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Do I need to do this glue-up again?

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Doug71

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Thanks Doug, that's useful to know. I'll look to add some to the glue collection. Titebond's PU glue seems to need above 10 degrees though so any pointers on a low-temp brand would be welcomed.

I tend to use the Everbuild Lumberjack range, just looked and they recommend a minimum of 5 degrees.
 

Adam W.

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Hi Adam,

I tentatively tried to flex the panel at the centre to see if it had any strength at all and it seemed solid. I then supported the two long edges and placed a 10kg kettle bell on the joint and it didn't fail but I only left it there for a few minutes. I'm not expecting it to get any real stress in its intended use, so I guess the only thing that might cause an issue is any movement once it is in the house and acclimatises?
I'd say you were OK and that you should just move on and keep building with confidence.
 

grumpycorn

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When it happened to me, it was pretty obvious straight away the glue up had failed. You’d know by now!
 

Baball

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Phew, thanks all. It's going to be close getting this complete in time anyway, so not having to re-do anything is a relief!
 

Baball

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I think I've had my first hard lesson in wood movement. I haven't been able to do anything on this project for a week or so, I left the panel flat on my bench (a sheet of MRMDF levelled on top of an old table) in the garage, and found it has bowed like this. I've brought it into the house as that is where it will live anyway, hoping it might move back, but I'm doubtful.

Is there anything I can do to salvage this? Even if I had hand planes or a planer, I would lose too much thickness flattening it out, I think.

PXL_20211216_201519978.jpg
 

Baball

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Breadboard ends might do the trick, but you'll need to clamp it flat whilst you cut the rebates.
That's a great idea, thanks.

I do wonder if trying to clamp it straight will stress the possibly questionable glue joint. I guess it either will or it won't. If it doesn't; great, if it does; I'll just glue it up again (in the warm this time).

I fear this hiccup has pushed delivery of this project past Christmas now though :(

Heads off to learn how to do breadboard ends...
 

Sgian Dubh

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I think I've had my first hard lesson in wood movement. I haven't been able to do anything on this project for a week or so, I left the panel flat on my bench
Try wiping a damp cloth on the concave face. Repeat as necessary for a few hours(overnight?) and see what happens. If the cup is stubborn you could even leave a folded up damp cloth (wood chips) or some other moisture retaining material on the concave face for a few hours/overnight. You have to approach trying to take out cupping fairly cautiously. You can over compensate, and sometimes, even if you get the panel to straighten out, the fix is only temporary, and it will cup again.

I'm guessing the lesson you've learned is that you need to let air circulate all around a panel to reduce the likelihood of warping, including cupping. So, in future, sticker up panels and boards to allow the necessary air circulation. Slainte.
 

Baball

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Try wiping a damp cloth on the concave face. Repeat as necessary for a few hours(overnight?) and see what happens. If the cup is stubborn you could even leave a folded up damp cloth (wood chips) or some other moisture retaining material on the concave face for a few hours/overnight. You have to approach trying to take out cupping fairly cautiously. You can over compensate, and sometimes, even if you get the panel to straighten out, the fix is only temporary, and it will cup again.

I'm guessing the lesson you've learned is that you need to let air circulate all around a panel to reduce the likelihood of warping, including cupping. So, in future, sticker up panels and boards to allow the necessary air circulation. Slainte.

Thanks Slainte, I'll give that a try first. Just so I'm doing this right: it was the concave face that was down on the bench, does that still fit with making that side damp?

And thank you for the information about the air circulation. I hadn't yet considered what had caused it and probably wouldn't have worked it out.
 

sometimewoodworker

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And thank you for the information about the air circulation. I hadn't yet considered what had caused it and probably wouldn't have worked it out.
you currently have a moisture gradient across the board because the face that was in contact with the MDF didn’t get as much moisture as the open face. The moisture has allowed/caused the fibres in one face to swell slightly, your hope is that you may be able to add moisture to the other face to counter this. It might work, it might not. If it doesn’t then ripping down the centre and glueing it back together with one board flipped is the common fix.
 

Baball

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you currently have a moisture gradient across the board because the face that was in contact with the MDF didn’t get as much moisture as the open face. The moisture has allowed/caused the fibres in one face to swell slightly, your hope is that you may be able to add moisture to the other face to counter this. It might work, it might not. If it doesn’t then ripping down the centre and glueing it back together with one board flipped is the common fix.

