How to Repair a Damaged Sash Window Frame
If exterior woodwork is painted at regular intervals, this should afford full protection against changing weather conditions, but if exterior painting is neglected, water may enter the woodwork and cause a great deal of damage. If window putties are allowed to dry and crumble, water will enter and attack the joints which will eventually result in a failure of the sash-bar. Sash-frames needing this type of repair should be removed from the window-frame as described above in ‘Replacing a Sash Cord’. With the sash removed the rotted part of the joint should be hooked out with a wood chisel or screwdriver.
The sash-frame should be clamped in a bench vice with bottom rail and side stile correctly aligned. Keeping these two parts lined up, two holes should be drilled into the damaged joint. This may be done with a hand drill or electric drill. A reasonable diameter for the drill bit is 1/8 in. The drilled holes are then pinned with lengths of dowel rod of the same diameter as the drill bit. The dowel rod should be coated with woodbefore gently hammering it into the drilled holes. The waste end of the dowel is then trimmed flush with the side of the sash-frame. Any cavity under the frame resulting from the removal of rotted wood should be filled with plastic wood and the repair should be coated with priming paint before replacing the sash.
Obviously the decayed putty should be hooked out, the rabbet primed and new putty inserted at the first opportunity.