Author: Bob Yapp
Title of Treatment: Dutchman Tenon Repair
Class of Treatment: [ ] Maintain, [ ] Stabilize, [x ] Repair, [ ] Upgrade, [ ] Exception
Type of Treatment: [ ] Traditional, [x] Modern
Condition to be Treated:
On Test Window W2, one tenon on lower sash, bottom rail was rotted beyond repair.
Replaced the lower rail tenon that was rotted from excessive water migration.
1. Removed all steel pins in both mortise & tenon joints in the bottom rail of lower sash by driving them through the tenon and out the interior side of the bottom rail with a scratch awl that was blunted on its end with a bastard file.
2. Inspected both bottom rail tenons and discovered one was rotted beyond use. The mortise was in good shape at the same joint. Determined the sash was constructed of northern white pine.
3. Using a dovetail saw and chisels, the rotted tenon was removed flush to the end of the rail.
4. Using a dovetail saw a slot was cut into the end of the rail at the same thickness of the original tenon. The slot was cut the same depth as the original tenon projected out from the rail (approximately 2").
5. Using a piece of salvaged northern white pine a new tenon was cut approximately 4" long x 3" wide.
6. Using a waterproof, one part, polymer glue, the new tenon was glued and clamped into the 2" deep slot on the end of the rail.
7. After 24 hours, the tenon was shaped to fit into the good mortise using a block plane and chisel.
8. The good original and the new Dutchman tenon were clamped back together with a pipe clamp and the sash was squared up.
9. Both joints were pinned with two, 3/32" x 1" stainless steel pins at opposing angles into each joint and set 1/8" below the surface for filling with boiled linseed oil based glazing putty after alkyd oil based priming.
•Salvaged northern white pine
•Waterproof, one part, polymer glue
•4, 1/32" x 1" stainless steel sash pins
Quality of Results:
Tight joint where the new tenon was glued into the rail. Tight fit where the end of the new tenon bedded into the existing mortise joint.
The mortise and tenon joint is a tight fit between rail and stile. No gaps in the slot where the tenon fit into the rail or where stile and rail meet.
Everything fits snugly with some minor gaps that can be filled with either glazing putty or architectural epoxies.
The mortise and tenon joint is glued. The joint is not snug and there are large gaps at the joint. If a putty knife can slip into the gap, the gap is too large.