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Ridges in glue joints

M

Michael Mendelsohn

Joined
Feb 4, 2013
Messages
38
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Location
Cary, NC
I have tried several projects with blanks made of laminated boards. I laminate the boards using Titebond II and clamp them overnight. I usually wait at least several days before turning. The joints are parallel long grain. The woods are a combination of cherry, maple, walnut, oak and sometimes padauk and jatoba.

I sand to 400 or 600 and the piece seems smooth. I finish with a shellac/BLO/DNA mixture and then wax. After a couple of days there are slight ridges on the glue lines. I have also noticed this problem on other turner's work at our club show and tell.

Am I using the wrong glue or doing something else wrong?
 
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Michael Mendelsohn said:
I have tried several projects with blanks made of laminated boards. I laminate the boards using Titebond II and clamp them overnight. I usually wait at least several days before turning. The joints are parallel long grain. The woods are a combination of cherry, maple, walnut, oak and sometimes padauk and jatoba.

I sand to 400 or 600 and the piece seems smooth. I finish with a shellac/BLO/DNA mixture and then wax. After a couple of days there are slight ridges on the glue lines. I have also noticed this problem on other turner's work at our club show and tell.

Am I using the wrong glue or doing something else wrong?
Click to expand...

Micheal,
I don't know what is causing your problem but I laminate and turn large bowls and items and have not had any problem so maybe what I do will help you, maybe not. I use titebond III and clamp over night only then wait another day before turning. The only procedure I am always very careful to adhere to is I coat both boards that are going together with a coat of glue being careful to cover every square inch with a roller. Then I clamp with every clamp I can find and then some, many might say I over clamp but my joints are solid and never have ridges that I have seen. There is always some squeezing out of the excess glue but not a great deal. You will have to draw your own conclusions based on what you do and don't do. I plane the boards if they are rough cut if not then I just laminate them, no sanding before gluing.
 
There are several issues at work here and all of them have to do with expansion/contraction. First, the different woods will expand and contract at different rates so the thickness of the different woods will vary as the humidity changes. Second, the glue adds moisture locally at the point of the joint. As the moisture eventually evaporates, the wood will move. Sometimes, this effect can be minimized by letting the wood come to equilibrium moisture content (a few weeks to a few months) and then sanding again.

On an unrelated note, I suggest that you use TiteBond original for gluing laminated work. Many of us that do segmented work prefer the original (although this won't solve the issue that you asked about). Titebond III appears to have an aging issue than can cause failure over time. I had a piece glued with Titebond III that fell apart at the glued joints after 9 months.
 
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billooms said:
There are several issues at work here and all of them have to do with expansion/contraction. First, the different woods will expand and contract at different rates so the thickness of the different woods will vary as the humidity changes. Second, the glue adds moisture locally at the point of the joint. As the moisture eventually evaporates, the wood will move. Sometimes, this effect can be minimized by letting the wood come to equilibrium moisture content (a few weeks to a few months) and then sanding again.
Click to expand...

billooms has a great conceptual understanding of this issue, and I'd like to expand on one point he has made. (See bold highlighted in his post.)

He is correct that moisture is added locally and transferred from the glue to the surrounding wood. The glue does not stay at the seam, but clamping pressure forces it into the wood itself. How much of this occurs depends on how much glue is applied, clamping pressure, and the ability of the wood to absorb.

There is one more factor that does enter this equation, and that is how much heat is generated when sanding the glued surfaces. If there is already some moisture transfer surrounding the glue joint, then heat at that point will expand the host wood closer to the glue joint at a greater rate than it will further away from the glue joint. If during the sanding process, more wood is removed close to the glue joint, because of a combination of moisture content, heat, and expansion......then all of these things will mean the wood will contract after sanding at a different rate than the wood that is further from the glue joint, and unaffected by the added moisture.

