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Oct 15, 2021 - 9:10:20 PM
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2350 posts since 2/7/2008

Banner Blue asked for a thread on the Strengths and Weaknesses and Pros and Cons of Various Epoxies and since I use it regularly, I thought I'd kick it off.

West System is considered the gold standard for epoxy in boat building. They make an all purpose resin and a variety of hardeners that allow you to adjust cure time according to the project. They also make a whole bunch of fillers that can thicken epoxy to make everything from easily sandable putty to making structural fillets. The mixing ratio is critical, but once mixed properly, the cure times are very predictable. The predictable cure time is one of the things I really like about it.

This will be anathema to the hide glue folks, but one of the really great things about epoxy is that it contains no water, so it won't make wood bow. I have glued a fingerboard to a neck using a slab of marble as a clamping caul. Once cured, it came of the clamps dead flat and stayed flat.

West also makes an epoxy called G-Flex. It works like most other epoxies, but it's just a tad more flexible when it cures. It's good for gluing dissimilar materials or where the may be more than usual expansion and contraction.

Last in the West fleet is an epoxy called Six10. It comes in a caulk tube and the tip mixes the epoxy. It comes out thick and it will stay put, but if you work it with a brush or a tool, it becomes liquidy and will penetrate well. It borders on ridiculously expensive, but sometimes it's just the ticket.

Many Epoxies including West Epoxy create a surface film when they cure called amine blush. It will prevent a second coat of epoxy from adhering unless you wipe it off first. Since I rarely use epoxy as a coating, this is seldom a problem for me.

I also use MAS Epoxy. They make most all of the stuff West does, but they also have a low viscosity resin. This stuff is really thin and is ideal for fixing cracks or filling around inlays. It will flow through a fairly fine syringe. Mas Low Viscosity can also be used as a grain filler on open pore woods. Because it's clear, it doesn't impart extra color on the wood. It is messy though and if you leave runs, there will be extra sanding to do. MAS does not have the amine blush, so is better as a coating. You can also thicken the low viscosity resin to make a variety of glues and fillers.

The biggest con of epoxies are the start up costs. The resin usually comes in quarts which are expensive of themselves but then you also need pumps to accurately measure the stuff which adds even more cost. For me, a quart lasts a looooong time. I've recently added a small scale to my bag of tricks so I can measure by weight allowing me to mix up small batches so I'm not wasting epoxy.

Another con of epoxy is that if you mix up a big batch, the chemical reaction that "kicks" off the cure generates heat; the heat accelerates the cure which generates more heat and before you know it you've got a cup of boiling goo. The way to get around this is to spread it out; usually on the surface you plan to glue.

Epoxy doesn't reverse the way hide glue and Titebond do. There's a widely held misconception that epoxy doesn't reverse. An epoxy joint can be made to loosen with heat; it just a huge pain in the neck to clean up to get a fresh start. For the most part, I don't use epoxy on anything I expect to take apart.

Epoxy, especially thickened, has the ability to bridge a gap and maintain structural strength. I'm not aware of another glue that does this.

I don't use epoxy for everything, but I do think it has its place.

I hope this is of some value...

Edited by - Quickstep192 on 10/15/2021 21:13:55

Oct 15, 2021 - 9:37:51 PM

65 posts since 8/31/2015

Thanks for starting this thread. Although I've at times cursed other repairmen for using epoxy and I don't particularly enjoy using it either, epoxy definitely has its place in a repair shop. I use the West Systems epoxy for structural repairs (that nobody will need to undo in the future). It is great stuff, I also mix in small cups on a little digital scale to minimize waste.

Broken headstock on a Yamaha? Yes!
Neck reset on a vintage Martin? No!

For epoxy putty, Mohawk is the best I have tried. I keep it with my lacquer and finishing supplies because I use it almost exclusively for finish touchups: put down a white base layer (blank canvas), work on color matching, then carefully paint in grain lines and finish with a lacquer topcoat for a virtually undetectable touchup.

