How to fix gaps in miter joints

How to fix gaps in miter joints

Cutting perfect miter joints is in most cases much tougher than you think. You have to measure perfectly and cut all the parts perfectly. If you get only one side slightly wrong, you will have a gap. If you are installing molding in your home, always first measure the corners because they are rarely perfect 90°. You are probably wondering how do people make perfect miters if it is so hard? Well, in most cases miters just look perfect because the gaps are well concealed. In this article we will teach you how to fix gaps in miter joints and make your miters look perfect with a few little handy tricks.

The first method is the most obvious one and the best one if you want a permanent result. The best material for filling gaps in miter joints is real wood. It is best to use this option when the void is large enough and regular in shape. If the void is irregular you can straighten it out with a back saw or dovetail saw. Use a chisel to take a sliver from another piece of matching wood, but be sure to make it deeper than the gap. Rub the sides of the sliver on sandpaper until it fits the width of the gap perfectly. Then force the glue into the opening with a knife or a piece of paper and slip the filler into place. Wait after the glue dries and then use the flat face of a chisel to trim the protruding filler piece flush with the surface of your project. Follow that with light sanding and you will have a perfect miter joint.

The second method is filling the gaps with wood fillers. You can buy various brands of paste-like wood filler that will disguise smaller gaps. The downside is that it won’t take stain like wood, but a repair that runs parallel to the grain will blend in nicely.

The third method is somehow strange, but it really works in some cases. You can really close the joint in a matter of minutes using nothing more than a round-shafted screwdriver. Just rub the screwdriver shaft back and forth across the joint, applying just enough pressure to compress the wood fibers. The general idea is to slightly round over the corner and conceal the gap. Normally that will work only on small gaps but it is really neat inexpensive trick.

How to fix gaps in miter joints - screwdriver




The method with finishing nails is also very effective for small gaps in miter joints. You just need to clamp the mitered corner together with enough pressure so that the corner comes together and any gap that was present is closed. This method works best on trim pieces that have opened up once installed, or on mitered frame corners that have a gap in them. After the gap is closed, hammer a finishing nail through one side of the mitered corner into the other side, so that it goes straight through the mitered joint. Then hammer a second finishing nail through the other side of the mitered corner into the side you nailed through first. In that way the cross nailing will hold the mitered corner closed once the clamp is released.

The method with back saw or dovetail saw has also proven very effective for small gaps. Just firmly clamp the members of the joint at the angle needed and gently run a fine tooth saw (a back saw or a dovetail saw works perfectly) down the joint between the two pieces. When finished, slide the members of the joint together and fasten in place with glue or nails. If your gap is larger then bring the two members of the joint together and run the saw between them again. Don’t worry, in most cases, you will not create a fit problem for the other joints by removing a tiny bit more material at this corner.

How to fix gaps in miter joints - saw

The following method is very common when making a new joint, but it can be very effective for gaps on existing miters also. First measure both edges of an unattached mitered corner to find the end that is closest to a perfect 45-degree angle. Then hand-plane the edge of the second-best mitered end, shaving off very small portions at a time until the two mitered ends match perfectly. Hand sand the mitered edges and once you have sanded the miter to a point where it mates well to form a corner, you can connect the lumber into a mitered corner.

Thank you for sharing, Handyman tips team!
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55 comments

  1. Bobbg

    Always cut your parts slightly long.
    Set the first side, place your next pec of trim
    Mark top and bottom of joint, cut join to marks
    Fitting in tight, when doing 2 end walls and a long center you can cut the trim slightly long and bow it into place. If its still to long you can find tune it a tiny bit at a time. You can also trim away Sheetrock to make a joint tighter.
    Only fill gaps if its painted wood.
    On stained wood you’ll have to take your time, you can always cut off but you can’t fill in.

  2. Buddy

    When I have gaps sometimes I might cut the trim in half. Then you can make each corner end joint tight. Then fill the gap in the middle of the trim with caulking, where probably nobody is looking.

  3. John Wehler

    I have a longer room where the picture hanging molding is made from two pieces. With expansion and contraction going on during the seasons its hard to putty up the gap created by the wall changing size. Is there a slip over product or an idea for something that would allow movement between the two pieces of molding?

