# Why my joints fail in summer!



## akirapix (Jul 2, 2021)

Hi everybody,

i am an happy hobbyist who tries to became a better woodworker. I have a question for who will be so kind to help me. 
I built a chair a month ago using fir wood and toulipier wood.

I am sure wood moisture was almost ok (because i measured with an electronic tool and saw it was 8%). I used mortice - tenon joints and some cross-lap joint. Everything was ok until summer arrived. After some hot days (40°) i noticed a small gap appearing in my crosslap joint (about 1/64 inch)

This is one of my joints

__
https://flic.kr/p/2m8UX1z

As you can see there is a dark line (1/64 inch) that was perfect one month ago.

I know wood moves and there is nothing to do, but which approach i would have been following?

I used a wrong join that could never resist? 
Wrong wood type?
Wrong glue?

Please tell me what was my mistake.

Thanks


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## controlfreak (Jun 29, 2019)

Is the gap or separation equal on all sides of the joint? If not if may be the tenon deflecting or warping in relation to the mortice. No expert here but I am curious.


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## ocean (Feb 13, 2016)

I am no expert either but I'm going to blame it on the fir. It has swelled up in the increased atmospheric moisture of summer.


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## akirapix (Jul 2, 2021)

> Is the gap or separation equal on all sides of the joint? If not if may be the tenon deflecting or warping in relation to the mortice. No expert here but I am curious.
> 
> - controlfreak


nice question. it looks like the gap is only relative to the horizontal piece (toulipier). something like toulipier is shrinking and fir is stable….


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## splintergroup (Jan 20, 2015)

The horizontal piece shouldn't change in length so assuming the concerns raised by controlfreak are not happening, I highly suspect the fir has shrunk. In your area, how does the humidity change between summer/winter?


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## akirapix (Jul 2, 2021)

> The horizontal piece shouldn t change in length so assuming the concerns raised by controlfreak are not happening, I highly suspect the fir has shrunk. In your area, how does the humidity change between summer/winter?
> 
> - splintergroup


i am in the south of italy. humidity changes a lot and temperatures too. this chair was built at 25° celsius and started showing gaps at 40° celsius.

I wonder what a professionist would have been building this chair. Which joints or wood to be used…


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## MadMark (Jun 3, 2014)

Yes, its the fir shrinking. Those fat growth rings are sponges changing size with the humidity.

This is why you want to build with Kiln Dried (over dry) lumber. It is at it's smallest and can only expand, tightening, not loosening, the joints.


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## akirapix (Jul 2, 2021)

> Yes, its the fir shrinking. Those fat growth rings are sponges changing size with the humidity.
> 
> This is why you want to build with Kiln Dried (over dry) lumber. It is at it s smallest and can only expand, tightening, not loosening, the joints.
> 
> - Madmark2


thanks, but….
i measured wood moisture and was 8%. Has Kiln dried wood a moisture level lower than 8%?


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## AlaskaGuy (Jan 29, 2012)

Kiln dried lumber @ 8% will become 10-12% after sitting in my shop for a spell. Lumber will adjust to its environment.


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## MadMark (Jun 3, 2014)

KD should be ~3-5% drier than air dried. *Don't* acclimatize it. Use it BEFORE it swells back up to 8%+.


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## AlaskaGuy (Jan 29, 2012)

> KD should be ~3-5% drier than air dried. *Don t* acclimatize it. Use it BEFORE it swells back up to 8%+.
> 
> - Madmark2


Good luck with that. By the time lumber get shipped to my region, it's already changing moisture content. No kiln here to pick up lumber, rush home and build immediately. In 50 years in Alaska, recall seeing 8% lumber.


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## Unknowncraftsman (Jun 23, 2013)

It also could have been the horizontal piece didn't have a shoulder that was square to the face.
Clamps could close the joint at the time of assembly but time and Mother Nature uncovered the defect.
Seems like awful lot of shrinking for such a small part.
This is my guess from 5000 miles away 
Good Luck


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## Ocelot (Mar 6, 2011)

That seems pretty normal to me. M & T is a cross-grain joint. It's near impossible for it not to move, no matter what glue you use.

