Epoxy resin curing time

[KompetentKrew]

My boat is woodcore epoxy and when cutting out old through-hulls this week I found some of the core exposed.

When one through-hull was removed I found the hole to be very neatly lined with epoxy, but I damaged it just a little and it needed touching up. The other looked like it had never been epoxy lined, so I used a hole-cutter to enlarge it and then gave it a waterproof lining.

When I insert the replacement through-hulls I'll use Sikafix to seal them properly.

For the epoxy I used West System 105 + 206 slow hardener. West System give a 10-15 hour time for a thin film to cure to solid.

This is not a thin film - how long do you think I should wait before putting in the new through-hulls and launching, please?

I'd like to be back in the water tomorrow, but I rather feel I should give the epoxy closer to 48 hours to cure properly, which means waiting until Monday.

https://www.westsystem.com/hardener-selection-guide/

Thanks in advance for any thoughts you may have.

 

[DownWest]

Thoughts... Once epoxy is mixed and starts going off, being under water is not to much of a factor. Temp is, I use epoxy for setting thing in concrete. In the current temps, I keep the the stuff in a cool bag with blocks, so I can use it with in the stated limits.
Your West mix will actually cure faster if thicker than the 'thin film' as it cannot dissipate the exothermic heat as fast.
Frankly, I would not worry.

 

[lw395]

A thick film will cure faster than a thin film, because it warms up. If you've got several CC's left over in the mixing pot it can get hot and go hard long before the job in hand cures.

 

[oldharry]

Thickness of the epoxy makes no difference. Curing is by chemical reaction, not by solvent evaporation. If it feels hard on the surface it will be hard all through if you have mixed it properly. Note what they say about thicker layers, the heat generated by the chemical reaction will speed up the setting time, so that the 'thin layer' setting time is the longest.

There's no mention of needing longer to come to full strength in the publicity that I can see, and I would expect 'hard' epoxy to at full strength, but then Im not a chemist or an expert!

 

[rotrax]

I glassed in a 1 inch marine ply bed to carry the generator mountings in the generator garage of our boat two years ago. The job was done in cool April weather. After 36 hours the epoxy was still tacky.

I put both our winter tube heaters in the space for 48 hours, solid as a rock now.

 

[KompetentKrew]

A thick film will cure faster than a thin film, because it warms up. If you've got several CC's left over in the mixing pot it can get hot and go hard long before the job in hand cures.

I experienced that today - the pot got quite hot and I already had a ball of solid epoxy in it as I was finishing up the job.

Lesson learned! When the instructions suggested using a shallow layer of liquid epoxy in a wider tray they certainly weren't joking or exaggerating!

 

[AntarcticPilot]

A thick film will cure faster than a thin film, because it warms up. If you've got several CC's left over in the mixing pot it can get hot and go hard long before the job in hand cures.

+1. And when it starts to harden, it can go very quickly, getting surprisingly hot - too hot to hold when it happened to me. It wasn't West epoxy, it was East Coast Fibreglass's own brand, thickened to make fillets in a dinghy I was building. But I was quite suprised how quickly it went and how hot it got once it started. ECF only do one hardener, which reckons to have a pot life of an hour or two.

 

[ithet]

+1. And when it starts to harden, it can go very quickly, getting surprisingly hot - too hot to hold when it happened to me. It wasn't West epoxy, it was East Coast Fibreglass's own brand, thickened to make fillets in a dinghy I was building. But I was quite suprised how quickly it went and how hot it got once it started. ECF only do one hardener, which reckons to have a pot life of an hour or two.

I made up a pot using left over winter hardener whilst on board on a hot summer day. Luckily I spotted the flames and quicky chucked the pot overboard!

 

[MonniotC]

If you want to speed it up, just set a hot air gun on low, or a hair dryer blowing on it for a while. The raised temperature will speed up the cure time no end.

 

[Lon nan Gruagach]

Cold = slow, hot = (too) fast, too hot = do it again! You want Goldilocks on the job, warm is just right.

Ok, so we know about cold, it will take so long to cure bad things can happen, movement causes weaknesses and moisture can dissolve in.
Hot can cure so fast it will not penetrate the material or even go off before you can use it.
Too hot is a technique used by artists to create a crazed resin block, looks nice but is weak.

From what I have read from Gurit SP 106 datasheets is that after the initial hardening the epoxy will continue to become stronger over a very long time. However the increase in strength is minimal.

If the application is only sealing and not intensively structural, calculated to be at the best potential strength then, as mentioned a gentle hair drier and use as soon as it is touch hard.

http://www.ecfibreglasssupplies.co.uk/images/TechnicalDataSheet/1858.pdf see page 4: cured system properties (28 days @ 21^oC)

 

[JumbleDuck]

+1. And when it starts to harden, it can go very quickly, getting surprisingly hot - too hot to hold when it happened to me. It wasn't West epoxy, it was East Coast Fibreglass's own brand, thickened to make fillets in a dinghy I was building. But I was quite suprised how quickly it went and how hot it got once it started.

I've had polyester get far too hot to hold in a mixing pot too. It's thermal runaway - the hotter it gets the faster it cures, the faster it cures the more heat it releases, the more heat it releases the hotter it gets. As a rule of thumb, chemical reaction rates double for every 10^o rise in temperature.

 

[Poignard]

If you want to speed it up, just set a hot air gun on low, or a hair dryer blowing on it for a while. The raised temperature will speed up the cure time no end.

If you don't have either of those handy, a hot water bottle will help.