Article

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.


There 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
DescriptionExamples of Methods of Finishing
As Fabricated
M10
Unspecified 
M11
Specular, as fabricated 
M12
Nonspecular, as fabricated 
M1X
OtherTo be specified.
Buffed
M20
Unspecified 
M21
Smooth SpecularPolished 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
SpecularBuffed with aluminum oxide compound using peripheral wheel speed of 7,000 fpm.
M2X
OtherTo be specified.
Directional Textured
M30
Unspecified 
M31
Fine SatinWheel or belt polished with aluminum oxide grit of 320 to 400 size; peripheral wheel speed of 6,000 fpm.
M32
Medium SatinWheel or belt polished with aluminum oxide grit of 180 to 220 size; peripheral wheel speed of 6,000 fpm.
M33
Coarse SatinWheel or belt polished with aluminum oxide grit of 80 to 100 size; peripheral wheel speed of 6,000 fpm.
M34
Hand-RubbedHand-rubbed with stainless steel wool lubricated with neutral soap solution. Final rubbing with a No. 00 steel wool.
M35
BrushedSeveral 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
OtherTo be specified.
Non-Directional Textured
M40
Unspecified 
M41
Extra-fine MatteAir-blasted with finer than 200-mesh washed silica or aluminum oxide. Air pressure 45 lb. gun 8-12 in. at 90º angle.
M42
Fine MatteAir-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 MatteAir-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 MatteAir-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
DescriptionExamples of Methods of Finishing
Nonetched
Cleaned
C10
Unspecified 
C11
DegreasedOrganic solvent treated.
C12
Inhibited-chemical cleanedInhibited chemical type cleaner used.
C1X
OtherTo be specified.
Etched
C20
Unspecified 
C21
Fine MatteTrisodium phosphate, 3-6 oz. per gallon used at 140-160 ºF for 3 to 5 minutes.
C22
Medium MatteSodium hydroxide, 4-6 oz. per gallon used at 140-150 ºF for 5 minutes.
C23
Coarse MatteSodium fluoride, 1-1/2 oz., plus sodium hydroxide, 4-6 oz. per gallon used at 140-150 ºF for 5 minutes.
C2X
OtherTo be specified.
Brightened
C30
Unspecified 
C31
Highly SpecularChemical bright dip solution of the proprietary phosphoric-nitric acid type used, or proprietary electrobrightening or electropolishing treatment.
C32
Diffuse brightEtched finish C22 followed by brightened finish C31.
C3X
OtherTo be specified.
Anodic Coatings
Type of Finish
AA Designation
DescriptionExamples of Methods of Finishing
Protective & Decorative (coatings less than 0.4 mil thick)
A21
Clear (natural) coatingCoating thickness to be specified, 15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft.
A22
Coating with integral colorCoating thickness to be specified. Color dependent on alloy and processing methods.
A23
Coating with impregnated colorCoating 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
OtherTo be specified.
Architectural Class 11 (0.4 to 0.7 mil coating)
A31
Clear (natural) coating15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft. for 30 minutes, or equivalent.
A32
Coating with integral colorColor dependent on alloy and anodic process.
A33
Coating with impregnated color15% 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
OtherTo be specified.
Architectural Class 1 (0.7 mil and greater anodic coating)
A41
Clear (natural) coating15% H2SO4, used at 70ºF +/- 2ºF, at 12 amp per sq. ft. for 60 minutes, or equivalent.
A42
Coating with integral colorColor dependent on alloy and anodic process. May include Duranodic and certain architectural colors.
A43
Coating with impregnated color15% 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
OtherTo be specified.

 

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

 

To talk to an expert regarding your aluminum railing system, contact us today.