If it will comfort you, read Paul Sellers's account of learning about miters when he was an apprentice. Of course, miters are different but some of the same forces are at work in a M & T joint.

https://paulsellers.com/2020/09/i-stood-back/


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## EdWeber (Jun 17, 2021)

A swell as the seasonal changes in the wood, with a cross-lap joint you have much less glue surface than with the M&T joints which could be one reason. 
You can also use the kigoroshi technique when assembling for an added level of security in the fit of the joint.


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## MikeB_UK (Jul 27, 2015)

Did you cut the mortice deeper than the tennon?
Leaving a gap at the end can help it not pushing out when it moves.


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## rwe2156 (May 7, 2014)

Well I'm going to say if the lumber was 8% if anything it would swell if living outside.

So, I think its a glue joint failure. Possibly not enough glue.

If you pin those tenons it will be rock solid.


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## EdWeber (Jun 17, 2021)

OP used M&T and cross-lap, it's the cross-lap that's failing


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## therealSteveN (Oct 29, 2016)

Instead of the wood type, joinery, or the plus or minuses of wood movement relative to it's current moisture, which is a known. I'm going to suspect said moisture meter is a low dollar not worth buying model, of which the world is filled, and builders everywhere then become perplexed with questions about why my wood did this or that?

More information about the meter used, cost, name brand, etc.

If the meter is problematic, and the wood was actually 22% do you see how that could make a difference.



> Did you cut the mortice deeper than the tennon?
> Leaving a gap at the end can help it not pushing out when it moves.
> 
> - MikeB_UK


Of the things unexplored, this question is actually one instance where it might be the joint, as the vertical wood widens, shrinks, if the tenon inserted into it is bottoming out, it will appear to move the horizontal piece. When in reality the joint didn't allow movement we know will happen.


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## akirapix (Jul 2, 2021)

> It also could have been the horizontal piece didn't have a shoulder that was square to the face.
> Clamps could close the joint at the time of assembly but time and Mother Nature uncovered the defect.
> Seems like awful lot of shrinking for such a small part.
> This is my guess from 5000 miles away
> ...


Maybe you are right. I honestly do not remember if i did a lot of clamp pressure, so maybe you are right


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## akirapix (Jul 2, 2021)

> Did you cut the mortice deeper than the tennon?
> Leaving a gap at the end can help it not pushing out when it moves.
> 
> - MikeB_UK


i do not understand your question. the two pieces have a square section of 1.5inch x 1.5inch and horizontal piece was cutted in the middle. i think they can be considered equal


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## akirapix (Jul 2, 2021)

> That seems pretty normal to me. M & T is a cross-grain joint. It s near impossible for it not to move, no matter what glue you use.
> 
> If it will comfort you, read Paul Sellers s account of learning about miters when he was an apprentice. Of course, miters are different but some of the same forces are at work in a M & T joint.
> 
> ...


i'm not alone


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## akirapix (Jul 2, 2021)

> Instead of the wood type, joinery, or the plus or minuses of wood movement relative to it s current moisture, which is a known. I m going to suspect said moisture meter is a low dollar not worth buying model, of which the world is filled, and builders everywhere then become perplexed with questions about why my wood did this or that?
> 
> More information about the meter used, cost, name brand, etc.
> 
> ...


yes my moisture meter is absolutely a cheap one. 40 dollars pin-meter


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## MikeB_UK (Jul 27, 2015)

> Did you cut the mortice deeper than the tennon?
> Leaving a gap at the end can help it not pushing out when it moves.
> 
> - MikeB_UK
> ...


If your tennon is exactly 1 inch long and your mortise is exactly 1 inch deep, any wood shrinkage in the mortise will push the shoulder out because the tennon is pushing on the bottom of the mortise.

If your tennon is 7/8ths long in a 1 inch mortise you don't have this issue.


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## Lazyman (Aug 8, 2014)

^He said in the OP that it is a cross lap joint that is having a problem not a M&T joint.

One way that you can test the theory that moisture loss & movement is the issue is to wrap the area in a moist cloth for a little while and see if it closes up. If it does, that is absolutely the problem. What is the relative humidity difference between when you built it compared to now. If where this chair will be will experience significant swings in humidity, you may have to use wood that moves less than fir and toulipier (we call it poplar or tulip tree here). Both are relatively soft and prone to movement with large swings in humidity.

Are you noticing that the chair is less rigid because of this or is this just a cosmetic issue so far?


