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Cleaning Aluminum

While aluminum is a low maintenance material, don’t make the mistake of thinking of it as a “no maintenance” material. Cleaning aluminum is a key step in assuring that your architectural aluminum will last for many years.

First thing to understand when cleaning aluminum is the finish.

Metal Polishing, stainless steel, aluminum, brass and bronzeThere are three types of finish that you will find in aluminum — mechanical (e.g., mill, satin, or polished), chemical (anodic) and organic (e.g., paint or wax).

The table below comes from the Aluminum Association and describes the designations for anodized finishes.

For many years, anodizing was the finish of choice for aluminum. The preparation of aluminum for organic finishes — paint or wax coatings — was difficult. Aluminum oxidization occurs quickly. Cleaning aluminum to remove this oxidization was critical to the success of a painted finish.

With the development of powder-coat and electro-static painting methods, painted aluminum has become more prevalent.

While aluminum does not rust, it will oxidize if the surface is not protected. Oxidized aluminum will come off as black when handled. This is not welcome in particular for handrails so keep this in mind when specifying your aluminum handrail. While going with a mill finish is appropriate for a low-traffic industrial area such as a waste water treatment plant, an aluminum railing in a high-traffic shopping mall should be anodized or otherwise sealed to prevent oxidization.

Aluminum Association Finish Designations

Example: To obtain an etched, matte surface protected by an anodic treatment suitable for unmaintained exterior exposure, the designation would be as follows:

  • AA — Aluminum Association
  • C12 — Chemical Treatment (inhibited alkaline coating)
  • C22 — Medium Matte etched surface
  • A41 — Clear anodic coating at least 0.7 mil thick

The designation would read: AA-C12-C22-A41

Mechanical Finishes
Type of Finish
AA Designation
Description Examples of Methods of Finishing
As Fabricated
M10
Unspecified
M11
Specular, as fabricated
M12
Nonspecular, as fabricated
M1X
Other To be specified
Buffed
M20
Unspecified
M21
Smooth Specular Polished with aluminum oxide compound. Grits coarser than 320; final polishing with a 320 grit using peripheral wheel speed of 6,000 fpm.  Polishing followed by buffing using aluminum oxide buffing compound and peripheral wheel speed of 7,000 fpm
M22
Specular Buffed with aluminum oxide compound using peripheral wheel speed of 7,000 fpm.
M2X
Other To be specified
Directional Textured
M30
Unspecified
M31
Fine Satin Wheel or belt polished with aluminum oxide grit of 320 to 400 size; peripheral wheel speed of 6,000 fpm.
M32
Medium Satin Wheel or belt polished with aluminum oxide grit of 180 to 220 size; peripheral wheel speed of 6,000 fpm.
M33
Coarse Satin Wheel or belt polished with aluminum oxide grit of 80 to 100 size; peripheral wheel speed of 6,000 fpm.
M34
Hand-Rubbed Hand-rubbed with stainless steel wool lubricated with neutral soap solution.  Final rubbing with a No. 00 steel wool.
M35
Brushed Several varieties of directional finish with parallel scratch lines may be produced by using power-driven stainless steel wire-wheel brushes, brushed-backed sander heads, abrasive-impregnated foam nylon discs or abrasive cloth wheels.
M3X
Other To be specified
Non-Directional Textured
M40
Unspecified
M41
Extra-fine Matte Air-blasted with finer than 200-mesh washed silica or aluminum oxide. Air pressure 45 lb. gun 8-12 in. at 90º angle.
M42
Fine Matte Air-blasted with finer than 100- to 200-mesh   silica sand if darkening is not a problem; otherwise aluminum oxide type abrasive.  Air pressure 30 to 90 lb. (depending upon thickness of material);   gun distance 1 foot from work at angle of 60 º to 90º.
M43
Medium Matte Air-blasted with finer than 40- to 50-mesh   silica sand if darkening is not a problem; otherwise aluminum oxide type abrasive.  Air pressure 30 to 90 lb. (depending upon thickness of material);   gun distance 1 foot from work at an angle of 60º to 90º.
M44
Coarse Matte Air-blasted with finer than 16- to 20-mesh   silica sand if darkening is not a problem; otherwise aluminum oxide type abrasive.  Air pressure 30 to 90 lb. (depending upon thickness of material);   gun distance 1 foot from work at an angle of 60º to 90º.
Chemical Finishes
Type of Finish
AA Designation
Description Examples of Methods of Finishing
Nonetched
Cleaned
C10
Unspecified
C11
Degreased Organic solvent treated
C12
Inhibited-chemical cleaned Inhibited chemical type cleaner used
C1X
Other To be specified
Etched
C20
Unspecified
C21
Fine Matte Trisodium phosphate, 3-6 oz. per gallon used at 140-160 ºF for 3 to 5 minutes
C22
Medium Matte Sodium hydroxide, 4-6 oz. per gallon used at 140-150 ºF for 5 minutes.
C23
Coarse Matte Sodium fluoride, 1-1/2 oz., plus sodium hydroxide, 4-6 oz. per gallon used at 140-150 ºF for 5 minutes.
C2X
Other To be specified
Brightened
C30
Unspecified
C31
Highly Specular Chemical bright dip solution of the proprietary phosphoric-nitric acid type used, or proprietary electrobrightening or electropolishing treatment.
C32
Diffuse bright Etched finish C22 followed by brightened finish C31
C3X
Other To be specified
Anodic Coatings
Type of Finish
AA Designation
Description Examples of Methods of Finishing
Protective & Decorative (coatings less than 0.4 mil thick)
A21
Clear (natural) coating Coating thickness to be specified, 15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft.
A22
Coating with integral color Coating thickness to be specified.   Color dependent on alloy and processing methods.
A23
Coating with impregnated color Coating thickness to be specified, 15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft. followed by dyeing with organic or inorganic colors.
A2X
Other To be specified
Architectural Class 11 (0.4 to 0.7 mil coating)
A31
Clear (natural) coating 15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft. for 30 minutes, or equivalent.
A32
Coating with integral color Color dependent on alloy and anodic process
A33
Coating with impregnated color 15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft. for 30 minutes, or equivalent followed by dyeing with organic or inorganic colors.
A3X
Other To be specified
Architectural Class 1 (0.7 mil and greater anodic coating)
A41
Clear (natural) coating 15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft. for 60 minutes, or equivalent.
A42
Coating with integral color Color dependent on alloy and anodic process.   May include Duranodic and certain architectural colors
A43
Coating with impregnated color 15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft. for 60 minutes, or equivalent followed by dyeing with organic or inorganic colors.
A4X
Other To be specified

Once you understand the finish, refer to this document for information on cleaning aluminum:

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