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How to Prepare Concrete For Acid Staining

Preparing the concrete surface is the most crucial step to a successful concrete staining project outcome. Familiarize yourself with the condition of your concrete as knowing what contaminants to remove will guide you on which cleaning technique to follow.

Test Concrete Porosity

Spray water on the concrete surface and observe how quickly the water soaks in.

  • If water “beads up” and doesn’t readily absorb, the concrete will need to be sanded or chemically profiled using Hard Trowel Floor Prep before staining. For details click here
  • If water creates “Rainbow Sheen”, the concrete has an oil spill. Clean the concrete with a solution of ProClean Degreaser and water
  • If water absorbs readily, then clean with a diluted solution of concrete cleaner and water
How to Know if Concrete Floor is Ready for Staining

Remove Sealer From Concrete

How to Remove Pre-Existing Sealer from Concrete Surfaces

  1. Determine if Concrete Was Sealed With A Solvent-Based or Water-Based Concrete Sealer: Pour a small amount of Xylene on the sealer to be removed and wait 30 seconds. Pat dry and touch the area. If the surface becomes tacky or sticky then the concrete was sealed with a solvent-based sealer. If surface does not become tacky or sticky, the concrete was sealed with a water-based sealer
  2. To Remove Solvent-Based Concrete Sealer: Use Xylene to remove solvent-based sealers. Pressure wash and allow to dry
  3. To Remove Water-Based Concrete Sealer: Soap and hot water can be used to remove water-based sealer from applicators immediately after application but a sealer stripper required to strip water-based sealers from concrete
  4. Scrub: Brush off the remaining residue from the concrete with a concrete degreaser and water solution
  5. Rinse: Wash until all cleanser residue have been removed

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Remove Paint From Concrete

See complete project here

Basement floor with old stains, spray paint and overspray on it
Basement floor with old stains, spray paint and overspray on it
Removing Old Paint with a Concrete Grinder
Remove old paint or stubborn carpet glue with a concrete grinder

How to Remove Paint from Concrete Surfaces

  1. Remove Debris: Use a shop vacuum or a broom to remove all dirt and debris from concrete surface
  2. Apply Paint Stripper: Apply a professional paint stripper. There is no need for harsh chemical products. Industrial strength and environmentally-friendly products such as the Soy Gel & Sealer Stripper get the job done. Apply Soy Gel to the surface between 1/16 and 1/18 inch thick
  3. Let Paint Stripper Work: Don’t brush or scrape the surface until the stripper has had time to work (about 30-60 minutes). Check the progress of the stripping action by using a scraper to see if the coating is softened down to the surface. If not, recover area with the soy gel and recheck again later
  4. Remove Softened Material: Once the coating has released from the surface, remove with a scraper, industrial wet vacuum or another stripping tool
  5. Scrub: Scrub the remaining residue from the concrete with a concrete degreaser and water solution
  6. Rinse: Wash until all cleanser residues have been removed

Cleaning the Concrete Surface

  1. Apply Concrete Cleaner and Degreaser: The vast majority of concrete slabs only require minimum cleaning using an organic degreaser  diluted at a medium concentration with water.
  2. Scrub Surface: Clean the surface with a soft nylon bristle brush or power wash on a low setting to prepare most floors for staining.
  3. Rinse Cleaner and Degreaser: Thoroughly rinse the surface with clear water to remove any remaining cleanser.
  4. Remove Excess Water: Use a shop vacuum, mop and/or squeegee to remove excess water
Cleaning Concrete Floors for Staining

Do I Need to Sand Concrete Before Staining?

You only need to sand concrete surfaces if you cannot remove paint stains or carpet glue manually with mastic remover

sanding to remove mastic - carpet glue
Sanding to Remove Old Carpet Glue
Applying Etching Solution on Machine Troweled Concrete Floor
Applying Etching Solution on Machine Troweled Concrete Floor

For acid staining smooth surfaces, there are other less intensive alternatives to sanding such as simply applying a Hard-Troweled Floor Pre-Treatment 

Remove Carpet Glue From Concrete

Carpeted Floor - Before
Carpeted Floor
Removing Carpet
After removing carpet

See complete project here

How to Remove Carpet Glue from Concrete Surfaces

  1. Remove Debris: Use a shop vacuum or a broom to remove all dirt and debris from concrete surface
  2. Apply Mastic Remover: Pour Mastic Remover undiluted directly on the concrete surface. Applying too much mastic remover does not increase removal time but will contribute to impeding the complete residue removal. Where there are wide cracks or seals, fill with a commercial absorbent like diatomaceous clay, sawdust, or synthetic absorbent, before pouring the mastic remover on the surface
  3. Let Paint Stripper Work: Don’t brush or scrape the surface until the stripper has had time to work (about 30-60 minutes). Check the progress of the stripping action by using a scraper to see if the coating is softened down to the surface. If not, recover area with the soy gel and recheck again later
  4. Allow Mastic Remover to Work: Wait until the glue softens (generally 45 – 60 minutes). For best results, cover areas with a plastic sheet or tarp to reduce evaporation. Cover all outdoor applications with plastic
  5. Remove Softened Glue: Use a long-handled scraper or squeegee to remove softened carpet glue and excess product
  6. Scrub: Brush off the remaining residue from the concrete with a concrete degreaser and water solution
  7. Rinse: Wash until all cleanser residues have been removed
What happens when acid stain is applied without removing carpet glue

