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Historic Preservation - Technical Procedures
Replacing Broken Glass In Wood And Metal Windows
Hspg Prepared For Nps - Sero
Doors And Windows
Glass & Glazing
Replacing Broken Glass In Wood And Metal Windows
REPLACING BROKEN GLASS IN WOOD AND METAL WINDOWS
A. This procedure includes guidance on replacing cracked,
broken or missing panes of glass, replacing cracked or
missing window putty and cleaning glazing.
B. Broken or cracked glass panes and missing or cracked
window putty may be the result of weather, neglect, or
vandalism. In any case, it is a matter that requires
C. For temporary repairs to broken glass until permanent
replacement can be performed, see 08800-02-R "Temporary
Patching of Chips and Cracks in Window Glazing".
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. A window glass is in proper condition when it is set
securely and tightly into the window frame, is properly
caulked, and is not scratched, cracked, or broken.
1.03 SEQUENCING AND SCHEDULING
A. Coordination of Work: The coordination of glass
repairing/replacing with other proposed work on the
windows must be considered. For example, if window
elements (frame, sash, trim, hardware, lintel, sill,
etc.) paint removal, cleaning, or repairing is
anticipated, it is generally better to postpone glazing
work until after the completion of these activities.
A. For Glass:
1. Advanced Coating Technology
2. AFG Industries, Inc.
3. Cardinal IG
4. Environmental Glass Products
5. Falconer Glass Industries
6. Ford Glass Division
7. Guardian Industries Corp.
8. Hordis Brothers, Inc.
9. LOF Glass, Inc.
10. Pilkington Sales (North America) Limited (wire
11. PPG Industries, Inc.
13. Spectrum Glass Prod. Div., H. H. Robertson Co.
14. Viracon, Inc.
A. Linseed oil putty (for wood windows)
B. Glazing compound or elastomeric sealant (for metal
1. Two-part polysulfide glazing sealant such as "Chem-
Calk 200" (Bostik Construction Products Division),
"Synthacalk GC-5" (Pecora Corp.), or approved
2. One-part non-acid-curing silicone glazing sealant
such as "Chem-Calk 1000" (Bostik Construction
Products Division), "Dow Corning 790" (Dow Corning
Corp.), "864" (Pecora Corp.), "Omniseal" (Southern
Building Products Div., Rexnord Chemical Products,
Inc.), "Spectrum 1" (Tremco, Inc.), or approved
3. These glazing sealants should comply with the
a. Must be compatible with other materials with
which they will come into contact.
b. Must be suitable for applications indicated
and conditions at time of installation.
c. Colors: Provide color of exposed sealants as
selected by the RHPO from manufacturer's
d. Hardness: Consult the manufacturer to
determine the actual hardness recommended for
the conditions of installation and use.
e. Sealants and materials used with laminated
glass to be 100% solids, containing no
C. Materials for Removing Glazing Compound:
1. Paint remover
Mineral Spirits (for lacquer thinner):
a. A petroleum distillate that is used especially
as a paint or varnish thinner.
b. Other chemical or common names include
Benzine* (not Benzene); Naphtha*; Petroleum
spirits*; Solvent naphtha*.
c. Potential Hazards: TOXIC AND FLAMMABLE.
d. Safety Precautions:
1) AVOID REPEATED OR PROLONGED SKIN CONTACT.
2) ALWAYS wear rubber gloves when handling
3) If any chemical is splashed onto the
skin, wash immediately with soap and
e. Available from construction specialties
distributor, hardware store, paint store, or
printer's supply distributor.
Muriatic acid (generally available in 18 degree and
20 degree Baume solutions):
a. A strong corrosive irritating acid.
b. Other chemical or common names include
Chlorhydric acid; Hydrochloric acid; Hydrogen
chloride; Marine acid*; Spirit of salt*;
Spirit of sea salt*.
c. Potential Hazards: TOXIC, CORROSIVE TO FLESH;
CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS,
d. Available from chemical supply house,
drugstore or pharmaceutical supply
distributor, or hardware store.
Linseed oil or thinned primer
D. Glass to match existing (see 2.01 Manufacturers)
E. Glazier's points (if old ones are not usable)
F. Neoprene setting blocks and shims
G. Clean, potable water
I. Paper towels or rags
A. For Replacing a Window Pane:
1. Goggles and gloves for protection when removing
2. Hammer and chisel
3. Soldering iron wrapped in foil, or a heat plate to
remove old glazing compound
4. Pliers and chisels for maneuvering glazier's points
6. Very fine 0000 steel wool
7. Paint brush to apply primer
8. Glass cutter and straight edge
9. Putty knife or glazier's tool for smoothing glazing
A. Check for cracked, broken, chipped, or otherwise damaged
B. Inspect glazing putty on both sides of pane for cracked,
loose, or missing sections which allow water to attack
the metal components, especially at the joints.
