5 minute epoxy as clamp?

[Ben Fleis]

I have been told that 5-minute epoxy isn't strong enough for long term and/or structural bonds, and that its original intended use is as a 'clamp' for longer epoxies to dry. Sounds great.

But, how does it work? I assume you don't simply mix 5-minute and 'normal' epoxy. And if I am using it as an adhesive between layers of wood (in lamination, for example), what is sensible? Stripes of 5 minute with wider swaths of regular strength?

Anybody have a notion here? Thanks!

] b [

[John Coloccia]

I've never heard of this. I'm also searching through my memory and cannot recall an instance where I've seen a 5 minute epoxy joint failed because of glue failure as opposed to poor design or poor technique. The main reason to avoid it, in my opinion, is that by the time you're done mixing it, you have about the same open time left as hot hide glue.

[ian maybury]

5 min may possibly produce a marginally weaker polymer as a result of the fast cure (as also is the case when a slower epoxy is used in colder than ideal conditions), but i've seen it used in critical applications for many years and never a failure. (model aircraft engine mountings and the like) As John says the open time is so short though that it's really only suitable for spot applications....

ian

[Mike Cutler]

Ben

You have some "Mis information", and 1/2 truths.

"Normally", commercially available epoxies cure by exothermic reaction, or heat. So while sometimes the two components are are referred to as the resin and catalyst, they are in fact the resin and the hardner. It isn't a chemical reaction taking place, as with a catalyst, but cures exothermically which is why the resin to hardner ratio is pretty important.
In a 5 minute epoxy, you have 5 minutes of "Pot life", or "Open Time", before the epoxy exothermically beging to cure. The thinner the epoxy is spread, the longer the cure, because of the time it takes to develop sufficient heat over a given area.
The 5 minute Epoxy you can buy at a Home Depot wouldn't be my first choice to use, but it does work. Used properly it will create a sufficient bond.

Generally speaking you would not mix epoxies by different manufactures,and within their own epoxy lines you can't mix them either unless they've already been proven compatable. So no, you would not mix 5 minute epoxy from Home Depot with another epoxy.

In a normal epoxy glueup you would use an epoxy from one single manufacturer, ie Sytem 3, or West ( The two most available brands commercially).
You would pick the hardner based on the ambient temperature in the area you will be working, and the difficulty of the glueup. A complex glueup, would require a longer open time, and an epoxy rated for low temps would not be used in a higher temperature ambient environment, or it would have significantly decreased open time and cure very fast. You can go the other way though, sometimes. A higher temp hardner in a low temp environment will have a longer cure and open time.

Epoxy does not require the clamping force of a PVA glue, and this is where most people have problems. Very little clamping force is required for an epoxy joint, not much more than it takes to align the joints and bring them together. In a lamination the weight of the materials stack on top of one another can be enough if the epoxy is prepared properly.
If you'd like to test it, take the 5 minute epoxy, mix it up, smear it on a scrap board, and lay another scrap board on top with no clamp. Maybe a brick to keep them flat against each other. Come back the next day and see if you can seperate them.

If you need to do a lamination, use one epoxy, properly selected, for ambient temps and complexity of the lamination. Don't mix them.
"Paint" the surface(s) evenly ( not real thick), covering the entire laminated face. Place the boards together, and align them with slight, uniform clamping pressure. Don't rely on squeeze out to cover the area, and try to keep the squeeze out to a minumum. Epoxy can be difficult clean up.
Clean the excess squeeze out with a flat scraper, or chisel when it gets gummy, a few hours later. Release the boards the next day and you should be set.
The actual cure for epoxy can take upwards of a week, but about 80% of the cure is set in the first 24 hours with normally available epoxies.

It sounds complicated, but it's not. Epoxy is very easy to use.

[Ben Fleis]

Ben
You have some "Mis information", and 1/2 truths.

