Epoxy Glue/Filler

[David Ragan]

Do you all find that Epoxy is brittle? The two part stuff. I thought it was the best thing ever, until it broke a couple of times when stressed/shocked (I dropped the items).

Do you all use on end grain? As a filler?

When is it a "go to" glue/filler?

When is it absolutely not to be used?

[David Ragan]

Am i only one to yse epoxy, or i already stated its limitations?

[Stan Calow]

David I use it too some degree on almost every project, often when I have a less than perfect M/T joint, or a gap that is too big for C/A and sawdust. Almost always on outdoor projects. I don't know a substitute that is as versatile. I use it to build-up damaged edges often, on on bottom surface of table legs. I have not noticed brittle, but you are probably right.

[Wade Lippman]

I used it once when I glued up a really complicated outdoor table and needed an hour open time. Only other time was penetrating epoxy to waterproof the plywood on a boat.

Do you use it for normal woodworking? Question then is why you don't, rather than why we don't.

[Mac McQuinn]

I've used a couple well known (2) part epoxies for boat building, utilizing marine plywood and softwoods/hardwoods and have never experienced brittleness of any type. That said, I'm a bit anal on using the correct formulas, fresh product and applying it in optimal climate conditions. Wooden boats typically experience quite a bit of flexing in use, if there was a problem with the epoxy, I'd expect something to show up by now. I've used it to coat wood, saturate fiberglass matting, mix with a filler for fillets and used as a adhesive, both with and without fillers depending on the fit-up.
Mac

[Phil Stone]

I used it on the bottom of my workbench legs, to seal the end grain against moisture up-take. I either got the mix a little wrong, or built it up too thick too fast, but I had some residual stickiness that I've had to sand out. Haven't noticed any brittleness, though.

[Chris Padilla]

Brittleness might be indicative of old product or mixing improper ratios of resin and hardener (catalyst).

However, it can dry hard as a rock and if you smash it with a hammer, it will crack and break apart like, well, a rock. :)

[Larry Edgerton]

Call West System and ask for a copy of their users manual. It is free and they know epoxy as well as anybody. Its probably not the epoxy.

[Wade Lippman]

Brittleness might be indicative of old product or mixing improper ratios of resin and hardener (catalyst).

West says epoxy can't get old. I have some about 15 years old and it still works normally. Well, if you don't mind it being brown.

The fact that epoxy/fiberglass is flexible kinda means it isn't brittle.

[Chris Padilla]

I've heard that, Wade, but nothing lasts forever. It must break down a bit...maybe more so in different environmental conditions. Perhaps it can get contaminated in some way?

[Mike Cutler]

I use epoxy pretty much exclusively. It shouldn't be brittle by itself unless something is wrong. The two chief causes would be improper hardner/resin mixture ratio, or a starved joint. If you "clamp" an epoxy joint, it's an odds on bet that it will be starved.

I don't use it because it is any better than a Titebond, or similar product ( Pretty similar yield strengths when compared). I use it because I learned to use it repairing boats and it's just easier for me.
I'm not sure what you mean by "filler". QuickWood and Mohawk Finishes make epoxy sticks for filling in holes and repairs but these are a stand alone product. Add enough wood dust as a a thixotropic and I guess you could make a filler, but the color would be weird.

When shouldn't you use it?
Most luthier work,any fine furniture, antique restorations, or repairs to fine furniture. These are better suited by the use of hide glues, because they are more easily repairable.

[David Ragan]

That makes me feel better about the suspected (not now) brittleness
i posted months ago about having used epoxy in nice furniture, and nobody said anything (of course) but i later (not much) said to myself......epoxy not really something you use in fine furniture.... Choose anothrr option. I dropped the item, it broke @ seam, redesigned the joinery and bingo👍😀
i am probably as good as the next guy/gal w mixing 50/50
thixotropic? Cool word. Something to do w flow/leveling, right?

[Larry Edgerton]

i am probably as good as the next guy/gal w mixing 50/50


Not sure what brand you have but the two major brands I use are not mixed 50/50. That could be the brittle.

