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topic 17334

Spilled cement has stained anodized aluminum extrusions


Dear Sir,

We are into Anodizing of Extrusions for Architectural applications. At one of our sites Extruded sections Matte finished in Light Bronze (Tin Electrocolor) were supplied. At the site the contractors have used White cement. When dried up cement spillage was removed from the anodized surface there seams to be some stains remaining on the surface. Similar stains did not remain on anodized sections supplied by another anodizer some 3 to 4 months ago.

We have a standard sulphuric acid anodizing bath. The applied parameters are as follows. (1) Acid content 160 gms/ltr. (2) Current density 13 - 14 amps/sq.ft. (3) Time 50 mins. (4) Coating thickness 20 microns. (5) Temp. 17 °C. Our coating was supplied only some 3 weeks ago. Cold sealing used Passes dye test. Can you tell me the coating which did not stain was due to aging. If yes how do I convince the customer that the coating supplied by us is good.

Expect an urgent reply.

Hrishikesh M [last name deleted for privacy by Editor]
- Vadodara, Gujarat, India

April 29, 2009

Hi, Hrishikesh. If you need an urgent reply, please retain an anodizing consultant from our Directory of Finishing Consultants. This page is merely a public forum where readers participate if and when a topic interests them, without feeling any sense of obligation to be timely :-)

You seem to be implying that the reason your competitors' extrusions did not stain was that they had time to "age" before being exposed to the cement, whereas yours did not. And that for that reason, you feel that yours are acceptable even though they are stained.

I see many flaws on all sides of the argument:

First, do you have a reference that suggests that aged extrusions do not stain as readily? It may be true, but I haven't personally heard of it. The mere fact that your extrusions stained and older ones didn't does not prove a causal relationship.

Second, the present condition of the extrusions is either acceptable or it isn't. The construction sequence and whose "fault" it was should have no bearing on whether they are acceptable. Before discussing whose fault it is, get the owner to sign a statement that the extrusions are unacceptable and he will therefore pay to replace them if it is found that he is at fault. If he won't sign on, then perhaps he is just nitpicking.

Third, I'm confident that nothing in the spec requires that the extrusions not stain if cement is spilled on them, and I don't think it would be a reasonable claim that "fitness to purpose" implies this. Cement is very caustic, and neither aluminum nor an anodized coating will stand up to it. letter 45234 talks about mortar staining aluminum window frames, and a search of the site will reveal dozens of threads about aluminum damaged by caustic cleaners and other materials. Good luck!


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


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