How to Fix an Oversize Mortise?

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Forum topic by jasoncarpentry posted 04-21-2017 05:57 PM 4101 views 0 times favorited 16 replies Add to Favorites Watch
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149 posts in 3454 days

04-21-2017 05:57 PM

Topic tags/keywords: mortise tenon epoxy gorilla glue

I’m repairing the wobbly footboard from a 50+ year old bed. Once I got the existing pieces separated, I realized the main reason for the wobble. The mortises are too long and too deep to make a snug fit w/ the tenons. Now, I could insert pieces to make the mortises smaller, and maybe that’s the best way to do it. But I’m inclined to just use a filler/glue, partially fill up the mortises, and then insert the tenons, apply clamps, and let the filler do its thing.

Assuming you agree w/ this method, what type of filler/glue do you recommend? I’d like to use epoxy because I’ve had good results w/ it lately, but there’s also Titebond III and Gorilla Glue. What about the last two? Do they form a hard filler like epoxy does?

Many thanks!

-- Jim in Tennessee

16 replies so far

View chrisstef's profile


18098 posts in 3806 days

#1 posted 04-21-2017 06:01 PM

Id go with epoxy. Gorilla glue is going to expand too much for my liking and I don’t fell as if TB3 will have enough gap filling properties to do a good job.

-- Its not a crack, its a casting imperfection.

View bondogaposis's profile


5802 posts in 3151 days

#2 posted 04-21-2017 06:09 PM

I would not try and fill the mortises but rather add thickness to the tenons. Just glue slips wood to the tenon that make the tenon oversize then pare them to tight fit w/ shoulder plane. It is much easier to work with a tenon than inside a mortise.

-- Bondo Gaposis

View HorizontalMike's profile


7874 posts in 3714 days

#3 posted 04-21-2017 06:14 PM

  • Too “long”—not really an issue
  • Too “deep”—this neither

How about the width of the mortise compared to the tenon? If the tenon width and mortise width are reasonably snug/not-sloppy, then I would just glue it up including gluing the butt joint portion as well.

Not really needed IMO, but you could also add some loose tenon material in the length of the mortise using plenty of glue. EG: cut up a series of tooth-picks as filler (but make sure you don’t interfere with the existing M&T fit).
I use TB III personally.

My 2-cents…

-- HorizontalMike -- "Woodpeckers understand..."

View SignWave's profile


472 posts in 3835 days

#4 posted 04-21-2017 06:14 PM

I’m not a big fan of filling a loose joint with glue. If you can somehow get it to fill the gaps properly without running out, it will probably loosen over time and be harder to repair the next time.

Assuming the mortise is cut decently, I’d build up the tenons by gluing some thin material of the same or similar hardwood. I’d make them a tad oversized and true them up to a snug fit with a plane after the glue dries.

-- Barry,

View 000's profile


2859 posts in 1699 days

#5 posted 04-21-2017 06:31 PM

+1 bondogaposis

View Fred Hargis's profile

Fred Hargis

6302 posts in 3293 days

#6 posted 04-21-2017 07:06 PM

I agree with Mike, the too long and too deep issues aren’t issues. If you have good cheek to mortise wall fit, some wood glue is all you need. But the only glue I would use as a gap filler is epoxy, the TB and especially the Gorilla glue aren’t going to do much for the gap. If the cheek to mortise fit is too loose, it would be easier to glue wood to the cheek and then size it down to fit the mortise.

-- Our village hasn't lost it's idiot, he was elected to congress.

View HorizontalMike's profile


7874 posts in 3714 days

#7 posted 04-21-2017 07:07 PM

Assuming the mortise is cut decently, I d build up the tenons by gluing some thin material of the same or similar hardwood. I d make them a tad oversized and true them up to a snug fit with a plane after the glue dries.
- SignWave

Bingo! +10
After building up the tenon, as above, use a shoulder plane (Stanley #92, #93) to thin the new tenon width to a snug fit.

-- HorizontalMike -- "Woodpeckers understand..."

View jdmaher's profile


468 posts in 3379 days

#8 posted 04-21-2017 08:31 PM

You don’t really need all this piling on, but forget about using a filler.

Build up the tenon, slightly oversize, then pare it, sand it, plane it – whatever – to make at least the cheeks fit nice and snug.

-- Jim Maher, Illinois

View EricTwice's profile


248 posts in 1333 days

#9 posted 04-21-2017 09:01 PM

You have 2 choices; building up the ill fitting tenon with wood, or building it up with plastic.

Wood is best if the piece is of any importance.

If you just want a quick fix plastic will work too. I would not use gorilla glue. It will fill the joint, but only with foam. it leaves a mess on the surface that is a pain to deal with. your other choices are epoxy or polyester resin.

Epoxy will work well, but it a one shot deal and you can’t undo it. Make sure the interior of the joint is full and there are no air pockets these will be weak points.

polyester resin can be used in exactly the same way. Bondo (Polyester resin paste) can also be used. if the joint is filled, it will hold well. (It can also be removed with solvent and repaired with wood at a later date.)

-- nice recovery, They should pay extra for that mistake, Eric E.

View pintodeluxe's profile


6173 posts in 3613 days

#10 posted 04-21-2017 10:12 PM

Cross peg the tenons while you’re at it. Years down the road when the glue fails, the M & T will still hold together just fine.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View pontic's profile


797 posts in 1408 days

#11 posted 04-21-2017 10:20 PM

I agree with all the “add to the tenons” group. When adding the shims plane and fair both sides as even as you can.

-- Illigitimii non carburundum sum

View bobro's profile


320 posts in 2110 days

#12 posted 05-07-2017 02:02 PM

Another vote for building up the tenons rather than tryign to fill up the mortises!

-- Lao Ma: You are so full of anger and hatred. Xena: Everybody's gotta be full of something.

View shipwright's profile


8570 posts in 3598 days

#13 posted 05-08-2017 12:18 AM

I agree on the building up of the tenons. I would use veneer (because I have a LOT) and would not likely need to pare at all.
Next point: if the piece is as previously mentioned “of any importance” you should determine the glue originally used. If it is that age it may well be hide glue and if so the repair should be done with hide glue.
The advantages are that it maintains the value as an antique, does not require complete cleaning of the mortise and the tenon, cleans up with water making patina retention easier, and is truly reversible. Of course it is stronger than the wood provided the fit is good.
Just my thoughts.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View Just_Iain's profile


326 posts in 1216 days

#14 posted 05-08-2017 12:57 AM

I’ll also vote for building up the tenons. And pintodeluxe might be onto a good additional point of cross pegging if it won’t show.

-- For those about to die, remember your bicycle helmet!

View runswithscissors's profile


3105 posts in 2825 days

#15 posted 05-08-2017 04:14 AM

IF you should decide to try filling, only epoxy will do that. And mix the epoxy with wood flour, ideally from a sander. The wood thickens the epoxy, strengthens it, and helps fill the gap. No other glue (that I’m aware of) has epoxy’s gap filling qualities.

Another idea: saw a thin slit (like with a bandsaw) up the tenon from the end. Made a thin wedge to go in that slit. Using clamps, carefully press the wedged tenon into mortise. Glue, of course. The wedge will spread the tenon and lock it in place. Tricky, admittedly, as you want just the right thickness of wedge. I would prefer this over gluing face pieces on the tenon.

You could try this dry, before glue, but getting the assembly apart again to glue it might be challenging

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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