Epoxy for loose (bad) tenons ?

[Steve1]

I am seeing a lot of affection for epoxy. 
I'm going to give it a try.
I don't normally use epoxy for glue ups, but I have been challenged many times trying to assemble a larger glue-up within the pot life of PVA glue, so having an additional adhesive  in my proven toolbag would be helpful.

A little while back, I used epoxy on a dovetailed drawer.  The dovetails were a rather tight, and when I applied PVA glue to the first drawer, they swelled up and I was literally pounding them with a hammer, very hard, to assemble them.  Second drawer I glued with epoxy and it went much better.  Notwithstanding that I was using a low viscosity penetrating epoxy (that's all I had at the time), I masked the edges and don't recall it having any adverse effect on finishing. 

I will use Wast Systems 206 hardener, for the longer pot life.  I am a not a pro, so the longer clamp time is irrelevent. 

 

[jeffinsgf]

Sounds like you're on your way, but if you are looking for an alternative to epoxy, given the gap you're talking about, my leaning would be toward polyurethane glue, like Gorilla Glue (ducking). Lots of folks have had negative experience with polyurethanes, but you just need to understand what they're going to do and account for it. First, they expand...quite a bit. That's both their best and worst feature. It will fill and bond loose joints, but it has been known to push joints apart. The way to control that is to not use too much. Since I don't tend to drown my joints in glue in the first place, I've never had an extreme problem with poly expansion.

It's hard to wash off your hands, but then, so is epoxy. Wear gloves.

As for open time and assembly, I like the fact that you apply glue to only one surface and lightly moisten the other surface. Open time is a little better than PVA. Clean up is a sharp chisel after the squeeze out is dry. If you try to wipe it off while it's wet, you'll regret it. Just wait and it will shave off cleanly.

And one more key difference between poly and epoxy is shelf life. Poly has none. Don't buy a big bottle, buy just more than what you need. Epoxy seems to have a very, very long shelf life.

Both will do the job. I find poly to be more like working with PVA. Epoxy needs space to create a bond and that goes against my normal joinery methods. If a joint is just a little loose, I would lean toward Poly and leave the epoxy for serious void filling.

 

[Birdhunter]

My practice is to pack two-part wood filler into the bad mortise and let it dry for 24 hours. I then redrill the mortise.

Another fix is to fit two Dominos into the mortise. I have to trim the Dominos so that they have to be tapped smartly into the mortise (of course, glue is applied first. This works if the mortises are misplaced but not if the dominos are very loose in the mortise.

 

[Koamolly]

If you end up with left over epoxy, the hardener tends to discolor to a dark red over time.  It’s still good, just mix as normal. 

 

[Cheese]

Another fix is to fit two Dominos into the mortise. I have to trim the Dominos so that they have to be tapped smartly into the mortise (of course, glue is applied first. This works if the mortises are misplaced but not if the dominos are very loose in the mortise.

Something like this...

[attachimg=1]

[attachimg=2]

[attachimg=3]

[attachimg=4]

 

[luvmytoolz]

Sounds like you're on your way, but if you are looking for an alternative to epoxy, given the gap you're talking about, my leaning would be toward polyurethane glue, like Gorilla Glue (ducking). Lots of folks have had negative experience with polyurethanes, but you just need to understand what they're going to do and account for it. First, they expand...quite a bit. That's both their best and worst feature. It will fill and bond loose joints, but it has been known to push joints apart. The way to control that is to not use too much. Since I don't tend to drown my joints in glue in the first place, I've never had an extreme problem with poly expansion.

It's hard to wash off your hands, but then, so is epoxy. Wear gloves.

As for open time and assembly, I like the fact that you apply glue to only one surface and lightly moisten the other surface. Open time is a little better than PVA. Clean up is a sharp chisel after the squeeze out is dry. If you try to wipe it off while it's wet, you'll regret it. Just wait and it will shave off cleanly.

And one more key difference between poly and epoxy is shelf life. Poly has none. Don't buy a big bottle, buy just more than what you need. Epoxy seems to have a very, very long shelf life.

