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I've seen a lot of posts here that mention the appearance of a glue line over time. I have always used Titebond I and II in up to 2" thinck glue ups for tabletops, etc. and have never experienced this. I typically use hand applied finishes and pre/post cat lacquer. Am I just not understanding this??
The only times I have had a glue line swell was when using an oil finish. I am no chemist but I suspect PVA can absorb oils and in doing so causes the glue to expand. It didnít seem to affect the strength of the joint. Unsightly though.
One instance where glue lines swell is when there is a heated finishing oven or when there is heat generated in sanding. The heat softens the adhesive so that the pressure of the glue line is able to squeeze out this adhesives slightly.
We've had this discussion many times on Woodweb. Check the Knowledge Base.
Softer formulas of PVA seem to get crushed and protrude out of the joint causing a raised glueline. They can be sanded back flush; unfortunately, they typically reappear in a matter of weeks or months, after finishing.
Titebond 2, 3 and white are the typical problem children. Titebond 1 never has this issue. It is almost brittle after curing.
I have seen this in entire houses of mitered casings that have never seen a sander. Franklin white glue was the adhesive.
A glue joint is typically under pressure, so if the glue is soft naturally, or from heating, or from moisture, it will likely squeeze out. It shows up worse with a thicker glue line or glossy finish. Perhaps the finish can soften a glue...I do not know.
I have only seen this on softer woods like pine and bass. I chalked it up to the wood shrinking . It was more prominent in the winter months . Even though it was finished on all six sides the wood moved more than the glue.
I am using powder type (old-fashion) adhesive, mixed with water, and some industrial chemical for hardening purposes. The technique i use is, wiping very thin adhersive on the edge, then clamp them hardly. Wipe with wet cloth on the glued line, and leave for 12 hours. Then plane the surface. You will never see the border or glue line.
The "old fashioned" powder glue contains formaldehyde. Most shops should avoid this, as there is more evidence about the long term damage from formaldehyde, and many staes such as California strictly control such products.