Problem Solving Forum
July 26 - July 30, 2021
On guardrails on a marine wharf, grating panels consisting of mild steel bars about 1/8-inch by 1-inch on a 2-inch-square grid were painted with a three-coat zinc/epoxy/urethane system. Inspectors are finding numerous pinholes in the finish coat along the inside corners of the grating where the 1-inch-thick bars meet at a 90-degree angle. These pinholes were not noticed in the zinc or epoxy coats, but the final coat's visual inspection is more detailed. What is the likely cause of the pinholing, and what could be done to prevent it on future applications? Also, what should the disposition of the parts with pinholes be, as in, repair, accept as is, reblast and recoat, or an alternative?
Selected Answers
From
Neil Pittman of Lake Superior Consulting on
July 27, 2021:
My first instinct is to jump to conclusions and sa ...read more
My first instinct is to jump to conclusions and say "one of the coats is too thick" or "maybe the inside of the corners was still damp." But the best idea is to cut some samples of the grating and look at the cross sections of the paint to see where the pinholes are originating and what the thickness of each coat is. The question of whether to repaint, repair, or do nothing will be much easier to answer once we have a better handle on the root of the issue.
From
Mahendra solanki of abc on
July 27, 2021:
If there are use inorganic zinc silicate primer an ...read more
If there are use inorganic zinc silicate primer and tie coat of second coat is applied properly then there are chance of pinhole.
Coating system required to chane epoxy zinc rich primer instead of zinc silicate primer.
so reblast it and applied epoxy zinc rich primer as manufacture recommanded dft to avoid pinhole.
