epoxy for mortise and tenon joints

[pviser]

I just viewed a video from AskWoodMan.com about using a chisel to square up mortises. On the audio track, the guy said that he swears by using PC-7 epoxy for the adhesive in his MT joints, citing its gap-filling properties and its longer working time to check for perfect alignment. I plan soon to glue up 32 MT joints with Titebond yellow glue. I'd be interested in others' thoughts about using epoxy instead. Thank you.

 

[Joe Scharle]

I've used epoxy on gates, but never found it necessary for interior joints. The very fact he mentioned 'gap-filling' speaks volumes itself.

 

[ehpoole]

My own thoughts on the subject are as follows.

If you routinely make well-fitted mortise and tenon joints, then a water-based blue (e.g. PVA) will cause the wood fibers to swell up and ensures a solid tight-fitting glue joint with minimum gaps and maximum strength.

On the other hand, if you make loose ill-fitting mortise and tenon joints, then you are going to need a glue with excellent gap filling properties. Even so, such joints are never going to be as strong or true was a well-fitted mortise and tenon joint.

The only good argument in favor of epoxy is its availability with long open times for complex joinery. However, there are extended open-time PVA glues (not as extended as Epoxy, but 2-3 times longer than regular PVA) for such applications. Unlike water-based glues, wood fibers do not swell when Epoxy or Polyurethane glues are applied, so water-based glues are usually preferred for such joinery since the swelling brings the wood surfaces into tight contact with one another.

 

[michaelgarner]

I've used epoxy on gates, but never found it necessary for interior joints. The very fact he mentioned 'gap-filling' speaks volumes itself.

Read and then Re-Read what Joe said ^.

 

[shopsmithtom]

Although there's no substitute for a tight fitting joint, I have tested Harbor Freight clear quick setting epoxy that comes in 3 oz tubes. I was using some dowels that fit (I thought) a little too loosely in the holes I had drilled. I did some test joints with the epoxy & was pleased that there was no way to separate the pieces short of breaking apart the dowels. The open work time was reasonable & the resin is clear. Isn't PC-7 gray in color?

 

[Bas]

+1 on making sure the joints are tight to begin with. I've fixed the occasional undersized tenon by simply gluing a thin slice on. As for longer open time, Titebond III and Titebond Extend are good choices. My favorite glue for complex glue-ups is plastic resin glue, made by DAP. The brand name is Weldwood. Ace Hardware generally stocks it, it's a powder you mix with water. It has a very long open time, which makes for stress-free glue-ups.