Remove Motor Oil From Concrete

One of the most common challenges encountered when Acid-Staining Garage Floors is the effective removal of motor oil in the driveway—the same issues arise with vegetable oil and animal fats that spill around outdoor grills and eating areas. Depending on the severity of the spill, oil that builds up over time can be very challenging to remove. Unless properly cleaned, oil will prevent acid stain or sealer from penetrating the concrete.

Because oil penetrates deeply into concrete, it’s essential to clean up a spill the moment it happens. Once oil enters porous concrete, nothing else can penetrate or adhere to its’ surface. If nothing is done to clear the oil, acid stain won’t take to the concrete and the sealer will likely bubble up or flake off after application. Not the desired outcome.

How To Know If Your Concrete Surface is Stained With Oil  

The best way to determine if you have a stain requiring additional cleaning is to spray water across suspected areas. Spotting either of the following means you likely have an oil stain:

  • Water “beads up”
  • Water displays a “rainbow sheen”

Sometimes an old oil stain is visible but nothing remains at the concrete surface. If it passes the water test, it should be ready to stain.

This is what happens if you apply acid stain to concrete floors without removing oil stains.

Acid stain did not take on new concrete with oils stains

REMOVING OIL STAIN STEP BY STEP

  1. Clean the concrete with a solution of Concrete Cleaner & Degreaser and water.
  2. Observe after cleaning whether water is beading up over any oil spill area. If there is no indication of a spill that needs attention, rinse the concrete thoroughly, allow to dry and proceed with staining.

If some evidence of beading or oil sheen persists, we recommend the following procedure:

  1. Purchase a bag of “oil absorbent,” such as Oil Dri™
  2. Create a mound of the material to cover the spill area
  3. Pour a solvent like, “Odorless Mineral Spirits” or “Xylene” over the mound and leave until completely dry (Solvents can be purchased at your local DoitBest Hardware Store)
  4. Once the solvent has evaporated, sweep the oil-dry away and dispose of responsibly
  5. Clean again with the degreaser and water solution, rinse and look for beading

Successful removal will not reveal a perfect looking concrete slab; instead, some signs of staining will remain beneath the surface. In most cases this should not affect acid staining.

What If I Continue to See Water Beading & Rainbows?

Sometimes it will take more than one application to remove the oil from the concrete surface altogether. Repeat the steps until the beading and sheen disappear.

The process may need to be repeated up to 4 times if the oil stain is particularly large or very old. Vegetable oil, oddly enough, is one of the most difficult oils to dissolve and sometimes requires mechanical abrasion using a floor sander and a 50-100 grit pad to resolve finally.

How to Stain Concrete with Oil Stains That Will Not Come Out 

If the residual oil is too difficult to remove, or if there is noticeable discoloration of the concrete following oil removal, we recommend using Antiquing Stain Color, which dramatically improves the appearance of old concrete.

Antiquing Stain is available in over 40 striking colors that will make even the toughest oil stain less noticeable.  Antiquing stains are formulated for outdoor projects so it will have a strong smell so keep your garage door open during application for proper ventilation.

garage concrete floors with oils stains
Concrete floors with persistent oils stains after cleaning
Concrete floors with oils stains stained with Antiquing stains
Same floors stained with Silver Gray and Black Antiquing stains

My project was to give my garage an updated and clean look. With the whole family being home during these crazy times (Covid) and on top of that a very rainy spring on the East Coast.

Our family spent lots of time in the Garage riding bikes/scooters, playing hockey/ soccer and everything else we could do to change our minds of being at home.But the main problem was the garage floor was a mess not matter what we did to clean,we all ended up pretty dirty after we came back inside the house.

The garage floor slab is around 50 years old and was in pretty good shape with how old it was. But there were some oils spots and paint areas that needed some cleaning. This was one of the first projects that turned out exactly how I expected it to turn out.

The smooth, shiny and cleanable floor is exactly what I expected. Comments from friends and neighbors on how great it looks!

Personal Tips:

  • Clean, clean, clean. I think the exceptional results that I had for my project with direct colors was because I spent a week or so cleaning everything to the best of my ability and the best of the cleaning products ability.
  • Beware of the smell of the sealer. Since I was working in a garage I was able to keep the doors open. But I did where a professional mask because the sealer was a-lot stronger than I thought. You need to make sure you have a couple of nice days and follow the best application temperatures before applying.
Stained Concrete Floors on a Budget

With Concrete Dye

Direct Colors Concrete Dye is a topical dye used for smooth concrete surfaces such as floors, countertops, and similar applications. Concrete Dye is ideal for projects where fast drying time and ease of application is important.