Marking Removal
Removal Scar
Waterblasting Scar
Skid Steer Grinder
Waterblasting Truck
Airfield markings that are no longer needed should be removed. FAA Advisory Circular 150/5340-1H, Standards for Airport Markings, states:
“Pavement markings that are no longer needed should be physically removed by sand blasting, chemical removal or other means, not painted over. Painting over the old markings merely preserves the old marking, will require additional maintenance, and in certain conditions, can be misleading to pilots.”
Additionally, markings should be removed prior to overlays or seal coats and should, at a minimum, be surfaced prepared when they are to be painted over. Most paint marking contractors will have substantial experience with roadways and parking lots but may or may not have substantial airfield experience.
General Removal Guidance
- Degree of removal. The specification for marking surface preparation is often “85% of loose and flaking paint”. This involves removing most of the loose and flaking paint but does not involve removing the old paint that is still adhered to the pavement. Owners and contractors should be aware of this distinction. If paint removal is desired, it should be specified as paint removal. A typical paint removal specification may call for waterblasting or milling to remove 95% of the poorly bonded paint from the existing surface.
- Paint removal prior to overlay or seal coat. Old paint should be substantially removed prior to an overlay because it could result in a weak bond between the existing pavement and new HMA. Substantial removal is usually specified as 85% paint removal.
- Changing marking patterns. If new markings will coincide with the old, then removing 85% of loose and flaking paint should suffice. If new markings will conflict with old ones, then 90-95% of the conflicting paint should be removed.
- When to remove paint before repainting. If more than six layers of paint have been applied since the pavement was new or since the paint was previously removed, consider removing 85%-90% of the existing paint prior to repainting the markings.
Methods of Removal
Several different methods of paint removal exist and have been used satisfactorily. The goal is to remove existing paint while minimizing damage to the existing pavement surface. When removing paint from HMA, some degree of surface abrasion will happen, which usually leaves a visible scar (see Images). Typically, this scar disappears over time. Newer HMA scars less than older, aged HMA. The basic methods of paint removal are:
- Grinding (see Image). The most common method of removal, grinding machines have small grinding heads that scrape the pavement surface to remove paint. They work well for old HMA surfaces with noticeable cracking and they will not worsen existing cracks. Grinding’s limitation is that since it scrapes the surface it cannot remove paint inside grooves or large cracks. Grinders leave an etched surface that will disappear over time.
- Milling. Generally larger heads and deeper scars than a grinding machine. Milling machines are a good option when the entire surface will be overlayed because the surface condition is not as important.
- Sandblasting. The least damaging method. Sandblasting is generally slow, leaves sand that may have to be cleaned up, and requires operator protective gear to prevent inhaling the silica in the sand.
- Shotblasting. Like sandblasting only steel pellets are used in place of sand. HMA is generally too soft for shotblasting so it should be avoided.
- Waterblasting (see Image). Involves using high pressure water from 5,000 to 40,000 psi. Generally, lower pressures (below about 20,000 psi) should not be used on badly cracked HMA since the water will penetrate the cracks and, through hydraulics, expand the cracks and possible move pavement chunks. Ultra-high pressure waterblasting (25,000-40,000 psi) will not further damage badly cracked pavement because the water is used at a much lower rate and acts as grinder or milling machine.
