How To Prepare Aluminum For Finishing
This article helps subcontractors, specifically glazers, in the commercial construction industry avoid problems when preparing aluminum for finishing. Glaziers trained on glass often encounter problems when specifying metal finishing and coatings, turning profitable jobs into disasters.
General Metal Application Guidelines
First rule: understand metal specifications. If the drawings are confusing, call the architect who drew them. Start asking questions. You can also get advice from a curtainwall consultant or your metal supplier.
Study the material compatibility of the sealants, flashings and steel anchors to be used with the metal system. Sealant manufacturers are the best source for researching the compatibility of their products with metals.
Flashings should not be used next to a dissimilar metal, i.e. corrosion will occur if copper roofing is placed next to an aluminum fascia with no protection. A galvanic action between two dissimilar metals will result in premature failure. In addition, steel anchors must be primed to eliminate possible corrosion.
Pretreatment chemicals for both the aluminum anodizing and painting process are so harsh they can destroy non-aluminum parts.
Distinguish what situations are appropriate for anodizing or painting. We don’t recommend anodizing for coastal locations due to salt corrosion – instead, painting is the preferred coating for aluminum.
On the other hand, paint coatings should not be used in entryways. Paint is not abrasion-resistant enough for a door. Few powder coatings are hard enough for entrances, but anodizing is always safe.
Be certain the aluminum assembly you send to be finished has adequate drainage holes to prevent entrapment of the chemical solutions used for aluminum pretreatment in a dip tank. Pretreatment chemicals that leak later can damage a final finish. Inks and dyes used in packaging materials are another potential cause of staining.
Remove hardware or accessories before sending your part to be finished. Stripping any hardware by the finisher will result in an additional charge. We suggest that the assembly’s hardware remain unpainted. However, painting the hardware later will generally not match or last as long as a factory-applied finish.
Have assemblies finished after fabrication where practical. Though doing so may not be practical for large assemblies, the result is a cleaner appearance. We especially recommend this if welding or brake forming are involved.
It’s best to talk to an SAF Anodizing & Finishing Pro before fabricating an aluminum assembly or part. Painting and anodizing each present special requirements for different applications.
Preparing Aluminum – Your Aluminum Paint Coating Order
If sending aluminum to SAF for finishing, rather than purchasing SAF aluminum extrusions or sheet, send a purchase order as far in advance of the metal’s arrival as possible. If special order paint is required, allow up to three to four weeks.
With each purchase order, include shop drawings of your material. This allows SAF to confirm surfaces for painting and serve to identify your aluminum. If your aluminum finish project is based on square foot coverage, you could save money by noting exposed areas requiring paint on drawings.
Remove all non-aluminum parts from any assemblies you need painted before shipment. Painting pretreatment may damage steel and plastic. Keep in mind a curing oven operates at temperatures as high as 475° F.
Because of the high temperature used to cure paint, flat aluminum sheets may warp in the oven as the metal expands and contracts. If flatness is critical, consider painting the metal after fabrication. Curved extrusions can change shape, so we recommend welding a temporary support rod across the base of an arch before painting.
Ask your SAF Aluminum Finishing Pro about any maximum weight concerns. Extra charges may apply over extraordinary part or assembly size or weight.
Aluminum painting price includes paint costs, and varies from color to color. Including custom aluminum color requirements will result in a more accurate quote.
Aluminum Anodizing Guidelines
Always confirm the alloy to be sure it’s anodizing quality (AQ). Order all your anodizing metal from the same lot to reduce color variation caused by the aluminum’s metallurgical composition.
Die-castings are difficult to anodize because of the porous nature of the surface, even if the alloy is anodizing quality.
Because anodizing is only as good as the metal you use, it will not hide scratches or water stains.
Assemblies must have drainage holes to prevent solution entrapment. Top holes admit air, while bottom holes drain. Anodizing chemicals can leak through even the tightest weld joints over time and ruin finishes.
Assemblies must not include non-aluminum materials. Be sure to select the correct alloy welding rod — we recommend 5356. Never use 4043 since it will turn a smutty black in the anodizing process.
Last but not least, be sure that specialty aluminum assemblies, parts or fabrications you ship to SAF for finishing, such as curved arches, assemblies, or formed metal, are packaged soundly.
For more information see our article about color variation.
See our 8 Point Anodizing Checklist