I have a slight gap in a mortise & tenon joint. anyone have a cover-up or fix for slight gap in joinery?
Obviously the best solution here is to avoid the gap in the first place by careful test-fitting of joints prior to final glue up and then during final assembly using sufficient clamp pressure to close up joints to their full extent.
When you do get a gap (and everyone does on occasion!) there are of course commercial wood fillers, but it seems the commonest solution given on the Internet is to use a mix of sanding dust from the same species and glue. I wish it were that simple but see this previous Answer:
Making wood filler from sawdust
As I covered previously, despite claims to the contrary this is almost never a good colour match to the surrounding wood unless you use hide glue. But if you were you'd be unlikely to have a gap like this in the first place since, unlike with other glues, the joint could be opened with careful application of heat and moisture and then the cause of the gap fixed.
Helping to prevent gaps at the shoulder in future
- Slightly undercut your shoulders by paring with a sharp chisel.
- Make your mortises a fraction deeper than the tenon is long (also provides a glue reservoir to prevent all excess being squeezed out when you clamp up).
- Don't apply too much glue as this can cause a hydraulic seal in the joint which can physically prevent the tenon going fully home. You do however need to ensure you use enough adhesive so that all glue surfaces are fully wetted.