Removing Paint from Wrought Iron, Cast Iron and Steel Using Abrasive Methods

Procedure code:
0501005S
Source:
HSPG prepared for NPS - SERO
Division:
Metals
Section:
Metal Materials
Last Modified:
07/20/2016

PREFACE 

The cleaning or stripping of metals may involve the use of abrasives, liquids or solvents which may splash or run off onto adjacent materials. Take special care to protect all adjacent materials, and do not use this procedure on metals other than those specified in the summary.

Projects involving paint removal are subject to state and federal laws on lead paint abatement, disposal and use of Volatile Organic Compounds (VOCs). Specified products may not be permitted or appropriate for all locations. Products containing chemicals known to present health or environmental hazards should be used only as a last resort, where permissible, in accordance with manufacturer's directions and government requirements. Test milder formulations for effectiveness before proceeding to stronger alternatives.

CAUTION: Mechanical/abrasive methods of cleaning may damage historic fabric. This method of cleaning should be performed only by an experienced professional and only upon approval from the regional historic preservation officer.

PART 1---GENERAL

1.01 SUMMARY

  1. This procedure includes guidance on abrasively removing paint from wrought iron, cast iron and steel. These metals should be repainted immediately following paint removal in order to prevent exposure to the atmosphere and subsequent corrosion.

  2. For information on painting and coating these materials see "Primers and Paints for Wrought Iron, Cast Iron and Steel", "Applying a Sacrificial Coating to Wrought Iron, Cast Iron and Steel", and "General Guidelines for Painting Exterior and Interior Surfaces".

  3. There are several causes for paint failure on metal. Excess moisture can cause rusting. As metal rusts, the rust expands breaking the bond between the metal and the paint. Inadequate or improper surface preparation can interfere with the proper bonding of the new paint. The wrong primer can cause anything from pitting of the metal surface to peeling of the new paint.

  4. It is not necessary to remove all previous coats of paint if:

    1. They are adhering soundly.

    2. The new painting system is compatible.

    3. Important design details are not being obscured by the paint layers.

  5. An archive of the paint history of the building is to be maintained. This is to include the paint samples taken during research, samples of the new paint colors and the manufacturer's technical information.

  6. Safety Precautions:

    1. No food or drink shall be allowed near any work station so as to prevent contamination from paint, paint chips or paint dust which may contain lead and other toxic substances.

    2. Paint being removed most likely will contain lead. All workmen must wear protective clothing, (including hair), goggles and respirators with proper filters

    3. FOLLOW ALL APPROPRIATE REGULATIONS PROVIDED BY THE EPA REGIONAL OFFICE AND/OR THE STATE OFFICE OF ENVIRONMENTAL PROTECTION.

    4. Protective clothing shall be removed at the end of each day and kept at the site to prevent workers from taking dust and paint chips to other parts of the site or to their homes.

    5. Wash hands and face often, especially before eating and at the end of the day.

  7. Read "General Project Guidelines" along with this specification. 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). The 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)

  8. See also:

    1. "Cast Iron: Characteristics, Uses and Problems"

    2. "Wrought Iron: Characteristics, Uses and Problems"

    3. "Checklist for Inspecting Cast Iron Failures"

  9. Abrasively cleaned surfaces are usually specified in terms of surface cleanliness and surface roughness.

    1. These standards generally apply to modern commercial and industrial applications.

    2. Their applicability to historic metal surfaces must be carefully studied.

    3. Additionally, newer techniques include the use of soda or other particulates from organic sources as a gentler abrasive, as well as laser cleaning.

  10. Consultation with a qualified conservator is recommended in choosing the most appropriate treatment for the subject metal surfaces.

  11. A successful job is directly related to the skill of the operator. The individual must be able to judge pressure and grit of abrasive, and be diligent about masking all other surfaces.

1.02 DEFINITIONS

  1. Mechanical/Abrasive Methods: as used herein shall apply to the approved methods of mechanical or abrasive removal. These include:

    1. Sanding blocks.

    2. Sand paper.

    3. Flexible sandpaper wheels and rotary wire brushes made to be chucked into a power drill.

    4. Limited use of wet and dry air-abrasive cleaning.

  2. Controlled air-abrasive cleaning with a fine grit may be considered for cast iron features and on heavier wrought iron sections.

  3. Dry air-abrasive cleaning - No water is involved in process. Excessive amounts of dust are produced which may be illegal in local municipality. Airborne dust which may contain lead will also be a problem.

  4. Wet air-abrasive cleaning -Water is mixed with abrasive and air to cut down on dust generated. Useful in washing soluble iron salts from pitted areas. Good also for removing paint from iron structures in marine and heavily polluted environments.

