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What type of Epoxy?

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Forum topic by PPK posted 10-17-2018 04:44 PM 490 views 1 time favorited 18 replies Add to Favorites Watch
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PPK

1182 posts in 983 days


10-17-2018 04:44 PM

I’m a little lost.
I’ve heard a lot about West Systems epoxy, a fair amount about System Three, and I’ve personally used a ton of the big box store brands like Locktite, Permatex, and Harbor Freight stuff.

I don’t really trust the 5-minute-cure Locktite or Harborfreight stuff though for some of the things I want to do. On the other hand, I don’t need a huge gallon or even quart can of the West Systems stuff.

I want to use for things like gluing up oily exotic woods, and making those large, important joints like trestle table legs. I want plenty of open time (1/2 hour or so)

Got any recommendations? Specific?

-- Pete


18 replies so far

View RobHannon's profile

RobHannon

165 posts in 704 days


#1 posted 10-17-2018 04:54 PM

Never used the stuff from HF, but had no issues with Devcon, Locktite, Hobby King, etc. for adhering.

I agree West and System 3 are probably not the most economical solution for small surfaces.

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Aj2

1789 posts in 1971 days


#2 posted 10-17-2018 04:58 PM

I use West systems with the 206 slow hardener. It has it place but it also has some drawbacks. In some woods it will leave a dark glue line, it’s very expensive so mixing up the right amount without being wasteful is challenging.
Mostly I use tite bond or plain old Elmer’s glue. I try to carefully plan my glue up in the cool mornings evenings.

-- Aj

View DrDirt's profile

DrDirt

4492 posts in 3915 days


#3 posted 10-17-2018 05:06 PM

West Systems, and System 3 are the same company now.

For Joinery stuff – I use “T-88” from System 3.
Available a lot of places, I get it on Amazon.

Gel time is 60 minutes, full cure is 72 hours, but generally I find it is an “overnight” clamp-up and is no longer tacky… just takes 72 hours to be at full strength.

Comes in many sizes from 1/2 pints to gallons.
https://www.systemthree.com/products/t-88-structural-epoxy-adhesive

-- “The two most important days in your life are the day you are born and the day you find out why.” Mark Twain

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John Smith

1436 posts in 336 days


#4 posted 10-17-2018 05:52 PM

there are dozens of good epoxy products on the market.
you just have to weed through them to fine one that works for you.
I keep a supply of the West System G/flex 650 on hand. it is a slow set
and easy to work with – and cheaper than the quart kits.

.

-- I started out with nothing in life ~ and still have most of it left.

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Redoak49

3596 posts in 2162 days


#5 posted 10-17-2018 06:00 PM

I use a couple brands. I recently have been using System 3 T88 for a Maloof style rocker and it works fine.

I also use Bob Smith from Amazon in both Quick Cure and Mid Cure with very good results. I mix it by weight using a small digital scale.

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CaptainKlutz

527 posts in 1667 days


#6 posted 10-17-2018 06:18 PM

All clear retail (IE sold in retail store) epoxies are basically same stuff. :(

Best example – Bob Smith Industries provides private labeling programs for any hobby shop or distributor that buys in bulk. That is why Hobby Lobby/Rockler/Woodcraft epoxy or cyanoacrylate adhesives all come in same bottle(s) and look almost same – they are same!

The key difference between the hardware store 5/10/15/60 minute cure varieties sold in less than 1 quart bottles is the type of curative used. They all use similar blends of same resins (bisphenol A diglycidyl ether & bisphenol F diglycidyl ether, with maybe some low viscosity reactive diluent oligomers).

The FAST cure (less than 15 min) types use an aromatic amine curative that reacts quickly and is least temperature sensitive of typically retail epoxy curatives. These are most forgiving of stupid human tricks, like mix ratio errors, or cooler temps. :)

The SLOW cure (30 minute plus) types use an polyimide curative that reacts much slower, and cure speed is much more dependent on ambient temp. Some will NOT cure at all below 60F, or will take weeks to cure, and months to reach full strength. These are less forgiving of stupid human tricks; such as mix ratio errors, and dirty bond surfaces, etc.

Generally speaking, The shorter the cure time; the lower bond strength, and lower bond strength is at elevated temperatures. So despite challenges with longer cure time epoxies, one should always use the longest cure time your process allows for best adhesive performance. Also must know that while fast/slow epoxy may begin cross linking and ‘set’ in 5 or 30 minutes, that full bond strength is not reached for days, some even require weeks (length of time is temperature dependent).

The small bottle retail epoxies described above are different than epoxy systems typically sold by West Systems, System 3, etc; in quarts and gallons. These epoxies were developed for (fiberglass, Kevlar, carbon fiber) composite lamination of water and air craft parts. These laminating resins have significantly lower viscosity to help with fabric wet out. They use slightly different resin and curative blends to provide this lower viscosity. These lower viscosity resins typically have lower bond strength (PSI), but when used over large area strength is not as important as flexibility or consistent performance across a wide range of temperatures.

