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Preparing the Concrete Surface

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.

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

Do I Need to Sand Concrete Before Staining?

You do not need to sand the concrete  before staining unless you are using Acid Stains and the surface to be acid stained is not capable of absorbing liquids. For acid staining smooth surfaces, there are other less intensive alternatives to sanding such as simply applying a Hard-Troweled Floor Pre-Treatment 

How to Test Concrete Porosity for Staining

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.
  • If water creates “Rainbow Sheen”, the concrete has an oil spill. Clean the concrete with a solution of Concrete Degreaser and water.
  • If water absorbs readily, then clean with a diluted solution of concrete cleaner and water.

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.

    To Remove Solvent-Based Concrete Sealer: Use Xylene to remove solvent-based sealers. Pressure was and allow to dry.
    To Remove Water-Based Concrete Sealer: Soap and hot water can be used to remove water-based sealer from applicators immediately after application but Soy Gel & Sealer Stripper or a similar product is required to strip water-based sealers from concrete.

  2. Scrub: Brush off the remaining residue from the concrete with a concrete degreaser and water solution.
  3. Rinse:  Wash until all cleanser residues have been removed

How to Remove Paint from Concrete

  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

How to Remove Carpet Glue from Concrete Floors

  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. 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.
  4. Removal: Use a long-handled scraper or squeegee to remove softened carpet glue and excess product.
  5. Scrub: Brush off the remaining residue from the concrete with a concrete degreaser and water solution.
  6. Rinse:  Wash until all cleanser residues have been removed.

WHAT TO DO ABOUT OIL STAINS

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.

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 Add Beautiful Concrete Color Despite Ugly Oil Stains on the Surface of Concrete 

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. 

Question:

We recently acid stained a bedroom floor in our house but had some acid staining issues. We think it’s because of the poor surface prep done prior to staining and possibly even the floor was too smooth to acid stain. We’re not sure. At this point, we have an acid stained floor that looks kind of weird and we’re not sure how to fix it. What products and application steps would you recommend to resolve surface prep problems on our floor? Thank you.

Answer:

You’re absolutely right that surface prep is the most important step in the acid staining process, but never fear this too can be overcome! As to why the acid stain might have taken unpredictably to the concrete, that could occur for a number of reasons. As you said, the surface could have been power troweled at the time the concrete was poured and rendered too smooth to stain. Pouring water on the concrete prior to determine if water readily absorbs or simply beads on the surface will help you determine if profiling will be required or not. Hard Trowel Floor Prep will quickly and easily profile the concrete to create a sand papery like floor finish. If you have other widespread contaminants or if you think the insulation might have been blown into the ceiling during construction, I would definitely recommend sanding the floor with a machine to ensure the best possible staining outcome.

So, what do we do from here? First, clean the floor with a light concrete degreaser and water solution, thoroughly rinse all residues from the surface and allow the floor to dry. The best product we have to correct acid staining imperfections is Concrete Dye. Our concrete dye can be applied where needed to hide the problem areas and accent the entire floor. For best results, I would recommend applying one coat of Water Based Acrylic Sealer prior to spraying the dye colors. Feel free to use multiple colors and apply accents as needed or desired across the entire slab according to the instructions. The last step is a second coat of sealer followed by a concrete wax. All done!

If you have more widespread acid staining issues caused by very smooth concrete or possible insulation over spray, a Tinted Concrete Sealer could also be used in place of the first coat of Water Based Acrylic Sealer to provide a more uniform color before dyeing.