PART 2---PRODUCTS

2.01 MATERIALS

NOTE: Chemical products are sometimes sold under a common name. This usually means that the substance is not as pure as the same chemical sold under its chemical name. The grade of purity of common name substances, however, is usually adequate for stain removal work, and these products should be purchased when available, as they tend to be less expensive. Common names are indicated below by an asterisk (*).

  1. Mineral spirits:

    1. A petroleum distillate that is used especially as a paint or varnish thinner.

    2. Other chemical or common names include Benzine* (not Benzene); Naphtha*; Petroleum spirits*; Solvent naphtha*.

    3. Potential Hazards: TOXIC AND FLAMMABLE.

    4. Safety Precautions:

      1. AVOID REPEATED OR PROLONGED SKIN CONTACT.

      2. ALWAYS wear rubber gloves when handling mineral spirits.

      3. If any chemical is splashed onto the skin, wash immediately with soap and water.

    5. Available from construction specialties distributor, hardware store, paint store, or printer's supply distributor.

  2. Trisodium Phosphate:

    1. NOTE: THIS CHEMICAL IS BANNED IN SOME STATES SUCH AS CALIFORNIA. REGULATORY INFORMATION AS WELL AS ALTERNATIVE OR EQUIVALENT CHEMICALS MAY BE REQUESTED FROM THE ENVIRONMENTAL PROTECTION AGENCY (EPA) REGIONAL OFFICE AND/OR THE STATE OFFICE OF ENVIRONMENTAL QUALITY.

    2. Strong base-type powdered cleaning material sold under brand names.

    3. Other chemical or common names include Sodium Orthophosphate; Tribasic sodium phosphate; Trisodium orthophosphate; TSP*; Phosphate of soda*.

    4. Potential Hazards: CAUSTIC TO FLESH.

    5. Available from chemical supply house, grocery store or supermarket or hardware store.

-OR-

Sudsy ammonia mixed in clean, clear water. Follow manufacturer's instructions for proper dilutions.

  1. For light surface rust:

    1. Emery paper

    2. Sandpaper - useful for smaller jobs or final feathering of high paint edges, corners or hard to reach places.

    3. Fine steel wool.

    4. 600 grit aluminum oxide.

  2. For medium surface rust:

    1. Putty knife.

    2. Wire brush - removes rust and flaking metal as well as loosened paint.

    3. Scrapers - help to get under the paint and crevices. Do not chip or bang the paint off cast pieces as the iron may become fractured.

    4. Rust remover solution containing orthophosphoric acid. Several are available in gel form from retail outlets.

  3. For heavy rust:

    1. Coarse to medium grits of open-coat aluminum oxide or flint sandpaper.

    2. Emery paper.

  4. Soft rags.

  5. Clean, potable water.

2.02 EQUIPMENT

  1. Rubber gloves.

  2. Eye and skin protection.

  3. Paint scrappers and putty knives.

  4. Ball peen hammer.

  5. Sanding blocks, sanding sponges, sanding wheels.

  6. Wire brushes.

  7. Stiff natural bristle brushes.

  8. Rotary wire wheels.

  9. Proper, heavy-duty extension cords.

  10. Air-abrasive cleaning equipment (80-100 psi) for use with fine grit dry and wet abrasives. Consult RHPO.

  11. Water hose.

PART 3---EXECUTION

3.01 EXAMINATION

  1. Before work is begun on removing the existing paint film or otherwise preparing the surface, all sources of excess moisture shall be determined and repaired as required.

  2. Execute test samples of the cleaning methods specified in this procedure to determine which method(s) are to be used. Sample areas shall be selected by the RHPO and shall include at least one ornamental area and one flat area, or as necessary to include all surface types likely to be encountered in this work.

  3. Method(s) used in the actual cleaning shall be the one(s) which provide the necessary level of cleanliness with the least amount of surface alteration. Final selection of methods shall be made by the RHPO.

3.02 PREPARATION

Protection:

  1. Protect adjacent surfaces, including grass, shrubs and trees with paper, drop cloths and other means. Items not to be painted which are in contact with or adjacent to painted surfaces shall be removed or protected prior to surface preparation and painting operations. All methods of enclosure and protection should be approved by the supervisor.

  2. Work area shall be sealed to prevent the spread of dust, debris and water beyond the work site, and to assist in the collection of contaminants.

  3. Provide protection boards to vulnerable decorative work and maintain for the duration of operations.

  4. All waste material shall be collected at the end of each work day and properly disposed of. It is considered Hazardous Waste.

  5. After each days paint removal work is complete, area shall be vacuumed with machines equipped with HEPA (High Efficiency Particulate Air) filters to insure all lead dust has been removed.

3.03 ERECTION, INSTALLATION, APPLICATION

Note: All methods require the removal of rust to achieve a clean surface before beginning the application of final coating. As soon as the cleaned surface is dry and clear of any particles or dirt, one must promptly apply an appropriate base coating to inhibit further corrosion from setting in before moving on to the finish coatings.