Both will do the job. I find poly to be more like working with PVA. Epoxy needs space to create a bond and that goes against my normal joinery methods. If a joint is just a little loose, I would lean toward Poly and leave the epoxy for serious void filling.

I'm not a fan of PU glue used as a filler generally, it bonds timbers beautifully, but it is quite weak as a filler. If it was a stress joint it would more than likely fail.

 

[PaulMarcel]

I'm not a fan of PU glue used as a filler generally, it bonds timbers beautifully, but it is quite weak as a filler. If it was a stress joint it would more than likely fail.

The little I used it, the 'fill' is just foam that really isn't structural at all.

I was, however, shocked to learn that my marquetry mentor Paul Schürch now uses PU glue for all his veneer work. He used to use ProGlue (IIRC) and even sold it as he really liked it. Then, there was a chemistry change and he started getting failures. He'd use PU glue to repair all the failures and decided to use it instead. Zero failures since. I bought some to give it a try before my next-up project. I couldn't fathom using foamy glue for marquetry/veneer work, but he says the key is to spread it so thin that it looks like you don't have any. Experiments should be coming up in a month...

 

[luvmytoolz]

I'm not a fan of PU glue used as a filler generally, it bonds timbers beautifully, but it is quite weak as a filler. If it was a stress joint it would more than likely fail.

The little I used it, the 'fill' is just foam that really isn't structural at all.

I was, however, shocked to learn that my marquetry mentor Paul Schürch now uses PU glue for all his veneer work. He used to use ProGlue (IIRC) and even sold it as he really liked it. Then, there was a chemistry change and he started getting failures. He'd use PU glue to repair all the failures and decided to use it instead. Zero failures since. I bought some to give it a try before my next-up project. I couldn't fathom using foamy glue for marquetry/veneer work, but he says the key is to spread it so thin that it looks like you don't have any. Experiments should be coming up in a month...

Used as a bonding agent, and aside from the foaming which can really be problematic, PU is really hard to beat, incredibly strong, great for moisture resistance, wood movement, etc. But as a filler, useless.

The foaming, and the fact it reaches a point where the remainder in the bottle "suddenly" oxidises and hardens, makes a no-no for me. Especially when it's double the price of PVA.

 

[PaulMarcel]

Used as a bonding agent, and aside from the foaming which can really be problematic, PU is really hard to beat, incredibly strong, great for moisture resistance, wood movement, etc. But as a filler, useless.

The moisture resistance is why I first ever used it. Was for an outdoor project and it still has no issues despite the Arizona sun trying to vaporize it. In that sense, it seems better than epoxy, which is pretty rigid.

 

[Birdhunter]

Cheese nailed exactly my trick of using two half plus tenons to fill a bad mortise.

 

[Packard]

I'm not a fan of PU glue used as a filler generally, it bonds timbers beautifully, but it is quite weak as a filler. If it was a stress joint it would more than likely fail.

The little I used it, the 'fill' is just foam that really isn't structural at all.

I was, however, shocked to learn that my marquetry mentor Paul Schürch now uses PU glue for all his veneer work. He used to use ProGlue (IIRC) and even sold it as he really liked it. Then, there was a chemistry change and he started getting failures. He'd use PU glue to repair all the failures and decided to use it instead. Zero failures since. I bought some to give it a try before my next-up project. I couldn't fathom using foamy glue for marquetry/veneer work, but he says the key is to spread it so thin that it looks like you don't have any. Experiments should be coming up in a month...

Used as a bonding agent, and aside from the foaming which can really be problematic, PU is really hard to beat, incredibly strong, great for moisture resistance, wood movement, etc. But as a filler, useless.

The foaming, and the fact it reaches a point where the remainder in the bottle "suddenly" oxidises and hardens, makes a no-no for me. Especially when it's double the price of PVA.

There is an exception to the foaming issue.

I was an early adopter of polyurethane hot glue guns.  The gun itself was a gem.  It had a holder that kept it hot, but it allowed you to use the gun itself unencumbered by any cords or batteries.

