Are the painted safety lines on your factory or warehouse’s concrete floor in need of repair? You can recoat them—although the process is more involved than you might think.
Few people put much thought into repainting until the time comes when the safety lines become shabby and something needs to be done about it. If you decide to repaint your floor’s safety lines, here are four mistakes to avoid.
#1: “I can simply slap down another coat of paint”
Contractors know that no concrete repainting job done this way will last very long. The paint will pull off, especially if the safety lines are in a heavily trafficked work area.
What is the correct way to do the job? Some concrete professionals will strip all of the paint so that they can get the best and most durable bond when they repaint. Others remove as much of the paint as possible without damaging the concrete surface and then coat over it; they figure that whatever paint is left is at least well bonded. If the lines are in good enough shape, some contractors may remove paint only in damaged spots, making sure that the juncture between these spots and the rest of the floor blends in a feathered manner (see ASTM D6237).
In addition, professionals will follow the paint manufacturer’s instructions. The instructions are likely to require degreasing the surface and removing any incompatible coatings such as sealers. Sealers pose a particular problem because they block moisture from penetrating and thus will hinder new paint from sticking.
#2: “Painting a concrete floor is just like painting anything else”
Paint does not naturally stick well to concrete, and this is why so much surface prep is necessary. “Concrete painting is trickier than painting most surfaces,” says Pat Curry, a former senior editor at Builder magazine. “While you can paint drywall in a day or two, you’ll need a week or more to finish painting concrete.”
Paint bonds better if the concrete surface has been roughened. In painters’ language, a rough surface has “teeth” for the paint to “bite.” Contractors refer to this roughness as “surface profile” and they measure it carefully before applying the paint, since they know that the surface profile makes all the difference in how long the coating will last. Independent standard-setting organizations have issued numerous standards regarding how to roughen concrete in preparation for applying coatings such as paint (see ASTM D4259, ASTM D4260, ICRI Guideline No. 310.2R, SSPC SP 13/NACE No. 6).
#3: “There is no way this could possibly need so much time to dry”
Painted concrete requires a surprisingly large amount of time to dry. Valspar Paint recommends giving painted concrete at least 72 hours to dry. Sherwin-Williams urges waiting between 48 and 72 hours before subjecting the painted concrete surface to heavy traffic.
BEHR offers these guidelines:
Allow 24 hours for light foot traffic.
Allow 72 hours for heavy foot traffic and furniture.
Allow 7 days before subjecting to automotive tires….
TIP: Premature heavy traffic will cause paint failure which will require spot re-coating.
In short, painted concrete takes at least several days to dry.
#4: “I don’t need to do a test patch. I’ll just jump in.”
The sensible thing is to do a test patch. Choose a small, inconspicuous area of the safety line to repaint and see if the results are satisfactory. This way, you will have a good idea what to expect. A test patch is particularly important if you are leaving some of the old paint in place. Until you do a test, there is no sure way to know whether the new paint will stick to the old; not all types of paints adhere well to one another. If there is going to be a problem of this kind, it is better to find this out before repainting the whole safety line.
The appearance and visibility of your safety lines is important. If the time has come to repaint them, go ahead and do it.
And if in the future you need to place new safety lines, consider using industrial floor marking tape. Cosmetic repairs or touchups, when desired, are quite a bit simpler: Remove the old tape, clean the floor, and lay down a new piece of tape.
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.
ASTM D7234, Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers (2012), ASTM International, West Conshohocken, PA.
ICRI Guideline No. 310.2R–2013, 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.