Preservation Tech Notes: Windows 14 Reinforcing Deteriorated Wooden Windows

Procedure code:
Preservation Tech Notes, National Park Service, Pad
Doors And Windows
Wood Windows
Last Modified:



Paul Stumes, P. Eng.
Parks Canada

This standard includes the bulk of information contained in the
original Preservation Tech Notes developed by the National Park
Service and the Center for Architectural Conservation at Georgia
Tech.  The Preservation Tech Notes are case studies of exemplary
projects designed to provide specific examples of sound
preservation techniques.  To obtain a complete copy of The Window
publications, including figures and illustrations, please contact:

         Historic Preservation Education Foundation
         P.O. Box 77160
         Washington, DC  20013-7160

The Window Handbook, jointly prepared by the National Park Service,
Preservation Assistance Division and the Center for Architectural
Conservation at Georgia Tech, also contains all of the Tech Notes
on Windows and is available for purchase from the Historic
Preservation Education Foundation for $32.00.  The Window Workbook
is available for $49.00.  The two publications together can be
purchased for $72.00.

Kingston, Ontario, Canada


Erected in 1889-91 for a United Church of Canada congregation, the
Chalmers United Church is a handsome structure, designed by Gillen
and Gillen, and constructed from local limestone.  Among its most
striking features are the stained glass windows (artist unknown) on
the north and south facades.  Each set of tripartite windows
consist of a 9' x 24' center portion, flanked by 5' x 20' wing
sections on both sides.  The center portion depicts scenes from the
New Testament; the side windows feature geometric designs.  All of
the windows were fabricated at the time the church was built.


Over time the windows had suffered severely on the southern facade
of the church, which is exposed to sun and constant strong winds
blowing in from nearby Lake Ontario.  This wind not only carries
dust and dirt, but also has a high moisture content.  Because of
weathering and the lack of regular maintenance, the wooden frames
which secured the stained glass panels had gradually deteriorated.
The decay finally became so acute that by 1982 the windows were in
imminent danger of collapsing.  The parishioners at that point had
no choice but to arrange for the urgent repair of the windows.

The original plan formulated by the parish was to remove the large
windows from the openings, frame and all, and ship them to a
stained glass manufacturer's plant for repairs.  There the leaded
stained glass panels would have been removed from the deteriorated
wood frame; then new mullions would have been fabricated and the
glass reset in this new frame.

To design and supervise the work, the church hired architect
Wilfred B. Sorensen.  After reviewing the situation, the architect
realized that following the usual repair procedures, as proposed by
the parish, would not be the best way to tackle this job.  Not only
was the cost estimate quite high, but also there was a very real
danger that the fragile stained glass panels would be damaged
during removal and transportation.  In addition, the large openings
left on the wall while the windows were away for repair would have
presented another major problem; costly temporary closures would
have been required to withstand winter weather.


After studying the options available, the architect decided to
restore the windows, in situ, thereby avoiding the risk of damage
during removal and transportation.  Instead of making new mullions,
the decayed frame was reinforced in an unusual manner, using a
method developed by Paul Stumes, the consulting engineer for the
project.  The method involved the use of epoxy consolidants along
with steel reinforcement rods.  To permit the work to take place
undisturbed by the weather, a "cocoon" formed out of vinyl sheet
was attached to the temporary bracing installed to stabilize the
windows while the restoration work was underway.


The first step in the restoration process was the careful removal
of the remains of old paint on the wood frame.  This exposed the
true extent of the deterioration.  In some areas, as much as 40-50%
of the wood had been lost.  The wooden parts of the window frame
that were found to be crumbling were saturated and consolidated
with a commercially available liquid epoxy.

