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Thread: Veneer seams opening

  1. #16
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    Thanks for the vote of confidence Andrew. But as I mentioned earlier, I don't think my bathroom gets much humidity. Certainly there are swings when we shower, but the vent fan does a great job of removing moisture so there's never any condensate anywhere. But, OK, let's assume it was due to humidity swings. What would you do to overcome the problem? BB Ply with Unibond 800? I'm nervous about some future jobs, even though they are not for bathrooms, and want to take the most conservative approach.

    John

  2. #17
    Quote Originally Posted by John TenEyck View Post
    Thanks Mel. I never wait after mixing, but certainly can do so and then remix. I've never had a batch that didn't cure really hard, so it's hard to believe it wasn't mixed sufficiently, but you never know and it costs nothing.

    John
    I find that waiting and then stirring helps to reduce the lumps in the glue. Otherwise, it doesn't do anything.

    Mike
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  3. #18
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    You definitely sealed up the MDF with the ash and then further with the finish. It sure doesn't seem like a moisture issue. Are the panels that failed all still coplanar? I'm betting so.

    So this leads to a glue problem that might perhaps be getting stressed from the slight moisture increase.

    I don't edge glue my shop-sawn veneer panels either but I know David Marks does. I just pull them very tight with veneer tape. I usually get squeeze-out along this line so I figured that the edges are getting some glue.

    Another stretch thought is possible contamination of a foreign substance around the veneer edges and so they didn't glue well and then are being stressed by the moisture.

    My 1/16" shop-sawn walnut veneers on a double 5/8" MDF sandwich all glued with BetterBonds and vacuum pressed but not in a high-moisture environment tansu is fairing well several years later.
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  4. #19
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    Quote Originally Posted by John TenEyck View Post
    Thanks for the vote of confidence Andrew. But as I mentioned earlier, I don't think my bathroom gets much humidity. Certainly there are swings when we shower, but the vent fan does a great job of removing moisture so there's never any condensate anywhere. But, OK, let's assume it was due to humidity swings. What would you do to overcome the problem? BB Ply with Unibond 800? I'm nervous about some future jobs, even though they are not for bathrooms, and want to take the most conservative approach.

    John
    I torture test samples. Keep records of exact processes including finish.
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  5. #20
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    Quote Originally Posted by John TenEyck View Post
    Hi Chris, I ran a strip of ash about 1/2" wide around all the edges of the MDF first, then veneered both sides. After trimming it looks almost like a solid wood door. The doors are finished with a shellac toner and then 3 coats of GF's Enduro Clear Poly.

    Here's a pic of the doors during installation. The veneer seams are not where those shallow dados are.

    Attachment 310544
    John, this looks great, too bad about the seam lines showing now. Its also too bad that the seams aren't coincident with the shallow dado's because then you wouldn't see anything at all. Having said that, where are the seams?

    No doubt the issue you are experiencing though has something to do with moisture uptake and now drying out (in the ash). More so I think than moisture uptake in the MDF. Weldwood Plastic Resin Glue should be pretty stable against moisture when cured. It could be that those ash strips were just higher moisture content than you expected or they sucked the moisture out of the glue before it cured. It would therefore seem that an adhesive change might be the best fix for the next laminations you do
    Last edited by Pat Barry; 04-02-2015 at 12:48 PM.

  6. #21
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    Thanks Pat and every one else for your thoughts. I'll take some photos of the seams when I have a chance, so you can see what I'm talking about. At this point I think the best thing I can do is change to Unibond 800.

    John

  7. #22
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    I don't think this one has been answered: Did you use a backing or balance veneer on the other side? Another thought; is the edgebanding moving and pulling or popping the seams apart?

    K

  8. #23
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    Yes, veneered both sides with the same stuff. Edges pulling? Doesn't look that way to me.

    John

  9. #24
    I looked for a copy of the older "let it sit" directions but did not find them. But in comments made by users I did see
    several mentions of it being a good idea. From curiosity I would be compelled to glue up a sample in that manner using
    the same materials and compare results.

  10. #25
    Your procedure seems correct, so it would seem that the conditions as installed must be drier than the fabrication conditions. Granted, bathrooms experience intermittent high humidity, but will fall back to whatever the prevailing humidity is in the house, which can be pretty low in our region in the winter. Do you have records or a recollection of the shop conditions at the time, and the ambient humidity of the house when the problem showed up?

    Gluing the joints might have held them together under whatever stress they are experiencing. I usually glue joints on shopmade veneer, figuring the extra thickness will make the joints more prone to shrinkage at the surface.I don't know if I would want to use epoxy on ash as it can show a dark glueline on light woods and fill the grain on open grained ones, but one feature (good or bad) of epoxy in a vacuum press is that it will wick up through the joints and bond them if they are sawn or sanded. The same effect could be achieved with ppr by folding back and gluing the taped joints during the layup process, thus avoiding an extra step of pregluing and cleaning them up.

  11. #26
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    My basement shop has been 30 - 40% RH all Winter. My house was in the 25 - 35% range during and after installation of the cabinet.

    How would you fold back the joints and apply PRG during glue up without risking fracturing the veneer tape and still stay within the time window for open and clamp-up times? That just seems like a difficult and risky approach, as much as I like the concept.

    John

  12. #27
    That doesn't seem like enough of a discrepancy to be a problem- and yet there is a problem that seems to be moisture related. I don't have the answer. You might try posting on the Woodweb veneer forum and the Vacupress forum ) for some more ideas.

    I have not actually done what I suggested in one step; I have blue-taped seams, folded them back for gluing with pva and then cleaned up the joints prior to layup. It's hard to keep everything perfectly flush, though,if the veneer is not completely docile, thus my suggestion. I would use a heavy veneer tape, lay the taped sheet upside down, let the first leaf hang over the table edge to open the seam for gluing with a syringe, slide over to open the next joint and so on until the middle of the sheet, then slide over to the table's opposite edge to finish. It shouldn't add much more than five minutes to the process for a moderate size piece. The white (30 gram?) tape I usually use for sliced veneer might well not stand up to that, but I have some heavier Kraft paper tape that should with careful handling. It's always a good idea to do a dry run on something new like that before committing to it.

  13. #28
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    Here's a photo of one of the seams that's opened enough that you (hopefully) see a white line of the underlying white ash.

    IMG_3880.JPG

    To answer someone's earlier question, the doors are still nice and flat. Not all the seams have opened, and of the ones that have, they have not opened across their entire length of about 22". More of the seams on the inside have opened than on the outside of the doors, but the veneer on the inside is narrower than on the outside so there are more seams.

    Anyone have any additional thoughts?

    John

  14. #29
    Two points, probably neither of which gets at the root of this problem.

    1) substrate. Since having a drawer front laid up on mdf swell up at a corner adjacent to an improperly vented dishwasher, we have gone to Medex as a substrate for interior panels that may experience high moisture/humidity. It has the added advantage that the edges require no sizing for painted work, so we keep it in stock.

    2) glue. Unibond is not free of water. I believe some of the water in the mix is replaced with alcohol, so it may reduce water-related issues, but not completely. Polyurethane adhesives may be worth experimenting with in this regard.

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