A Squared said:

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A couple of observations in no particular order:

Gluing two pieces of framing lumber together, with no surface prep is probably not an ideal case for an adhesive.

From your description, the glue failed because of the force of the 2x6's trying to re-bow and pulling apart. This is "peel" and frequently this is the direction that a glued joint is the least strong. generally, they are stronger in shear, which is keeping the two pieces from sliding across each other.

If you;re gluing two bowed pieces of wood together, you'll probably have better results doing it by placing them with the ends touching and squeezing the middle together. this makes it so that the ends are held together by the tension in the wood, and keeps a 'peel" failure from developing at the ends and progressing to the middle

I don't think that I'd use liquid nails or other construction adhesive for anything but gluing up panels, and never for the sole means of attaching a panel which is a part of a structural assembly.

Gluing two 2X6's side by side for a header adds almost no strength over the combined strength of the two individual 2X6's.

None of this really answers your question, but it's food for thought.

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KC said:

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If you had left the screws in would the bow have pulled the pieces apart? I'm not sure this was a 'fair test' of the LN.

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Herb G said:

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I'd replace the wood you tried to join with new stock.
Rough it up first, then use Gorilla glue. Spray one piece of wood with a mister bottle, put the glue on the other piece, then join & clamp for a good 12 hours.
I guarantee you it won't pull apart.

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Quote:

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As for the original problem, it may have simply been an old tube of LN.

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SkyGlider said:

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When building the door header for my shed, I used a 2x6 that I already had. The 2x6 was slightly bowed (not crowned). I cut 2 pieces from that 2x6 to make the double 2x6 for the door header. Then I put "Heavy-Duty Liquid Nails Construction Adhesive" on one 2x6 in a sine wave pattern all the way down one 2x6. Since the 2x6s were bowed, the center touched with gaps on both ends. I screwed the 2x6's together which removed the bows from them.

About a week later, I changed my mind and decided to use 2x8s for the door header. So I did the same thing to the doubled up 2x8s. In that process, I removed all of the 3" screws from the 2x6 header to use on the 2x8 header.

Well about 2 weeks later, I discovered that the 2x6 header had pulled apart due to the previous bow. The break was on the Liquid Nails so there was Liquid Nails on both 2x6s. IOW, the Liquid Nails itself failed and was not stronger than the bond to the wood.

I have lost confidence in using Liquid Nails. Did I do something wrong? Maybe it was the wrong application for using Liquid Nails. Googling, I notice that others have had things come apart using Liquid Nails.

Do you use a different (better) construction adhesive that comes in a caulking gun tube for gluing things together like for doubling up 2x8s for door headers?

Thanks,
Skyglider

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