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Historic Preservation - Technical Procedures

Spectitle:

Repairing & Replacing Corroded Tinplate & Terneplate Roofing

Procedure code:

0761009R

Source:

Hspg Prepared For Nps - Sero

Division:

Thermal And Moisture Protection

Section:

Sheet Metal Roofing

Last Modified:

10/22/2014

Details:

Repairing & Replacing Corroded Tinplate & Terneplate Roofing



REPAIRING AND REPLACING CORRODED TINPLATE AND TERNEPLATE ROOFING


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on repairing corroded
         tinplate and terneplate roofing.

    B.   "Tin" roofing is actually covered with sheets of tinplate
         or terneplate.  

         1.   Pure tin is soft, ductile, malleable, bluish-white
              in color, non-magnetic, and fairly resistant to
              corrosion.  

         2.   In the early days of the tinplate industry, iron
              sheets were coated with tin, while later in the
              nineteenth century steel sheets replaced the iron
              sheets.  

         3.   During the early nineteenth century tinplates were
              used as a roofing material but were gradually
              replaced by terneplate, an iron or steel sheet
              coated with an alloy of lead and tin.  

         4.   Weather resistance is due primarily to the lead;
              tin improves the bond to the base plate metal.

    C.   Historic Structures Precautions:

         1.   Historic and regional roofing craftsmanship
              examples characteristic of the structure are to be
              treated with sensitivity, to be preserved and
              followed.

         2.   Replacement and repair  work shall be equal to
              original workmanship.  Roofing repair shall match
              prototype exposure, size, pattern and material.
              Reinstall using existing or compatible fastenings.
              Before repairing or replacing roofing, prepare a
              working drawing showing sheet width and length
              between seams.  Prepare typical exposed seam
              details and fastening patterns for reroofing
              guidance.

    D.   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).

1.02 SYSTEM DESCRIPTION

    A.   There should be no evidence of pitting, nor signs of
         wearing, holes, or rust around drip points.

    B.   Paint film should be sound, with no cracks, peeling
         layers, or rust showing through.  The metal panels should
         be properly and securely attached, and the ends of the
         panels should be laying flat.

    C.   Tinplate and terneplate were most commonly used in sheets
         10 inches by 14 inches or in multiples thereof (14 inches
         by 20 inches, 20 inches by 28 inches, and so forth) for
         roofing.

1.03 DEFINITIONS

    A.   Tin pest or tin plague - When pure tin is heated at low
         temperatures for long periods of time, it deteriorates by
         disintegrating and crumbling to a nonmetallic gray
         powder.  THIS TYPE OF DETERIORATION IS USUALLY NOT A
         PROBLEM WITH TINPLATE SHEETS USED FOR ARCHITECTURAL
         PURPOSES.

    B.   Breaking of the patina - When the tin- or terneplating
         corrodes or breaks, exposing the iron or steel below to
         oxygen.  Deterioration is then accelerated by galvanic
         corrosion between the tin and iron.

         1.   When exposed to the atmosphere, tin develops a thin
              film of stannic oxide, which helps resist
              corrosion.  

         2.   Pure tin is mildly corroded by exposure to acids,
              marine atmospheres, and certain alkalis.  Tinplate
              roofing, however, is generally very durable as long
              as the tin or terne coating maintains its
              integrity.  

    C.   Galvanic corrosion - The increased corrosion of a metal
         due to its contact with another metal, or in some cases,
         the same metal.  Tinplate and terneplate roofing may be
         corroded by any of the following:

         1.   Contact with copper, (i.e. in gutters).

         2.   Contact with asphaltic and bituminous roofing
              compounds and building papers.

         3.   Contact with paints containing acids, bitumen,
              asphalt and aluminum.

    D.   Condensation corrosion - Tinplate roofing can corrode on
         the underside from water vapor condensation if the tin is
         not protected by a coating of paint and/or a nonacidic
         vapor barrier.

1.03 DELIVERY, STORAGE AND HANDLING

    A.   Packing and Shipping:  Manufacturer's delivery or job
         markings on metal, and adhesives for manufacturer's
         labels shall be a neutral material.  In no case shall
         such material be alkaline; any staining of the metal by
         alkaline materials will be cause for the rejection of the
         piece.

    B.   Storage and Protection:

         1.   Material storage:  Keep uninstalled roof materials
              under cover, dry, free from scratches,
              condensation, and distortion during delivery,
              storage, and handling.

         2.   Salvage storage:  Historic material to be used as
              example of original construction shall be stored as
              directed by the Regional Historic Architect.  Often
              original roof metal scrap pieces with exposed
              weather can be found in attic spaces.

1.04 PROJECT/SITE CONDITIONS

    A.   Environmental Requirements:

         1.   Do not repair metal roof in misty or rainy weather.
             
         2.   Do not apply metal roofing to wet roof sheathing.

         3.   At the end of each work day, provide building
              protection for any exterior roofing element removed
              for repair or replacement.