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## akirapix (Jul 2, 2021)

> ^He said in the OP that it is a cross lap joint that is having a problem not a M&T joint.
> 
> One way that you can test the theory that moisture loss & movement is the issue is to wrap the area in a moist cloth for a little while and see if it closes up. If it does, that is absolutely the problem. What is the relative humidity difference between when you built it compared to now. If where this chair will be will experience significant swings in humidity, you may have to use wood that moves less than fir and toulipier (we call it poplar or tulip tree here). Both are relatively soft and prone to movement with large swings in humidity.
> 
> ...


Thank you for your clarifications,

i am still learning 

Well i did not tried to wrap the piece with an humid cloth but i will do!!!!

My workshop has no heater or humidity control system so i guess that, between the time i built the chair and the time i put the chair in home (a month) there was for sure an high temperature change (from 25° to 41°) and that changed humidity in air

My chair is absolutely rigid and both cross lap and M&T stay strong. It is a cosmetic issue. Until i build such things for myself i can ignore them, but what if i do a present for a friend or worse someone asks me to build for money?

I think a need to face a truth. I cannot buy here were a i live a better wood that the ones i used, so i am thinking to which kind of joints i have to use. Here in Lecce (south of Italy) is absolutely normal to have temperatures from 2° to 42° in a year.

Is there a better joint? or more simply is a matter of buying higher quality wood? To i have to resign to use composite woods (multilayer, OSB, MDF) because using real wood is almost impossible if i do not have a workshop with heater, humidity control or a kiln?

Thanks!


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## Lazyman (Aug 8, 2014)

Plywood, MSD and MDF are not a great material for chairs. I would rather have small gaps like this than use those materials. Plywood can be made to look nice in some situations but the others are ugly and MDF is not strong enough.

The half lap joint is plenty strong. I think that you will get better results with better wood., though if it will be in a place where humidity changes significantly over the seasons, even better wood is likely to show small gaps like this as the moisture changes. If the chair is in direct sunlight, that will also cause the wood to move more drastically, even between night and day. Using the same wood for both horizontal and vertical pieces will give you a better looking result as well. One way to make this less visible in future projects is to make it so that the horizontal piece is not flush with the vertical one. By having the horizontal piece inset from the edge, small gaps like this will not be as obvious. It does not take much of an inset. Another option to hide gaps is to actually accentuate it by putting a small chamfer on the horizontal edge.

What type of finish did you put on it? The finish won't eliminate the problem but a good finish does slow down wood movement due to moisture changes which may result in less of gap. Also, using the same wood or staining the wood a darker color will help hide the gap too.


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## akirapix (Jul 2, 2021)

> Plywood, MSD and MDF are not a great material for chairs. I would rather have small gaps like this than use those materials. Plywood can be made to look nice in some situations but the others are ugly and MDF is not strong enough.
> 
> The half lap joint is plenty strong. I think that you will get better results with better wood., though if it will be in a place where humidity changes significantly over the seasons, even better wood is likely to show small gaps like this as the moisture changes. If the chair is in direct sunlight, that will also cause the wood to move more drastically, even between night and day. Using the same wood for both horizontal and vertical pieces will give you a better looking result as well. One way to make this less visible in future projects is to make it so that the horizontal piece is not flush with the vertical one. By having the horizontal piece inset from the edge, small gaps like this will not be as obvious. It does not take much of an inset. Another option to hide gaps is to actually accentuate it by putting a small chamfer on the horizontal edge.
> 
> ...


The chair is near a window so it also takes direct sunlight. 
As a finish i used this:
https://www.amazon.it/Oli-natura-olio-legno-naturale-contenuto/dp/B01EYF758Q?pd_rd_w=bzKwe&pf_rd_p=a0641ff0-aee9-440e-a85e-bfcebd3346ac&pf_rd_r=YX9VH2JTN0C156Y9Y675&pd_rd_r=817d5e00-ea0d-459b-ae74-95e68546011b&pd_rd_wg=yV95b&pd_rd_i=B01EYF758Q&psc=1&ref_=pd_bap_d_rp_1_i

an hardening oil similar to Danish oil (i think)

You are helping me very much with this issue. I also fight with edge joins (when building tables or panels). Even if i cross the grain my panels never stay flat…

I ask myself how advanced hobbists and professionists deals with such issues…


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## Lazyman (Aug 8, 2014)

I don't read Italian but that finish appears to be fine. A few extra coats may provide a little more protection?

