What To Know About Line Marking on Concrete

The two surface types that line markings are applied to are usually asphalt or concrete and they are very different. Both can be marked successfully, but there is a lot more to consider for good performance and longevity on concrete.

Asphalt in it's simple form is a mixture of hot cut bitumen and aggregates, or crudely rocks and tar. It cools to harden, and once hard it leaves a relatively impervious, inert surface, but a surface that has some surface roughness. These properties make it ideal to accept paint coatings, and line markings adhere predictably well so long as the surface is reasonably clean and dry. Asphalt being impervious means it drys fast and completely, also good for line marking.

Concrete is a mixture of cement, sand and aggregate. It goes through a chemical process called hydration to cure and harden, where it gets stronger with time. While it cures, the pH of the surface is high. It also stays damp while this process occurs as hydration is where the cement reacts with available water. High pH and a damp surface are not good for adherence of coatings, like line markings. We recommend at least 30 days of curing time before applying markings.

The problem with concrete doesn't stop there. Contractors often apply curing agents to the surface, to aid hydration and help stop cracking. These are great for the concrete, but are often wax based, and form a film to keep water in. This film has the unwanted consequence of stopping paint sticking to the concrete. So if you know you are going to be marking your concrete car park of warehouse, best ask the contractor to use another method like water flooding, or wetted hessian.

Concrete also comes in a range of surface finishes, like exposed aggregate, broom finish and troweled. Paint likes some surface roughness to help it mechanically grab on to the surface. Exposed aggregate and broom finish are both good for this. Troweled concrete, or polished, like that found inside parking buildings and warehouses are difficult to mark. They are designed to be easier to clean by having a dense, smooth finish. They often also have a sealer applied which makes it even hard for the line marking paint to hold on. Adhesive marking tapes can be a good option for this type of concrete, or the concrete needs to be mechanically prepared to give some surface roughness by grinding, shot blasting or acid etch.

Concrete is porous, which is also not good for line marking. It means the concrete can hold water longer, even when it appears dry, and in shop environments contaminants like oil can sink it and stop paint adhering.

Because of these reasons, most line marking companies can not guarantee work done on concrete surfaces, there are just too many variables and unknowns to consider.

Precision Line Marking can inspect your concrete surface and advise the best solution given the surface type and condition.