Unhardened epoxy at scarf joints

[jenshenliu]

I recently purchased a w&c Chestnut of 1970s with scarf gunwales which had become separated at the joints. I glued the joints with Three System two-part epoxy left from building a stripper 10 years ago, but the epoxy has not hardened over a week at the joints. I am pretty sure it is a failure caused by inaccurate mix ratio. Does anyone know how to remove the unhardened epoxy and regain clean joint surfaces for the next attempt? Thanks.

 

[Andre Cloutier]

Acetone will do it, sanding lightly after will help once its dried. Good luck

 

[Douglas Ingram]

While you could remove the unhardened epoxy with solvent, the greater issue is that the wood surfaces for the joint need to be properly prepared for gluing.

I would carefully cut along the glue joint, fold a piece of sandpaper so that the grit is exposed both sides, and rub, rub, rub, till you've cleaned the wood. Then pry the joint open as much as you dare, then smear some unthickened epoxy in, let it sit 5-10 minutes, then shove in some thickened epoxy, and clamp till snug.

Let cure, then clean.

 

[Mark Adams]

10 year old epoxy has probably gone bad. Epoxy resin does have a shelf life, and I think it is about a year. That being said, I regularly use system 3 epoxy that is years old. I make sure to mix the hell out of it, and I don't use it on high stress joints.

 

[Paul Miller]

You can breakdown any epoxy with a heat gun, cured or not cured. I think its at about 250 degrees that it goes opaque and crumbles.

Be careful not to burn the wood. The epoxy will go opaque and then should release the joint. I would continue to use the heat gun to get most of it off the faces of the joint and finish up with Acetone.

I agree with the age problem. Get new stuff.

Good luck,

Paul

 

[jenshenliu]

Thanks for all the input. There are four joints for me to try all the methods you suggest.

 

[pklonowski]

Please let us know how it all comes out... What method worked better than others? Which was easiest?

We're still learning, too... or at least, I am...

 

[Bill P]

You need to sweat the old glue out of the wood pores with heat and then scrape it off. Simple surface scraping when cold didn't work for me when I inadvertently applied a wrong epoxy ratio mix.

 

[Dan Lindberg]

Mark,


This seems a bit contadictory.

I have also used very old resin without problems but as you said, mix well,
not only the mixed material but each part prior to mixing as well.

In my experience, the resin solidifys and has to be heated to melt the solids back into a liquid.
The hardener usually has turned a redish color due to absorbing moisture but it still works, it's just not clear any more.

I don't know, but suspect, that the components in either the resin or hardener my separate over time and need to be remixed to get the proper components into the finished mix.

My "guess" is that this may be what happened and what caused the possible wrong mix ratio.


"Epoxy resin does have a shelf life, and I think it is about a year. That being said, I regularly use system 3 epoxy that is years old. I make sure to mix the hell out of it"

Dan

 

[Mark Adams]

Dan,

Even the System 3 website is somewhat contradictory. They have this to say:

What is the shelf life of your epoxy resin products?

All solvent-free epoxies have essentially unlimited shelf lives so long as they are stored in sealed containers. The resin may crystallize or the hardener may darken but this does not affect its performance. If the material is more than a year old do a test to satisfy yourself that it cures properly.

The bulk of my experience is with Polyester resin in the aviation industry. We definitely had shelf life times we had to adhere to with that stuff per the FAA.

 

[pklonowski]

I've used West System that's well beyond a year after I opened the cans, and it has worked well. I wrap the pump heads in aluminum foil after use, no special handling, really.

 

[jenshenliu]

I had used numerous times the System 3 epoxy that was left from 10 years ago and had no problem up to last year. The only failure - unhardened on the scarf joints -was most likely due to incorrect mix ratio. Instead of using the measuring pump, I used a spoon. I believe the 2/1 ratio went wrong because the resin had much higher viscosity that day and thus less amount was dropped to the mixing cup Anyway, new West system epoxy has been ordered for the job and I will report back the results using all the useful input from the discussion. Thanks.

 

[Dan Lindberg]

jens,

Just a thought,

for small batches I use 10 cc syringes to measure the resin/hardener.

As a standard practice when I'm building I keep 2 full of resin and 1 of hardener, just to have them on hand.

Makes measuring the small batches easy and accurate.

I've successfully mixed up batches as small as 3 drops.

Dan

 

[jenshenliu]

Dan,

Good idea. Now I can use syringes for accurate mix ratio and check if my decade-old epoxy still provides structural bonding strength. Thanks for sharing the experience.

Jen

 

[Dan Lindberg]

And if you have't already, be sure to mix up the resin and hardener before you measure it to to use. And if the resin is crystalized, melt it down by putting the container in a pan of hot water.

Dan

 

[jenshenliu]

This is a report back on how the unhardened joints were fixed using the suggestions provided here in the forums.

1. Used heat gun to release the tacky joints.
2. Rubbed the tacky epoxy off as much as I could with cloth.
3. Put a piece of cloth between the two joint sufaces and soaked it with acetone for 10 minutes.
4. Rubbed and rubbed the surfaces with the acetone-soaked cloth.
5. Sanded the two surfaces simultaneously with a piece of folded sand papper.
6. Cleaned the surfaces with acetone.
7. Glued the sufaces with thickened epoxy.

Results: the fix seems very solid

Lesson learned: too muck acetone in step 3 and it dripped and blistered the paint.

Thanks for the inputs.