Rare is the woodworker who never has to a project complete with mitered trims and parts. Rarer is the woodworker who is such a master that he never misaligns mitered corners. They’re so tricky that it doesn’t matter your level of experience… odds are you’re going to screw it up sometime or later.
There are many reasons for this. The most common reason, however, is that the mitered corners on the wood pieces have been twisted, warped, or otherwise changed.
For example, imagine a plywood shelf that you’re working on. You’re supposed to wrap it with a mitered 1/2 trim. The miter, as far as you know, is beyond accurate. Biscuits were judiciously applied in all the correct ways. It seems unlikely that you won’t achieve perfection in this project, right?
Then you put on the trim. Next thing you know, you’re looking through a small gap right where the corners are supposed to come together. You can be a master carpenter or a total newbie. It doesn’t matter. This has happened to everyone and will keep happening. So what do you do?
The easiest thing to do comes with painting it. When you’re painting the shelf, simply caulk the gap and act like nothing ever happened. But if you’re staining it instead, then you’re still looking at this gap. It will stick out like a sore thumb and you just know that everyone will notice it. It seems hopeless. But did you know that you can still close the miters up without any more problems?
Start with two 4d finishing nails. Use a pair of clamps to pull the miters back together, and make sure that they never cross anywhere. Put the nails through one board and then the other. The smaller finishing nails you can use, the better this will turn out.
Drilling a hole first to make sure the wood doesn’t split is a good idea. Don’t worry about the miters coming back apart, as the tacking holds them in place when the clamps are released.
Use a nail set to set in the nails. Fill the holes with wood filler. Remember that the wood filler tends to absorb around the hole, and may not stain as well as the rest of the wood.
That’s why you should stain first and then fill the hole. This way the nail blemish isn’t as bad. You may have to restain and sand here, but that’s up to you.