I had high hopes for this gun.  It promised great strength and instant adhesion.  It should have sped up my picture framing glue-ups.  But no one told me that it would leave a prominent black line where the joint was. 

Or that the glue sticks had a short shelf life.

Or that you could not buy just a dozen sticks at a time. 

In any case, it did not work for picture framing.  It outlived its use-by date by the time I had a project that should have worked.

Impossible to use for complex glue-ups (but potentially usable for simple miter bonds).

Pluses:  Strong joints, instant adhesion, water proof (not a plus for picture framing), great gun for application, and no foaming or expansion.

Minuses:  Black line at joint, short shelf life, inability to buy small quantities.

Note:  I did not research P/U hot glue guns when I wrote this, and my adventures in P/U hot glue guns is about 22 years old.  So some of this will have changed.

But I suspect that the black line will remain, and the absence of expansion probably will too.

The system was intended for factory assembly use.  I was trying to use it off-label and I really had no valid (to the manufacturer) complaint.  I have not seen it in about 20 years, but I have a fairly good idea where it is.  I can’t think of how I would want to use it, however.

 

[smorgasbord]

I too still have a PUR hot glue gun. I guess I should add that to my list of disappointing tools, for the reasons cited above. What is great about it, and why I still have it, is that it's gap filling with a super-quick set time that can bond dissimilar materials well.

I used it recently (few years ago) to glue decorative end pieces at the bottom of stair newells to the newells and walls. I didn't want to nail the pieces (they're a pretty ebony), didn't know if there even studs behind them (probably not). They're not structural, but cutting them to a decent fit with the newell bottom on top and paster-coated drywall behind, I was able to slab some of the hot glue on, position the piece in place and hold it for 75 seconds, after which I could let go with no sagging.

But, yeah, I used only ¼ of the tube and even though I resealed everything I'm sure if I were to try to use it again it'd fail and I'd have to buy a whole new tube. Even new in sealed pouches, the shelf life is pretty short. But, where CA glue isn't thick enough (even the thickened kind), this works.

 

[Packard]

The PUR gun itself is a gem.  It was brand new to the market when I bought mine and the glue was only available in full cases—a substantial cost.

If single tubes are available now, I might take it out of mothballs.  The bond strength was very good.  I’m sure the short open time would make it unusable for some glue-ups, but it also would make others very easy.

The black line would be an issue in many instances.

It was designed for factory settings.  It is probably good for that purpose where a regular hot glue gun would not provide enough bond strength. 

In a factory where you might be building a refrigerator or washing machine or other assembly-line made equipment, most of the components are hidden permanently in the interior.  The high strength and quick cure could mean that the entire assembly line would move faster, a real cost savings.

But outside the assembly line it is hard to imagine that it is a suitable adhesive.

I see that there are lots of choices now.

This is the one I have:

 

[Cheese]

I'm a big fan of PUR guns...I don't need it that often but I'd willingly give up some other tools rather than the PUR gun.

I've finished a lot of window installs with traditional wood trim but every so often a different treatment is necessary to give the room a different look or to "lighten" up the feel. That's when I pull out the PUR gun and install pvc edging around the window for a cleaner look. The stuff cures in 30-60 seconds and really adheres to the drywall. A little mud, a little sanding and you're ready to paint. The down side is the extra time it takes to fit/install the edging and the additional mud work that's needed. I'd say it takes twice as long versus the traditional wood method.

Here's a 36" round window in a small walk-in closet. If this were to be trimmed in the traditional manner it would look like a porthole on a ship.

[attachimg=1]

[attachimg=2]

Here are 6 windows trimmed out in the same fashion. Again, using the traditional treatment around each window would create a "wall of wood", a look better suited for an old library or a court of law. During the day light hours especially, the use of pvc edging retains a light, airy look in the room.

[attachimg=3]

[attachimg=4]

 

[Cheese]

1. The PUR gun itself is a gem.  It was brand new to the market when I bought mine and the glue was only available in full cases—a substantial cost.