  4. Richard

    The best way to do any skirting angle inner or outer angle ,always use a 2foot steel rule what folds in half . You can now bend it into or over the outer angle to be cut , pencil round the 2foot angle onto a piece of paper cut out then just fold in half and that gives you the perfect angle you need to cut regardless if it’s 47degrees or what ever , just cut both pieces to this angle fit perfect .

  5. Orlando

    Not on my Job Site, I’d Fire that Finish Carpenter! Cherry, Mahogany. or Red Oak, I don’t think so!

  6. K

    Miter joints are hard– but that is no excuse to fudge them. you generally only have 4 per room so take the time do them right. Even as a DIY, if you fudge it now you might not notice in your fatigue but over time you are going to learn to see the hack job you did and will likely start to piss you off. If measuring isn’t your strong suit (or you simply lack the tools), grab some practice wood to make test cuts and build custom jigs (you can saw off the end each time so you only need a few). Build the jig and use that. Make sure your saw is SHARP. Get a few extra pieces of the material you are using and actually test out how the stuff behaves (i.e. does it chip easily– do you need to support the wood while cutting etc).

  7. Julia

    Came across this discussion doing a Google search for “how to fix gaps in moulding corners”. I have decided that having your house remodeled can be hard on a person who is generally nice. I feel like an ogre and very picky. It is somewhat comforting to know this sort of thing happens often and I’m not the only one who has to deal with it. I am dealing with an amature contractor and a very defensive painter whom the contractor hired. I will be doing a lot of touch up myself, and decided to remodel and paint the family room myself (can’t do any worse, will take me a long time, and it might be fun). Thank you for the suggestions. If I need help, I’ll be back.

  8. rottenrollin

    The wood sliver is BS……..for most of us, it is IMPOSSIBLE to cut a sliver with a laser, much less a chisel.

    Fill the crack with caulk. Easy and quick. Let dry.

    Then apply the last suggestion, burnishing, to close the mitered wood over the gap some.

    If necessary, THEN use a sanding block across the corner to even it up some. Then final prime and paint and you’re done.

    JMHO.

  9. William

    Bob Knapp got the right answer … remove the pieces and plane (or sand) the back until the miter fits. Then use Hartford Miter Clamps to glue the miter before reassembling.

    All the other answers are homeowner “amateur” and or “painter” kluges.

  10. Mark Macdonald

    Another method is simply to go back to your chop saw. Don’t change the setting but cut another very thin piece, say 1/8 ” from the same stock you just used. Tap the new piece into place and sand or round file the edges so that it matches the existing moulding.

  11. Anonymous

    Another method is to take off each bit and buzz plan or sand off the back so the join closes but it will depend on the angle and how much you are out by in bad cases you may have to change the miter angle

  12. Anonymous

    If you lay your trim ontop of the other trim board, then mark where they intersect they always come out perfect.

  13. MWycombe

    When you have an old Victorian home (we do) very few of the angles are exactly 90 degrees square. So, the 45 degrees for the common miter doesn’t work that well – especially if you are doing crown molding. The approach I have found most satisfactory is first measure the angle – a digital protractor ($15) works best. Then, using high school geometry, compute the size of the bisected angle and note carefully which is the left end and right end angles. Cut your first length and cut a small ‘key length’ from scrap wood for the next turn that should mate with the first piece. Work your way around the room, cutting a short ‘key length’ to check the correct mating of the miters at each turn around the room. For modern houses that are usually very square this is not necessary, but for old wooden Victorian houses, which are rarely square, using a ‘key’ cut from scrap wood ensures the best possible mating at each turn of the room.

  14. Phillip

    Try to cut your longest runs first, so if you goof it up you can see what you did, use another piece and do it right, and save that goofed piece for a space where you can cut it shorter.

  15. Curtis Delong

    Listen if you got through high school, and you passed your math , and you check all your angles and use a chop saw and set the angle on the saw to the reading on the square, you can get it right even if you chcpeck yourself with a short piece of cut off first. If it doesn’t fit tight, don’t continue with the thought that it will be ok because it’s not ok.

  16. Aad

    Make a paste of glue and much sawdust where you’ve worked with. Spread into the gap and shed it as the glue has dried. It wil work in most of all the cases. However, when you are a cabinet maker ( like
    discribed in one of the comments) it’s quite an insult if you making daps like this!

