Fix Gaps In Miter Joints

Fix Gaps In Miter Joints

Have you ever walked around your house and noticed random gaps in your window trim or baseboard?

Maybe that’s just me that notices that stuff haha! But if you have then it might mean it’s time to fix those gaps. (Especially those gaps in the mitered corners of your window trim!)

Whether you installed your own window and door trim or a (not-so) professional did, it’s easier than you think to fix those gaps.

How Bad Miters Occur

First off, let’s discuss how bad miters occur.

Oftentimes, walls and corners in houses (especially older homes) aren’t as square as we need them to be to create perfect mitered corners.

As a result, exact 45-degree angles might leave little gaps on corners that aren’t truly 90-degree angles.

For window trim specifically, there is a trick on how to cut a perfectly mitered corner that I will discuss below. For now, though, let’s fix your current problem of gaps in your mitered joints!

Fixing Gaps in Miter Joints: 6 Ways

1. Using Real Wood

This method will provide good results with permanent results. I have found to get the best results is to fill the gap with a similar piece of wood. This method is great if the gap is large enough and is shaped from nothing to about 1/16th of an inch. Using a sharp chisel make a sliver of the same wood that will fit the gap.

I have found that if you make the sliver a bit thicker you can use a piece of sandpaper until it fits the gap. Next squeeze some glue into the gap using a thin knife and then insert the sliver into the gap. Let the glue dry and then using a sharp chisel remove any of the sliver that is sticking past and then give it a light sanding.

2. Using Wood Filler

There are many different types and brands of wood filler. Some are thicker and provide a paste like compound that you can fill the gap in the miter joint with. The problem with wood fillers is they don’t stain very well, and if the repair is parallel to the grain of the wood the wood filler will not be as noticeable.

3. Screwdriver Fix

This mod may seem a little out of the ordinary, but it does work well in a lot of cases. Using a screwdrivers round part of the shaft simply rub the shaft back and forth to the joint and use just enough pressure that the wood fibers will begin to close. This is a great fix for outside miters and works good on smaller gaps.

4. Using Finishing Nails

This method is also quite effective with fixing small gaps in miter joints. First… You clamp the joint together until the joint is closed; next you pre-drill the holes for a small finishing nail. Before nailing the finishing nails into the joint add some wood glue into the holes you just drilled. Now hammer in the finishing nails, one through each side of the joint, this cross nailing and gluing will secure the joint in place. Once the glue has dried you can remove the clamp.

5. Cutting Out the Joint

All you do is clamp the joint as tightly as possible and then using a back saw or other fine toothed hand saw cut down the center of the joint. Once this is done remove the clamp and clean up any sawdust and then proceed to glue and nail the joint together.

6. Plane and Sand the Mitered Joint

Begin by checking each piece to see which one is closest to having a 45 degree cut on it, than begin planning the other piece with a small plane and remove some material and keep fitting the pieces until they fit together nicely. Hand sand the edges and the top of the joint to get a nice finish, glue and nail the joint together.

How to Use DryDex to Repair Open Miters

DryDex is a great product for filling nail holes, cracks, and miters. This isn’t a DryDex commercial, it’s really a great product and has tons of good reviews on Amazon.

The open miter in this example was about 1/16″ wide. So DryDex was a good option.

I recommend taping off hardwood floors or protecting the carpet with cardboard. This prevents the DryDex from getting onto those surfaces.

Apply DryDex to the woodwork with a 2-inch or 3-inch putty knife. Then tool the open miter joint to fill it.

Wipe away excess DryDex and allow it to turn from pink to white. At that point, the woodwork can be sanded smooth with a damp sponge.

Primer and paint can be applied over the woodwork to make the woodwork look like new.

How to Use Bondo to Repair Open Miters

Homes get a lot of foot traffic. Kids and pets frequently bump into the woodwork and cause damage. If there’s an open miter in a high traffic area, it’s best to use Bondo All-Purpose Putty.

There’s one drawback to Bondo: it stinks! Open windows and make sure the house has good ventilation. Also, protect any carpets with pieces of cardboard or cereal box tops – this is a cheap way to ensure your floors remain in good shape.

Furthermore, wear gloves before working with the Bondo. Woodwork has to be sanded down with 80-grit and 180-grit sanding sponges or paper. This should reveal the bare wood.

Bondo has a cream hardener and putty component. It’s important to read the directions and spread a 3-inch by 1/2″ thick circle of Bondo putty on a non-porous surface, like a tile.

Then apply a 3-inch bead of the cream hardener into the putty. Mix both the cream hardener and putty for 2 minutes. Once the Bondo is mixed it can be applied into the open miter using Bondo spreaders. Quickly work the Bondo into the miter and remove any excess before it hardens.


Where is a Mitre joint used?

A mitre joint is used for joint two boards at an angle (or compound angle). You can see the joint most commonly in small wooden boxes or wooden frames. The latter of these is a very strong joint, given the strength of modern wood glues.

Are mitered corners stronger?

Might mitered corners A mitered corner is one of the weaker joints in woodworking because it relies on gluing end grain to end grain. But there are good reasons to make a mitered corner. And wood grain can be made to wrap continuously around a mitered corner.

What is a rabbet joint?

A rabbet or rebate is a recess or groove cut into the edge of a piece of machinable material, usually wood. When viewed in cross-section, a rabbet is two-sided and open to the edge or end of the surface into which it is cut. A rabbet can be used to form a joint with another piece of wood (often containing a dado).

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