Where the
world gathers for metal finishing
Q&As since 1989


-----

Wood stains from finished metal brackets

We are renovating and adding on to our house in Anchorage, Alaska, and had a problem the other day with wood staining on exposed glulam beams apparently caused by the metal or the finish on the metal brackets attaching the beams to posts. The brackets were made with 10-gauge steel and coated with Birchwood Casey Super Blue Liquid Gun Blue [on eBay or Amazon] to give them a uniform black appearance. They were then coated with Minwax Clear Aerosol Lacquer before installation. It is possible that they're not adequate time before coating the brackets and installation for proper drying. Temperatures were cool and conditions damp, including the beams. Holes were also drilled in the brackets after coating and no lacquering was put on the holes after the drilling. Then it rained pretty hard that night. The next day, there were unsightly blue-black stains around most of the brackets extending out horizontally mostly about six inches onto the glulam beams and around the base of the posts where the shavings from the drill holes fell. From what I can tell, this could possibly be due to iron staining on the wood, perhaps made worse by the application of the gun blue instead of paint. Is that correct? Any suggestions on how to remove the stains from the wood and otherwise correct the problem? Will we be seeing premature rust on the brackets as a result of this? Will that cause them to corrode prematurely? Any help would be much appreciated. Thank you!

Elizabeth Manning
general contractor, homeowner - Anchorage, Alaska
September 30, 2009

---

October 2, 2009

Well it's kind of hard to say without having a first hand look see. But, cold blues are evil things that are feared by most sane gun plumbers and many of the nuttier ones as well.
Its very hard to fix the stuff to kill all of the acids after the bluing is completed. Parts blackened with the stuff can continue to smut (acids still working) for months or even years.
I think what you are seeing may be some of this smutting that is weeping out through the finish that you have applied and flowing into the wood with the aid of moisture.
The gunk created by cold blues will eat though a lot of finishes like a hot knife slides through butter. Hot caustic bluing would have been better but even that and coated with a clear two part epoxy is not the best way to approach this.
Probably a good epoxy paint or a powder coat finish would have been better. But hindsight is 20/20 and there's no use in pointing fingers at this time, the damage is done.
You may be able to lightly sand the wood to remove some of the stain. After sanding a few applications of bleach [adv: bleach/sodium hypochlorite in bulk on eBay or Amazon] or hydrogen peroxide can be used to lighten the stain even more. Having the site in direct sunlight is a big help when doing this. It speeds up the bleaching a lot!
You might also try to drive the stain in deeper with lacquer thinner [on eBay or Amazon] or acetone [on eBay or Amazon]. This also may lighten it somewhat. Good luck!

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada