Glue Lines On Table Top

[Scottb]

I have recently glued up a table top from maple and sheaoak boards. I used biscuits with standard PVA glue. After sanding down to 400 grit I left the top overnight. Next day I noticed that I could feel slight raised lines along the glue join in the boards. I gave them a quick sand and it appeared to fix the problem. I have then proceeded to apply a hand rubbed oil finish (polyurathene/tung/linseed) to the table top and when I went to give it a second coat noticed that the slight raising along the glue lines had returned.

Two questions:
1. How can I stop this from happening to any future projects?
2. Is there any way to stop the glue lines raising on the current table top?

I hope someone can help with this. http://ubb.ubeaut.com.au/ubb/smile.gif

[Shane Watson]

Scott,

What causes this problem is moisture along the timber of the joint. What sets it off is the use of a water based glue, eg PVA. It unsettles the current moisture along the joint and sets off a reaction of moisture escaping. What happens when you seal the timber the moisture tends to jump from board to board thus causing the continual rising after sanding.
I had this problem come and go when I first went into business. I had never even heard of it so it took some tracking to find a solution. I now use a Ureaformeldahyde Glue, which is not water based. Since using this glue I have not had one raised glue line. There are other adhesives you can use though, but stay away from water based.
There are also other thechniques that should be adopted to reduce any movement along joints. Such as gluing as soon as possible after machineing.
I have heard of people wiping down the joint surface with metho or thinners etc to try and help remove any moisture along the joint line, although I cant speak from experience whether this helps or not.
To remedy your problem, I would break your joint remove any glue and let it dry for a week or two, then remachine and rejoint with a non-waterbase adhesive and yes refinish. Thats what I would do, others may have simpler solutions for you.
Others may also have a simpler explanation as well http://ubb.ubeaut.com.au/ubb/wink.gif

HTH

Cheers...



------------------
Shane Watson..

Combine Love & Skill & You Can Expect A Masterpiece!

[RFNK]

Ordinary ol' PVA is infamous for creeping, even over extended periods. That's why you can also buy cross-linked PVA (yellow glue) which isn't supposed to creep. Its only disadvantage, as far as I know, is that it sets really quickly, so you have to have your clamps etc. all set to go.