Repairing Corrosion Pitting And Cracks In Cast Iron

Procedure code:
Us Custom House/New Orleans, La - Fromherz Engineers, Inc.
Metal Materials
Last Modified:




  1. This procedure includes guidance on using plastic metal and weldment to repair corrosion pitting and cracks in cast iron.
  2. See"General Project Guidelines" for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
    1. Safety Precautions
    2. Historic Structures Precautions
    3. Submittals
    4. Quality Assurance
    5. Delivery, Storage and Handling
    6. Project/Site Conditions
    7. Sequencing and Scheduling
    8. General Protection (Surface and Surrounding)
      These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).


  1. American Society for Testing and Materials (ASTM),



  1. Devcon Corporation
  2. Belzona, Inc.
  3. Dumond Chemicals, Inc.
  4. Diedrich Technologies, Inc.


  1. Plastic Metal Material: Two-part product composed of a silicone/steel alloy blended with a high molecular weight polymer, such as "Plastic Steel 5 Minute Putty (SF)" (Devcon Corporation), Belzona IIII "Super Metal" (Belzona, Inc.), or approved equal.
    1. Material shall be machinable grade after curing, of a paste consistency having negligible slump at a 1" thickness or less.
    2. Material shall show no evidence of measurable shrinkage from plastic state to hardened state.
    3. Cured material shall show no visible signs of corrosion after 5000 hours exposure in ASTM B 117 salt spray testing procedure.
    4. Submit samples of the two components of the plastic metal material, prior to mixing. Also submit samples of the completed, cured plastic metal materials.
  2. Weldments: Shall be done in accordance with AWS standards. Cast iron shall be welded with pure nickel rods.
  3. Chemical Stripper: "Peel Away 1" (Dumond Chemicals, Inc.), "404 Rip Strip" (DiedrichTechnologies, Inc.), or approved equal.
  4. Emery paper
  5. 600 grit aluminum oxide paper


  1. Wiping cloths
  2. Eye and skin protection
  3. Welding equipment
  4. Electric drill
  5. Pneunmatic chisel
  6. Electric Grinder



  1. Surface Preparation:
    1. Surface preparation shall be done under the supervision of the RHPO.
    2. The RHPO will designate sample areas for testing of surface preparation on the various different components that require repair. No other surface preparation is to be done until sample areas have been approved. Approved areas shall become the standard of comparison for all surface preparation work. Protect from weathering, but do not alter or opaquely cover sample areas until all preparation work has been completed and approved.
    3. The time interval between final cleaning and application of primer shall not exceed two hours. Prime coat shall be applied prior to application of plastic metal materials. Allow 48 hours between application of prime coat and application of plastic metal material.
    4. See 05010-05-R for cleaning of metal surfaces which receive plastic metal repairs.


  1. For corrosion pitting larger than 1/4" in diameter with a depth of at least 1/8":
    1. Abrasively clean with sandpaper the pit and surrounding materials until all evidence of paint and corrosion is gone and a "white metal" condition is achieved. If the RHPO judges that the area cannot be adequately cleaned it shall be ground out.
    2. Prime paint the area immediately (see"Primers And Paints For Wrought Iron, Cast Iron And Steel" and"General Guidelines for Painting Exterior and Interior Surfaces" for guidance).
    3. Carefully and completely fill the corrosion pit with plastic metal no sooner than 48 hours after prime painting and allow to dry.
      1. When accessible from both faces of components, fill holes and cracks and build up the missing portions of component from each face utilizing a temporary form as a backing.
      2. Temporary form shall be polyethylene or be faced with polyethylene or other similar material to which plastic metal will not adhere. Do not remove temporary form until the plastic metal has cured to the extent recommended by the manufacturer.
      3. If filling from the opposite side is not accomplished within the time limits recommended by the manufacturer, grind out the material that has been placed and repeat the procedure.
      4. When dry, apply finish coat of paint over the patch.
  2. For smaller pits than those described in A.1. above, clean and paint only (see Removing Paint from"Wrought Iron, Cast Iron and Steel Using Abrasive Methods","Repairing Fractured Cast Iron Features" and"General Guidelines for Painting Exterior and Interior Surfaces").
  3. For Non-structural Open Cracks in Existing Cast Iron Components: HAIRLINE CRACKS SHOULD NOT BE OPENED
    1. Abrasively clean the area along and in the immediate vicinity of the crack until all evidence of paint and corrosion is gone and a "white metal" condition is achieved. Cleaning shall extend a minimum of 4" beyond the visible ends of the crack.
    2. Drill a 1/2" diameter hole at the ends of the crack and grind out a 1/4" wide, full depth vee groove along the path of the crack, between the two 1/2" diameter holes.
    3. Immediately prime paint the area (see"Removing Paint from Wrought Iron, Cast Iron and Steel Using Abrasive Methods","Repairing Fractured Cast Iron Features" and"General Guidelines for Painting Exterior and Interior Surfaces").
    4. Carefully and completely fill the groove and two holes with plastic metal. Finish the surface smooth and flush with the surrounding base metal.
  4. Repair of Deep Corrosion Pitting Using Weldment: Follow the procedures outlined in Section A. above, except use weldment instead of plastic metal to fill holes and cracks.

Last Reviewed: 2017-08-13