Replies

1. 
   HowardAcheson | Oct 15, 2009 10:32pm | #1

   First, let me say I am not a fan of the poly glues primarily because I have found no advantage to them over standard PVA glues when gluing wood to wood joints except for gluing oily, exotic woods. "Creep" is much less of a problem but there are other adhesives that are creep resistant such as plastic resin and hide glue. I'm sure there are other opinions however.

   That said, like any PVA glue (white or yellow) the poly's are no stronger than the wood itself--and may be weaker if they are not used correctly. In some recent tests in a woodworking magazine, Gorilla Glue was significantly weaker than PVA adhesives. Poly adhesives cure by a reaction with moisture but many use too much adhesive and moisture. Excess moisture increases the reaction but shortens open time--one of their claimed benefits--and results in excessive foaming and a weaker joint. If the wood is at a moisture content of 10% or more, additional dampening is probably detrimental, not helpful. There are now PVA glues with extended open time. In fact the white PVA has virtually exactly the same open time as the poly. The yellow PVA was formulated originally to respond to woodworkers who wanted a faster setting adhesive. Strangely, some poly glues are now being marketted that have a shorter open time and faster cure because some wood workers have complained about the longer clamp time required for the original polys.

   Some poly adhesives are certified to meet the ANSI Type 1 waterproof standard which means they can be used for totally submerged applications. However, for normal, non-submerged outdoor use, a type II adhesive will work as well.

   While "gap filling" they fill gaps with foam which has no strength. The adhesive expands as it cures tending to force glued surfaces apart so tight clamping is required. They also require that the clamp pressure be maintained for much longer than most other adhesives. Many find poly adhesive unsuitable for laminations as the agressive expansion pushes surfaces apart.

   It contains hazardous materials and should be used in a ventilated area and kept away from skin if you believe the Material Safety Data Sheet. If it gets on your hands, only time will will remove the stain.

   They cost much more than other glues and IMO, do not offer many
   advantages over less expensive adhesives.

   Finally, some magazine tests showed it did have the strength of PVA adhesives.

   Howie.........
2. 
   hammer1 | Oct 15, 2009 10:36pm | #2

   The polyurethane glues pull moisture from the air to cure. They foam a little or a lot depending on the amount of moisture. It makes for a mess on the work, your hands, tools and clothes. Once you have used a little and air gets into the bottle, it has a very short shelf life. It's also expensive, especially if you end up throwing most of it out.

   There may be some specialized applications where it would be a favorable choice. I can't think of any where other glues wouldn't work as well, or better. It really doesn't have any gap filling properties, although, the foam will expand in an open area. The foam just doesn't have any structural strength. It a good glue as far as performing in the proper application and fit but these other issues make it a loser for me. I have a couple hard as a rock bottles on my shelf, one never opened.

   Beat it to fit / Paint it to match