Coating Aluminum Surfaces

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Coating Aluminum Surfaces with Minimal Fairing Needs
Surfaces and manufactured components composed of aluminum and aluminum-alloy are found in a variety of places on many vessels. These surfaces include – but are not limited to – sailboat spars, window and door frames, brackets and other miscellaneous parts.

Note
Most parts do not require a chemical pre-treatment prior to painting.
Recommended procedures for coating aluminum components typically fall into two categories; depending on whether the metal has been chemically pre-treated or not.

Aluminum Surfaces Not Pretreated with Chemicals

  1. Degrease the bare aluminum substrate with ALEXSEAL Surface Degreaser (A9091) using the “Two Rag Cleaning Method”.
  2. To achieve optimum adhesion and performance, the aluminum should be sanded with 120 - 180 grit to a very clean, silver/white surface.
  3. Abraded aluminum surfaces should be cleaned using clean, dry compressed air and a bristle broom to remove all dust before product application.

Important
DO NOT wipe the surface with rags after sanding or grinding. The aluminum surface will snag fibers, which will act as wicks through the protective primer and could decrease corrosion resistance.

Note
Application of an ALEXSEAL Protective Primer should occur within 12 hours of the abraded metal preparation. Cor Spec Primer 135 is recommended where minimal or no fairing is required. Protective Primer 161 may also be used in this application, but the higher film thickness of Protective Primer 161 will create more surface texture in the final topcoat application if the surface is not sealed with Finish Primer 442 and sanded, prior to applying Premium Topcoat 501.

After the application of an ALEXSEAL Protective Primer, but before each subsequent product application, all surfaces should be cleaned using clean, dry compressed air and clean rags to remove all dust and contaminants. An additional wipe down with ALEXSEAL Wipe Down Solvent using the “Two Rag Cleaning Method” is recommended to ensure the removal of surface contamination. Final dust removal with a tack rag is also recommended before applying an ALEXSEAL Topcoat.

Overview of Steps to Prepare and Paint the Aluminum Surface:

  1. Apply an ALEXSEAL Protective Primer per the TDS recommendations or see instructions for Protective Primer 161 and Cor Spec Primer 135 in “Substrate Preparation & Priming”.
  2. Based on the fairness quality level, proceed to steps 3, 4, or 5 as needed. If the fairness of the surface is of acceptable quality after applying an ALEXSEAL Protective Primer, you may proceed directly to applying to topcoat (step 6).
  3. Optional: Apply ALEXSEAL Fairing Compound 202 as needed to achieve the desired fairing quality level. Fair the surface per TDS recommendations or refer to Fairing Compound 202 instructions in “Fairing”.
  4. Optional: Apply ALEXSEAL Super Build 302 or Fine Filler 303 as needed. Apply surfacing products per TDS recommendations or refer to instructions for Super Build 302 and Fine Filler 303 in “Surfacing” starting on page 36.
  5. Optional: Apply ALEXSEAL Finish Primer 442 per TDS recommendations or refer to Finish Primer 442 instructions in “Final Priming & Sealing”.
  6. Apply ALEXSEAL Topcoats per TDS recommendations or refer to Premium Topcoat instructions in “Finishing”.

Aluminum Surfaces Pretreated WITH Chemicals
Chemical pretreatment is not allowed in all regions of the world due to environmental impact concerns. It is important to consult your local regulatory office to determine if chemical pre-treatment can be performed in your area.

Chemical pretreatment can improve the surface condition and provide longer service life if applied correctly. These treatments work by washing the surface of the bare aluminum with an acid cleanser and then treating the surface with a conversion coating which stops the oxidation of the aluminum. This process is very effective at creating a clean, paint-ready surface that will provide a long service life. In some situations acid cleanser may be used to clean the surface prior to the use of ALEXSEAL Protective Primers.

Caution
The Pretreatment process creates wastewater that must be contained and disposed of properly in accordance with local government and environmental regulations.

Worker safety must be monitored to ensure that the chemicals do not come in contact with any part of the body.

Important
During the pretreatment process it is critical that ALL surfaces be completely rinsed with clean water. Residue left from the chemicals can dry on the surface and create corrosion on the aluminum.

Consult the manufacturer of the chemical pretreatment for additional information regarding the use and disposal of these chemicals.

Preparing Aluminum for Chemical Pretreatment

  1. Prior to using a chemical treatment, degrease the bare aluminum substrate with ALEXSEAL Surface Degreaser (A9091) using the “Two Rag Cleaning Method”.
  2. To achieve optimum adhesion and performance, the aluminum should be sanded to a very clean surface. Use 36 - 60 grit for heavily faired projects and 120 – 180 grit on surfaces which require little or no surfacing and only requiring a protective primer and topcoat.
  3. Abraded aluminum surfaces should be cleaned using clean, dry compressed air and a bristle broom to remove all dust before chemical treatment. 
    Important DO NOT wipe the surface with rags after sanding or grinding. The aluminum surface will snag fibers, which will act as wicks through the protective primer and could decrease corrosion resistance.
  4. Follow the manufacturer’s instructions for application of the chemical pretreatment.

Note
Application of an ALEXSEAL Protective Primer should occur after the pretreated surface has completely dried. Cor Spec Primer 135 is recommended where minimal or no fairing is required. Protective Primer 161 may also be used in this application, but the higher film thickness of Protective Primer 161 will create more surface texture in the final topcoat application if the surface is not sealed with Finish Primer 442 and sanded, prior to applying Premium Topcoat 501.

After the application of an ALEXSEAL Protective Primer, but before each subsequent product application, all surfaces should be cleaned using clean, dry compressed air and clean rags to remove all dust and contaminants. An additional wipe down with ALEXSEAL Wipe Down Solvent using the “Two Rag Cleaning Method” is recommended to ensure the removal of surface contamination. Final dust removal with a tack rag is also recommended before applying an ALEXSEAL Topcoat.

Overview of Steps to Prepare and Paint the Pretreated Aluminum Surface:

  1. Apply an ALEXSEAL Protective Primer per the TDS recommendations or see instructions for Protective Primer 161, Cor Spec Primer 135 in “Substrate Preparation & Priming”.
  2. Based on the fairness quality level, proceed to steps 3, 4, or 5 as needed. If the fairness of the surface is of acceptable quality after applying an ALEXSEAL Protective Primer, you may proceed directly to applying to topcoat (step 6).
  3. Optional: Apply ALEXSEAL Fairing Compound 202 as needed to achieve the desired fairing quality level. Fair the surface per TDS recommendations or refer to Fairing Compound 202 instructions in “Fairing”.
  4. Optional: Apply ALEXSEAL Super Build 302 or Fine Filler 303 as needed. Apply surfacing products per TDS recommendations or refer to instructions for Super Build 302 and Fine Filler 303 in “Surfacing”.
  5. Optional: Apply ALEXSEAL Finish Primer 442 per TDS recommendations or refer to Finish Primer 442 instructions in “Final Priming & Sealing”.
  6. Apply ALEXSEAL Premium Topcoat 501 per TDS recommendations or refer to Premium Topcoat instructions in “Finishing”