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April 13 - April 19, 2015

What can be done to prevent rust bleed in crevices when applying a zinc/epoxy/urethane system?

Selected Answers

From Jim Johnson of CHLOR*RID International Inc. on April 21, 2015:
Rust bleeds out of crevices because there is ongoing corrosion occurring within the crevice. In most cases this is caused by salts having gotten down into the crevice. To stop the corrosion requires the removal of the salts. This is commonly accomplished by the use of a minimum 3000 psi pressure washer with a 1% solution of a chemical salt remover, holding the nozzle very close to the crevice and the crevice or joint is flushed as well as possible to remove those salts. Since there is no way to test for any remaining salts down in the crevice, it requires best efforts to get the crevice as clean as possible. Often, such crevices are washed at the rate of 2 feet par minute, or some similar rate. There is a coating manufacturer who uses a neutralizing agent after the wash to neutralize any acid within the crevice or joint. Once the salts have been removed, then coating can be applied. Some contractors use an added step of caulking the joint after the salt removal and before applying coating. There is also a coating manufacturer that offers a 5- year warranty against rust bleed from crevices when their process is followed.

From Denis Pazio of LiRo Engineers on April 21, 2015:
Adjust the coating system. Add an epoxy with micaceous iron oxide and a sealer on top  and then a top coat. Of course, these two (stripe) coats should be only to the crevice, by brush only.

Prepare the surface either with blasting or power tool cleaning. Remove the entire contamination as much as possible and then apply the primer coating by brush. Then seal the area with either caulking compound or epoxy sealers and let it dry. Upon drying, abrade the filler surface and reapply with midcoat and topcoat to permanently avoid the rust bleeding.

From Larry Muzia of Exceletech LLC on April 13, 2015:
I suggest the use of a high-quality, exterior-grade caulk to minimize moisture (electrolyte) from having access to the unprotected areas. With the right type of caulk, it is possible to apply the caulk over the inorganic zinc before overcoating.

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Tagged categories: Asia Pacific; EMEA (Europe, Middle East and Africa); Epoxy; Extractive Bleeding; Latin America; North America; Paint application; Quality control; Quality Control; Urethane; Zinc

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