Making Repairs To Sheetmetal Flashing

Procedure code:
762004S
Source:
Maintenance, Repair & Alteration Of Hstrc Bldgs - Gsa/Pbs
Division:
Thermal and Moisture Protection
Section:
Sheet Metal Flashing And Trim
Last Modified:
04/20/2015


MAKING REPAIRS TO SHEETMETAL FLASHING


PART 1---GENERAL

1.01 SUMMARY

A. This procedure includes guidance on repairing various
types of problems found in sheetmetal flashing work.
Typical causes of the problems are also listed.
GENERALLY, THIS WORK SHOULD BE PERFORMED BY AN
EXPERIENCED CONTRACTOR.

B. Flashing is an integral part of a roofing system and
protects against water infiltration at roof hips and
valleys; penetrations such as chimneys; where roofing
meets a vertical surface such as a parapet or at a porch
roof; or at drip edges.

C. Copper, with copper nails, galvanized sheet metal with
hot-dipped galvanized nails, or terne-coated stainless
steel with stainless steel nails are the primary
materials used for flashing.

CAUTION: THE DIFFERENT METALS SHOULD NOT BE MIXED.
RAINWATER RUN-OFF FROM COPPER FLASHING WILL CORRODE BOTH
GALVANIZED SHEET METAL AND STAINLESS STEEL THROUGH
GALVANIC ACTION. GREAT CARE SHOULD BE TAKEN TO USE A
FLASHING MATERIAL COMPATIBLE WITH THE REST OF THE ROOF
SYSTEM.

D. Safety Precautions:

1. Wear rubber-soled shoes that have non-slip or grid
type tread (preferably high top sneakers for good
ankle support. Avoid wearing loose clothing.

2. Wear a safety belt or harness secured to a
substantial chimney or to a window on the opposite
side of the building. Leave only enough slack to
work comfortably in one area, and adjust the slack
as work proceeds on other sections of the roof.

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

4. Do not work on wet or snow covered roofs, or on a
brittle roof surface. Work on cleated walkboards.

5. On steep roofs:

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

b. Safety lines should be tied and secured with
rope of sufficient strength.

c. Carry a limited amount of materials so that
balance and footing are not impaired.

E. Flashing may deteriorate for a number of reasons. Some
common problems are listed below:

1. Cracks: Common at bends in sheetmetal work; often
caused by metal fatigue and erosion.

2. Buckling: Occur in running lengths of sheetmetal;
often caused by inadequate provision for expansion
and contraction, inadequate gauge of metal,
adhesion of asphalt building felt to back of metal,
or movement in wood backing of metal.

3. Splitting of solder at the seam: Often caused by
using too soft a solder, not pre-tinning the seams,
movement in metal on either side of the seam,
cracked, deteriorated or improper sealant.

4. Cracked sealant: Often caused by deteriorated or
improper sealant, or loss of cohesion due to
movement of metal.

5. Crumbling and powdering of the metal: Often caused
by galvanic action from two incompatible metals,
atmospheric corrosion, erosion, or deterioration of
the galvanic coating.

6. Pitting and corrosion: Pitting is often caused by
the settling of chemical particles from the
environment; corrosion is often caused by galvanic
action from two incompatible metals or the
decomposition of atmospheric chemicals on the
surface.

7. Blister-like mounds: Most common in running copper
work; often caused by insufficient number of
expansion joints for the length, or the gauge of
metal is too light.

8. Fastener deterioration: Often caused by
incompatibility of fastener with base metal.

F. 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).

G. See 07620-03-R and 07631-03-R for guidance on patching
sheetmetal. For more extensive flashing repairs, see
07620-02-R.

1.02 SYSTEM DESCRIPTION

A. Flashing is performing as it was intended when there are
no cracks, splits or torn areas. It should not show any
signs of corrosion. Where flashing meets a vertical
surface, all cap flashing should be secure and the
flashing itself should be soundly anchored.

1.03 MAINTENANCE

A. Check flashings as a part of the annual roof inspection
(preferably in late autumn). Repair defects immediately
because flashing is a critical part of the roof fabric.
Small leaks in the flashing which are neglected may lead
to major faults in the roof system. See also Section
3.01 Examination below.


PART 2---PRODUCTS

2.01 MANUFACTURERS

A. Dow Corning Corporation
www.dowcorning.com


B. General Electric Silicone Products Div.,
www.ge.com

C. 3M Consumer Products Group
wwwshop3m.com

2.02 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. Sheetmetal flashing, of gauge and type of metal to match
or be compatible with existing.

B. Metal fasteners, compatible with existing and/or new
metal.

C. Solder

D. Rosin soldering flux

E. Bituminous felt backing or wood backing

F. Metal primer such as Rust-Oleum, or approved equal

G. 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.

H. Backing Rod - closed cell polyethylene foam or butyl rod
stock (diameter of rod should be 25% greater than width
of joint).

