Our specifications for Historic Wooden Window Restoration
The sash will be removed from the frames for inspection and restoration. The sash and any other parts of the frame removed will be labeled for reinstallation in their original location. The sash will be restored off site. During the sash's absence the window opening will be filled and secured with plywood or hardboard insulation filler until the sash is re-installed.
If the paint on the sash is failing, thick, a rough finish or tests positive for lead the paint will be stripped completely either by steam stripping or infrared heat. If any of the putty is failing the glass will be removed and reglazed. If the exterior putty is sound but the interior bed glazing is failed the glass will be removed and reglazed. Failing bed putty can be assessed by sight and sound; if you wrap on the glass and it rattles it is failing. If the putty is cracked and most likely over 30 years old it is beyond its serviceable life and should be removed.
The sashes will be inspected and necessary repairs made. Repairs shall consist of either epoxy consolidation or wood patches depending on the nature of the damage. In all repairs made with wood patches the wood will be the same species as the wood used in the original sash. If repair work is required at the joints, the joints will be separated, repaired, reassembled and pinned. Joints will not be glued together or repaired in any way that results in the joint being permanently fixed.
Once the sashes are repaired they will receive a coat of heated boiled linseed oil in order to recondition the wood. The glass rabbits will be primed with shellac to seal the wood where the glazing is installed. The first finish coat of paint will be applied prior to reglazing the sash. Once the sashes are re-glazed two coats of finish paint will be applied. These coats of paint will over-lap from the wood and glazing onto the glass no more than 1/16th of an inch to create a weather tight seal. All of the paint used will be oil-based.
The sashes will be reglazed with a raw linseed oil based glazing compound. The glass will be set into the glass rabbit on a bed of glazing compound. The glass will be held in place with appropriate glazing points. The glazing points will be set so that the bead of glazing will completely cover them. The exterior will be glazed in one continuous bead around the window. There will be no fissures or cracks in the glazing. The sashes will be painted immediately after glazing. These procedures produce a weather tight seal between the glass and the sash.
S. A. Fishburn uses organic Allback Linseed Oil Glazing and Paint. This is a no VOC paint based on traditional paint formulas. The paint will not peel but it will dull over time. Regular maintenance consisting of oiling the sash with boiled linseed oil every 5 – 10 years as the paint dulls will extend the life of the paint and glazing to 50 years.
The sash will be refit to the frames prior to re-installation. The sashes should fit so that they hang squarely in the opening with an even gap between the sashes and the window frame. The type of weather-strip used will determine the size of the gap. The meeting rails will line up and close tight when the sash lock is engaged.
Once the sash is removed the frame will be inspected and repaired as necessary. Broken or missing parting beads and stops will be replaced. The replacement parts will be milled of the same species and design as the originals.
Any extraneous pieces of wood or hardware added over the years to prop the sash in place will be removed. The sash channels will be cleaned and check for any objects that would obstruct the movement of the sash.
Where the wood is rotted or broken the failing wood will be removed to a sound surface and repaired. Repairs will consist of epoxy consolidation, wood patches, or part replacement depending on the nature and extent of the damage. Any wood patches and replacement parts will be made with wood that matches the original species used. The repairs will be primed if the original surface was painted.
If the sills are weather checked the checks should be cleaned out and a good wood grade epoxy should be used to fill the checks. Once the epoxy has cured any excess on the surface of the wood should be cleaned back so that the epoxy fills the checks only.
Re-installation of the Sash
The sash will be re-installed in the frames and checked for proper movement. The stops will be replaced. If the screw holes in the frames are stripped out they will be filled with wood and the screws re-installed. If the upper sashes are to be fixed in place, stops will be installed in the upper sash channel, running from the meeting rail to the sill. The stops will be screwed into place to facilitate sash removal in the future.
The hardware on the sashes will be removed and cleaned. The sash locks will be lubricated and returned to good working order. Any missing or broken sash locks will be replaced. The sash pulls will be cleaned and those missing or broken replaced. The pulleys will be lubricated with a graphite lubricant.
Where weights and pulleys are present the weight pockets will be cleaned out and all sash cords and pieces removed. The weights will be checked to assure proper placement. If sash chords or chains are missing, worn, or broken new sash cords or chains will be installed. When the lower sash is fully open and the upper sash is tightly closed, the sash weights will be suspended 1" above the bottom of the sash pockets.
Unless it will interfere with a counter-balance system, V-bronze or Spring Bronze weather-strip will be installed in the window frame. This is a V shaped piece of bronze or copper that is nailed into the window jamb with the open end of the V facing the exterior.
This weather strip is applied to side jambs to fill the space between the sash and frame with the sash in the closed position. It is also applied to the head jamb above the top sash and sill below the bottom sash. The V-bronze weather strip stops the flow of air around the sash and lowers the friction when moving the sash.
If the V-bronze weather strip will interfere with the counter-balance system then a nylon pile weather strip can be installed in grooves cut into the window stiles.
These specifications are consistent with the Secretary of the Interior's Standards for Rehabilitation, 1990.
Sally Fishburn, Updated February, 2013