If I need a color filler I will sand the same wood with a RO with the canister filter on it, empty the canister and mix it with epoxy to make my filler. Slightly darker but a good color match.

[Wade Lippman]

If you "clamp" an epoxy joint, it's an odds on bet that it will be starved.

I helped build a boat last summer with epoxy. It was so weird using the minimum possible pressure on the clamps, instead of cranking them down.

[Brian Elfert]

Some epoxy resins can get really thick when they get old. I have had old resin that was so thick it was basically unusable. I have no idea if the resulting bond was worse when I did use some old epoxy. I finally switched brands of epoxy because the resin for the one brand got thick so fast with age.

I use epoxy for high power rocketry. Some in the hobby are using Gorilla glue instead of epoxy if not using fiberglass tubes as Gorilla glue is easier to deal with and seems to be just as strong or stronger.

[Mike Cutler]

thixotropic? Cool word. Something to do w flow/leveling, right?

More like "rebar" for epoxy resins. It can come in all forms. micro-ballons, wood flour, aluminum powder,silica, graphite and kevlar strand dust, etc. Basically an agent that causes a thickening and support for epoxy. Not so much flow, although that is a property of the mixture.
T-88, by System Three, is an example of a structural epoxy with the thixotropic agent already mixed in. There are many others.

[Mike Cutler]

I helped build a boat last summer with epoxy. It was so weird using the minimum possible pressure on the clamps, instead of cranking them down.

Wade
It takes a little getting used to. Next time you use some, mix a little extra and glue two boards together, edge to edge, face to face, whatever, except end grain. Clamp these like you would a Titebond joint. Do the same thing with two more pieces of scrap material and just kind of ensure they are making contact and use some painters tape to hold them in place.
When they cure. The one that was clamped can be easily split along the joint line. The one taped will not.

[Brian Ashton]

I've used a couple well known (2) part epoxies for boat building, utilizing marine plywood and softwoods/hardwoods and have never experienced brittleness of any type. That said, I'm a bit anal on using the correct formulas, fresh product and applying it in optimal climate conditions. Wooden boats typically experience quite a bit of flexing in use, if there was a problem with the epoxy, I'd expect something to show up by now. I've used it to coat wood, saturate fiberglass matting, mix with a filler for fillets and used as a adhesive, both with and without fillers depending on the fit-up.
Mac

When you mix your next batch try this. Mix a bit extra and put equal amounts in two pots. One with nothing added and the other with a bit of fine sawdust added and let set... The disk without filler will shatter like glass with even a light tap of a hammer. The other will take quite a beating before breaking.

It doesnt happen often but ive had a couple projects in the past fail so now I add a bit of filler now to all jobs just for that added strength to the epoxy crystaline
matrix

[David Ragan]

What a great thread!
bondo is only other kind i seen w/o 50/50 mixture
so adding a bit of appropriate particulate helps structural ntegrity?

[Michael Weber]

I just purchased some T88 to glue up a screen door made of lyptus. I wasn't aware it had filler in it. Was planning to add wood flour for my imperfect M/T joints, but now maybe not. Since it already has filler would it be a waste to add some wood flour? I don't want to jeopardize the structural integrity.

[Shawn Pixley]

Epoxys are known to be more brittle than other adhesives. They are especially susceptable to shock.

That said, I have never experienced epoxy failure in woodwork only other types of repairs.

[Mike Cutler]

I just purchased some T88 to glue up a screen door made of lyptus. I wasn't aware it had filler in it. Was planning to add wood flour for my imperfect M/T joints, but now maybe not. Since it already has filler would it be a waste to add some wood flour? I don't want to jeopardize the structural integrity.

Michael
On the carton it came in, or at System Three's website, it will give the maximum gap spec for T-88. If your M&T joints are close at all, just use the T-88 as is. They'd have to be really far off for T-88 to not work, so far that you probably would have done them again.
T-88 is a great product. It's very forgiving on the mixture ratio, but try to be close. I like T-88.
Smear any excess over some scrap material to dry. The "pot" generates a pretty good amount of heat, so don't just throw it in the trash.;)