Skip to main content

Historic Preservation - Technical Procedures

Spectitle:
Replacing Broken Glass In Wood And Metal Windows

Procedure code:
0880001R

Source:
Hspg Prepared For Nps - Sero

Division:
Doors And Windows

Section:
Glass & Glazing

Last Modified:
02/24/2012

Details:
Replacing Broken Glass In Wood And Metal Windows



REPLACING BROKEN GLASS IN WOOD AND METAL WINDOWS


PART 1---GENERAL

1.01 SUMMARY

    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
         immediate attention.

    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

         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.   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.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    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
              glass)

         11.  PPG Industries, Inc.

         12.  Saint-Gobain/Euroglass

         13.  Spectrum Glass Prod. Div., H. H. Robertson Co.

         14.  Viracon, Inc.

2.02 MATERIALS

    A.   Linseed oil putty (for wood windows)

    B.   Glazing compound or elastomeric sealant (for metal
         windows):

         1.   Two-part polysulfide glazing sealant such as "Chem-
              Calk 200" (Bostik Construction Products Division),
              "Synthacalk GC-5" (Pecora Corp.), or approved
              equal.

         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
              equal.

         3.   These glazing sealants should comply with the
              following requirements:

              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
                   standard colors.

              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
                   solvents.

    C.   Materials for Removing Glazing Compound:

         1.   Paint remover

         -OR-

              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
                        mineral spirits.

                   3)   If any chemical is splashed onto the
                        skin, wash immediately with soap and
                        water.

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

         -OR-

              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,
                   FLAMMABLE.

              d.   Available from chemical supply house,
                   drugstore or pharmaceutical supply
                   distributor, or hardware store.

         -OR-

              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

    H.   Ammonia

    I.   Paper towels or rags

2.03 EQUIPMENT

    A.   For Replacing a Window Pane:

         1.   Goggles and gloves for protection when removing
              broken glass

         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

         5.   Sandpaper

         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
              compound


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Check for cracked, broken, chipped, or otherwise damaged
         glass.  

    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.

3.02 PREPARATION

    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
              glazing.

         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
              glazing).

         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
         reinstallation.

    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
              reinstallation.

         2.   Apply glazing compound to the grooves of the window
              sash.

         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
         opening.

         1.   Practice cutting on an unusable piece of glass
              first.

         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
                   tensions.

              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
              guide.

              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
              craftsperson.

    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.

3.04 ADJUSTING/CLEANING

    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
         soapy water.

         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