2. If single tubes are available now, I might take it out of mothballs.  The bond strength was very good.  I’m sure the short open time would make it unusable for some glue-ups, but it also would make others very easy.

3. The black line would be an issue in many instances.

4. It was designed for factory settings.  It is probably good for that purpose where a regular hot glue gun would not provide enough bond strength. 

In a factory where you might be building a refrigerator or washing machine or other assembly-line made equipment, most of the components are hidden permanently in the interior.  The high strength and quick cure could mean that the entire assembly line would move faster, a real cost savings.

But outside the assembly line it is hard to imagine that it is a suitable adhesive.

I see that there are lots of choices now.

This is the one I have:

1. It is a well constructed piece of equipment. Gotta love the no cord situation.  [smile]

2. Single tubes are available from Rockler, just be sure to check the expiration date.

3. I've never seen a black line when I've used mine, then again I wasn't looking for one. I've always used the MP75 adhesive.

4. The bond strength is tremendous. 3M produces their own PUR adhesives and they characterize them thusly:
"A one-part formulation that combines the initial speed of a hot melt adhesive with the strength of a structural adhesive.
The bond forms in two stages: when the adhesive cools back down and solidifies like a hot melt it reaches holding strength, then the moisture-curing reaction proceeds over the next 24-48 hours to reach final structural strength. These adhesives are resistant to temperature extremes and flexible to provide vibration and impact resistance."

The one issue I've had with the Titebond MP75 product is a short shelf life. MP75 is an adhesive designed to adhere multiple materials to each other including metals. If the tube is left in the atmosphere for any length of time, it starts to absorb moisture and will bond the aluminum "pusher" to the aluminum tube. The adhesive may still be good inside but the strength of the aluminum pusher-PUR-aluminum tube bond is so high, you'll never break the pusher free.

I've taken to vacuum packing the tube and then placing it in the freezer. It seems to work well.

[attachimg=1]

 

[Packard]

The black line was from a minimal squeeze-out.  Thinking back, if I used less adhesive, it might have worked.

Instead I bought an underpinner which allowed me to work with the glued frame right away.  It cost about $2,500.00 in 1982 (about $10,000.00 in current dollars) and I was trying to avoid that expense.

The cost of underpinners shave not risen that much however. I just looked on line and there are versions available for $700.00.

 

[PaulMarcel]

So for the PUR glue gun... is the glue pretty thick like most craft glue guns? I use a craft glue gun to help with jigs, temporarily pin something, etc. But regardless the glue strength, it is just too thick to build something. Is the PUR glue relatively thin then? I'd be interested in something like that. I use CA glue during parts of glue-ups to act as mini clamps to keep parts from moving while getting the rest done and eventually putting real clamps on. This sounds like I could hold it and mostly leave it.

 

[Cheese]

So for the PUR glue gun... is the glue pretty thick like most craft glue guns? I use a craft glue gun to help with jigs, temporarily pin something, etc. But regardless the glue strength, it is just too thick to build something. Is the PUR glue relatively thin then? I'd be interested in something like that. I use CA glue during parts of glue-ups to act as mini clamps to keep parts from moving while getting the rest done and eventually putting real clamps on. This sounds like I could hold it and mostly leave it.

Unfortunately for your application Paul, the PUR adhesive consistency is very similar to hot melt adhesives...it's just 4-5 times stronger than hot melt...let's put it this way, it's a hot melt on steroids for strength. The shear strength is incredible, that's the reason I chose it for my project.

 

[Steve1]

So I glued up the pieces with epoxy.
Worked out pretty good.  But I think I will still put a dowel through the tenon just for good measure, blind, from the inside, so it won't be visible.
I taped up the surrounding wood, and I was careful with applying the epoxy, so had minimal epoxy on the wood surface.  And even that sanded off pretty quickly.
Kinda fortunate I went with the epoxy.  I spent close to 20 minutes applying the epoxy, and then on the first glue-up, I put the raised panels in facing the wrong way.  Could have been a disaster if I reworked the tenons for a tight fit and then used PVA glue.
That is Sapele framing and (pre-finished) Khaya (African Mahogany) panels.