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What coating for steel exposed to rock salt?
Our company builds pedestal stands for mounting outdoor display cases. Rusting is a serious problem at the base of this stand due mostly to rock salt application during the winter. We currently paint the stands an appropriate primer and a top coat of urethane paint. Doesn't last too long. What would you recommend for plating or painting to solve this problem. Thank You.
Bradford Warren- Austin, Texas, USA
July 6, 2011
You inform us "We currently paint the stands in an appropriate primer and a top coat of urethane paint". I think your problem is partially due to inadequate pre-treatment of the substrate. It is necessary that you include another stage (self sacrificial coating) to your painting system, i.e. zinc phosphate. Then should your primer/top coat become damaged. the Zn Phos coating will delay corrosion rust creep. However, I believe that you need to completely reconsider the coating system you are currently using. My recommendation would be
1) 5 or 7 stage zinc phosphate.
2) Apply an epoxy powder primer.
3) Finalise with a super durable polyester powder.
Some years ago, the coating specification produced by one of the largest automobile mf for under-body components (these must resist rock salt in the winter) required 1000 hour pass to ASTM B117 (salt spray). This was achieved by following the aforementioned procedures 1 & 3. The top coat in this instance was a powder mix of polyester/ polyurethane resulting in a black powder of about 18� gloss level.
Birmingham, United Kingdom
July 11, 2011
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