Next, a 1/2" wide groove was cut into the mullions on opposite
faces to receive a steel reinforcement rod.  The depth of this
groove ranged from 3/4" to 1-1/4", depending on the location.  This
delicate exercise was carried out with utmost care.  After some
experimentation was carried out on scrap wood, a hand-held electric
router was adapted for the job.  Special rollers were installed to
guide the rotating cutting bit.  Notwithstanding the usefulness of
this apparatus, the real success of the operation can be attributed
to the skill of the craftsperson who guided the tool.  The wooden
mullions varied in size; on a typical 3 1/4" wide mullion, the
outer edge where the groove was cut was 1-1/2" wide.  In cutting a
1/2" groove on the outer edge, only 1/2" of wood remained on either
side.  A slight deviation of the tool could have seriously damaged
the mullions.

After the grooves were cut, the wood was treated with a wood
preservative on all exposed sides to prevent possible decay.  The
wood preservative had to be selected with special care because most
such products are not compatible with the epoxy resins which were
used for the stabilization work.  Wood samples were treated with
different types of preservatives and tested for compatibility with
the epoxies selected for the project.  A relatively inexpensive,
locally available product was found to be most suitable, and all
exposed wood was saturated with it.

For reinforcement, 1/4" diameter steel bars (the same type used to
reinforce concrete) were painstakingly bent to match the curves of
the mullions.  The shape of the bars had to be accurate, within a
tolerance of 1/8" in any direction, in order to fit comfortably in
the 1/2" wide grooves which followed the complex curves of the
windows.  Because of the deteriorated condition of the wood, the
steel bars could not be forced into the grooves without the danger
of splitting the frames apart.  In a few instances where the steel
rods could not be suitably shaped, braided fiberglass strands were
used instead.

With the reinforcement in place, the grooves were filled with an
epoxy compound, thus completely embedding the steel in epoxy.  The
epoxy used for this project - the high-modulus, thixotropic Sikadur
gel in which some Union Carbide phenolic microballoons had been
added for more firmness and improved workability - had the
consistency of a stiff paste.  This mixture had the advantage of
remaining in position and retaining its shape wherever it was
placed.  If a fluid epoxy had been used on these vertical windows,
special molds would have had to be fabricated and positioned to
prevent the liquid from spilling out before it hardened.  After
this paste epoxy cured, it achieved a strong adhesive bond with the
wood of the mullions and the reinforcing steel bars, creating a
sturdy composite window frame.

In many places, due to the advanced decay, the fine details of the
mullions crumbled into unrecognizable shapes.  In these areas, the
original form was recreated using the epoxy paste like modeling
clay.  Skillful hands of the craftsperson sculpted fill-ins which
blended perfectly into the curvature of the wooden mullions.  After
the epoxy paste hardened, only the color was different from the
wood; the shape and the texture were the same.  To complete the
work, the windows were then primed and painted.


This method not only restored the church windows without any
breakage of the precious stained glass, but also retained as much
of the original fabric of the wooden frame as possible.
Fortunately the frames were wide enough to permit the installation
of reinforcing rods.  Problems associated with placing a new frame
into a usually deformed old opening were avoided.  In addition to
preserving the original architectural components, this method was
successful in terms of church operations and budget.  Since the
windows were not removed, the functioning of the church was not
disturbed during restoration, and the repair of the windows in situ
was achieved at a cost 25% less than that of just fabricating a new



-    Chalmers United Church
    Kingston, Ontario, Canada



-    Wilfred B. Sorensen
    Kingston, Ontario, Canada


-    Paul Stumes, P.Eng.
    Parks Canada
    Ottawa, Ontario, Canada


-    Whitby Gather
    Kingston, Ontario, Canada


-    Epoxy Paste:  High-modulus, thixotropic Sikadur Gel with Union
         Carbide's phenolic microballoons added.

-    Epoxy Consolidant:  Sika's liquid Colma-Dur epoxy

-    Manufacturer:

    Sika Chemical of Canada, Ltd.
    Point Claire, Quebec, Canada


    Sika Chemical Corp.
    Post Office Box 297
    Lyndhurst, New York

PROJECT COST:  $11,000.00

                             END OF SECTION
Last Reviewed 2012-02-24