Repairing and Replacing Corroded Tinplate and Terneplate Roofing

Procedure code:
761009S
Source:
Division:
Thermal and Moisture Protection
Section:
Sheet Metal Roofing
Last Modified:
08/16/2016

PART 1---GENERAL

1.01 SUMMARY

  1. This specification provides guidance on repairing corroded tinplate and terneplate roofing.

  2. "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.

  3. 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.

  4. 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)

1.02 SYSTEM DESCRIPTION

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

  2. 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 lying flat.

  3. 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

  1. Tin Pest/Tin Plague: When pure tin is heated at low temperatures for long periods of time, it disintegrates into a nonmetallic gray powder. However, this type of deterioration is usually not a problem for tinplate sheets used for architectural purposes.

  2. 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.

  3. 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.

  4. 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

  1. 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.

  2. 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. Original roof metal scrap pieces with exposed weather can often be found in attic spaces.

1.04 PROJECT/SITE CONDITIONS

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 in the same day.

  5. 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

  1. Check annually for failing paint or rust spots.

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

  3. 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 (*).

  1. 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.

  2. 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.

  3. Cleats: Cleats shall be 2 inches wide by about 3 inches long, spaced 12 inches apart on center, and shall be made of tinplate or galvanized iron or steel.

  4. Sheet metal which matches original in weight, temper, color, etc.

  5. Chemical paint stripper (see "Removing Paint from Wrought Iron, Cast Iron and Steel Using Chemical Methods" for more information).

  6. 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.

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

2.02 EQUIPMENT

  1. Chicken ladder, safety belt or harness

  2. Protective gloves and gear

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

  4. Soldering copper, soldering iron

  5. Handy tongs for bending the edges of the solder

  6. Metal seamer

PART 3---EXECUTION

3.01 EXAMINATION

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

  2. 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.

  3. 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.

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

  5. 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

Protection:

  1. Work on cleated walkboards.

  2. Do not work on wet snow covered roofs.

  3. Wear rubber-soled shoes that have non-slip or grid type tread (preferably sneakers with a high top for good ankle support).

  4. Avoid wearing loose clothing.

  5. 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.

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

  7. 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.

  8. Use scaffolding, ladders, and working platforms as required to execute the work.

    1. Scaffolding legs shall be planked to distribute load so as not to exceed 20 pounds per square foot on roofs.

    2. Ladders shall not be supported on hanging gutters. They may be distorted, which can affect the slope to drain.

3.03 ERECTION, INSTALLATION, APPLICATION

  1. 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:

      1. Eradicate the cause of attack.

      2. 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.

    4. 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.

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

    2. With chemical paint stripper, remove any paint from the metal surrounding the patch (see "Removing Paint from Wrought Iron, Cast Iron and Steel Using Chemical Methods" for guidance on paint removal).

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

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

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

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

NOTE: If nails are used, make sure they are of the same metal as the roof in order ot avoid galvanic corrosion.

    1. Brush zinc chloride flux around the patch edges.

    2. 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.

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

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

  1. Replacing Sections of Tinplate and Terneplate Roofing:

    1. 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.

    1. Fasten tinplate and terneplate sheets using only tinplate 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.

    1. Prime and paint replacement tinplate or terneplate sheets:

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

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

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

  1. Replacing Entire Roof:

    1. If the entire roof is to be replaced, lead-coated copper or terne-coated stainless steel may be substituted for tinplate or terneplate.

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

    3. Match the size, configuration, and construction details of the original roof. 

    4. 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

Last Reviewed 2016-08-16