Gorilla glue for mortise and tenon joint?

[David Winer]

I’m building a workbench for a canoe club’s unheated utility shed/workshop. There is a possibility, but not high likelihood, of the workbench being subjected to flooding. I’m considering Gorilla glue for its water resistant properties, but also for its gap-filling qualities. The tenon surfaces are cut by a carbide-tipped band saw and are therefore slightly rough.

My only use of Gorilla glue has been in glued and screwed lap-joints of large garden gates that have stood the test of time. I’m aware of the general messiness of using this glue and am not concerned. However, the mortise and tenon joints will not be reinforced by screws, so I wonder if Gorilla glue is strong enough.

Would Gorilla glue or Titebond III be the better choice for this mortise and tenon application? The choice is about gap-filling and strength.

[Harvey Melvin Richards]

Gorilla Glue will fill gaps, but it has no strength in a gap. The only glue I'm aware of that still has strength in gaps is a 2 part epoxy. I built some outdoor furniture out of Redwood. I used mortise and tenons,floating tenons and Gorilla Glue. I had several glue joints come apart. I repaired the failures with epoxy and the chairs have been fine for at least 8 years.

[Stephen Cherry]

I'd use through tenons, with wedges. Loose sides (well, not too tight), and pound the wedges into bandsawn slots near the top and bottom of the tenons. Little bit of tightbond III for glue.

[Morey St. Denis]

Does anyone still use the two part resorcinol glues for exterior woodworking where part A is usually a red powder and part B an amber liquid? From personal experience, it has good working time, is gap filling, impervious to moisture when cured, hugely strong & weather resistant and seemingly would make an apt candidate. Believe these dark colored phenolic based resins are still used in laminating exterior grades of commercial construction plywood... DAP Weldwood Resorcinol Glue is one brand I have successfully used on exterior facia restorations and coarse wood tenon joinery.

[Ellen Benkin]

I second the epoxy suggestion. Gorilla glue looks like it is gap filling because of the expansion but it really isn't gap filling in terms of strength.

[Dennis Ford]

Even epoxy is weak when used as a gap filler. Add some shims if needed to tighten up the joint if you want it to last. I like gorilla glue for outdoor use with softwood but it has poor strength in sloppy joints.

[Mike Henderson]

For well fitting joints, any good waterproof glue will work: Titebond III, Gorilla Glue, epoxy, and maybe others. For a poor fitting joint, I'd fix the joint. You can glue a piece of veneer to bulk out the tenon and can even trim it afterwards if it's too tight in places.

Mike

[Peter Quinn]

Work bench for kids club? Galvanized bolts would be my choice with stub tenons. Water resistant, can be snugged up over time to accommodate wood movement, can be disassembled should transportation be necessary, can be on the blind side of the board. Lots of advantages. Skip the gorilla glue, that foam is mush, no strength unless the joints are tight. If the joints are basically tight with a few scratches from BS, it may be fine, but so would titebond III.

[Steve Rozmiarek]

I'm not a Gorilla glue fan at all, but aside from that, if the bench does go under water, you probably have bigger problems that I suspect no glue will solve. Seems to me that at the least it is likely the bench top will delaminate or something else nasty, and leave you with a mess.

Guess I'd be inclined to either build it knock down fashion so you can take it apart to fix it easily, or build it to be tossed if it floods.

[Howard Acheson]

>>>> Would Gorilla glue or Titebond III be the better choice for this mortise and tenon application? The choice is about gap-filling and strength.

While Gorilla Glue will fill voids, it fills the void with a foam, not the adhesive. As a result, the joint will be weak as the foam has no inherent strength. In other words, the joint must be properly made or it will not be strong. Here is something I wrote a few years ago. It still applies.

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. 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.

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

[Andrew Hughes]

I use gorilla glue, for cedar gates and aquarium stands and canopys I build.I have had no problems with jointery letting go.From my own testing titebond 3 not acceptable.I made a arched entry gate with matching archway.The archway delaminated after two years.so I remade it with gorilla glue and I did see it over the summer it was hold strong 8 years now.The other thing I like is that it fills voids this keeps water from filling pockets like the bottom of mortises.
When I was a roofer we also used poly caulking.I thought it was much better.

[David Winer]

Thanks, everyone for all the suggestions and comments. It’s good to have your experience as a guide. Addressing most of the suggestions, and after further web research:

Resorcinol glue: Out. I had forgotten about this waterproof, strong stuff—but it requires clamping.

Through tenons with wedges: Out. Stub tenons are already cut. Maybe next time.

Gorilla glue: Out: Not strong in these joints according to comments.

For a poor fitting joint-- fix the joint: Not the problem (yet). The tenon surfaces are only rough-textured from the band saw.

Design for kids club? Galvanized bolts … with stub tenons: Not appropriate. Workbench is primarily for adult use in a permanent setting.

Titebond III: Maybe. The workbench won’t be outside, but might one day get soaked. So far, no response favoring its use.

Epoxy: This seems to be the best solution for this application since it is strong, waterproof, and doesn’t require smooth surfaces or clamping. I hadn't considered it but it's now the the top candidate.

[Paul Symchych]

How about simply pinning a glued M&T joint? A hardwood dowel or two would make plenty of pins.

[ian maybury]

I did a lot of digging some time ago David on the topic and ended up highly frustrated at the minimal quantitative data available for the performance of pretty much any of the mainstream wood glues - be it polyurethane or the white/yellow types.

Sweeping but in the end highly subjective marketing claims seem to be the norm for an industry that seems to have little interest in generating or publishing the sort of hard design data that a design engineer might recognise. Part of the problem is admittedly that performance so much depends on the type and condition of the wood, and the nature of the joint.

Liquid polyurethane (PU) is in fact a very capable adhesive with some key benefits like creep resistance, water resistance (not quite to the total immersion that resorcinol can supposedly handle, but very close with the right primer), multiple/difficult surface wetting capability and high strength.

The last (high strength) is in use subject to the repeatedly mentioned need for good joints and high clamping forces on wood - it has minimal strength if allowed to foam into a space. My impression is that it's suffered by the reluctance of those selling it to qualify their claims (it's been pitched as a more or less universal wood adhesive - which may have meant that some have come unstuck (Ha!! ) as a result of not being aware of/responding to these needs), and because the well entrenched white/yellow glue interests seem to have seen it as a threat and done all possible to undermine it.

The mag test that found it to be weak (in a joint format that was about as unsuitable for it as you can imagine) without offering any explanation or qualification of the result did nobody any favours.

As ever it depends on the specifics of the situation. It's fairly clear that liquid PU is an important part of the toolkit, in that there's stuff it does that isn't that easily managed by other means. It's wetting abilities mean that it apparently manages decent strength in an end grain joint for example. I was very happy recently to use it to make some face joints with phenolic ply - sanding and solvent washing are important in that case because there can be a barrier film on the phenolic, but the stuff it seems is otherwise hard to glue and the PU did a very good job. Handled properly it seems in addition to be more than capable of handling pretty much all normal woodworking needs...

ian

[Todd Burch]

There are additives available for epoxy to assist with gap filling, but thin wood shims would be appropriate as well, or, just fix the joints (ala, via wood shims epoxied and fitted before assembly). As mentioned, you can pin the joints with a through dowel as well for additional mechanical strength. Epoxy loves additional mechanical assistance.

Todd