Repairing & Replacing Corroded Tinplate & Terneplate Roofing
- Procedure code:
- Hspg Prepared For Nps - Sero
- Thermal And Moisture Protection
- Sheet Metal Roofing
- Last Modified:
REPAIRING AND REPLACING CORRODED TINPLATE AND TERNEPLATE ROOFING
A. This procedure includes guidance on repairing corroded
tinplate and terneplate roofing.
B. "Tin" roofing is actually covered with sheets of tinplate
1. Pure tin is soft, ductile, malleable, bluish-white
in color, non-magnetic, and fairly resistant to
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
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
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
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
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
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
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
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
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
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
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.
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
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
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
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,
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*;
3. Potential Hazards: TOXIC AND FLAMMABLE.
4. Safety Precautions:
a. AVOID REPEATED OR PROLONGED SKIN CONTACT.
b. ALWAYS wear rubber gloves when handling
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.
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
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
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.
1. Do not work on wet snow covered roofs. Work on
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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