The strength of laminating resin .vs a structural resin is mute point for most wood working applications. We really only need to be concerned with shear strength and peel strength. Practically every retail branded structural or laminating epoxy is stronger than wood in these stress modes. :)

So you can choose an epoxy to use for wood working based on how much time you need for assembly, clamp retention time, ambient temperature during assembly & cure, and even price. :)

Hope this helps explain hobby epoxy for you.

PS –
There are also retail structural epoxies intended for metal bonding, these are typically grey or black in color. This ‘metal’ epoxies use powdered metal as fillers, and weak acids that react with epoxy system to etch the metal for stronger bond. JB Weld is common brand, and it uses flake aluminum powder to help dissipate heat in epoxy and improve high temperature performance. Devcon/Loctite sell a black epoxy that uses powdered steel as filler for bonding metal castings. These can be used for bonding wood, but would not be best choice.

NOTE:
The above is extreme simplification of differences between varies retail epoxy types. There many more subtle differences left out, and many more epoxy systems available from commercial/online sources that some might consider retail materials. If you need more information on epoxy adhesives, PM me offline, and I can suggest a couple of polymer reference books for your library. :)

Best Luck!

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

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PPK

1182 posts in 983 days


#7 posted 10-17-2018 07:14 PM

Capt. Klutz! Wow, thanks! Very interesting. I learned a lot.

The strength of laminating resin .vs a structural resin is mute point for most wood working applications. We really only need to be concerned with shear strength and peel strength. Practically every retail branded structural or laminating epoxy is stronger than wood in these stress modes. :)

So you can choose an epoxy to use for wood working based on how much time you need for assembly, clamp retention time, ambient temperature during assembly & cure, and even price. :)

- CaptainKlutz

This does not surprise me, makes sense. ^

-- Pete

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PPK

1182 posts in 983 days


#8 posted 10-17-2018 07:16 PM

John, Dr. Dirt, Red Oak,
Looks like the T88 or Gflex 650 would be great options for me – not huge amounts and reasonable price. Thanks for the help!

-- Pete

View ArtMann's profile

ArtMann

1104 posts in 989 days


#9 posted 10-17-2018 08:56 PM

Is it a “mute” point or is it a “moot” point?

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newwoodbutcher

774 posts in 3023 days


#10 posted 10-17-2018 09:52 PM

Thank you Capt. Klutz! For your time, effort and helpfulness. Very well written and informative

-- Ken

View OnhillWW's profile

OnhillWW

139 posts in 1405 days


#11 posted 10-17-2018 11:12 PM

C Klutz nice post, most appreciated. I have used a lot of epoxy and this fills in a lot of gaps in my understanding.

-- Cheap is expensive! - my Dad

View MJCD's profile

MJCD

571 posts in 2544 days


#12 posted 10-17-2018 11:18 PM

I’ve used the West System G/flex 650 extensively; and, aside from the epoxy-associated issues, it is excellent.

Epoxies tend to leave a thicker, more noticeable glue-line (though TB3 is noticeable on light woods); and is much more expensive. The longer open time is very helpful in specific situations; and, in exterior work (outdoor benches, for example), I would default to epoxy.

These days, all interior builds are TB3 (Titebond III).

MCJD

View CaptainKlutz's profile

CaptainKlutz

527 posts in 1667 days


#13 posted 10-18-2018 01:13 AM

Couple more data points for those that care about epoxy differences:

1- The epoxy systems designed for composites mentioned above can have significant differences in material properties depending on curative used, even with same resin. While most people only look at whether curative is fast, med, or slow; these same curatives can provide significantly different values for hardness, flexibility, water resistance, or clarity (yellowing). So while picking your curative for optimum cure time, be sure to check the overall properties are what you need.

2- There are many epoxy suppliers available online. Not saying anything bad about West Systems, or System 3 ‘retail’ brands; but if your application needs quarts/gallons of epoxy, WWW has cheaper sources. I have used Fibreglast for many, many years with great success. Us Composites private label epoxies also offer nice price break with as few as 2 gallons. :)

3- If you are interested in longevity of epoxy in any surface coating applications where you want minimal yellowing as it ages, do not forget to protect the epoxy with UV inhibiting top coat. ALL epoxies will turn yellow as they age and are exposed to UV, even the ‘clear’ top coat epoxies sold for coating bar tops.

Best Luck!

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View lumbering_on's profile

lumbering_on

563 posts in 663 days


#14 posted 10-18-2018 01:32 AM



Is it a “mute” point or is it a “moot” point?

- ArtMann

Technically, it should be a ‘mute’ point, as ‘moot’ means something that is arguable. This is why law students participate in a ‘moot court’. However, as with so many misspoken phrases, the term ‘moot point’ is considered something not worth arguing.

It’s like when you hear someone say ‘pompom’ when the term is actually ‘pompon’. A ‘pom-pom’ is actually a British naval gun.

View Pixxture's profile

Pixxture

13 posts in 244 days


#15 posted 10-18-2018 01:41 AM

I have seen marine epoxies at the big box stores. Does this mean some epoxies are affected by moisture or water?
I had always thought epoxies were waterproof.

showing 1 through 15 of 18 replies

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