Get rid of the dust. A concrete job that has not cured properly can have a dusting on the top of the surface, and paint has difficulty adhering to this dusty layer. This dust can foil your efforts to make paint adhere to the concrete. While sandblasting and washing with high-pressure air can help prepare a surface, scarifying will remove the very top layer of the cement, giving you a strong, clean surface the paint can bond with.
Rough it up. Paint will stick to concrete better if the surface has some texture to it.
"Concrete that is outdoors is usually rough trawl concrete, a very good surface for paint adhesion," Swafford says.
If the concrete surface you're painting seems too smooth, however, try roughing it up with a light sandblasting or grinding. This is also suggested when painting a smooth trawl concrete in indoor heavy-traffic areas.
Have a stable bottom coat. If you want to stripe over existing lines on an older concrete surface, remember that the adhesion power of your top coat can only be as strong as the adhesion of your bottom coat.
"Preparation is very important," Lazarus says. "Make sure the old paint is adhered well and then restripe over it. Otherwise, do a light grinding before applying fresh paint."
Remove stains. Paint will not bond to a concrete surface where oil and gas stains are present. Remove those stains before painting.
"In some situations, such as a gas station where there is oil which is soaked deep down into the concrete, you may have to leech that out with an emulsifier in order for the paint to adhere," Swafford says.
When applied to concrete, emulsifier seeps under the surface to turn oil and grease into a soapy solution that can be rinsed away with water.
Watch out for aged concrete. Payton explains that if the mix design was proper when the concrete was applied, stripers should have little problem painting an older concrete surface. But if there were flaws in the mix design, there could be failures in the concrete.
"Older concrete has a tendency to be oxidized, and it's going to be crumbly," he says. "So you're paint is only as good as the substrate you're putting it on top of. And if you put it on a bad substrate, then your paint is just going to lift with the substrate, because that's what it's adhered to."