I. Sealant such as (Dow Corning, General Electric, 3M) or
approved equal.

J. Clean, soft cloths

2.03 EQUIPMENT

A. Soldering copper, soldering iron

B. Safety belt or harness; protective gloves and gear.

C. Chicken ladder; ladders and scaffolding.

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

E. Tongs for bending the edges of the solder

F. Wire brush or steel wool

G. Stiff bristle brushes


PART 3---EXECUTION

3.01 EXAMINATION

A. Flashing is usually a weak part of the roofing system
and, therefore, should be inspected regularly for damage
or deterioration.

1. Outside, inspect flashing for splits, holes or
corrosion.

2. Inside, inspect the underside of the roof deck for
evidence such as water stains or damp wood; inspect
the ceiling and walls around fireplaces and chimney
flues for stained or spalling plaster or wallpaper,
or peeling paint.

3. Look for daubs of roofing cement on the flashing -
this is an indication of previous leaks. This type
of repair is not recommended and may not have
completely stopped the leak.

4. Look for uncaulked openings at the tops of flashing
where water may enter.

3.02 ERECTION, INSTALLATION, APPLICATION

NOTE: WHEN REPLACING SHEETMETAL FLASHING, USE GAUGE OF METAL
SUITABLE FOR STRENGTH AND REQUIRED PERFORMANCE. INSTALL
ACCORDING TO METAL MANUFACTURER.

CAUTION: BE SURE REPLACEMENT METALS ARE CHEMICALLY COMPATIBLE
OR CORROSION BY GALVANIC ACTION IS LIKELY TO OCCUR.

A. For Cracks:

1. Remove entire section of cracked flashing; cut out
damaged area the full width of the piece.

2. Replace piece with similar metal; join the new
piece using a lock seam, loose, sealant filled seam
or by lapping, riveting and soldering.

NOTE: THE METHOD OF JOINING WILL DEPEND ON THE
TYPE OF METAL SELECTED AND THE SURROUNDING
CONDITIONS.

B. For Outward Buckling:

1. Examine flashing to determine cause of buckling.
Lack of expansion joints for length of sheetmetal
may have lead to the problem.

2. Remove entire length of affected flashing.

3. Inspect condition of backing material:

a. For wood, remove and replace damaged material
as required.

b. For bituminous felt, remove felt and replace
with heavy weight rosin-sized sheathing paper.

4. Clean bituminous felt with a solvent such as
mineral spirits.

5. Reinstall the sheetmetal flashing; add expansion
joints as needed.

C. For Splitting of Solder at the Seam:

1. If damage is localized, remove entire length of
flashing and replace it to match existing.

2. If damage is widespread, replace all affected metal
with new metal to match existing or substitute
compatible metal.

D. For Cracked Sealant:

1. Remove sealant.

2. Clean metal using a solvent such as mineral
spirits.

3. Check width of joint to make sure it is at least
1/4 inch wide. If is less than 1/4 inch, carefully
move the metal edges to allow a 1/4 inch gap.

4. Prime surfaces of joint following manufacturer's
instructions.

5. Check depth of joint. If joint is at deeper than
5/8 inches and there is no backing material, insert
a continuous backing rod.

NOTE: DISTANCE BETWEEN FACE OF BACK-UP MATERIAL
AND FACE OF JOINT SHOULD BE BETWEEN 1/4 TO 3/8
INCH.

6. Fill the joint with sealant following
manufacturer's instructions.

7. Immediately remove excess sealant from the face of
the metal.

E. For Crumbling and Powdering Metal:

1. If damage is localized, remove entire length of
flashing and replace it to match existing.

2. If damage is widespread, replace all affected metal
with new metal to match existing or substitute
compatible metal.

F. For Pitting and Corrosion:

1. If damage is localized, remove entire length of
flashing and replace it to match existing.

2. If damage is widespread, replace all affected metal
with new metal to match existing or substitute
compatible metal.

G. For Blisters:

1. Carefully inspect the affected metal; examine
expansion joints to see that they are properly
formed or do not exceed the recommended spacing.

2. Cut out existing expansion joints; fabricate and
install new joints with matching metal.

3. Cut out other problem areas the full width of the
metal; replace with new metal, compatible with
existing and of same gauge.

4. Fasten edges by soldering and riveting.

H. For Fastener Deterioration:

1. Remove all fasteners from sheetmetal.

2. Remove residue from around the holes by cleaning
with a light abrasive material such as steel wool,
emery cloth or other.

3. Replace fasteners with new ones made of compatible
metal and neoprene washers to make a weathertight
connection.

NOTE: For aluminum and stainless steel metal, use
stainless steel fasteners; for copper, lead-coated
copper or brass metal work, use brass or copper
fasteners; for copper-clad stainless steel metal,
use stainless steel, brass, or bronze fasteners;
for zinc, lead and galvanized steel metal, use
galvanized steel or coated steel fasteners.

4. If the metal around the fastener connections is too
deteriorated to prevent leakage and enable a
weathertight connection, remove entire length of
flashing and replace it to match existing or
substitute compatible metal.


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