T-88 Epoxy

[Robin Cruz]

T-88 seems a good less expensive alternative to the other slow set epoxy products. Says you have 40-60 minutes of working time. I was thinking of using it for chair mortise and tenon joints or maybe for the joints that take the most stress. Any experience with it? Is it thick enough to stay in joints well during glueup (other epoxys you have to buy thickener)?

Is there a significant strength advantage of epoxy over Titebond III. TBIII says it as 10-15 minutes working time which will be good enough.

Any thoughts?

[Richard Wolf]

Robin, epoxy is a poor choice to repair chairs. It cures to hard and allows for no flexibility when the chair is stressed under load. You would have better luck plugging the mortise and redrilling to fit.

Richard

[Robin Cruz]

I thought hard would be bad too, but their website says it stays flexible. These are new chairs Im building. Right how its 3/8 wide tenon into stretcher (thats 3/4 thick). Maybe ill just go with the TitebondIII and give it a stress test. Ill be making more chairs once I get the process down.
thanks for the input.


Robin, epoxy is a poor choice to repair chairs. It cures to hard and allows for no flexibility when the chair is stressed under load. You would have better luck plugging the mortise and redrilling to fit.

Richard

[Mike Henderson]

I use epoxy for the high stress joints in chairs and have found that it works well and last. Failure occurs not because of the glue failing, but because of the wood that the glue is adhering to fails. No matter what glue you use, the joint will eventually fail - but we're talking decades of hard use.

That being said, epoxy is good because you can use epoxy on top of epoxy and it will adhere. But as Richard points out, if you're repairing a chair, your first approach should be to get a tight mortise and tenon joint (or tight dowels if that's what was originally used). For dowels you can just drill out the old ones and use the next larger size. For M&T, you may have to glue veneer to the tenon (match the grain direction).

You should NOT have to use filler. The joint MUST be good fitting before gluing. If it's not, fix the joint and don't try to use glue to make up for poor joinery.

Also, you normally glue up a chair in parts. I generally glue up the back first. Once that's set, I glue up the seat parts which is only six joints (assuming no stretchers). A normal slow epoxy should be plenty long enough to get that much glued up.

But to answer your question, T-88 is a good slow epoxy.

Mike

[Mike Cutler]

Robin

While T-88 is a slow setting epoxy. it's advantage over the other System Three epoxies is that it already contains the filler agent for applications where gap filling is a need. The 50:50 ratio also seems to be a little more forgiving than the 2:1 mix requirement of the other System Three products
That being said all epoxies, and T-88 included, will have a cure time dependent on the ambient temperature environment, and the amount of heat allowed to generate in the "pot" while in use. If you mix a large volume in a small cup/container it will "cook off" on you.
I like to mix epoxy in a cup, and then pour it into a plastic tray that sits on ice packs to keep it cool. This technique can extend the working time of the pot for a long,long time.

Is epoxy stronger than Titebond? Not really. If you look at all the technical data available, Titebond is actually a pretty good product, very good in fact and has adhesion properties every bit as good as epoxy. Epoxy's advantage is in being able to manipulate the working time, and the reparability of the joint in the future, and of course increased gap filling properties when mixed properly.

I use epoxy pretty much exclusively for everything. In a properly prepared joint, Titebond or epoxy, is a good choice.

One question. Why T-88 over System Three resin and the medium, or high temperature hardner?

[Robin Cruz]

It seemed that with the System 3 products I need to purchase are the 1qt resin, 1pt hardener and filler and measuring spigots. Seems like it approached $90 for all those. The T-88 was $22 for 8 oz and ready to mix 50/50. I guess Ill build up the first chair with Titebond III. It has a long enough working time, especially doing the back only first, and then the seat to the back. I already dry fit it in just a few minutes.

[Mike Cutler]

Robin

I have the pumps from System Three,and have basically found them not applicable for my uses. I think if someone mixes a lot of epoxy on a consistent basis, they would be of more adavantage. I use syringes from a vet supply catalog.

The T-88 can be mixed effectively in very small quanities. I use old jar lids to do it. I like T-88.

[Wayne Cannon]

I would consider System Three's "SilverTip GelMagic" instead of T-88. While T-88 is formulated as a structural adhesive, GelMagic is especially formulated for woodworking -- in particular, it mixes to a non-sagging paste and is a better fit for the expansion and contraction of wood.

Someone asked why use T-88 (or GelMagic) instead of the general-purpose resin and hardeners -- used alone, general-purpose epoxy is really designed for coatings and should be mixed with fillers for the "toughness" desired for adhesive use (or other characteristics for other applications). T-88 and GelMagic, on the other hand, are specifically formulated as adhesive epoxies.

You really have to read between the lines in the SystemThree web pages -- specificallly the individual product data sheets and their FAQs. The SystemThree "Epoxy Book" provides better explanations, but is still more focused on boat-building applications.

GelMagic: http://www.systemthree.com/p_st_gelmagic.asp
T-88: http://www.systemthree.com/p_t_88.asp
General-purpose: http://www.systemthree.com/p_sys3_gpepoxy.asp

[Wayne Cannon]

I find the pumps work well for the thinner products, but are downright poor for the thicker products unless you store them in a warmer to keep them less viscous.

[Billy Chambless]

I would consider System Three's "SilverTip GelMagic" instead of T-88. While T-88 is formulated as a structural adhesive, GelMagic is especially formulated for woodworking -- in particular, it mixes to a non-sagging paste and is a better fit for the expansion and contraction of wood.

Someone asked why use T-88 (or GelMagic) instead of the general-purpose resin and hardeners -- used alone, general-purpose epoxy is really designed for coatings and should be mixed with fillers for the "toughness" desired for adhesive use (or other characteristics for other applications). T-88 and GelMagic, on the other hand, are specifically formulated as adhesive epoxies.

You really have to read between the lines in the SystemThree web pages -- specificallly the individual product data sheets and their FAQs. The SystemThree "Epoxy Book" provides better explanations, but is still more focused on boat-building applications.

GelMagic: http://www.systemthree.com/p_st_gelmagic.asp
T-88: http://www.systemthree.com/p_t_88.asp
General-purpose: http://www.systemthree.com/p_sys3_gpepoxy.asp

Bumping an ancient thread here, but do any of the WW suppliers carry GelMagic? I haven't seen it in any catalogs.

I've used T-88 and been happy with it so far.