look good in open spaces, like a porch.
Step 3. Decorate with paint
The concrete can also be painted with a brush, rollers or spray cans. Usually walls or ceilings are painted, but floors can also be painted. Some decorators get stunning results when working on the floor as well. Usually opaque colors are used, in order not to create a “wet” effect.
Step 4. Add some metallic powder if you want to get a shiny surface
You can give your concrete floor a shimmering look by adding some metallic powder before applying the sealant or during acid treatment. Sometimes this technique is also used indoors, especially in shopping malls and airports, to liven up the environment.
Part 4 of 4: Handle Acid Safely
Step 1. Put on protective clothing
All acids (especially the stronger ones, used to treat concrete) must be handled with care. If they come into contact with your skin, they can cause painful chemical burns or, even worse, they can disfigure or blind you if they hit you in the face. This is why it is important to always wear protection when working with acid, even if you are an expert. Below is a list of safety equipment to always wear in these cases:
- Protective laboratory goggles or full face mask
- Gloves
- Shirt with long sleeves
- Closed shoes
Step 2. Do not breathe the fumes
Stronger acids, for example muriatic acid, can release harmful vapors. Breathing in can cause chemical burns in the mouth and throat. It is rare, but possible, to be injured or even killed by acid vapors. Therefore it is good to always work in a well-ventilated area. Open all nearby windows and use a fan to ensure air circulation in the work area.
If the vapors are very strong, wear a gas mask with the appropriate acid vapor cartridges
Step 3. Always pour acid into the water, never the other way around
This rule is incredibly important. When mixing the mixture you must always pour the acid into the water and never the other way around. If you pour the liquid too quickly you risk causing splashes. As long as it's about water, that's no problem, but if it's acidic, you risk making yourself very ill. Always keep this simple rule in mind.
