Hi all.
Is there a benefit in post curing RR 2000/2100 or Kwik Kick epoxy? From the Resin Research website, there’s no apparant benefit. I’m primarily interested in benefits to strength than faster cure times.
Thanks in advance and kind regards
Sorry. Should read ‘rather than faster curing times’. If Greg’s out there, I would dearly love your word on this.
Thanks
Not sure about KK but traditionally, all resin needs a curing time to reach final "temper". It used to be said that a poly resin board takes at least three or more days to fully harden. I would assume Epoxy is the same but perhaps shorter time period. Some use hot boxes or oven type enclosures to cure Epoxy boards.
[quote="$1"]
Hi all.
Is there a benefit in post curing RR 2000/2100 or Kwik Kick epoxy? From the Resin Research website, there's no apparant benefit. I'm primarily interested in benefits to strength than faster cure times.
Thanks in advance and kind regards
[/quote]
It's a Proven Fact that a proper post cure will make an epoxy glass job stronger......NASSA.....
It's also understood that a not so proper post cure might make a weaker glass job.....and most Swaylock's post cure ovens are not NASSA..........many will disagree with me....thats OK....it's a surfboard not a Space ship.
If you Lam and hot coat at 70 degrees F. All steps in less than 24 hours. Let the board sit for a few days at 70F....
no problems............
I’m a big fan of post curing epoxy. There is definitely a ‘tougher’ feel to a postcured board vs an ambient temperature cure. I believe Greg said postcuring increases the strength but about 15% (don’t hold me to that number). There are lots of different theories on proper post curing, I cure boards at 110F-120F for about an hour and that seems to work. Make sure not to get the temp past 140F or the epoxy starts to flow again.
With Quik Kick and a postcure oven I can completely glass a board in less than 5 hours. It’s a good idea to turn the oven down to about 80F for the hotcoats and slowly raise the temp over an hour up to 100F to prevent orange peeling (I learned that the hard way!)
~Brian
Found the long quote below on an RC boat forum in regards to post-curing WEST Systems 105/205 epoxy, looks like each epoxy has it’s own characteristics so the best bet would be to contact the manufacturer and find out the best process for post-curing their epoxy.
There is a science to it as mentioned below to “ramping up” the post-cure temps to achieve best results.
Hopefully Mr. Loehr can chime in as to the best process for getting the most out of RR epoxies.
http://www.rcsailing.net/forum1/showthread.php?5519-Post-curing-of-epoxy
"Something
I didn’t know. I just read on Sails Etc that if epoxy cures at say 20C
then later it can soften (warp) at any temp above that. If it cures at
40C it doesn’t soften until the temp is above 40C. What this meant to me
is that if you build a fin(or hull) in the winter when your shop is
cool it will be more vulnerable to summer heat. I’m thinking we should
all be making an oven so that all our epoxy parts will be cured at 35 or
40C. That way we don’t have to worry about the sun so much. Apparently
you can heat treat it after to raise the softening temp
The response received:
Hi Dick,
Thank you for submitting this
questions and posting this answer in your RC Sailing forum. The physical
characteristics that you are referring to is a an epoxy’s Glass
Transition Temperature (Tg). The Tg is the temperature in which cured
(vitrified) epoxy becomes molecularly active after the initial curing.
When epoxy is formulated, the specific chemical compounds that used will
determine the epoxy’s overall attributes. This includes the compression
yield, hardness, tensile strength, tensile elongation, flexural
modulus, flexural strength, tensile modulus, annular shear, izod impact
and the Glass Transition Temperature.
Certain epoxy formulations are room
temperature cure, where the epoxy formula reaches its maximum physical
characteristics at room temperature. If these room temperature cured
epoxies are heated significantly beyond their Tg, they can start to
soften as a result. In the case of 105 / 205 system, the Ultimate Tg
is 142 degrees Fahrenheit. Now this is not to say that at 143 deg F that
105/205 turns to soup. This attribute is determined by a specific
test procedure on an instrument called a Differential Scanning
Calorimeter or DSC. The machine can measure subtle changes in the test
sample as a result of elevated heat. At 200 deg F a sample of 105/205 will become malleable, but when cooled, becomes just as a hard as it used to be.
There are epoxy formulation that are
used in more technical applications that benefit from a Post Cure. A
post cure is additional heat that is applied to an epoxy part to help it
reach its full physical characteristics. These formulations are such
that there is a significant amount of energy that is in the epoxy in the
form of chemical compounds that create higher physical properties.