  1. Removing paint from small pieces that can be detached from structure.

  2. NOTE: REMOVE ONLY AS MUCH PAINT AND RUST EACH DAY AS CAN BE PRIMED THAT SAME DAY. BARE IRON AND STEEL WILL BEGIN TO RUST AGAIN WITHIN A MATTER OF HOURS. IT SHOULD NOT BE ALLOWED TO SIT UNPROTECTED OVERNIGHT.

    1. Soak in a solution of hot water and TSP or sudsy ammonia to loosen the paint.

    2. Remove paint with scrapers and/or a wire brush.

    3. Wipe with mineral spirits to remove final traces of paint.

    4. Dry immediately and prime to prevent rusting. A heat gun, set at the lowest temperature, may be used to hasten the drying time.

CAUTION: DO NOT USE HIGH HEAT AS THIS MAY DISTORT THE METAL MEMBERS.

  1. Mechanical/Abrasive Rust/Paint Removal: OBTAIN RHPO APPROVAL BEFORE PROCEEDING WITH WORK.

    1. To determine the degree of deterioration and the level of paint removal required, clear away all dust and debris followed by rub-down with mineral spirits.

    2. To remove light rust and flaking, peeling paint:

      1. Begin with emery paper or aluminum oxide sandpaper.

      2. Use scrapers to get under loose paint and into crevices.

      3. Use a wire brush, or an electric drill with a special wire brush or rotary sandpaper whip attachment if above two methods do not remove paint.

  2. Air-Abrasive Paint Removal: OBTAIN RHPO APPROVAL BEFORE PROCEEDING WITH WORK.

  3. NOTE: AIR-ABRASIVE CLEANING (COMMONLY KNOWN AS SANDBLASTING) IS DESTRUCTIVE FOR SOFTER BUILDING MATERIALS. HOWEVER, IRON, AS A HARD MATERIAL WITH A NATURAL UNEVEN SURFACE, WILL NOT BE NOTICEABLY DAMAGED BY ITS CAREFUL USE.

    1. CAUTION: DO NOT USE AIR-ABRASIVE CLEANING METHODS IN THE FOLLOWING SITUATIONS:

      1. ON THIN SECTIONS OR FINE, INTRICATE DETAILS OF WROUGHT IRON FEATURES.

      2. ON ZINC AND GALVANIZED IRON AND STEEL.

      3. ON FEATURES FOR WHICH THE ORIGINAL SURFACE TEXTURE IS AN INTEGRAL PART OF THE DESIGN (AIR-ABRASIVE CLEANING WILL ALTER ORIGINAL SURFACE TEXTURE AND APPEARANCE).

      4. ON STAINLESS STEEL FEATURES.

    1. Air pressures at the compressor shall be between 40 psi to 70 psi.

    2. Grit size shall be in the range of #10 to #45 (copper should not be used as it will cause an electrolytic reaction). Other abrasives, such as organically based grit such as ground walnut shells, or other abrasive methods such as glass bead peening, may also be appropriate but should be performed only under the direction of an architectural conservator and/or the RHPO.

    3. A pencil-point nozzle shall be used to allow more complete control. Nozzle shall allow for independent control over air, water and abrasive and should be held no closer than 12" from the surface to be cleaned.

    4. Flush all surfaces with water to remove all traces of slurry and spent abrasive. Final rinse shall contain rust inhibitor with no more than 5000 ppm.

    5. CAUTION: LARGER CONCENTRATIONS OF RUST INHIBITOR WILL RESULT IN THE DEPOSITION OF SALTS ON THE METAL SURFACES, WHICH WILL CAUSE THE PAINT TO PEEL.

    6. Dry surfaces immediately, especially any horizontal surfaces or water traps which might collect water.

  4. Prime as soon as possible after surfaces have been dried but before rust has a chance to for again.

  5. Caulk all areas which have been damaged by the abrasive cleaning, especially seams, screw and bolt holes, and at junctures with dissimilar materials.

  6. Fill all holes, depressions and cracks with metal filler and sand to be flush with surrounding contours. See "Repairing Small Holes, Nicks and Minor Imperfections in Cast Iron" for guidance.

  7. Prime and paint all surfaces. For guidance, see:

    1.  "Primers and Paints for Wrought Iron, Cast Iron and Steel"

    2. "Applying a Sacrificial Coating to Wrought Iron, Cast Iron and Steel"

    3. "General Guidelines for Painting Exterior and Interior Surfaces"

3.04 PROTECTION

Protect cleaned or final finishes from damage during building or project cleaning period by use of temporary protective coverings approved by RHPO. Remove protective covering at time of Substantial Completion.

END OF SECTION

 

Last Reviewed 2016-07-20