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Historic Preservation - Technical Procedures

Spectitle:
Removing Paint From Wrought Iron, Cast Iron And Steel Using Thermal Methods

Procedure code:
0501016R

Source:
Developed For Hspg (Nps - Sero)

Division:
Metals

Section:
Metal Materials

Last Modified:
02/24/2012

Details:
Removing Paint From Wrought Iron, Cast Iron And Steel Using Thermal Methods



REMOVING PAINT FROM WROUGHT IRON, CA= ST IRON AND STEEL USING
THERMAL
METHODS


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.

BEFORE UNDERTAKING ANY PROJECT INVOLVING PAINT REMOVAL, APPLICABLE
STATE AND FEDERAL LAWS ON LEAD PAINT ABATEMENT AND DISPOSAL MUST
BE
TAKEN INTO ACCOUNT AND CAREFULLY FOLLOWED.  STATE AND FEDERAL
REQUIREMENTS MAY AFFECT OPTIONS AVAILABLE TO OWNERS ON BOTH PAINT
REMOVAL AND REPAINTING.  THESE LAWS, AS WELL AS ANY REQUIREMENTS
PROHIBITING VOLATILE ORGANIC COMPOUNDS (VOCs), SHOULD BE REQUESTED
FROM THE STATE HISTORIC PRESERVATION OFFICER IN EACH STATE.  (From
Preservation Brief 28, "Painting Historic Interiors".)  REGU= LATORY
INFORMATION MAY ALSO BE REQUESTED FROM THE ENVIRONMENTAL
PROTECTION
AGENCY (EPA) REGIONAL OFFICE AND/OR THE STATE OFFICE OF
ENVIRONMENTAL QUALITY.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes 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.

    B.   For information on painting and coating these materials
         see 05010-13-S "Primers and Paints for Wrought Iron, Cast
         Iron and Steel", 05010-18-R "A= pplying a Sacrificial
         Coating to Wrought Iron, Cast Iron and Steel", and 09900-07-S
         "General Guidelines for Painting Exterior and
         Interior Surfaces".
=0C     C.   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.

         1.   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.

              a.   Heat higher than 1100 degrees fahrenheit will
                   vapor= ize lead paint and is hazardous.

              b.   The hot air blast produced by the heat gun can
                   ignite debris within a wall cavity or behind a
                   corni= ce 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.  

              c.   As with flame cleaning, the hot air of a heat
                   gun can overheat cast iron and steel features
                   creat= ing localized thermal stresses, or
                   causi= ng small sections to become distorted.  

    D.   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.

    E.   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.

    F.   An archives 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
         manufacturers technical information.

    G.   Safety Precautions:

         1.   Make sure that a fire extingui= sher is readily
              available in case of emergency.

         2.   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 substance= s.

         3.   PAINT BEING REMOVED MAY CONTAIN LEAD.  ALL WORKMEN
              MUST WEAR PROTECTIVE CLOTHING, (INCLUDING HAIR),
              GOGGLES AND RESPIRATORS WITH PROPER FILTERS.

         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.

    H.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precaution= s

         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).

    I.   For additional information on cast and wrought iron see
         the following HBPP procedures:

         1.   05010-04-S, "Cast Iron:  Characteristics, Uses and
              Problems."

         2.   05010-11-S, "Wrought Iron:  Characteristics, Uses
              and Problems."

         3.   05010-01-S, "Checklist for Inspecting Cast Iron
              Failures."


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 adequa= te
    for stain removal work, and these products should be purchas= ed
    when available, as they tend to be less expensive.  Com= mon
    names are indicated below by an asterisk (*).

    A.   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:

              a.   AVOID REPEATED OR PROLONGED SKIN CONTACT.

              b.   ALWAYS wear rubber gloves when handling
                   miner= al spirits.

              c.   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 distribu= tor.

    B.   Soft, clean rags

2.02 EQUIPMENT

    A.   High velocity oxyacetylene or oxypropane flame.

    B.   Heavy duty electric heat gun with metal case.  Operating
         temperature between 500 and 750 degrees Fahrenheit.
         MASTER'S Model Number 499, MASTER'S HG-501 or equal are
         recommended.  A number of replaceme= nt heat elements
         should also be kept on hand.  

    C.   A variety of putty knives and paint scrappers of
         different shapes and flexibility.

    D.   Proper, heavy-duty extension cords are required.
    E.   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.


PART 3---EXECUTION

3.01 EXAMINATION

    A.   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.  

3.02 PREPARATION

    A.   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.

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

         3.   Work area shall be sealed to prevent the spread of
              dust and debris beyond the work site.

         4.   After paint removal is complet= e, area shall be
              vacuumed with machines equipped with HEPA (High
              Efficiency Particulate Air) filters to insure all
              lead dust has been remove= d.

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 MATTER OF HOURS.  IT SHOULD NOT BE ALLOW= ED TO
    SIT UNPROTECTED OVERNIGHT.

    A.   Flame cleaning:

         NOTE:  FLAME CLEANING MUST BE PERFO= RMED 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.

         1.   Flame cleaning may be executed under both damp or
              wet conditions and will help dry the surface.  

         2.   Flame cleaning is NOT recommen= ded on cast iron
              because of thermal stress= es which can be created by
              overheating in localized areas.  Nor is it
              recommended for thin sections of steel or wrought
              iron, i.e. window sash and frame members, because
              of the danger of distorti= ng the metal.

    B.   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 PRESERVING THE METAL
         SUBSTRATE.

         1.   Aim nozzle at painted surface until the paint
              begins to bubble.  <= br>
         2.   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.

         3.   Using a clean, soft cloth, wipe the surface with
              mineral spirits to remove all residue.

                         END OF SECTION