Thank you sometimewoodworker! I was starting to think that the exposed faced would have dried more but taking on moisture makes so much more sense! My experience so far has mostly been with birch plywood, MDF, and redwood but I would really like to be able to use this oak in this project. Off to give the panel a wipe...
 

sometimewoodworker

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Thank you sometimewoodworker! I was starting to think that the exposed faced would have dried more but taking on moisture makes so much more sense! My experience so far has mostly been with birch plywood, MDF, and redwood but I would really like to be able to use this oak in this project. Off to give the panel a wipe...
It’s impossible to predict if an exposed board face will gain or loose moisture and move without quite a bit more information than was given, things like the ambient humidity (likely to be high in the [sarcasm] hot sunny [/sarcasm] winter months in the UK, the air movement across the board, the dew point (this could have allowed even more water on the surface), the starting moisture content of the wood, if there is stress in the wood etc.

But since the exposed face has increased its dimensions (the bow proves this though not exactly why) added moisture to the cupped side may correct this. Also a slight dryer airflow across the bowed side while keeping the cupped side slightly damp may help.
 

Sgian Dubh

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... Just so I'm doing this right: it was the concave face that was down on the bench, does that still fit with making that side damp?
Essentially, yes. The alternative is to induce drying of the fibres on the convex surface to cause cross grain shrinkage leading to straightening. It's often easier to add moisture to the concave face, e.g., wipe with a damp cloth, or similar.

sometimewoodworker has basically explained the mechanism or cause of the cupping, i.e., one face of the panel shielded from the room's (workshop's) relative humidity (RH) through lying directly on a flat surface; the other face was exposed to the atmospheric RH and, in this case absorbing moisture causing the upper surface to expand leading to cupping with, in this case, the convex side uppermost. The result would have been the opposite of what you got if the upper surface of the panel had been exposed to RH conditions (drying conditions) that caused cross grain shrinkage of the panel's upper surface rather than expansion. Slainte.
 

Baball

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Thank you both for the detailed information; I have learnt a lot.

Over two or three days I wiped the panel several times on the concave surface, but it mostly held its form. Thinking that I might also be able to use the cause as the cure, I moved it back to the garage and placed it the other way up on the bench, checking on it every 12 hours or so. It has now mostly straightened out so I have put it on sticks in the hope it doesn't now cup in the other direction!
 

sometimewoodworker

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Thank you both for the detailed information; I have learnt a lot.

Over two or three days I wiped the panel several times on the concave surface, but it mostly held its form. Thinking that I might also be able to use the cause as the cure, I moved it back to the garage and placed it the other way up on the bench, checking on it every 12 hours or so. It has now mostly straightened out so I have put it on sticks in the hope it doesn't now cup in the other direction!
Just putting it with sticks isn’t going to be enough. You need, quite urgently, to get another board or several on sticks on top of the board you are trying to get the bow out of and get some significant weight on to it then get air movement through the stack so as to dry it all out, if you don’t do that when you bring it inside into a less humid environment it’s just going to cup again
 

Baball

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Just putting it with sticks isn’t going to be enough. You need, quite urgently, to get another board or several on sticks on top of the board you are trying to get the bow out of and get some significant weight on to it then get air movement through the stack so as to dry it all out, if you don’t do that when you bring it inside into a less humid environment it’s just going to cup again
Argh! Understood. I have some kettle bells in the garage, I can use those to add weight to the board.

Seeing the discussion in another thread about unheated workshops and the potential for an oak door to move when fitted, I was thinking once it is straightened out, I should bring it in and leave it inside, stored somewhere on its end to allow air to most of the surfaces, taking it back out to the garage only for working on that particular part?
 

sometimewoodworker

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Argh! Understood. I have some kettle bells in the garage, I can use those to add weight to the board.

Seeing the discussion in another thread about unheated workshops and the potential for an oak door to move when fitted, I was thinking once it is straightened out, I should bring it in and leave it inside, stored somewhere on its end to allow air to most of the surfaces, taking it back out to the garage only for working on that particular part?
Just putting weight on the board itself is probably a poor choice, get another board (anything will do from MDF throgh plywood to any species that you have available ) on stickers onto your project board then any weights of anything onto that board. I personally would have an inexpensive fan blowing on the stack for a few days.

You will find that a moisture meter will help a lot, even the cheapest ones will give a good guide to the difference in surface moisture between boards in your garage and in the house, they won’t be accurate as to the exact level but then you don’t need that, you just need to find out the difference and for that they are excellent.

As to taking wood out to work on it and bringing it in, that’s a good choice. Also once joints are cut fitting them together asap even if you aren’t gluing them is a good idea.
 
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