This effect will obviously vary with different skill levels of different turners. The better tool finish one is capable of producing, the less sanding is required. The less sanding required, the less heat will be generated. This is not to mention that some turners apply excessive heat to their turnings simply because they don't know how to sand properly......yet! 😀

There is no way to eliminate the effects of moisture transfer between wood and glue, but many turners can definitely eliminate the need for sanding more than the bare minimum........by becoming better at leaving a tool surface which requires only the bare minimum of sanding, and by using sanding techniques that produce less heat.

ooc
 
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billooms said:
...the different woods will expand and contract at different rates so the thickness of the different woods will vary as the humidity changes. Second, the glue adds moisture locally at the point of the joint. As the moisture eventually evaporates, the wood will move. Sometimes, this effect can be minimized by letting the wood come to equilibrium moisture content (a few weeks to a few months) and then sanding again.
Click to expand...

The woods may also be starting with different moisture contents. Perhaps placing the pieces in a warm (100F) oven for a couple of hours prior to gluing would help ensure you are starting with minimal differential.
 
I've noticed this effect when I fill voids and cracks with super glue and saw dust, which I assume contains no water moisture. I attribute it to the wood not being thoroughly dry and shrinking, ever so slightly around the joints.The wood looses moisture and shrinks and the glue remains somewhat stable. I have come to believe that wood will always shrink and change it's shape, no matter what is done to it. The glue on the other hand is a more stable material.

cmg
 
I used to make a lot of chessboards and that involved a lot of glue joints. I tried many different glues but ended up coming back to Titebond ("Original"). In my opinion, it is the best wood glue ever and there is no reason to use anything else unless you are making stuff for outdoor use where water resistance is an issue. I also found that, as has been mentioned, a difference in moisture content between the different woods can cause raising of the glue line. On my chessboards, I called it "ridging". You could run your hand over the surface and feel the glue lines. This might occur anywhere from a week to several months after the board was made. People who bought the boards would get upset about it and, for a while, I offered to resand the boards for them. But that got way too expensive and I ended up using only kiln dried woods and measuring the MC before making the boards. I would only use woods with an MC that was within a few percent of each other.

There is another concern and that is the "bound" water in wood. Some of the moisture in wood is simply "free" water and will evaporate as the wood dries. Bound water is part of the molecular structure of the cell walls and remains in the wood even after it is "dry". This is one of the reasons wood never really totally stabilizes and, even after years, will continue to expand and contract with the seasons. The level of bound water will vary from one species to another so the amount of movement in adjacent pieces can still vary even thought their MC might measure the same or close to it. Finicky stuff, wood.
 
I think mostly it's the water from the glue swelling the joint. You sand it flush, then later the wood dries and shrinks, the glue doesn't and you get a line. Wait as long as you can between glue up and turning, and then again if you can between turning and sanding. This lets the wood stabilize. Even then I occasionally feel the glue joint months later which I'm sure is due to the wood moving at a different rate than the glue does.
 
The notorious "glue creep" phenomenon.....

Michael:

What you are describing is what some people call "glue creep".

About three years ago (almost to the day!) this was discussed on Woodcentral in the following thread: http://www.woodcentral.com/woodwork...110/md/read/id/241802/sbj/first-segment-bowl/

Have a read through the first half of the replies, particularly to the response from Malcolm Tibbetts. This appears to be a phenomenon of varying moisture, wood movement, and properties of the glue used.

You may also want to do some searches on "glue creep" and "wood adhesive properties". If I am not mistaken, I recall a discussion of this topic on the Franklin web site (manufacturer of the Titebond adhesives) providing some advice as well.

Rob Wallace
 
I have not done any gluing on turnings, but I have experienced this issue on flat woodworking. The worst case of this was on a eastern red cedar blanket chest. It took two or three months before the glue creep finally quit. My solution there was to use a cabinet scraper along the glue joints to clean off the ridges.I think that I used either hide glue or Titebond II on that project.
 
At work we used gorilla glue poly based from memory and moisture cured .Now retired I still use it and don t have that problem that I have noticed even on the Chess boards It may be that it moves with the wood. Any thoughts on that welcome it may solve the problem.

Ian
 
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