Darryl Keil Last Activity 2025-09-09 11:09 AM
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Jason Stumpf

 
Subject : Unibond and solid wood
Posted : 2004-02-23 1:16 PM
Post #31300
I recently built a set of walnut chairs using unibond 800. The seats are 8/4 walnut boards, edge glued with a few biscuits in them, and the top rails were two curved 8/4 boards laminated together to finish at 3 3/4" thick. Everything went great in the shop, and the longer open time of the unibond was key to successful glue-ups. Now, however, after a few months, a glue line on one of the seats is opening up! I brought the chair back to my shop, cut out the bad joint, fit and glued in a new piece, re-carved the seat, and was sanding it when I noticed that the edge of the laminated top rail is starting to open at the glue line as well. In fact, i can insert a feeler gauge about 1/2" into the joint. I would usually use 2-part epoxy for this kind of joinery and laminating, but I thought the unibond 800 would do as good a job. The glue cured as usuall, and I gave all the parts at least 24hrs before any serious cutting/carving. Do I have a disaster on my hands here? And was I wrong in assuming that I could use unibond 800 for solid wood joinery? Thanks in advance...


 
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Brian Gray

Posts: 339

Joined: 2004-01-21
Location: Sandusky, OH

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Subject : RE: Unibond and solid wood
Posted : 2004-02-23 2:48 PM
Post #31301 - In reply to #31300
I have used Unibond for joinery many times, when a long working time is needed.

The only time that Unibond has not worked for me is when it's my fault...by not speading enough on....I like to make sure there is plenty of adhesive by buttering it up.

That's the only thing that I can think of.


 
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Steve Jenkins

Posts: 15

Joined: 2003-12-19
Location: Dallas,TX

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Subject : RE: Unibond and solid wood
Posted : 2004-02-23 4:46 PM
Post #31303 - In reply to #31300
I haven't used Unibond but use another brand that is essentially the same thing and it is pretty temperature sensitve during curing. It says 70 degrees and talking with the mfg. he said that it is probably ok down to 65 but below that it will harden but not have the strength it should have. Could that be the problem? Steve


 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Unibond and solid wood
Posted : 2004-02-23 7:02 PM
Post #31306 - In reply to #31300
Jason,

Its hard on a forum where you dont get a back and forth conversation to properly indentify what the cause really is. With that said, here are a few thoughts. First, you should know that the problems you are experiencing now was actually there the day after you glued it up. Unibond 800 is a glue that achieves its final bond by chemical reaction. Once that reaction is completed nothing changes with the bond. The reason you are seeing it show up a couple of months later is probably due to climate changes that are causing movement in the wood or the customers use of the chairs, chairs get a lot of flexing with use. Its not that the problem wasnt there the next day, just that conditions are bringing it to light now.

As far as the cause, my first question would be the same as Steve's, were you up to proper temperature? This is important with any urea resin glue like Unibond 800. Unibond 800 also needs a sanded or sawn surface for good bonding on solid wood rather than a jointed one. In general Unibond 800 works just as well on solid wood as it does on veneer so you shouldnt really have a problem.

Sincerely
Darryl Keil


 
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Jason Stumpf

 
Subject : RE: Unibond and solid wood
Posted : 2004-02-24 6:40 AM
Post #31310 - In reply to #31306
Thanks everyone for the responses. Brian, I did have plenty of squeeze-out on all the glue-lines. Steve, the temperature issue is interesting (and a bit scarry). Darryl, I agree with you that whatever is going on is due to the glue-up, and simply showing now as the wood moves. The temperature issue is very likely, as i'm working in a small shop heated via wood stove. The ambient temperature is usually in the low 60's. But it can fluctuate during the day, and drop down into the low 40's/high 30's at night if its very cold outside. The unibond did cure though, and the squeeze-out was all hard and brittle as expected. Can unibond cure with less than full strength? Thats a new property to me. I've always thought that with glue, it would either cure or not. Everything was jointed or planed flat before glue-up. Unibond wants a little tooth in the wood surface? Will a scuff-sanding with 100g or 120g do?
At least this client is very understanding.
Thanks again everybody...
Jason



 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Unibond and solid wood
Posted : 2004-02-25 10:46 PM
Post #31318 - In reply to #31310
Jason,

Even though Unibond 800 will get hard below the minimum temperatures that alone does not mean you will achieve a good bond.

As far as providing a bit of "tooth" for the glue, 100 grit is fine. Its not needed in every case, just an extra precaution.

Sincerely
Darryl Keil


 
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Jason Stumpf

 
Subject : RE: Unibond and solid wood
Posted : 2004-02-26 6:20 AM
Post #31319 - In reply to #31318
Darryl,

Sorry to re-state this, but just for my personal education, let me get this straight: if Unibond 800 (or any urea-formaldahyde resin) cures in temps less than 65 degrees far., the bond formed onto the wood may (or will?) not be as if it cures at above 65 degrees? This brings some interesting limitations for those poorly heated shops...

Thanks for the advice so far...

Jason



 
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Steve Jenkins

Posts: 15

Joined: 2003-12-19
Location: Dallas,TX

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Subject : RE: Unibond and solid wood
Posted : 2004-02-26 8:13 AM
Post #31320 - In reply to #31319
You got it Jason. Depending on the size of the item you are gluing up maybe you could take it into the house. It does kpresent a prob;em though. I like to keep my shop at about 60 or so in the winter and turn the heat down at night but when using the urea-resin glue I have to crank up the heat and leave it on. Doesn't help the gas bill any. When veneering I use an electric blanket to keep things wram. Steve
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