Getting square and straight edges is essential for gluing up good panel glue ups and you must have enough clamps to get uniform pressure along the entire length. Options are to get a good jointer or to make a jointing jig for the table saw (and have a good quality saw with a good fence). You can also use a hand plane but it takes some practice to get good long joints.

Not sure what you mean by cross the grain? In most cases, you should not have cross grain on panels. Crossing grain can actually cause a panel to warp but perhaps that is a translation issue?

Warping table tops is often caused by one side losing or gaining moisture more than the other. It is very important to put the same type of finish on the underside of the table as the top help keep the moisture changes on the top and bottom uniform to minimize warping. Again, a table that sits in direct sunlight during the day can move more drastically so where the table is can make a big difference. One thing to note is that after gluing up boards to make a panel for a table top, it is important that the panel not be left sitting on top of a bench, even for a few hours. This may cause the top and bottom surfaces to lose or gain moisture at different rates and will almost certainly cause it to warp. You need to either put some slats under it so that air can get to the underside or better, lean it vertically against something (wall or bench) so that air can circulate on both sides.

Table tops is one place where plywood can come in handy. It is much more stable and less likely to warp due to moisture changes. If you cannot find nice looking plywood, you can try applying a veneer of your choice.


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## splintergroup (Jan 20, 2015)

Nathan has a worthy solution if it is indeed wood movement causing the problems. Plenty of ways to construct a joint so any gaps are hidden in the design. Another common solution is to make the joint a visual stopping point with the joined edges rounded over where they meet.

If there is a gap between two surfaces that are otherwise flan and smooth, the gap will be a distraction. If you bury the gap in other joint details, it will disappear.


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## akirapix (Jul 2, 2021)

> Not sure what you mean by cross the grain? In most cases, you should not have cross grain on panels. Crossing grain can actually cause a panel to warp but perhaps that is a translation issue?
> 
> - Lazyman


Yes a translation issue. I read many articles that explain that, when putting together different boards to build a table, you have to alternate the end grain direction (https://www.canadianwoodworking.com/get-more/table-tops-and-wood-movement).

Even if i try to follow this rule there is always something that goes wrong (2mm of cupping)



> Nathan has a worthy solution if it is indeed wood movement causing the problems. Plenty of ways to construct a joint so any gaps are hidden in the design. Another common solution is to make the joint a visual stopping point with the joined edges rounded over where they meet.
> 
> If there is a gap between two surfaces that are otherwise flan and smooth, the gap will be a distraction. If you bury the gap in other joint details, it will disappear.
> 
> - splintergroup


so if i understand well, is not possible at all to use a joint that remains flat and smooth. I always need to plan a way to hide the unavoidable gap?

Otherwise i need to use a finish so "heavy" that covers wood making it looks like plastic

Some much things to learn….

By the way thank you all for you patience and advices. Here in Italy i am having trouble to find someone that help me!


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## splintergroup (Jan 20, 2015)

> so if i understand well, is not possible at all to use a joint that remains flat and smooth. I always need to plan a way to hide the unavoidable gap?


It's always possible to find a way. Consider the Maloof chairs, seamless joints. There is plenty of information on-line about how these chairs are built.

You can construct a simple sample of your joint with leftover scraps. Make the joint and see how it reacts over the seasons. Try alternatives like installing cross pins or using locking joints (dovetails, through tenons, etc.) with samples. 
Your environmental issues are trying, but there is always somewhere that has it worse, and there are always ways people have dealt with it.


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## akirapix (Jul 2, 2021)

> so if i understand well, is not possible at all to use a joint that remains flat and smooth. I always need to plan a way to hide the unavoidable gap?
> 
> It s always possible to find a way. Consider the Maloof chairs, seamless joints. There is plenty of information on-line about how these chairs are built.
> 
> ...


I am looking for info, but i don't understand to which kind of joint you are talking of…
is this one? https://www.popularwoodworking.com/editors-blog/the-maloof-chair-joint/


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## Lazyman (Aug 8, 2014)

I would not say that you need to go with a heavy finish but a good finish will slow down and may reduce the affects a bit. I think that in the case of that joint in your chair, simply using a hardwood like maple, oak, black cherry, walnut, etc. instead of fir would significantly reduce the problem. Given your humidity issues, other tactics like insetting the horizontal piece or other tricks will help hide the issue.