C. Examine the condition of the metal window components for
corrosion, loose connections, etc.
1. Does glass rattle or move in the glazing system?
2. Are glass stops intact?
D. Inspect all surfaces which are to receive glass and/or
glazing sealant for any defects or condition which will
interfere with, or prevent a satisfactory installation.
Correct all defects prior to installation of new glass.
E. Verify the glass type in each window type prior to the
installation of new glass.
A. Surface Preparation:
1. Prior to reglazing, remove all oil, dirt, rust and
other materials from the glass and the metal
framing members using solvents such as toluol or
xylol or using other rust removal techniques.
2. Prime and clean all glazing rabbets prior to
3. Maintain glass in a reasonably clean condition
during construction so that it will not be damaged
by corrosive action.
3.03 ERECTION, INSTALLATION, APPLICATION
NOTE: BE SURE TO WEAR HEAVY GLOVES AND OTHER PROTECTIVE GEAR
WHEN HANDLING GLASS.
A. Remove existing glazing compound using one of the
following four methods:
1. A hammer and chisel (at the risk of adjacent
2. A soldering iron wrapped in foil or heat plate (can
soften the compound to ease removal).
3. Chemicals such as a paint remover, mineral spirits
or muriatic acid.
CAUTION: THESE ARE POTENTIALLY HARMFUL AND SHOULD
BE USED IN WELL VENTILATED AREAS ONLY.
4. Linseed oil (if the putty is linseed oil based -
which most are).
B. Remove glazier's points with pliers and reserve for
C. Special Procedures For Wood Windows:
1. Thoroughly clean the sash of any remaining compound
and sand grooves smooth.
2. Apply linseed oil or thinned oil based primer to
grooves to prevent wood from absorbing oil from new
putty. If primer is used it should be applied in
two coats, 24 hours apart.
D. Special Procedures For Metal Windows:
1. While the glass is out, clean/repair/replace, prime
and paint the metal frame, the mullions, muntins,
sash, and other window components prior to glass
2. Apply glazing compound to the grooves of the window
3. Salvage, repair, and reinstall existing metal
glazing clips, glazing beads, and other fasteners
that hold the glass to the sash. Where existing
metal glazing clips are missing supply and install
new wire (metal) glazing clips to match existing.
E. Cut new glass 1/8" smaller in length and width, than the
1. Practice cutting on an unusable piece of glass
2. Make sure the working surface is perfectly clean
and do not press too hard with the glass cutter.
a. Old window glass is often quite thin, and also
contains impurities and irregular internal
b. Pressure from the wheel cutter on even a tiny
piece of dirt can cause the pane to split or
"run" in all the directions.
3. Cut straight pieces, use a straight edge as a
a. Score the piece with one firm, even stroke of
a sharp glass cutter dipped in oil.
b. Tap along the line to break it off. Plastic
glass-cutter's pliers can also be used to
break the glass with a quick, downward snap.
4. For curved pieces:
a. Make a template out of thick cardboard or
masonite board for scoring.
b. Score the piece with a sharp glass cutter
following the edge of the template. DO NOT
TRY TO SCORE THE PIECE FREEHAND.
c. Starting in the middle and working toward both
ends gradually, use the ball end of the cutter
and tap along the underside of the score. The
score-line should fracture along the curve.
Gradual curves may be broken off in one piece,
but extreme curves must be cut by removing one
small section of glass at a time.
5. For pieces with complex cuts, use a stained glass
F. Apply a small bead of glazing compound around the groove
to cushion the new glass and then install glass spaced
evenly on all sides.
G. Replace glazier's points 4" to 6" apart around perimeter,
tap them halfway in.
H. Form glazing compound into a 3/8" diameter rope and press
around perimeter of new glass. Using a putty knife,
triangulate the surface of the compound. Hold the knife
at a 45 degree angle and align compound with the muntin
on the interior.
I. Allow the compound to dry for a week, then paint
accordingly with a 1/16" moisture seal extending onto the
surface of the glass.
A. After the installation of each light, remove all markings
and labels from the glass.
B. Wash the glass on both sides with a mild solution of
NOTE: IN NO CASE SHALL ALKALINE OR ABRASIVE AGENTS BE
USED TO CLEAN GLASS. CARE SHALL BE TAKEN DURING CLEANING
TO AVOID SCRATCHING OF GLASS SURFACES BY USING GRITTY
MATERIALS OR DRY CLOTHS.
C. Rinse thoroughly with clean, clear water or as
recommended by the glass manufacturer.
D. Dry both sides of glass with a soft cotton dry cloth.
E. Clean and trim excess glazing compound from glass, frames
and sash promptly after installation.
F. Clean adjacent surfaces if spills have occurred.
END OF SECTION