Would like to know if anyone has any experience with the holding power and longivety of a good constuction adhesive , like pl-400, will it be as strong as the wood its glue to and will it weaken over time?
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Replies
PL-400 is a rubber-based product. This means it has some "give" and will tend to creep if the joint is subjected to continuous stress. Also, most synthetic rubbers tend to degrade and have a finite lifetime (though in typical uses -- no UV or ozone exposure -- it'll probably last 20-50 years before being significantly degraded).
Traditional wood glue is probably better than PL-400 in terms of creep and lifetime, but only if kept reasonably dry. Something like resorcinol is probably the most "secure" glue for wood -- better than epoxy since it binds more intimately with the wood. Don't know how urethanes (and PVAs) would rate.
One significant issue affecting the choice is whether the joint will be subjected to any repeated flexing. Flexing requires a reasonably pliable product to avoid separation at the adhesive/wood interface.
Edited 7/12/2005 1:31 pm ET by DanH
The PL premium polyurethane stuff in particular is unbelievably strong, though the actual bond to wood is not as strong as the adhesive itself, meaning the bond will fail before the wood gives way in most cases. The bond strength on materials with more 'tooth', like masonry, is incredible. In the same way, rough sawn wood will make a stronger bond with construction adhesive.
Waterproof wood glue or polyurethane glue is stronger for tight wood-to-wood connections if properly clamped. These bonds are indeed stronger than the 'wood itself'.
Part of what is going on here is that the construction adhesive does not absorb into the wood fibers much at all, where the other glues do. This is evident based upon how much wood they take with them when forced apart.
Construction adhesive does have the advantage of bonding wood to non-wood materials very well. It also spans gaps very well, where wood glues require a tight fit for strength.
For very critical joints, consider epoxy.
You can do your own testing with your actual materials. For a shear test, adhere a block of wood onto a plank, than whack it apart with a big hammer. See what gives first.
But the OP was asking about long-term reliability. I've seen things glued with construction adhesive decide to disassemble themselves after months or years of being apparently well-connected. I think the flexibility of the adhesive can actually increase localized joint stress and hence lead to bond separation.Epoxy isn't generally a good choice because of its stiffness and lack of bonding ability to wood, leading to a probability of slowly advancing bond separation.Titebond III isn't recommended for joints under stress, presumably because of creep. Titebond II doesn't list this restriction, but doesn't make any statement about long-term creep either. (Haven't checked up on Gorilla glue yet.)The only "test" I can offer is some under-deck doors I made 18-20 years ago, using resorcinol. The joints of these have been exposed to the weather and under significant continuous stress for that entire time, and are holding fine.
Before the advent of metal plate truss construction we maufactured trusses with plywood gussets nailed and glued. We used CASEIN glue. It had no creep and the wood failed before the glue joint. Sorry, but I don't know where you can get the product today. It is not water proof so must not be used if subject to moisture.
It's been years since I used it but isn't there a LePage's "water resistant" glue which is a casein glue? I'm thinking of a powder which is mixed into a thin paste with water and clamped for a day or so. Tight joints only. Lasts forever.
If you want to make your own.http://sleekfreak.ath.cx:81/3wdev/VITAHTML/SUBLEV/EN1/GLUECONS.HTMAnd here is a commercial source.http://www.nationalcasein.com/
PL Premium is better than you are giving it credit for.For one thing, it also IS a polyurethene glue, like Gorilla glue, but with body. It cures by exposure to oxygen and moisture. Misting or otherwise allowing modest dampness to the wood to be joined will increasse the strength of the bond to wood.there are at least three kinds of bnond when talking about glues and adhesives. Some adhjesives employ a mix of more than one type. Old hide glue was primarily a suction type bond. Silicone for glass is another example. Chemical bonds are most evident with PVC glues for plumbers. Mechanical bonding is what we see when rubber hardens around the fissures of rough concrete block and rough cut lumber while they are clamped or mechanically held by fasteners while the rubber stiffens up.PL Premium employs all three typoes of bond. The shape forms a suction to surfaces. The curing process makes it expand slightly into fissures for a mechanical bond, and because polyurethene is so tenacious and sticky, it forms a bit of a chemical bond as well.
