What's New
By Mike Speidel

In the last issue of our webletter (Spring 2015) in an article entitled "'Mod' to Standard", we discussed some of the wording related to Surface Preparation within AC 150/5370-10G, P-620. Specifically, there was a paragraph added to the definition of surface preparation that was causing confusion and resulting in consulting engineers requiring paint removal when it may not have been necessary.

As it turns out, the FAA was already working on a modification to their own standard. On July 13, 2015, an errata sheet was published including changes (denoted in red) that read:

"At least 24 hours prior to remarking existing markings, the existing markings must be removed such that [ 75% ] [ 90% ] [ 100% ] of the existing loose markings are removed with low (3,500 - 10,000psi) waterblaster. After waterblasting, the surface shall be cleaned of all residue or debris either with sweeping or blowing with compressed air or both."

Although the paragraph still isn't exactly crystal clear, it's an improvement. The fact is, 100% of any loose and poorly bonded markings should always be removed. If not, the new coating has more potential to fail over time.

Further, the pressures needed to adequately clean a marking prior to repainting depends on several factors not discussed here. The most important thing to watch for is that all of the loose paint is gone so the contractor can certify it in writing: more about that in the article Contractor Certifications.