         4.   Remove only a quantity of roofing which may be
              repaired on that same day.  At the end of the day,
              use 15 pound roofing felt or polyethylene sheeting
              to drape over missing roofing and insert under roof
              unit laps or temporarily secure areas of existing
              roofing and roof as required to make roof
              watertight and windproof.

1.05 MAINTENANCE

    A.   Check annually for failing paint or rust spots.

    B.   Keep the roof clear of debris, and trim all overhanging
         branches that might cause mechanical damage.

    C.   Inspect the secureness of cleats and fasteners and the
         condition of the sheet metal after particularly heavy
         storms.


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.   Solder:  Solder for repair should be composed of 50% pig
         lead and 50% block tin and should be applied using an
         appropriate flux, i.e. zinc chloride for terne or
         tinplate.

    B.   Nails:  Terne and tinplate sheets should be fastened
         using only terne or tinplate cleats and galvanized iron
         or steel nails.  Copper alloy cleats and nails should not
         be used because of the potential for galvanic corrosion.
         Use nails with large flat heads and barbed or deformed
         shanks.  They shall not be smaller than No. 12 gauge
         (0.109 inch) and of sufficient length to penetrate
         roofing boarding.

    C.   Cleats:  Cleats shall be 2 inches wide by about 3 inches
         long, spaced 12" o.c., and shall be made of tinplate or
         galvanized iron or steel.

    D.   Sheetmetal which matches original in weight, tempe= r,
         color, etc.

    E.   Chemical paint stripper (see 05010-17-R)

    F.   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.

2.02 EQUIPMENT

    A.   Chicken ladder, safety belt or harness

    B.   Protective gloves and gear

    C.   Straight snips for cutting straight or slightly curved
         lines in sheet metal 24 gauge or lighter

    D.   Soldering copper, soldering iron

    E.   Handy tongs for bending the edges of the solder

    F.   Metal seamer


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Make inspection from ground, or from above if possible.

    B.   Inspect for build-up of debris and vegetation such as
         moss or lichen, which may form dams and stop natural
         drainage, resulting in various types of deteriorations.
         This is more apt to occur on north slopes.

    C.   Leaks:  Inspect the underside of the roof deck from the
         attic to detect leaks.  Flashings are the most vulnerable
         points.  Therefore, inspect the underside carefully at
         all flashing points for evidence of leakage such as water
         stains.

    D.   Note presence of modern roof appurtenances such as
         plumbing stacks, air vents, or TV antennas.  These all
         create maintenance problems.

    E.   In addition to scheduled inspections, inspect after each
         exposure to unusually severe weather conditions such as
         strong winds, hail, or long continuous rains.

3.02 PREPARATION

    A.   Protection:

         1.   Do not work on wet snow covered roofs.  Work on
              cleated walkboards.

         2.   Safety on the roof:
   
              a.   Wear rubber-soled shoes that have non-slip or
                   grid type tread (preferably sneakers with a
                   high top for good ankle support).  Avoid
                   wearing loose clothing.
   
              b.   Wear a safety belt or harness and secure it to
                   a substantial chimney or other substantial
                   object secured to the building.  Leave only
                   enough slack to work comfortably in one area,
                   and adjust the slack to work on other sections
                   of the roof.

              c.   Be sure the roof is clear of debris and water.

              d.   For steep roofs:  On roof slopes greater than
                   4 inches rise per foot, give special
                   consideration to both footing and materials
                   handling.

                   1)   Secure chicken ladders or cleats at the
                        top for adequate footing.

                   2)   Hang and secure approved safety lines
                        of sufficient strength.

                   3)   Carry a limited number of materials so
                        that balance and footing are not
                        impaired.

                   4)   Use scaffolding, ladders, and working
                        platforms as required to execute the
                        work.  Scaffolding legs shall be planked
                        to distribute load to not exceed 20 pounds per
                        square foot on roofs.  Ladders shall not
                        be supported on hanging gutters.  They
                        may be distorted which can affect the
                        slope to drain.

3.03 ERECTION, INSTALLATION, APPLICATION

    A.   Repairing Tinplate or Terneplate Roofing:

         1.   Evaluate the extent of damage to the metal due to
              corrosion in order to determine the appropriate
              repair.

         2.   For early stages of attack where the metal has not
              thinned or pitted:

              a.   Eradicate the cause of attack.

              b.   The exposed area will weather in the normal
                   way if it is no longer exposed to attack.

         3.   For rust-outs in sheet metal, repair by soldering a
              patch of the same metal over the damaged area.  If
              joint has opened, or a nail has popped up and
              punctured the tin, it can be repaired by cleaning
              the area and resoldering.

              NOTE:  DO NOT USE MATERIALS OTHER THAN TINPLATE OR
              TERNEPLATE TO PATCH TINPLATE.  GALVANIC CORROSION
              WILL OCCUR.

