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"Mod" To Standard
By Donna Speidel
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Anyone who has ever painted a house, a fence, a wall, or anything else knows that cleaning the surface first will ensure
a better bond of the applied coating. But since it’s the most tedious part of the job, preparation is often given short shrift. In our
industry, airports have traditionally been guilty of performing little or no preparation of the existing airfield markings. The FAA has
Recently, Advisory Circular 150/5370-10G,
Item P620 – Taxiway and Runway Markings was enhanced to include a definition of Surface Preparation by adopting language from the
Airfield Marking Handbook. If properly specified in new construction projects
and enforced by engineers and inspectors, airports will be the beneficiary, and we applaud the FAA for the revision.
However, the new guidance has caused some confusion by stating engineers must also specify paint removal, so I’m weighing
in in an attempt to clarify.
First, here’s what I love under section 620-3.3 Preparation of surface:
"Immediately before application of the paint, the surface shall be dry and free from dirt, grease,
oil, laitance, or other foreign material that would reduce the bond between the paint and the pavement. The area to be painted shall be
cleaned by [waterblasting,] [shotblasting,] [grinding,] or [sandblasting,] or by other methods as required to remove all contaminants without
damage to the pavement surface. Use of any chemicals or impact abrasives during surface preparation shall be approved in advance by the
Engineer. After the cleaning operations, sweeping, blowing, or rinsing with pressurized water shall be performed to ensure the surface is
clean and free of grit or other debris left from the cleaning process."
That paragraph is great all by itself. But the following paragraph is confusing:
"At least 24 hours prior to remarking existing markings, the existing markings must be removed such
that [75%] [90%] of the existing markings are removed with low (3,500-10,000 psi) waterblaster. After waterblasting, the surface shall be
cleaned of all residue or debris either with sweeping or blowing with compressed air or both."
I’m unsure as to why a paragraph about surface preparation requires specific degrees of paint removal.
Paint removal is not surface preparation. Surface preparation is the cleaning anything from the surface that would compromise
the bond of the new coating. Paint removal is very different – it is the eradication of the old coatings from the surface to a specified degree
based on the reason for the removal.
In a recent workshop we presented with the Massachusetts Department of Transportation and Massachusetts Airport Management
Association that attracted airfield managers, consulting engineers, FAA inspectors, and contractors from the northeast, considerable
conversation about the reference to paint removal under P620-3.3 ensued.
The consulting engineers and airports stated that since the language was in the AC, they were compelled to specify either
75% or 90% paint removal. However, the recommended pressures of 3,500 to 10,000 psi would most likely only clean the markings, not remove them.
So it became evident that the specification would have to be modified to yield intended results. A recommendation was made that consulting
engineers and/or airports could apply for a modification to standard so that a paint removal operation would not necessarily be required.
A "mod" to standard is not the most elegant solution, but the recommended course of action for the time being. We have
discussed the possibility of revisions to this section to remove the removal language.
We’ll cover all the changes to this advisory circular and much more at the Airfield Marking Symposiums. Join us for our next
symposium in Cincinnati, June 9-11, for the latest on markings.
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