Before you decide to paint safety lines on your concrete warehouse floor, brace yourself: It’s not nearly as simple to paint concrete as it is to paint other surfaces. This is especially true if you are painting a high-traffic area, like a warehouse floor or retail space, where the paint may be subjected to both foot traffic and heavy machinery traffic on a daily basis. Before choosing between floor tape and floor paint, read this concrete painting guide to fully understand the effort, labor, and cost involved in properly painting lines on concrete.
Assess Your Floor Marking Needs
Before you commit to your concrete painting project, consider your alternatives, like floor marking tape. Industrial floor marking tape is highly durable, easy to apply, and much simpler to remove or reposition.
If you need to apply new visual cues to a fresh concrete floor, or you’ve removed the existing paint and are ready to re-apply lines, floor marking tape or virtual lines are easy options for creating durable, long-lasting visual cues—and the damage-free removal saves the hassle of removing paint from concrete down the road.
How to Paint Concrete Floors
There are the four essential steps to painting a concrete floor or surface. These include assessing the condition of the concrete, preparing the surface to adhere to the paint, painting, and providing ample dry time. If the concrete is already painted, you must fully remove the old paint before repainting in order to allow the fresh paint to properly adhere to the surface.
1. Evaluate the Concrete Surface
While concrete is a relatively uniform material, not all concrete surfaces are created (or maintained) equally. Before you begin your project, you’ll need to take a moment to assess the concrete you’ll be painting: is it freshly laid concrete, or has the surface been coated, sealed, painted, or polished? Does it contain any grease, oil, or moisture? These factors can all impact how you proceed with your surface preparation and painting project, since any existing coatings or foreign materials will impact the ability to have paint adhere properly to the surface. Consider these specific scenarios with tips for how to proceed with each.
Newly Laid Concrete
Fresh concrete is highly alkaline in nature thanks to the concentration of lime. Wait at least 28 days after the surface is laid before applying a coating, paint, or floor markings—this allows the floor plenty of time to cure after installation.
Painted, Coated, or Sealed Concrete
Any coatings over the concrete make the surface resistant to moisture penetration, which prevents paint from adhering properly. While it will be easy to identify existing paint, other coatings and sealings may be more challenging to spot.
If you are unsure whether the concrete has been previously sealed or coated, sprinkle some water over the surface and watch to see how it responds: If the water is absorbed, the surface may be unfinished; if the water beads up, there is an existing coating that will need to be stripped away before you can begin painting.
When concrete is polished, the surface is too smooth and slick for paint to properly adhere to it. You will need to take extra care to properly roughen the surface following the process in the following steps before applying paint. Roughening increases the bonding surface area, creating a stronger bond between the paint and the concrete. In painters’ language, it provides enough “tooth” to enable the paint to “bite.” This is usually done via shotblasting or grinding.
Grease- or Oil-Stained Concrete
If the concrete floor has worn the test of time, it is likely to have developed some grease and/or oil stains. Unfortunately, a dirty canvas must be cleaned before you can begin painting, otherwise these materials will cause the paint to peel and chip away. According to ASTM International¹, you can remove grease and oil from concrete with a detergent, trisodium phosphate (TSP), or steam cleaning. Always remove any grease and/or oil spots before abrading or acid etching the concrete.
Concrete with Excess Moisture
Some concrete floors have high moisture levels, which will cause any paint to quickly peel and flake away. According to ASTM International², “You can test for moisture by taping a 2’ x 2’ piece of plastic wrap to the concrete using duct tape on all edges. Allow the plastic to sit for 24 hours. If water droplets appear on the underside of the plastic, or if the concrete is damp, the surface contains excess moisture and should not be painted. Moisture problems must be corrected before coating.” Consult an experienced contractor for assistance remediating concrete moisture issues.
2. Prepare the Concrete for Paint
Regardless of whether the concrete surface is freshly laid and cured or has some combination of paint, coatings, or stains, you must prepare the surface prior to painting. Because concrete is inherently smooth, you must prepare even newly laid concrete to facilitate paint adhesion.
ASTM International recommends a surface profile of CSP-3 before painting concrete warehouse floors, although the same concept applies to any residential or commercial concrete painting job.
While many contractors are tempted to use an electric sander to prepare the surface, this actually makes the surface smoother, further reducing the surface area for paint bonding. If the surface has an existing coating, you may opt to use a sander to help remove it, but you will still need to take additional care to prepare the surface before painting it.
