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Do you have painted safety lines that you would like to remove? Perhaps the floor area is being repurposed and the safety lines are no longer useful in their current location. What should you do?

This is a thorny problem. Unless you are willing to redo the whole floor, it may even be best to leave the safety lines in place. Here are some things to consider before you begin removing the safety lines.

How hard is it to get paint off of concrete?

It is not easy. Paint seeps into concrete’s pores, making removal a challenge. “Ask anyone who has ever stripped a sealer or coating from a concrete surface what they thought of the process, and I can pretty much guarantee you will get the same general reaction – misery,” writes Chris Sullivan of ChemSystems Inc., who also pens a column for ConcreteNetwork.com.[1]

Why misery? For one thing, chemical paint stripping is a messy process and involves sloshing around toxic chemicals. For another, it often takes several attempts before the paint is sufficiently gone. Interestingly, the paint will come off easier if the original painters did a poor job, especially if they lazily applied the paint on top of a coating. Paint should be applied only to uncoated concrete so that the paint can be absorbed into the substrate. This creates a stronger bond and prevents the paint from peeling off (see ASTM 4259, ASTM 4260, ICRI Guideline No. 310.2R).

What will be left once the painted safety line is gone?

Ghost Lines

This is a key question. Chemical paint strippers remove not only the paint but also other coatings. What will be left is bare concrete.

One popular mechanical paint-removal method, called soda blasting, uses a machine to blast baking soda (sodium bicarbonate) at a high speed at the concrete surface to remove coatings. Like chemical paint strippers, soda blasting will remove all coatings, including sealers and colorings.

More aggressive mechanical methods such as grinding and shot blasting will not only remove all coatings but also roughen the concrete’s surface, which is not helpful if you want to leave the floor as if no safety line had ever been there.

Will stripping the paint remove the tint from colored concrete?

Yes. Stripping off the safety line will remove the color from the concrete itself, leaving behind a ghost line.

Available methods of stripping paint cannot distinguish between paint, other coatings, and chemicals such as tints. Everything comes off. On labels for chemical paint strippers, for instance, there are warnings that the product must not be used on colored concrete floors. Why? The product strips the color from the concrete itself.

Will stripping the paint leave marks on the floor?

Stripping the paint may leave behind a roughened texture

Stripping the paint may leave behind a roughened texture

It might. An aggressive paint-removal method such as shotblasting will roughen the floor along the path where the line used to be.

Even if a gentler method such as chemical paint stripping is used, there is something else to keep in mind. Under standard industry practice, concrete is roughened before applying paint in order to enable the paint to bond more securely. Any competent contractor would have roughened the surface before painting the safety line. As a result, stripping the paint may leave behind a roughened texture, while the rest of the floor remains smooth.

Will stripping the paint also remove the sealer?

Yes. If your concrete floor has a shiny appearance, it may have a glossy sealer on top of it. By stripping the painted safety line, you will also remove the sealer. As a result, the area where the safety line used to be will end up being dull in appearance while the rest of the floor continues to be covered with the glossy sealer and thus shiny. You can of course re-seal along the safety line’s former path, but be aware that the new sealer may not exactly match the shade of the old. It is advisable to use the same kind of sealer that was originally put on the floor.

Is it worth doing a test patch?

Definitely, this would be sensible. Try out the paint-stripping method on a small, inconspicuous area of the painted safety line and see if the results are satisfactory. This way, you will know what to expect.

The bottom line

When asked to remove painted lines from concrete, some contractors will recommend redoing the entire floor. They do not want the customer to complain about mismatches in color, texture, or shade where the safety line used to be—in other words, ghost lines. Obviously, redoing the whole floor will be expensive and disruptive to operations.

One thing to do in this situation is plan ahead. For future safety lines, consider using an industrial floor marking tape. If the work area’s configuration ever needs to change, removing the safety lines will be simpler and less expensive.

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References:
ADDITIONAL REFERENCES
ASTM D4258, Standard Practice for Surface Cleaning Concrete for Coating (reapproved 2012), ASTM International, West Conshohocken, PA.
ASTM D4259, Standard Practice for Abrading Concrete (reapproved 2012), ASTM International, West Conshohocken, PA.
ASTM D4260, Standard Practice for Liquid and Gelled Acid Etching of Concrete (reapproved 2012), ASTM International, West Conshohocken, PA.
ASTM D6237, Standard Guide for Painting Inspectors (Concrete and Masonry Substrates) (2009), ASTM International, West Conshohocken, PA.
ICRI Guideline No. 310.2R, Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair (2013), International Concrete Repair Institute, Rosemont, IL.
SSPC SP 13/NACE No. 6, Surface Preparation of Concrete (reaffirmed 2003), The Society for Protective Coatings, Pittsburgh, PA.
[1] Chris Sullivan, “Chemical strippers for removing concrete sealers and coatings,” ConcreteNetwork.com, accessed January 6, 2015, https://www.concretenetwork.com/remove-concrete-sealer/.