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What would be the best way to glue two surfaces which have already been finished with Danish oil and then wipe-on poly?

One surface would be the cut edge of ply, the other surface would be solid wood. Specifically: a long 2 1/4” width of solid wood capping two other edges of ply separated by a 3/4” gap.

I won't be able to biscuit or dowel, but the good news is that this isn't structural - just a finished surface. Nevertheless, it's not an ideal situation, so some collective wisdom would be helpful here.

  • Follow-up note: The cut edges of ply still look fairly porous, so, the bigger problem is the solid wood. Perhaps if I just rough-up the solid wood with a file or something??? – Dale Feb 5 '19 at 17:45
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    Honestly, the best way is to remove the finish to bare wood so the surfaces mate properly and glue it up. This is especially true if edge grain is involved at all. (BTW, you should be in the habit of editing the question text to add details. Comments can be deleted and are not strictly part of the question.) – jdv Feb 5 '19 at 17:48
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    Some refs: woodworking.stackexchange.com/a/2348/5572 woodworking.stackexchange.com/a/6941/5572 woodworking.stackexchange.com/a/364/5572 (I couldn't find a specific Q&A that addressed the specific context here. This may be an open Q&A for a wiki reference answer.) – jdv Feb 5 '19 at 17:55
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    No, don't rough up the solid wood. Generally the smoother the surface the better for a strong glue bond (this is why the super-smooth edges a jointer plane can create glue together so very well). For a non-structural thing this isn't that critical, but something to bear in mind for the future. – Graphus Feb 5 '19 at 18:31
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    "There’s still a lot of porous bits there that should help the glue bond with the ply." You won't normally get any bond worth noting in porous stuff, this is why end grain joints glue weakly. And it's why edge joints in MDF and plywood are noted for not being strong. Most glues are only strong in a very thin film between two surfaces that are in intimate contact. I would recommend you glue with epoxy which is one of the only common adhesives that works well thick (and also does not require strong clamp pressure to achieve strength, which is the case with almost all other glues). – Graphus Feb 5 '19 at 18:57
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Short answer: remove the finish, smooth gluing edges, glue, and clamp.

Longer answer: apparently what is being joined are two slightly irregular surfaces that cannot be smoothed ideally. Recommended solution is to remove as much of the finish as possible (scraping should be more than enough removal) and epoxy the joint.

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