The primary methods for preparing concrete for painting include shotblasting, grinding, scarifying, and acid etching. These methods, as outlined below, are suitable options both to help remove existing concrete coatings as well as to roughen up the surface for better paint adherence.
Shot blasting is the most popular method of preparing concrete for coatings, including painting. This process includes using a machine that propels steel shot or other abrasives at high velocity onto the surface. The size or grade of the abrasive used and the speed at which the machine moves will determine the grading profile that this process will achieve.
However, when shot blasting concrete, you must take care to grade to the correct depth and avoid damaging the surface below. Additionally, while there are various types of shot blasting machines available, they do not exist in narrow enough widths to target a single line so this method may not be effective if you are only looking to remove existing painted lines prior to repainting concrete.
Surface grinding is an effective way to remove sealers, coatings, paint, and other contaminants. The result will vary depending on the style of grinder you use, including number of phases and heads as well as the material of the grinding plate. Note that grinders are also commonly used to polish concrete, thus the end result may still require another type of surface treatment in order to create the desired surface profile for paint adhesion.
Scarifying concrete is ideal for removing particularly thick coatings and enhancing the surface profile. Scarifiers use steel- or carbide-tipped cutters that attach to a rotating drum to break up coatings and contaminants while creating a rough surface.
Acid etching is a chemical process where a mixture of water and muriatic acid (also known as “hydrochloric acid”) is applied to the concrete and allowed to sit for a period of time before being rinsed away. This process produces a surface profile similar to coarse sandpaper, which is ideal for painting. However, acid etching is not effective for removing coatings or paint; in this case, you must use a different method to first remove any contaminants before proceeding with acid etching. After the process is complete, it is important to test the pH of the concrete surface to ensure that all residual chemicals have been completely removed.
3. Apply the Paint
Once you’ve followed the steps above to assess and prepare the concrete, you’re ready to begin the painting process. Your first step is to close the area to traffic—and it must remain closed while you paint and for many hours afterward to allow the fresh lines to cure. Floor marking tape, however, does not require excessive downtime, and there is no curing time.
Epoxy is generally considered the gold standard for concrete paint, though there are countless brands and formulas to choose from. Most concrete paints will require two coats to achieve the desired finish; be sure to follow all of the paint manufacturer’s instructions to achieve optimal results.
Always start by painting a test patch. While this extra step is easy to overlook, it is imperative to ensure that your surface is properly prepared and will produce the desired results. By taking the time to paint a test patch, you can save yourself significant time and effort in the long run.
Once you have assessed the test patch and the results are to your liking, thoroughly clean the surface to remove any debris that may have accumulated during the preparation process. Use painters tape and/or stencils to outline the desired safety lines and markings. Border taping and stenciling are imperative to ensure that the final painted lines are crisp, straight, and legible.
4. Allow the Paint to Dry
While you’re undoubtedly eager to get your facility back up and running, it is imperative that you allow the concrete paint adequate time to dry otherwise it will not adhere properly and may crack, chip, or fade quickly. The recommended dry time varies by manufacturer, with many suggesting that you wait 1 to 3 days before allowing heavy foot traffic and 3 to 7 days before subjecting the surface to heavy furniture or automobiles.
How to Remove Paint From Concrete
If your facility has painted concrete floors, you will eventually have to deal with removing paint from concrete—whether to prepare for re-painting, or to remove floor markings that are damaged and no longer required. Industrial floors generally experience heavy traffic, which will cause the paint to peel, chip, or fade over time. Even with proper surface preparation, painting concrete is not a permanent solution. On the other hand, many facilities are faced with the task of removing paint from concrete to accommodate reconfiguration of the work area, rendering the old safety lines and markings obsolete.
To repaint concrete, begin by removing as much of the old paint as possible without damaging the concrete; if you are only repainting small patches where the old paint is damaged or fading, you can save time by focusing on these patches. However, if you are reconfiguring the facility or if the old lines are in disrepair, you will need to treat the entire area. Select one or more of the methods outlined above for “preparing the concrete for painting,” including shot blasting, surface grinding, or scarifying, to clean the surface. Consider these common mistakes to avoid when repainting concrete to help ensure a job well done.
Depending on the age and thickness of the old paint and the size of the area being treated, the paint removal process can take multiple days to complete. Suffice it to say that stripping paint off of concrete is among most contractors’ least favorite jobs due to the time and effort it requires.
Whether you’re committed to taking on a concrete floor painting project or you just need tips to remove existing paint from concrete so that you can start fresh with floor marking tape, our comprehensive guide includes everything you need to know about painting concrete. For safety guidelines and floor marking tips, explore our Resource Guide.