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Historic Preservation - Technical Procedures

Spectitle:

Cleaning/Removing Paint From Wrought Iron, Cast Iron And Steel Using Mechanical/Abrasive Methods

Procedure code:

0501005R

Source:

Developed For Hspg (Nps - Sero)

Division:

Metals

Section:

Metal Materials

Last Modified:

01/10/2014

Details:

Cleaning/Removing Paint From Wrought Iron, Cast Iron And Steel Using Mechanical/Abrasive Methods



CLEANING/REMOVING PAINT FROM WROUGHT IRON, CAST IRON & STEEL USING
MECHANICAL/ABRASIVE METHODS


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.

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 REPAINTI; AS WELL AS ANY REQUIREMENTS
PROHIBITING VOLATILE ORGANIC COMPOUNDS (VOCs),  (See
Preservation Brief 28, "Painting Historic Interiors".)  REGULATORY INFORMATION MAY
ALSO BE REQUESTED FROM THE ENVIRONMENTAL PROTECTION AGENCY (EPA)
REGIONAL OFFICE AND/OR THE STATE OFFICE OF ENVIRONMENTAL PROTECTION.


PART 1---GENERAL

1.01 SUMMARY

    A.   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.  

    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 "Applying a Sacrificial
         Coating to Wrought Iron, Cast Iron and Steel", and 09900-07-S
         "General Guidelines for Painting Exterior and
         Interior Surfaces".

    C.   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.

    D.   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.

    E.   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.

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

         3.   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.

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

    G.   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 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).

    H.   For additional information on cast and wrought iron see
         05010-04-S "Cast Iron:  Characteristics, Uses and
         Problems", 05010-11-S "Wrought Iron:  Characteristics,
         Uses and Problems", and 05010-01-S "Checklist for
         Inspecting Cast Iron Failures".

1.02 DEFINITIONS

    A.   Mechanical/Abrasive Methods:  as used herein shall apply
         to the approved methods of mechanical or abrasive
         removal.  This includes sanding blocks or simple sand
         paper, power flexible sandpaper wheels and rotary wire
         brushes made to be chucked into a power drill, even the
         limited use of wet and dry air-abrasive cleaning.  

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

         2.   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.  

    C.   Abrasively cleaned surfaces are usually specified in
         terms of surface cleanliness and surface roughness.
         These standards generally apply to modern commercial and
         industrial applications their applicability to historic
         metal surfaces must be carefully studied.     

  D.   Additionally, newer techniques include the use of soda as the 
         tmore gentle abrasive and there are othe types of particules often 
         from organic sources.  Also, laser cleaning is another newer technique.
         Consultation with a qualified conservator is recommended in choosing 
         the most appropriate treatment for the subject metal surfaces.

  E.   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.


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 (*).

    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
                   mineral 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 distributor.

    B.   Trisodium Phosphate:  

         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.

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

         2.   Other chemical or common names include Sodium
              Orthophosphate; Tribasic sodium phosphate;
              Trisodium orthophosphate; TSP*; Phosphate of soda*;
              (also sold under brand names such as).

         3.   Potential Hazards:  CORROSIVE TO FLESH.

         4.   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.

    C.   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

    D.   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.

    E.   For heavy rust:  Coarse to medium grits of open-coat
         aluminum oxide or flint sandpaper, or emery paper.

    F.   Soft rags

    G.   Clean, potable water

2.02 EQUIPMENT

    A.   Rubber gloves

    B.   Eye and skin protection

    C.   Paint scrappers and putty knives

    D.   Ball peen hammer

    E.   Sanding blocks, sanding sponges, sanding wheels

    F.   Wire brushes

    G.   Stiff natural bristle brushes

    H.   Rotary wire wheels

    I.   Proper, heavy-duty extension cords

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

    K.   Water hose


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 determined and repaired as required.  

    B.   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.

    C.   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

    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.  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

    A.   Paint Removal, General:  Clean small pieces which can be
         removed.

         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.  

    B.   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:

              a.   Begin with emery paper or aluminum oxide
                   sandpaper.

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

              c.   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.

    C.   Air-abrasive Paint Removal:  OBTAIN RHPO APPROVAL BEFORE
         PROCEEDING WITH WORK.

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

         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 to avoid 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.

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

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

    D.   Prime as soon as possible after surfaces have been dried
         but before rust has a chance to reform.  

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

    F.   Fill all holes, depressions and cracks with metal filler
         and sand to conform with surrounding contours.  See
         05010-12-R for guidance.

    G.   Prime and paint all surfaces.  For guidance see 05010-13-S
         "Primers and Paints for Wrought Iron, Cast Iron and
         Steel", 05010-18-R "Applying a Sacrificial Coating to
         Wrought Iron, Cast Iron and Steel", and 09900-07-S
         "General Guidelines for Painting Exterior and Interior
         Surfaces".

3.04 PROTECTION

    A.   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
 


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