huangyhg

galvanized vs. zinc primer
i have back-up angle framing for a perforated metal panel used as an architectural feature that i specified to be hot-dipped galvanized. the contractor has asked if he can apply a "1-part zinc primer" in lieu of hot-dipping. for one, i have a hard time believing this would be more cost effective, but i could be wrong. i've seen them paint on a zinc primer after a field-welded connection is made, but never the entire element. is this common? should i accept the proposal? any thoughts? thanks.
give him the option of providing stainless steel angles.
seriously, if i specified hot dipped angles i would not accept 1-part zinic primer unless there were other factors that justify the change.
since you indicated the panels were perforated and were an architectural feature, i am assuming that the angles are exposed to the weather and the appearance of rust is undesirable.
if my assumptions are correct then i don't believe that zinic primer will provided the same level of protection as hdg.
there are some high quality painting systems out there that do provided protection in corrosive environments. the company i work for have used similair systems to protect steel in fertilizer buildings. i have been told that there are paint systems which provided the same level of protection as hdg. i don't have enough experience with coating sytems to voice my own opinion.
the contractor may be suggesting the use of a primer for several reasons. the lead time on hdg can be several weeks depending on where the project is located. also if the angles are fielded painted he may be concerned about applying a finish coat to the angles.

i do not believe that applying a zinc rich primer offers anywheres near the protection that hot dip galvanizing does. a lot depends on the original thickness of zinc coating originally specified to be applied in the hot dip process.
i work in heavy industry and in corrosive applications ask for steel to be hot dip galvanized. we would never accept a zinc rich primer that is field applied to be a substitute
when i was an owner's rep, and a contractor asked me to do this type of change, i would asked for a deduct proposed change order and if the cost were attractive enough to offset the risk, i would approve it. seldom did i get many proposed change orders when they realized i would be the benefactor of the change.
don phillips

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