This week’s Ask The Craftsman question comes from Desley.
“My windows have some cracks that go from the outside right through to the inside. How should I fix that?”
Desley, first let’s be sure what you are looking at is something that actually needs to be repaired. It’s a little difficult to tell from your picture, but cracks in window frames may be something you should leave alone. Let me explain.
A window sash consists of two stiles (vertical pieces of wood) and two rails (the horizontal pieces). These are joined together with fairly complex mortise and tenon joints and these joints make the frame very strong. The strength of these joints is also found in the fact that they can move with seasonal changes as the wood expands and contracts.
In colder weather the wood fibers contract and joints have tendency to open up. Then in the summer as humidity and heat increases the wood swells and the joints tighten up again.
If you fill those joints when they are contracted then when the wood expands again it will either push the filler out of the joint or cause the wood to bow due to the pressure.
To Fill or Not to Fill?
There are two guideline’s to use when determining to fill or not.
- Can you see light thru the crack?
- Is the crack large enough to fit a quarter in?
If it doesn’t meet those criteria then I would make sure any exposed wood inside the crack has been primed and painted to protect it from the elements and leave it be.