Generally speaking you would not mix epoxies by different manufactures,and within their own epoxy lines you can't mix them either unless they've already been proven compatable. So no, you would not mix 5 minute epoxy from Home Depot with another epoxy.


Hi Mike,

This is an excellent summary of epoxy usage, but I don't follow the mis-information / half truths. I don't want to sound antagonizing, because I don't feel that way -- but I don't understand your answer, relative to the question.

To be perhaps more clear with what I'm doing -- I have a bit of 3mm edging to apply to the end of a lamination, composed of 3 layers bending ply and 2 layer self cut veneer, ~18mm finished thickness. This piece is actually the bottom of a bookcase side, and mostly invisible, but it does receive the 'brunt of force' if the case gets dragged around, etc., thus I wish to be certain about its strength. However, the seam will be visible on the outer edge, so I need to have enough clamping pressure to make it clean. Since much of the material is glued to the end grain of this bending ply, my initial thought was that epoxy would be stronger than PVA.

In reality, I can use normal PVA glue, which I've actually already done for one of these joints, but my mind floated to this clamping notion, which I believe I picked up in furniture school, and I thought I'd see if anybody here had such experience.

(For the record, I've used quite a bit of epoxy, of both 'normal' and 5-minute forms, both for laminating and regular long-duration glue ups. Mostly west systems.)

Perhaps the practical question could be resolved to this: is 5-minute really that weak? Is that weakness qualified by mission critical application, or need I worry about the bottom 'runner' popping off when a piece gets dragged around on a floor?

But I am still curious about this 5-minute clamp idea -- I definitely didn't make it up ;)

Thanks again!

ben

[Mike Cutler]

Ben

Apologies. I misinterperted your post, relative to experience.

My own experience with the 5 minute stuff, is that it's strong, but brittle. In a shear force application I'm not certain I would trust it.
What you may consider is to use the partial cure technique. In this application the epoxy is allowed to begin the cure process to a "tack" surface, and the surface adhesion pressure is sufficient. Kind of like using contact cement.
Is there any way to tape or band the joint?

With the bending ply, I might be tempted to look at a structural adhesive because of the end grain. But, I tend to really overthink/overbuild things too;)

[Joe Angrisani]

....Perhaps the practical question could be resolved to this: is 5-minute really that weak? Is that weakness qualified by mission critical application, or need I worry about the bottom 'runner' popping off when a piece gets dragged around on a floor?

But I am still curious about this 5-minute clamp idea -- I definitely didn't make it up ;)

The short answer is "5 minute epoxy isn't that weak". It's just weaker than a good 30-min or 1-hour cure, and I'd almost always go with a slower cure epoxy. The other big thing to keep in mind is that epoxy fills gaps, while PVA glue wants a very tight fit. This fact makes the idea of "clamping" a PVA joint with some areas of epoxy a bit mis-matched.

I have just seen something done in regards to "clamping with epoxy". When the guys recently set our master bath tub deck (a man-made material called Nano Glass - see this thread (http://www.sawmillcreek.org/showthread.php?174168-Countertop-Material-Has-Anyone-Used-quot-Nano-Glass-quot&highlight=nano+glass)), it was bonded with troweled-on polymer thinset. But in addition to the thinset, they put down 8 or 10 dabs of a "polyester epoxy" that set up completely in 30 minutes. The installers said the fast dry stuff keeps the big slab from shifting, even slightly, as the thinset dries over a day or two. But in this case, both the thinset and epoxy "fill gaps", and neither works on the concept of dead-tight joints, so they "match" in that regard.

[Ben Fleis]

Hi Mike,

I appreciate it, but there's definitely no need to apologize. All is good :)

I clamped the joint up just fine -- by clamping down a block on top. I have a couple pics, and will put one up here. The question truly became academic, as I did the other end with PVA as well. I looked again, and in reality the wood surface is 80% long grain. As long as my clamping jig is enough, this will be plenty strong.

(The clamping on the right is "the one in discussion". The one on the left is fixing something else... bah.)

223316


Cheers,

ben