Maybe next week we can start a thread about the merits of different types of superglue ;)

-TD

Oct 15, 2021 - 11:30:07 PM

rcc56

USA

3844 posts since 2/20/2016

All that I will say about it is that anyone who brings me an instrument with an epoxied-on fingerboard that needs to be lifted will have to be prepared to pay for a new fingerboard.

Reversible with heat??   Well, maybe sometimes.  Often not.

Edited by - rcc56 on 10/15/2021 23:36:10

Oct 16, 2021 - 5:52:31 AM

Fathand

Canada

11826 posts since 2/7/2008

I used to use little tubes of 5 min. epoxy mixed with sawdust for inlay filler. One time it refused to harden and people here suggested I use CA instead. It works great but I have developed an allergy or sensitivity to it. Even a respirator doesn't completely prevent it. I may go back to epoxy.

Oct 16, 2021 - 6:10:50 AM

2350 posts since 2/7/2008

quote:
Originally posted by Fathand

I used to use little tubes of 5 min. epoxy mixed with sawdust for inlay filler. One time it refused to harden and people here suggested I use CA instead. It works great but I have developed an allergy or sensitivity to it. Even a respirator doesn't completely prevent it. I may go back to epoxy.


I've sometimes found it difficult to get a good mix with the twin tube epoxies because even though there's a single plunger, they can dispense the resin and hardener at slightly different rates. This is especially problematic when mixing small quantities because any differences in the resin to hardener ratio are magnified. 
 

One of the things I'd done to inlay with epoxy is to put some epoxy in the inlay cavity, then press the inlay into the cavity using a flat caul wrapped in clear packing tape and clamping. When the caul is removed, the inlay is dead level with the surface. I did this when inlaying a pre-engraved inlay that I didn't want to sand after inlaying. Oh by the way, I mixed in some mars black pigment to make the epoxy black. Mars black is blacker than any other black. 

Oct 16, 2021 - 8:26:17 AM

Owen

Canada

9810 posts since 6/5/2011

quote:
Originally posted by Quickstep192
<snip> I've sometimes found it difficult to get a good mix with the twin tube epoxies because even though there's a single plunger, they can dispense the resin and hardener at slightly different rates. This is especially problematic when mixing small quantities because any differences in the resin to hardener ratio are magnified.  <snip>

As a putterer, my workaround is to just remove a bit of the larger glob...so they look more equal in size, before mixing 'em.

Oct 16, 2021 - 9:34:19 AM

14028 posts since 6/29/2005

I use epoxy for a lot of things in banjo building— Inasmuch as it's not a traditional material, there is a lot of misinformation about it, but I'm not going to go into a tutorial of any kind., which would be a waste of time and energy.

I will say this: Epoxy is actually no more difficult to remove or soften with heat than Titebond, probably easier.

Oct 16, 2021 - 1:49:31 PM
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rcc56

USA

3844 posts since 2/20/2016

My experience has been otherwise.

Oct 16, 2021 - 2:20:39 PM

14028 posts since 6/29/2005

There are different kinds of epoxy and they are not all the same, just like there are umpteen kinds of Titebond and animal glues, which are not all the same.

I use 4 different kinds, one with with two different catalysts/hardeners and several kinds of fillers that alter the thickness and gap-filling characteristics. They are an industrial material used mostly in marine and aircraft applications, different than wood glue.

There is a learning curve with them, which is why I really don't want to go into a tutorial which would be ignored, or worse, disputed by many readers.

I do not use ANY of the ones you can buy at Lowe's / Home Depot for whatever it's worth.

Edited by - Ken LeVan on 10/16/2021 14:22:22

Oct 16, 2021 - 8:55:21 PM

140 posts since 9/30/2009

Epoxies can be rather picky things to use. If you are mixing small amounts, I recommend weighing the two parts on a gram scale. A small electronic scale has become an often used tool in my shop for everything from mixing epoxies to weighing bridges.

West System, MAS, and System Three are all used in boat building and are excellent adhesives. I don't know the sizes West and MAS sell in, but System Three does sell smaller size packages. Devcon is more available in hardware store situations and I feel is pretty reliable as well. JB Weld is awesome stuff, but may or may be right for these uses. Test it out if you can.