              NOTE:  DO NOT USE ASPHALT ROOFING COMPOUND OR
              ALUMINUM-BASED ROOF COATINGS TO MAKE PATCHES.
              THESE REPAIRS SELDOM LAST, CAN CAUSE GREATER DAMAGE
              AND ARE DIFFICULT TO UNDO.

              a.   Thoroughly clean the area to be patched of all
                   rust and/or roofing cement - clean to expose
                   shiny metal.

              b.   With chemical paint stripper, remove any paint
                   from the metal surrounding the patch.  See
                   05010= -17-R for guidance on paint removal.

              c.   Remove any roofing tar by scraping with a
                   spatula.  Scrub the surface with mineral
                   spirits.

              d.   Clean both the roof and the patch piece by
                   scouring with a wire brush or steel wool.

              e.   Fold the edges under one (1) inch and snip off the
                   corners; this makes the patch stronger and
                   takes off easily damaged sharp corners.

              f.   Apply patch and hold in place with weight or
                   nails.

                   NOTE:  To avoid galvanic corrosion if nails
                   are used, make sure they are of the same metal
                   as the roof.

              g.   Brush zinc chloride flux around the patch
                   edges.

              h.   With either a 3- to 5-lb. propane-heated
                   soldering copper, or a 200-watt electric
                   soldering iron, melt 50/50 lead-tin solder
                   into and over the seam.  

                   NOTE:  DO NOT TRY TO WELD THE PATCH, AND DO
                   NOT TRY TO SOLDER WITH A BLOWTORCH.  HIGH-HEAT
                   METHODS CAN DAMAGE LIGHT-GAUGE METAL AND START
                   FIRES IN A WOOD CORNICE.

                   NOTE:  THE PATCH MUST NOT MOVE UNTIL AFTER THE
                   SOLDER COOLS, OR ELSE THE SOLDER WILL START TO
                   BREAK.  IF THE PATCH MOVES, START OVER.

                   CAUTION:  TAKE PRECAUTIONS WHEN USING FLAME
                   TOOLS FOR SOLDERING ON THE ROOF.  THE DANGER
                   OF SETTING THE ROOF ON FIRE IS ALWAYS PRESENT.

              i.   After the solder cools, wipe the patched area
                   with mineral spirits, rinse off all excess
                   flux with water and wipe dry.

              j.   Prime all the bare metal with a suitable metal
                   primer.  If patch is galvanized, terne, or
                   tinplate, paint patch to match rest of roof.

    B.   Replacing Sections of Tinplate and Terneplate Roofing:

         A.   Replace rusted or damaged sections with new
              tinplate or terneplate of similar composition,
              configuration, and construction.

              NOTE:  DO NOT USE MATERIALS OTHER THAN TINPLATE OR
              TERNEPLATE TO PATCH TINPLATE.  GALVANIC CORROSION
              WILL OCCUR.

              NOTE:  IF THE ENTIRE ROOF MUST BE REPLACED,
              SUITABLE REPLACEMENT MATERIALS MAY ALSO INCLUDE
              LEAD-COATED COPPER OR TERNE-COATED STAINLESS STEEL.
              SEE SECTION 3.03 D. BELOW.

         B.   Fasten tin - and terneplate sheets using only tin -
              or terneplate cleats and galvanized iron or steel
              nails.  

              NOTE:  DO NOT USE COPPER ALLOY CLEATS OR NAILS
              BECAUSE GALVANIC CORROSION WILL OCCUR BETWEEN THE
              TIN AND THE COPPER.

         C.   Prime and paint replacement tinplate or terneplate
              sheets:  

              1.   Shop-coat both sides of sheet metal with one,
                   preferably two coats of metal primer of top quality
               .   and specified for use on metal roofing by manufacturer.
                   Protect underside of sheet metal from
                   condensation.

              2.   Add a coat of compatible high-gloss oil-base
                   finish paint prior to installation as an added
                   measure of protection.  

              3.   Apply finish coat immediately after
                   installation, and a second coat after two
                   weeks.

         D.   If replacing entire roof, lead-coated copper or
              terne-coated stainless steel may be substituted for
              tinplate or terneplate.  

              1.   Lead-coated copper and terne-coated stainless
                   steel are more durable and require less
                   maintenance, eventhough there is a higher
                   initial cost.

              2.   Match the size, configuration, and
                   construction details of the original roof.
                   Paint substitute materials to match the
                   original roof color.  

              NOTE:  USE CAUTION WHEN SUBSTITUTING TERNE-COATED
              STAINLESS STEEL IN THE REPLACEMENT OF TINPLATE
              ROOFING OR SIDING.  TERNE-COATED STAINLESS STEEL IS
              MORE DIFFICULT TO FORM AND SOLDER THAN TERNEPLATE.

                             END OF SECTION
 


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