Rebuild Sash Joint by Splicing (final)

Wood repairs for sashes, frames and sills.
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Joined: January 8th, 2012, 1:53 pm
Full Name: David Gibney
Location: Smithsburg MD
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Rebuild Sash Joint by Splicing (final)

Postby davidgibney » February 19th, 2012, 12:08 pm

Status: [ ] submitted work method, [ ] proposed treatment standard, [x] final treatment standard
Author: David Gibney
Contributors: John Leeke

Title of Treatment: Rebuild Sash Joint by Splicing
Class of Treatment: [ ] Maintain, [ ] Stabilize, [x ] Repair, [ ] Upgrade, [ ] Exception
Type of Treatment: [ ] Traditional, [x] Contemporary, [ ] Conservation

Condition to be Treated:
A mortise and tenon joint has completely failed allowing significant movement between the stile and rail.

Replace the deteriorated ends of the stile and rail with new wood that is spliced on and shaped to exactly match the original details of the joint. This treatment is suitable when the joinery, the mortise or tenons has completed failed, by fungal decay or physical breaking. This method saves much of the original fabric without having to make entire replacement parts.

Typical Procedure:
1. Disassemble the sash to remove the rail and style that has the failing joint from the sash.
2. At the failed tenon, cut a slot in the end of the style or rail the same thickness of the original tenon and to a depth of 1 1/2".
3. Shape a piece of wood to form the new tenon, the same thickness as the old tenon and long enough to fill the new slot and extend through the mortise.
4. Glue the new tenon into the slot and clamp. Allow glue to cure thoroughly.
5. Trim the new tenon into the original mortise for a snug or tight fit.
6. Cut the bottom off of the style at the failed mortise with a 45 degree angle sloping downward to the outside of the stile, to form a scarf.
7. Shape a piece of wood to match the original style in all dimensions and profiles, including an angled scarf to match the scarf on the stile. Make a wooden spline 1/8" thick by 1" wide and cut slots angles in the center of the style for reinforcement of the joint.
8. Glue the scarf joint together, assure alignment of the new piece with the stile. Allow glue to cure thoroughly.
9. Cut a new mortise in the new end of the stile, following the other stile as a model to the exact dimensions and shape.
10. Re-assemble the sash and pin or peg the mortise and tenon joints.

• Wood for the replacement parts; match species, grade, anual growth ring count and orientation
• adhesive glue

Quality of Results

Best Work: The joinery is tight showing no movement if the stile and rail are twisted. The spice joint is unnoticeable after the style has been painted.

Inadequate Work: Using dowels or screws and not re-creating the mortise and tenon joint

Posts: 385
Joined: April 13th, 2011, 7:34 pm
Full Name: John Leeke
Location: Portland
Organization: Historic HomeWorks
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Location: Portland, Maine

Re: Rebuild decayed sash joint

Postby johnleeke » April 22nd, 2012, 10:22 am

David writes in the original draft:
>>I have used this method for the past 25 years without failure as long as it is maintained kept painted.<<
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