Epoxies do have a life span so buying fresh and storing them in a cool and dark place helps. I recommend doing a test with anything old to make sure it still kicks and to know if the viscosity is suitable for your purposes.

The thread that started this talked about epoxy putties. I use them a lot and get mine from Aves Studio. avesstudio.com The main one I use is Apoxie Sculpt. It comes in lots of colors and the company has a variety of different formulations with slightly different working characteristics. I use it for making form fitting shims for museum objects and use saran wrap or very thin polyethylene as the barrier layer to keep the object and epoxy separate. It is water soluble in the mixing state and tools and hands clean up with water. Once cured, it can be cut, drilled, tapped, sanded, and polished. Very useful stuff to have in the repair kit.

Oct 17, 2021 - 4:42:11 AM

14028 posts since 6/29/2005

The gram scale is a must for very small amounts. You should buy a large container of disposable plastic cups.

You can get pump bottles where each stroke of the pump dispenses a small amount, and these are useful for small batches, too.  I buy the resin in gallons, various hardeners in quarts, and transfer it to the smaller pump bottles as I go along.  The larger containers are hard to pour from—especially small amounts, and they tend to drip and create a mess.

You can dispense tiny amounts to the cup on the gram scale using the pump bottles and it's much neater than pouring.  If you keep a record of how many grams it takes to do a certain thing, like gluing a fingerboard onto a neck, you can avoid wasting material.

Some of the fast-acting ones, 5 minute, 15 minute, etc. that are useful for inlay infill, repairs and a lot of odd things, can be measured out by making an equal sized little blob of each part and mixing it with a little stick—you can add color to these to match what you are doing.

Oct 17, 2021 - 6:09:08 AM

832 posts since 1/21/2004

When you mix epoxy is the mix ratio by volume or by weight?

Heavythumb

Oct 17, 2021 - 6:23:20 AM

9093 posts since 8/28/2013

Although this is a building and repair forum, I think there is a little too much emphasis in this particular thread on the "bulding part," and not enough on the "repair" portion. It;s one thing to spend a lot of money for a product when one uses it for dozens of builds, but quite another when a person needs epoxy for a few repairs per year. There are many individual looking for an answer for a repair to their own instrument, and maybe some others who are simply helping a frew friends with a repair. These people, I'm certain, would like to know more about how a few ounces of a product might work, rather than a ghallon or two of an expensive boat repair epoxy.

There are epoxies and epoxy pastes that are available in reasonable quantities from local hardware stores, and although these are not always the ultimate strenth-wise or workability-wise, they may be more than adequate for many uses. I, for one, would like to see a few specific pros and cons of some of these.

Oct 17, 2021 - 10:02:04 AM

14028 posts since 6/29/2005

George brings up an interesting point.  Epoxy that can be had from hardware stores, etc. can be used for various kinds of repairs.  There are pastes and liquids. Two that I have used are:

"PC Woody", which is a pine-colored paste 1:1 ratio, that can be used to fill cracks and voids and can be used as an adhesive in certain cases.

Another kind is System Three quick cure 5-minute, which is a clear semi-liquid 1:1 ratio, and can be used for various small repairs, filling holes, can be colored, and used as an adhesive.

I have not had any success bonding aluminum with JB Weld, despite what they say. It won't hold for long on  a tension hoop or bracket band, even with a cleaned and roughened a scarf joint—I think it would be great for filling a hole, though

Generally, you pay a lot for packages that supposedly dispense equal amounts with many "hobby/hardware store" brands.

Oct 17, 2021 - 10:36:52 AM

140 posts since 9/30/2009

To answer Heavythumb's question, you can mix epoxy either by volume or by weight. The problem is, that the smaller a total amount that you are mixing, any error in one component to the other will be a larger percentage of the whole. At some point that error will effect curing. With a gram scale, it is far easier to measure the two components accurately than with blobs or cups. Syringes can be good for accurate measurement, but the syringe packaging on much consumer epoxy is woefully inadequate. The commercial syringe systems with mixing nozzles are great but can be very expensive.