  17. Tony

    If you can’t cut a perfect mitre by hand then your only option is to buy an electric chop saw with a 45% angle cut, as long as you are confident enough not to cut your hand/fingers off, you still have a problem if the corner you are mitring is not square so it’s best to check that first before attempting to cut the mitre.
    There is no such thing as a Professional Handyman? there is no recognised qualifications in the name of Handyman you are either a Carpenter or Joiner or Carpenter & Joiner or Cabinet Maker, all handyman are non qualified and to call one of the professionals a handyman is taken as an insult

  18. Jd

    Yeah this is all for tree person tag doesn’t do it everyday, I have zero problem cutting a perfect mitter with 7″ + crown or base.
    But I will tell you that a lot of what your saying is way harder than just caulking it and painting. A handy man won’t do strain grade because he knows he can’t. So just throw some caulk in it and paint it.

  19. Bob Knapp

    If you have no other choice, out of matching stock, a method I Will use is to remove piece and sand the molding’s back tapering to feather out away from corner. Usually will need to do same on other piece. Most times you gain enough to even re cut the miter. Methods mentioned all have merit for painted work. Been finish carpenter 40 years. As others menyion, it is a good idea to cut inside and outside template pieces to check first b r fore cutting

  20. Handyman Tips

    Every method has it’s advantages and everybody prefers a different one! All of this methods work and we are confident that your method is also effective!

  21. Bob Carpenter

    No no no. The best way is to lay a piece of thin wood under the piece being miter, so when you cut your angle the expose side, the front, looking at you will be on a bevel and your 45. Here. If your wood was rubber then roll your miter down just a hair and do the other side to. The fronts will meet perfect but the back of the miters will not but you can’t see that and if you can by looking down, fill, it will never go anywhere. Plus, make up some short pieces of miters to test to see how far they are out. This is the best way for old and remodeling. New should be better but maybe not, so lay a shim down on the miter box and lay your piece of trim on top and cut your miter and this will give you your bevel 45 degree cut.

  22. Jim

    This is really a homeowner tip, not for a craftsman. Some of the methods may work with surfaces that may be painted but hardly for staining. More concern on quality is paramount, no need for filling/patching new joints.

  23. douglas a hanlon

    fj doyle…really you walk on water? so let’s say you in a medium quality house and down to your last stick of wood and since you are almost perfect every other miter in the house looks like it grew there…but it’s late and your supplier is closed and the job is forty miles from home and the supplier is ten in the other direction and you cut a mitre that has a 32nd gap…are you telling me a finish carpenter of 35 years that i am amateurish for using that trick with some glue and light sanding?….must be nice to be independently wealthy and a perfectionist with no concern for making a living(btw that’s why your wife hates you)

  24. Fjdoyle

    The screwdriver method should never be used. It’s very amateurish and rarely does more than crush the end fibers of the joint.

  25. rex

    Agreed Marc proper tools and knowledge of how to use them, there should be no reason to have a large gap on a miter joint.

  26. Dave

    Used to mix PVA glue with the same sawdust as the timber and fill the gap with that. Sand it smooth when dry.

  27. Fantastic Handyman

    One does not need to be the ultimate handyman to make good miter joints. I won’t say it’s easy and you don’t have to be a pro handy man, but still if you’re motivated, crafty enough, and you can afford the time investment, it will surely be a sip of helpful experience. When I have to take a job like that, I usually go for 6d nails, unless the miter joint / flooring doesn’t allow it. Of course, if we we’re talking about professional handymen, you should be capable of handling all 3 options, since different clients wan’t joints done differently. As a carpenter I would always avoid glue but in some cases that is the one and best option to get the job done.

    Dmitri,
    fantastic handymen

  28. Marc Friedman

    The other alternative is, get it right the first time. Unfortunately, their are enough people in the trades who do not understand the practical application of high school geometry. With over 40 years of building under my belt, I’ve seen it all the time, for years. If you know how to bisect an angle, a clean miter shouldn’t be an issue. That assumes that the equipment you are cutting with is set up properly.
    So the argument for using filler, other than nail holes, is nonsense. I would recommend gluing the miter. When it comes to putty,
    The epoxy wood putties that come in different colors are a good choice for gap filling. They can be tinted if you know how.

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