Removing Paint from Wrought Iron, Cast Iron and Steel Using Thermal Methods
- CSI Division:
- Division 5 - Metals
- Metal Materials
- Last Modified:
Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
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 and 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.
- This specification provides guidance on the selection of appropriate thermal methods of paint and rust removal 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.
- "Primers and Paints for Wrought Iron, Cast Iron and Steel"
- "Applying a Sacrificial Coating to Wrought Iron, Cast Iron and Steel"
- "General Guidelines for Painting Exterior and Interior Surfaces"
- "Cast Iron: Characteristics, Uses and Problems"
- "Wrought Iron: Characteristics, Uses and Problems"
- "Checklist for Inspecting Cast Iron Failures"
Thermal methods as used herein shall apply to high velocity oxyacetylene or oxypropane flame cleaning, a standard surface preparation method for steel and cast iron, or to the heat gun.
- The heat gun works using a hot blast of air at 500 to 750 degrees Fahrenheit. Extreme caution should be taken when using this method.
- Heat higher than 1100 degrees Fahrenheit will vaporize lead paint and is hazardous.
- The hot air blast produced by the heat gun can ignite debris within a wall cavity or behind a cornice or soffit. The dust can smolder only to ignite hours later after the work crew has gone home so extreme caution must be taken when using this method.
- As with flame cleaning, the hot air of a heat gun can overheat cast iron and steel features creating localized thermal stresses, or causing small sections to become distorted.
- 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.
It is not necessary to remove all previous coats of paint if:
- They are adhering soundly.
- The new painting system is compatible.
- Important design details are not being obscured by the paint layers.
- 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.
- Make sure that a fire extinguisher is readily available in case of emergency.
- 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.
- CAUTION: PAINT BEING REMOVED MAY CONTAIN LEAD. ALL WORKMEN MUST WEAR PROTECTIVE CLOTHING (INCLUDING OVER HAIR), GOGGLES AND RESPIRATORS WITH PROPER FILTERS.
- 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.
- Wash hands and face often, especially before eating and at the end of the day.
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:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- General Protection (Surface and Surrounding)
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 (*).
- A petroleum distillate that is used especially as a paint or varnish thinner.
- Other chemical or common names include Benzine* (not Benzene); Naphtha*; Petroleum spirits*; Solvent naphtha*.
- Potential Hazards: TOXIC AND FLAMMABLE.
- Safety Precautions:
- AVOID REPEATED OR PROLONGED SKIN CONTACT.
- ALWAYS wear rubber gloves when handling mineral spirits.
- If any chemical is splashed onto the skin, wash immediately with soap and water.
- Available from construction specialties distributor, hardware store, paint store, or printer's supply distributor.
- Soft, clean rags
- High velocity oxyacetylene or oxypropane flame.
Heavy duty electric heat gun with metal case.
- Operating temperature shall be between 500 and 750 degrees Fahrenheit.
- A number of replacement heat elements should also be kept on hand.
- A variety of putty knives and paint scrappers of different shapes and flexibility.
- Proper, heavy-duty extension cords are required.
- Power Supply: Heat guns draw approximately 15 amps of power. Each work station is to be provided with its own temporary power supply so as not to overload other circuits.
Before work is begun on removing the existing paint film or otherwise preparing the surface all sources of excess moisture shall be inspected and repaired or replaced as required.
- Protect adjacent surfaces, including grass, shrubs and trees by covering 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 waste material shall be collected at the end of each work day and properly disposed of. It is considered Hazardous Waste.
- Work area shall be sealed to prevent the spread of dust and debris beyond the work site.
- After paint removal is complete, area shall be vacuumed with machines equipped with High Efficiency Particulate Air (HEPA) Filters to insure all lead dust has been removed.
3.03 ERECTION, INSTALLATION, APPLICATION
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 FEW HOURS. IT SHOULD NOT BE ALLOWED TO SIT UNPROTECTED OVERNIGHT.
- Flame cleaning:
NOTE: FLAME CLEANING MUST BE PERFORMED BY AN EXPERIENCED OPERATOR FOR IF DONE TOO SLOWLY LOOSE SCALE AND OTHER FOREIGN MATERIAL CAN BE FUSED TO THE METAL RATHER THAN REMOVED FROM IT.
- Flame cleaning may be executed under both damp and wet conditions and will help dry the surface.
- Flame cleaning is NOT recommended on cast iron because of thermal stresses which can be created by overheating in localized areas. It is also not recommended for thin sections of steel or wrought iron, e.g. window sash and frame members, because of the danger of distorting the metal.
- Heat gun:
NOTE: A HEAT GUN MAY BE OF LIMITED USE IN REMOVING PAINT FROM CAST IRON AND STEEL. TESTING SHOULD BE DONE USING THERMAL, ABRASIVE AND CHEMICAL METHODS TO DETERMINE WHICH IS THE MOST EFFICIENT WHILE ALSO PRESERVING THE METAL SUBSTRATE.
- Aim nozzle at painted surface until the paint begins to bubble.
- Using scrapers or dental picks or other similar tools remove paint before it begins to cool.
CAUTION: DO NOT HOLD GUN TO ANY ONE AREA FOR AN EXTENDED PERIOD OF TIME TO AVOID OVERHEATING THE SUBSTRATE.
- Using a clean, soft cloth, wipe the surface with mineral spirits to remove all residue.