Epoxy combines chemically on a molecule to molecule basis, as opposed to Bondo and polyester resins which are more a catalyst reaction. This is why you can put extra catalyst in Bondo and have it kick really fast. The reaction speed of properly measured and mixed epoxy will be dependent on the type (5 minute vs 1 hour...) and the temperature as all reactions tend to happen faster at elevated temperatures. (I am not a chemist so this is a crude explanation, but I have chemistry as a peripheral component of my work.)

Oct 17, 2021 - 1:21:55 PM

14028 posts since 6/29/2005

quote:
Originally posted by jfhascall

To answer Heavythumb's question, you can mix epoxy either by volume or by weight. The problem is, that the smaller a total amount that you are mixing, any error in one component to the other will be a larger percentage of the whole. At some point that error will effect curing. With a gram scale, it is far easier to measure the two components accurately than with blobs or cups. Syringes can be good for accurate measurement, but the syringe packaging on much consumer epoxy is woefully inadequate. The commercial syringe systems with mixing nozzles are great but can be very expensive.

Epoxy combines chemically on a molecule to molecule basis, as opposed to Bondo and polyester resins which are more a catalyst reaction. This is why you can put extra catalyst in Bondo and have it kick really fast. The reaction speed of properly measured and mixed epoxy will be dependent on the type (5 minute vs 1 hour...) and the temperature as all reactions tend to happen faster at elevated temperatures. (I am not a chemist so this is a crude explanation, but I have chemistry as a peripheral component of my work.)


Some of them have different specific gravity for each component, so by weight is different than by volume. For instance, T-88, a widely used structural adhesive is 1:1 by volume, but 100 parts resin to 83 parts hardener by weight.  While it's always better to be precise, there is a little schnooly there, and I have mixed it 1:1 by weight a few times when in a hurry, and it worked just fine.

For the ones where you have to go by volume, I usually measure out the right amounts into a plastic cup using water or rice, and mark the cup with a sharpie as a "template" for future reference. a lot of silicon rubber mold compounds and some urethanes go by volume.

Oct 17, 2021 - 6:27:05 PM

2350 posts since 2/7/2008

For the MAS epoxy, I buy a quart of resin and I buy hardeners in pints. A quart of resin is about $35 and a pint of hardener is about $30. This seems like an extraordinary price, but a quart of resin normally last me 2+ years.

Oct 18, 2021 - 4:19:01 AM

14028 posts since 6/29/2005

quote:
Originally posted by Quickstep192

For the MAS epoxy, I buy a quart of resin and I buy hardeners in pints. A quart of resin is about $35 and a pint of hardener is about $30. This seems like an extraordinary price, but a quart of resin normally last me 2+ years.


Thanks to the info about MAS—I had never heard of them before, so got onto their site.

I think West System, System Three, and MAS are all pretty similar, catering to people who make glossy bar tops, boat & surfboard builders, and others like us who have unusual uses, like instrument building—they all have a general purpose resin, some dedicated adhesive, several hardeners, and several fillers, which is what I am interested in.  I have a very large extensive catalog from West System which I have gone over several times and they sell a lot of fibers, tow, and woven mats, like fiberglass, Kevlar and carbon fiber  For some reason I can't remember, there's some blocking issues with their products that stop me from investing in their system.

I have latched onto System Three because their various resins and hardeners are often interchangeable and they sell a lot of stuff useful to woodworkers.  They have been good with tech support answering some unusual questions I've asked.

It's worth mentioning that I got interested in these resins from some posts by a guitar builder from Santa Cruz guitars who explained why you don't want water in fingerboard assemblies very articulately, and several people who build guitars using the Greg Smallman method.  I think it's a technique who's time has come in instrument making, and it's worth going through the learning curve.

Oct 18, 2021 - 5:22:15 AM

2350 posts since 2/7/2008

The two differences I've noted between MAS and the others is that MAS has a low viscosity resin and the blush free hardener.

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