For table tops, one of the most important factors related to warping is how it is attached to the base. You must use attachments that allow for expansion and contraction across the width. If you do not, the only thing that the top can do is warp, break apart or both. The last section of the Canadian Woodworking article you listed above addresses that. Another tactic is to add breadboard ends to the top. When done right, they can help manage wood movement. They can also look quite nice.

Also note that generally quarter sawn boards, where the growth rings are parallel and oriented through the thickness of the board instead of the width, are more stable than other grain orientations so will have less movement across the width. QS lumber is harder to find but may be worth the effort to look for when selecting wood for table tops, that is if you like the look. QS oak for example can have quite interesting grain.


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## AlaskaGuy (Jan 29, 2012)

Top Five Uses of Doug-Fir

https://sherwoodlumber.com/top-five-uses-of-doug-fir/


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## akirapix (Jul 2, 2021)

thanks everybody !!


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## splintergroup (Jan 20, 2015)

Yep, for cross grain joints this is very strong and has features that allow any small changes in wood dimension to stay hidden.

Ideally if you can, in simple terms think of a dowel inserted into a hole. If the wood with the hole contracts, the gap doesn't show. For a simple mortise/tenon if there is a shallow (1/16") recess around the mortise hole sized to fit the tenoned piece, you get the same effect. Certainly a load of more work, but it's features like this that make a piece stand the test of decades.


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## akirapix (Jul 2, 2021)

thanks everybody !!


> Yep, for cross grain joints this is very strong and has features that allow any small changes in wood dimension to stay hidden.
> 
> Ideally if you can, in simple terms think of a dowel inserted into a hole. If the wood with the hole contracts, the gap doesn t show. For a simple mortise/tenon if there is a shallow (1/16") recess around the mortise hole sized to fit the tenoned piece, you get the same effect. Certainly a load of more work, but it s features like this that make a piece stand the test of decades.
> 
> - splintergroup


very interesting. thanks!


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## kelvancra (May 4, 2010)

Problem with that statement is, you could kiln dry to 0%, then leave the wood laying around the shop and it would pick moisture back up until it equalized with the atmosphere.

Finishes on furniture slow moisture transfer, but do not stop them. Take a chest of drawers, for example. Other than crazy types, like me, no one finishes the insides of drawers and such, so they are wide open to moisture changes.

All that aside, I'm in the "YEP" crowd on the shrinking fir. Oddly, I used a lot of 2x's (yes, they were kiln dried) to make picture frames, some six feet tall, and forty years later, the simple 45's are still tight (I might have used splines).



> Yes, its the fir shrinking. Those fat growth rings are sponges changing size with the humidity.
> 
> This is why you want to build with Kiln Dried (over dry) lumber. It is at it s smallest and can only expand, tightening, not loosening, the joints.
> 
> - Madmark2


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## akirapix (Jul 2, 2021)

Sadly, fir is the easiest wood to find here.
Also, it is not of good quality (i buy it in a big store). Not kiln dried at all.

So the question may be:

If i cannot find good quality wood how can i still try to build good furniture with such materials? Maybe it is not possible at all


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## kelvancra (May 4, 2010)

It's possible. Like a said, I used common 2x;s from the lumber yard. It was kiln dried and kept under cover from the Pacific Northwet weather. Then it was kept in my wood burner warmed shop, so moisture was low.

The guys in the lumber yards mocked me, but, hey, it all worked for me.


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## akirapix (Jul 2, 2021)

> It s possible. Like a said, I used common 2x;s from the lumber yard.
> - Kelly


What does "2x;s" means? Is it a measure of lumber size? Or a measure of quality?


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## kelvancra (May 4, 2010)

2x's are just common 2×4's and 2×6's used in construction to build houses. Of course, those measurements are from before the wood is dried and milled to become 1-1/2" x 3-1/2", for 2×4's.


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## MrRon (Jul 9, 2009)

You are joining a soft wood (fir) with a hard wood (toulipier or poplar) and they both have different rates of shrinkage. If you used only one wood, the shrinkage/warpage rate would be equal.


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