For concrete surfaces that are older, power-washed, or have been profiled using a machine, the surface of the concrete has to be virtually pristine before adding an acid stain. That means there should be no areas of damage revealing exposed underlying concrete or sand granules. If there are areas that are damaged, those areas are going to absorb the acid stain abnormally, and may cause areas of inconsistent coloring. The concrete slab should be free from waterproofing agents, or muriatic acid. The acid stain reaction cannot occur on surfaces treated with these products. You can usually tell if a concrete surface has a layer of waterproofing by performing a water test. All you do is pour water onto the concrete surface. If the water beads up and does not absorb into the concrete, it’s treated with a waterproofing agent. If the water sinks into the concrete, your concrete should readily absorb acid stain.
Some other factors that can affect your acid staining include different flooring material covering the concrete surface, how the concrete surface was troweled, if the concrete has ever been patched or repaired, and if there was carpeting, if the carpet underpad was glued onto the concrete. The ideal candidates for direct acid staining are usually new construction projects (where nothing has been applied to the concrete floor and it has been kept clean), and exterior projects. Remodels are harder, as any imperfections left behind from the previous floor covering (tile, linoleum, wood, carpet, laminate, etc. ) will show up to some degree in the final acid stained concrete floor. Remodels mostly require more prep work before the acid stain application.
You can remove this barrier by sanding the top layer of the concrete, or applying a micro finish overlay on top of your concrete. These barrier removal steps may also require a combination of chemical cleansers to dissolve any additions made to the concrete’s surface.
Sanding the floor with a high-speed buffer and an 80-grit sanding pad provides a roughened concrete surface that helps ensure maximum adhesion of the acid stain. Sanding also helps to remove superficial contaminants like paint or surfaces stains, while removing the top layer of a sealer. After sanding, the entire floor will feel like sandpaper and the surface debris will all be sanded away. [2] X Research source A micro finish overlay is a thin, smooth coat of concrete that resurfaces the floor to cover up defects left behind from previous flooring. This is because any residue from your previous flooring (carpeting glue, nail holes, tile adhesive outlines) can leave a “ghost image” that shows up later in acid staining process. A micro finish overlay is a little more expensive than a direct acid stain, but the resurfacing virtually eliminates all imperfections on the floor, and creates an even, covering over the original concrete that ends up looking a lot like leather. This step could get tricky for someone doing this project by themselves, and may require the professional assistance.
Knowing the differences between these cleaners will allow you to clean your concrete surface with a cleaner best suited for your surface’s deposits.
These pH cleaners can also be used on unsealed exterior or interior concrete that only requires gentle, non-irritating cleaning. [4] X Research source
Acidic stains come in ready-to-use applications or more concentrated solutions, and they are applied right onto any area that is affected by contamination. Acidic cleaners sometimes need to be scrubbed into the contaminated areas, and may even require more than one application. [6] X Research source
A big mistake people make when using this cleanser is not giving it enough time to work its magic and remove the stain. Depending on how bad the oil stain is and how far it has seeped into the concrete, you made need to apply this cleanser many times to fully eradicate the stain. Each application will require a sitting time of approximately 3 hours. [9] X Research source
Spread the tape out about every 12 inches to ensure the masking paper is applied evenly.
You can find a concrete chemical stripper at any home improvement store. Also consider using a poultice to remove mastic substances. To make a poultice, mix a fly ash or hydrated lime with denatured alcohol. This mixture makes a paste that can be added to contaminated areas. [13] X Research source After you apply the poultice paste to the areas that have mastic residue, wait for the poultice to dry (close to an hour, maybe more depending on how thick you applied the paste), and then scrape off the now crumbling mastic debris with a putty scraper or stiff brush. [14] X Research source
After the final rinsing of the concrete, again, use a wet vacuum to pick up all the remaining water and leftover particles.
Also consider wearing a long sleeve shirt and pants, combined with knee guards, in case you have to get on your hands and knees.
For floors that have been troweled and smoothed out by hand, dilute the acid stain with a 1:4 ratio of 1 part acid stain to 4 parts water. [17] X Research source For floors that have been troweled by a machine, (which are mostly industrial or commercial flooring), the acid stain mixture will be more concentrated, with a 1:1 ratio of one part acid stain to one part water. [18] X Research source When mixing and diluting the acid stain, you need to pour the acid into the water rather than pouring the water into the acid. This is because acids release a lot of heat when mixed with water. The water is added to the acid so you can start with a very diluted and weak acid mixture instead of adding water to the acid, and starting with a very strong acid mixture. [19] X Research source
Let the first coat of acid completely dry (about an hour) before adding a second coat. You can stop applying acid after the second coat, or keep adding coats until you get the coloring you want. Be very careful when walking around the stained area. Footprints from stepping in acid stain and then walking on unstained concrete can leave “burn” marks in the concrete (basically acid stains of shoe prints). Acid resistant spiked shoes (similar to soccer or golf shoes, and made with acid resistant stainless steel), are really helpful for walking around during the acid staining process, because they leave minimal shoe markings on the floor. The spikes cover less area, making foot prints a lot less visible and easier to blend into the rest of the acid stain. Don’t expect color consistency or perfection. Variations are inherent in the staining process.
You may need to perform many scrubbings to fully neutralizer the surface, especially if the acid stain used was a darker color.
If there is any remaining amount of moisture on the floor before the solvent-based sealer is applied, the concrete will have a cloudy haze covering the entire floor. This haze can only be removed by stripping the sealer and reapplying. One of the easiest ways to check if the floor is moist is to use blue painters tape. Try to stick the tape to the floor. If the tape sticks, the floor is thoroughly dried. If not, the floor is still moist and needs more time to dry.
Epoxies give a long lasting, durable finish while also being extremely water resistant. However, because of their nonporous nature, epoxies can sometimes trap water and moisture within the concrete. [32] X Research source
If you use a sprayer to apply your sealer, consider using a cone-shaped spray tip rather than a fan-shaped spray tip. [34] X Research source Allow a minimum of 4 hours before subjecting the surface to foot traffic. Within 3-4 days, the sealer will be fully dried and ready for everyday wear and tear.
If the masking paper pieces fall on a concrete floor that has just been sealed, hasn’t had time to dry, and hasn’t been waxed yet, they can stick to the floor practically like glue. However, if the pieces of parchment paper have the chance to fall on the wax coating, they can be picked up right away. Normally within an hour of applying the final wax coating, you should be able to walk on the concrete surface. However, you should wait at least 24 hours before you move any furniture onto the freshly waxed surface. The longer the wax gets to settle on the floor, the harder and more protective it becomes. Supplementary wax coats are usually applied every three to six months to ensure the finish continues to look its best.
