Darryl Keil
Posts: 1453
Joined: 2003-05-22
Location: Maine
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You’re issue here is the older, thickening glue combined with the density of birdseye maple. When Unibond 800 gets thick its a sign that the shelf life is nearing its end. Adding to this problem, maple, and especially birdseye maple can be difficult to get a good bond with, especially when the glue is thicker. Hard to get good penetration. From the picture, you’re other veneers did fine. Curly maple has a more open structure, due to the curl, than Birdseye, thats why I suspect it bonded OK. The shelf life was still good enough, (although a bit close for my tastes) to get a proper chemical reaction but not enough penetration.
So the question about Unibond 800 vs powdered urea version goes like this. Both are the same type of glue, bond and cure in the same way. Lets look at your situation to compare. Both types have limited shelf life, about a year or less depending on how they are stored. Unibond 800 tells you when the shelf life is up or near, by getting thick. Powered urea has almost no markers to let you know as its in powdered form, cant get thick on you. Had you used powered urea you would have mixed it to the consistency you would consider ideal so penetration would have been good. On the down side you may have ended up with total failure if the shelf life was fully past because the chemical reaction would not have taken place properly, depends on how close to expiration it would have been.
Unibond 800 lets you know when you’re nearing expiration by getting thick. Had you heeded this marker you would have probably gotten new glue and then been fine. There actually is one other thing you could have done, which is too thin your glue with water, but no more than 5%. This would have given you better penetration on the maple. The risk is, is the shelf life up? The only way you could have know was to do a thinned down test on sample and see if you got the proper bond or not. If you did then go ahead and press your real panel. To me its simply not worth it considering the work that goes into preparing veneers for pressing. Get fresh glue. Yes, I sell Unibond 800 so I may be partial to its properties, but having that thickening shelf life marker is very important to me in a urea glue.
Its interesting, I have folks that use powered urea having trouble and switching to Unibond 800 as well as customers using Unibond 800 switching to powdered urea. Its almost alway about preparation and conditions, not one glue over the other. I say this a little sheepishly, (dont want to upset my customers), but its pretty much always about the user and rarely the glue.
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