Epoxy hardening time .

[Len Biglin]

Hi everyone , I have been using West System 105 for years , but lately it doesn't harden ! The weather is cool but after a week it is still not real hard . Is there a use-by date ? which is not stated on the bottles ? Is it cool weather ? Will it harden at all ? Can it be removed from a joint if it wont harden? Will fresh epoxy stimulate it to harden if introduced to the joint ? Thanks Len

[Greg Mirken]

I've had West System epoxy old enough that it had darkened considerably. It didn't kick off as fast as fresh stuff but never failed to get rock hard. I think your pump didn't put out enough hardener. No way to reactivate it that I know; it will have to be mechanically removed.
Bummer.

[Russell Vance]

Hi Len,

As you know its been freaking freezing around here lately - are you using 205 or 206 hardener.  The 205 is the fast hardener and is used in lower temperatures.  The 206 is a slow hardener and is use in higher temps or when longer working time is needed.   The hardener appears to degrade over time and I've had the same problem whereby the stuff just sits there like old jam forever.   I now use an incandescent light bulb at a couple of inches to make sure the stuff reacts at the start to enable the curing to start and continue.   Warning: too much heat will cause it to bubble and show pin hole blowouts.  You may try a bit of warmth to restart the reaction and hardening process but that's just a straight out guess.

Acetone strips out the soft jam and prepares the wood for a new coat of fresh stuff.   I measure my proportions in medical "cc" cups (pill cups) and take West System's and Techniglues advice not to bump up the hardener amount as its counterproductive to strength.

But, I do add 10% extra hardener into the measure in most cases as the hardener is more viscous than the epoxy base and clings to the side of the measure in about that amount when poured at the same rate.   With small amounts, like we often use (as opposed to boatmakers and laminate makers who use it by the bucket load)  this cling amount can be a large percentage difference.   I use West systems for tight places but find Techniglue better for filling inconsistent substrates.    The colloidal thickening additives for West Systems  will also do the trick but I haven't used them.

Tell us how you go on this Len , I think this is a common enough problem.  

I'm also backing the Wallabies for the Bledisloe Cup - if I lose I get to wear an All Blacks cap for a week down at my Local (Kiwi Publican).

Regards.

Rusty.

[Len Biglin]

Ha Ha , good luck with the rugby Rusty , the hardener is 206 ( because I think you get stronger results ?) I use plastic syringes as they have pretty accurate markings and I may only be using 30mL . Its a bummer to have a Les Paul headstock only 1/2 stuck ! and also one of those Epi 12s with the bolt-on neck and loose block , a P.I.T.A  at any time ! I am hoping warmth will do the trick and not leave me looking ammateurish .

[Gregory Hites]

Through my experiences with epoxies and com

[Gregory Hites]

...composites as an aircraft mechanic, epoxies do have a shelf life. Particularly the hardner. Epoxies cure by a chemical process called cross-linking, which is directly related to strength. Many as Rusty points out cure stronger with heat, but be cautious as too much heat too soon will increase whats known as exothermic reaction, causing porosity. Three things can reduce the cross-linking (strength). 1) Incorrect ratio of resin/hardner. 2) Improper mix. Mix slowly and don't whip it into a froth. 3) Improper cure. Cure with heat only as prescribed by the manufacture. About a 5 degree/minute ramp up is optimal. If there's no expiration date on the package, I write a date of purchase on my epoxies and discard after a year. Hope this helps and sorry for the split post. Using my iphone is not easy! littleguitargreg

[Len Biglin]

Thanks for that Greg , I really do feel its the hardener thats at fault , but as it did go half way hard , I hope a little heat will finish it off . If not I will sprinkle it with Viagra powder !

[Mike Kolb]

Oh, I was just waiting for someone to post that!  Ka-boom! 

[Robbie Collins]

That'll be an expensive repair that fails after a few hours!

[J R Emmett]

Good synopsis of epoxy issues Gregory.  I'll offer a few comments based on my experience (Repair, Woodworking and a few decades in Microelectronics/MEMS packaging):

1.  I wouldn't necessarily assume it's just the hardener.  Typically, both parts are purchased at the same time and should be tracked in age (and discarded) together as Gregory noted.

2.  Surface Preparation is a frequent root cause of adhesion failure.  Contaminants on the surface (including other adhesives) can inhibit Epoxy cure.  In particular, oils and waxes will cause loss of adhesion and strength.  Cleaning the surfaces with Naptha or Acetone is a good idea (when possible).  However, if the contaminant has really soaked into the wood - there may not be a way to get it out. 

3. If solvents are used to clean the surface, allow sufficient time for them to evaporate.  Application of epoxy to a solvent wetted surface often produces unexpected results.

4.  High temperature storage conditions can accelerate chemical aging.  I tend to keep my Epoxy materials in temperature controlled spaces.

5.  Epoxy adheres well to most bare wood.  It may or may not adhere well to a smooth finish and you are now depending on the finish adhesion to the bare wood as part of the joint.  Bare wood joints generally work best.

 

Best of luck with your repairs. 

[J R Emmett]

Oh... and please send some of that cooler weather along.  It is bloody HOT here in Texas (105F today)!

[Russell Vance]

JR,

You do not want that - be very careful what you wish for - I have to take a heat-gun to the urinal.

Rusty

[Len Biglin]

Good one Rusty ! Down there must be freezing , its bad enuff here in Newy , Good news guys , I left the desk lamp on the LP all day which didnt fix it , but next morning it was hard ( after being cold all night ) I have found a source for new West Systems and wont be touching the old one again .