Removal of the upper sash on double-hung units is similar but the
parting bead which holds it in place is set into a groove in the
center of the stile and is thinner and more delicate than the
interior stop. After removing any paint along the seam, the parting
bead should be carefully pried out and worked free in the same
manner as the interior stop. The upper sash can be removed in
the same manner as the lower one and both sash taken to a convenient
work area (in order to remove the sash the interior stop and parting
bead need only be removed from one side of the window). Window
openings can be covered with polyethylene sheets or plywood sheathing
while the sash are out for repair.
The sash can be stripped of paint using appropriate techniques,
but if any heat treatment is used, the glass should
be removed or protected from the sudden temperature change which
can cause breakage. An overlay of aluminum foil on gypsum board
or asbestos can protect the glass from such rapid temperature
change. It is important to protect the glass because it may be
historic and often adds character to the window. Deteriorated
putty should be removed manually, taking care not to damage the
wood along the rabbet. If the glass is to be removed, the glazing
points which hold the glass in place can be extracted and the
panes numbered and removed for cleaning and reuse in the same
openings. With the glass panes out, the remaining putty can be
removed and the sash can be sanded, patched, and primed with a
preservative primer. Hardened putty in the rabbets may be softened
by heating with a soldering iron at the point of removal. Putty
remaining on the glass may be softened by soaking the panes in
linseed oil, and then removed with less risk of breaking the glass.
Before reinstalling the glass, a bead of glazing compound or linseed
oil putty should be laid around the rabbet to cushion and seal
the glass. Glazing compound should only be used on wood which
has been brushed with linseed oil and primed with an oil based
primer or paint. The pane is then pressed into place and the glazing
points are pushed into the wood around the perimeter of the pane.
The final glazing compound or putty is applied
and beveled to complete the seal. The sash can be refinished as
desired on the inside and painted on the outside as soon as a
"skin" has formed on the putty, usually in 2 or 3 days.
Exterior paint should cover the beveled glazing compound or putty
and lap over onto the glass slightly to complete a weather-tight
seal. After the proper curing times have elapsed for paint and
putty, the sash will be ready for reinstallation.
While the sash are out of the frame, the condition of the wood
in the jamb and sill can be evaluated. Repair and refinishing
of the frame may proceed concurrently with repairs to the sash,
taking advantage of the curing times for the paints and putty
used on the sash. One of the most common work items is the replacement
of the sash cords with new rope cords or with chains. The weight pocket is frequently accessible through a door
on the face of the frame near the sill, but if no door exists,
the trim on the interior face may be removed for access. Sash
weights may be increased for easier window operation by elderly
or handicapped persons. Additional repairs to the frame and sash
may include consolidation or replacement of deteriorated wood.
Techniques for these repairs are discussed in the following sections.
 Following the relatively simple repairs, the window is weathertight, like new in appearance, and serviceable for many years to come.Photo: NPS files. |
The operations just discussed summarize the efforts necessary
to restore a window with minor deterioration to "like new"
condition. The techniques can be applied by an
unskilled person with minimal training and experience. To demonstrate
the practicality of this approach, and photograph it, a Technical
Preservation Services staff member repaired a wooden double-hung,
two over two window which had been in service over ninety years.
The wood was structurally sound but the window had one broken
pane, many layers of paint, broken sash cords and inadequate,
worn-out weatherstripping. The staff member found that the frame
could be stripped of paint and the sash removed quite easily.
Paint, putty and glass removal required about one hour for each
sash, and the reglazing of both sash was accomplished in about
one hour. Weatherstripping of the sash and frame, replacement
of the sash cords and reinstallation of the sash, parting bead,
and stop required an hour and a half. These times refer only to
individual operations; the entire process took several days due
to the drying and curing times for putty, primer, and paint, however,
work on other window units could have been in progress during
these lag times.
"The Repair of Historic Wooden Windows" an Historic Preservation Brief
