|Home » Forums » Adhesives » Message||Login|
You are not logged in. Consider these WOODWEB Member advantages:
epoxy vs glue12/26
When it comes to laminating up stock for thickness I have always use 2 part West System Epoxy. As longs as it is mixed and applied correctly you are assured the chemical reaction will bond materials.
Recently a new employee with a extensive back ground has asked why I don't use titebond 3 or other standard wood glues. He says he has used it for years with no problems with delamination. My feeling is that if you use wood glue on a joint over 3" + that the glue will never fully cure? Does anyone have any factual insite into which is the better product to use? Thanks
I think you are dead wrong on this one! Where did you get your information on "cure?" I don't think Titebond cares how for it is to the edge!
I am aware of seeing/making/handling literally thousands of laminations in the last 42 years, and almost none of them were epoxy. Yellow glue (3 types), white glue, plastic resin glue, and urethane glue being the bulk of that work. Epoxy is probably 1% or less.
Epoxy stands out for 2 things: Cost and the fact that it requires a heavy glue line and light clamping. Many use it because they think it is the 'strongest' or 'best' glue there is, but it it all depends upon the application/use. Any major glue, properly applied, will be as strong or stronger than the wood it is bonding.
Your website shows some advanced assembled work, and you would certainly benefit from a review of your glues and where they would best be used. Call in a glue rep (Spectrum Adhesives) and see what they would have to say.
Dave has forgotten more about woodworking than I know, so I'd take his word on it!
I myself have done a fair amount of interior doors and other glue-ups and yellow glue has never failed me. Epoxy on the other hand is messy, time consuming, stinks, and is expensive! I have West System for those special applications....but it gets used sparingly.
So far I think the widest glue-up I've done with yellow glue was for a curved bar roughly 40" or so high and maybe 16' or so in length on both legs.....so plenty over the 3" mark. It's been in use at a restaurant for several years now and hasn't delaminated yet;>)
Thanks for your reply. I've done test samples in the past where we glue up 8" slabs and let dry for 24 hrs. Then come back and drill a hole with a fostner bit right to the glue line. At 1" off the edge the glue has cured. At 2" off the edge and it has cured, but when you drill a hole in the center of that 8" slab the glue is still wet or maybe tacky is a better word, after 24 hrs. Now this may be where I'm mistaken, but I have alway felt that wood glue needs the presents of oxygen to cure. With the glue cured around the perimeter of the lamination this would prevent the middle from ever being able to cure properly???? Maybe 24 hours in not enough dry time for wood glue for this type of application. Maybe in needs to stay clamped up for 2 days or a week???
I do a lot of mortise and tenon work, and I make the mortises about 3/16" deeper than the tenon for a little forgiveness and excess glue. If everything is tight at the bottom, too much glue will make assembly a hydraulic impossibility. Ask me how I know.....
But, with the glue receptacle in the mortise, I then make a haunch that usually has about 1/16 to 1/8" clearance. If I stand the assembled panel up, sometimes the excess glue will drain out in the first few hours after assembly. So I try to leave the panels flat on the bench to minimize this.
I have cut open mortises that still have some gelled glue in the mortise bottom 2-3 days after assembly, but the joints where the wood is tight to wood are dry and solid. This is what makes the difference - wood to wood in intimate contact (as they say) causes the glue to chemically bond. If there is no pressure, with resulting thin glue line, then there will be no bond.
Epoxy and Resorcinol cure chemically, in spite of oxygen, moisture, etc. Some glues wick the moisture to the wood to 'dry', and some take moisture to cure (Urethane).
Talk to a real glue expert and show them your work and see what he comes up with.
I have some test samples of several glues that are closing in on 10 years out in the weather, and one day soon, I'm going to open them up and see what is good, bad or indifferent. I do have a redwood ball laminated with resorcinol that is about half worn off by weather, but the glue lines are harder than the wood, so they protrude like a Southwestern rock formation.
Thanks for everyones input.
Gene, Need your input here.
A little late to the dance here, but I would suspect Chad that you did not have enough clamps, or not flat boards on that 8" slab. I don't know the other dimensions of that "slab", but if it is like an 8x8, it takes a mountain of clamps or cauls to bring up the correct pressure for PVA glue. Properly executed, their is a very, very fine amount of adhesive left in a joint.
I would toss that both have different properties and differ on there solubility and strength considerations. My friend had an outdoor furnishing business named EOD, i think you can take help from them. Just Google them out and you will get your queries answered.
A pva adhesive (white or yellow does make any difference, as the color is just an additive) requires a glue line of 0.002" to 0.006" thick. I wonder if you center area is perhaps a bit too thick and that is why you do not get a cure in 24 hours. The role of pressure is to smooth the thickness of the adhesive and to squeeze out any excess amount. With a large piece, you will have trouble getting the excess adhesive to squeeze all the way to the outside.
Pressure does not squeeze the glue into the wood cellular structure. So, if you surfaces are perfectly flat, you might have to use less spread int he center or maybe make a reservoir slot in the center area to hold the excessive glue. Of course, pressure is the key...not too much but not too little either. As you are used to epoxy which does need a thicker joint, when switching to pva, you will need more pressure than with epoxy. (Once the pressure is applied, do not let it be reduced, as that wood will then spread apart and there will no longer be enough glue to fill the gap...you squeezed the excess out already.
You can increase the temperature a bit to encourage the moisture to flow away and the joint to cure...maybe 80 F. It does not need oxygen to cure. In fact, the dry wood should be able to easily absorb all the excess moisture so the joint will cure
If the joint thickness is OK, how could the moisture stay in the center if the wood was dry? The only way I can imagine is if there is a lack of pressure (or a large gap over 0.006"). Epoxy does fill a gap and stay strong, but not pva adhesives. (I hope that your wood surfaces are perfectly flat and not hollow ground, as we sometimes saw in the past.
Note that a good pva joint will be 50% stronger than the wood itself, so epoxy is not needed in a simple joint where the surfaces are flat.
One other thought is that your surfaces may not be active for gluing, due to age, heating, etc. Put a drop of water on the surfaces to be glued and see if the drop soaks into the wood within a few minutes. If not, you need to have a better surface for gluing. I can discuss this further if needed.
I've done minimal furniture and construction work, being mainly a musical instrument builder. The needs may be slightly different, but not enough to be significant. I rarely use epoxy for laminating. Almost all PVA glues are more than adequate for laminating. Hide glue is commonly used, and I do use it for many joints, but PVA is the mainstay workhorse. I'll have to agree with Gene on all points. I started gluing things together over forty years ago, have used literally every type of glue, bonding agent, adhesive, really sticky goopy stuff, etc. I've had the same experience, that Chad describes, of PVA not drying in a lamination, and most certainly it was due to excess of glue and lack of drying - my fault. PVA glue joints, in my experience, suffer only from poor clamping, poor surface preparation, contamination, or glue being too old. I use epoxy extensively, but it is almost never my choice for laminating, unless (for some strange reason) the surfaces are irregular with large voids. I've never had a proper PVA joint fail. "Proper" means that I did my job well before the glue was applied. I've had epoxy fail in a number of cases, most due to incompatible material or contamination. As a side note, I've had very good results using PVA, when a gap exists, by adding fine wood flour as a filler/thickening material, though it's an infrequent occasion.
A cool way of developing equal pressure across the part is to use negative air pressure. if you run butyl tape around the outside of the part and cover it in poly, a small vac pump can be used to provide vacuum pressure across the entire part. Just make sure you cover the part with a moving blanket to protect the poly. The fiber glass industry has been using this method for years to compact dry glass stacks.