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PLPremium is rated under the APA-01 standard. I hear there are stricter standards. PL might be rated under these later standards as well.Supposed to make it suitable for built-up box beam, when I was looking into these structures. Most demanded glue and nail or screw fastening and that he adhesive had to be APA-01 rated. I would think this would preclude excessive creep at the beams are under constant stress for the life of the structure.I'll bet you could phone the company producing PLPremium and ask. Most companies want you to use the right adhesive for the job as using the wrong one often damages the companies reputation even when it's the fault of the user. I can say many years ago I made a counter and associated framing for a commercial kitchen. They wanted it strong. As strong as I could make it at reasonable cost. I glued and screwed using PLPremium and deck screws. Years later they renovated and had to remove what I had built. According to the carpenter it didn't come out in sections. Even after they removed the screws they had to reduce it to splinters to get it out. The glue joints were stronger than the wood.
"PL Premium is better than you are giving it credit for.For one thing, it also IS a polyurethene glue, like Gorilla glue, but with body. It cures by exposure to oxygen and moisture."
Good stuff indeed. I use it all the time. Just built some shear walls with it.
However, thin polyurethane glue and waterproof wood glue have both proved stronger in my tests, consistently taking the wood along with it.
PL Premium tends to fail at the wood/adhesive interface.
The right product obviously depends upon the application at hand.
I've taken PL Premium joints apart and the wood always gives before the glue does. The problem is that it's not a "penetrating" glue so all it really has to break are the surface fibers of the wood.
Depending on the amount of adhesive applied, it usually seems easier for me to break a PL-Premium bond than a ringshank bond for example. I've had better luck with Gorilla Glue on tight joints. It seems to penetrate a little deeper. I tried to pull a Gorilla Glue joint apart a while back and finally gave up. It was probably due to the fact that I applied the Gorilla glue as a film and the PL as a bead so there was quite a bit more bonded surface area with the Gorilla.
All the same, I trust a glued and mechanically fastened joint a lot more than a glue only joint - Especially over the long haul.
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Piffin is right on target. Mist the wood before you use the PL or the Gorilla Glue and you will be amazed at how much stronger the bond seems to be. The polyurethane glue needs moisture to cure.
Billy
Misting the wood speeds setting. I'm not sure if it makes for better adhesion or stronger joints. Maybe.One thing that I know will strengthen the joint is tight, but not too tight, joints. Similar to other wood glues. Loose joints won't hold well no matter which glue you use. The polyurethane, from experience seems more tolerant of gaps than most but performance does drop off rapidly as the gaps increase.I have heard of carpenters who find out that Gorilla Glue and PLPremium foams and fills gaps as it cures and assume that they can get sloppy. Leave a 1/8" gap, the foaming action will often fill a gap this wide, and the joint will be a fraction of the potential.
I'm not certain that it makes the joints stronger, but it seems to. It would be a good subject for a test. I wonder if could be a beneficial effect from the raised grain -- a better tooth for the glue?
Billy
It's my personal opinion that any water applied to the wood should be allowed to soak in well before applying the adhesive. While it is not scientific, my gut tells me that the poly goes after the moisture like a tree root to make a better bond.
Logicaly speaking, moisture wicked into the adhesive during cure would make for a stronger joint than surface moisture that allows the adhesive to cure without penetrating.
Surface relationships are always fragile, but if the poly has to penetrate the wood fibers, and suck the curing nectar from the dead limb's soul, they very well might be inclined to stick together a little longer.
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Surface relationships are always fragile, ... and suck the curing nectar from the dead limb's soul, they very well might be inclined to stick together a little longer.
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