However, there is a problem for these more technical epoxy systems to
reach these higher physical properties. When the epoxy is reacted, and
the material starts to plasticize (get hard), the ability for the
molecules of resin and hardener to find each other and crosslink becomes
increasingly difficult. In this case there are partial cross-links
formed and in some cases un reacted material. These initial room
temperature cures of these epoxy systems give way to a material that is
quite brittle, hence why we call this the ‘B’ Stage. These epoxy systems
require additional heat beyond the initial Tg to allow the material to
become chemically active again and aid the continuation of the reaction
and cross-linking.
Now achieving these high physical
properties is a little tricky, if you heat the part to fast and too high
of temperature, one can actually stunt the development of the physical
properties. This is known as over shooting the Tg. Let me provide and
example, if a technical epoxy system room temperature cures to a ‘B’
Stage and while at that ‘B’ Stage, the epoxy has an initial Tg of 135
deg F, If that epoxy system is then placed into a 200 F oven the
material may heat up too quickly beyond its ultimate Tg and there will
be additional reactions and cross linking but because of the rapid
heating molecules that could have cross linked become entrapped and can
not cross link thus creating a condition where the ultimate physical
properties can never be reached. Instead one should ‘chase’ the Tg,
where the part is slowly ramped up to temperature. During this ramp
time, as the part approaches and exceeds the initial Tg, additional
reaction and cross linking is occurring and the physical properties are
being increasingly developed, including the Tg. So at as the part
reaches and exceeds 135 F, the Tg is no longer 135 F, it may be 145 F,
but as the part reaches 145 F, now the material has had a chance to
additionally cross link and the Tg may increase to 150 F and so on until
the material reaches it highest possible physical characteristics.
There is however a ceiling on how high
these properties can be developed, this is based on the chemicals used
and the formulation. In the case of room
temperature cured epoxies, there is no significant advantage to laying
up a part at 20 deg C and then post curing at 40 deg C. The physical
characteristics will be achieved regardless of that additional heat. Now
heating a part up to a slightly elevated temperature with room
temperature cured systems, will help the epoxy system reach their
ultimate properties more quickly.
I hope this helps to answer your questions, please feel free to contact me directly for additional answers to your questions.
Best Regards,
John M Thomas
Technical Advisor
WEST SYSTEM Epoxy"
Epoxies that are designed to cure at or near “room temp” can benefit from post curing. The idea is that when the resin reaches “transitional” stage, and starts to harden, the ability of molecules to cross link is reduced. Post curing softens the resin to allow greater time for cross linking. But raising the temp for post curing has to be both timed and controlled… you have to ramp up the post cure temperatures at certain times in order for the post cure environment to “chase” the transitional stage of the epoxy. Too fast, too slow, too early, too late, too hot, too cool… and the benefits of post curing become minimal, or actually reduce physical properties.
What that strategy is for KK I don’t know. But I do know that I’ll let a board sit at room temp for two weeks after lamming before riding it.
So my post cure technique_ leaving it in my dark blue VW Vanagon on a sunny day with the windows rolled up (at the stage after hotcoating, but before finning, with the fin box holes cut and open)_ was proabably just pure silliness…
I can never wait two weeks before riding a new board. You have some patience there NJ. That, or long flat spells…
Wish GL would come on and explain the best cure for his resin…
Firstly post cure means after cure so I wouldn’t lose any sleep over post curing or not. However post cured epoxy does feel a bit tougher than before and a bit flexier I find. So it’s like a nice bonus if you do it, and nothing to worry about if you don’t and if it’s summer you’ll probably find the board post cures after a couple of weeks anyway.
and overheating the EPS surfboard while sanding makes everything soft.....Fun stuff...I'm 8 miles inland...down south...lot's of warm dry days to glass and let it post cure on it's own..I can heat my shop if needed.....My friend had a home made hot box go bad and a fire started.....board destroyed....House OK......could have been a $350,000 mistake....
Ray
I’ve found that there’s a huge difference if you wait a while before sanding epoxy. I waited a week on the last board, and it sanded so much easier than when I try to sand the next day. I think the epoxy sanded almost as easy as poly.
My biggest problem as a backyarder is patience. I only work on boards on weekends so I often rush.
All very useful. Thanks all. I think I’m beginning to understand the science a little better now.
I’m sure many of you would like to play around with different systems, but if you’re like me, cost and product availibility proclude this.
Thinking what would be really useful is if people could volunteer their curing schedules, including details of product used and resulting performance characteristics.
Cheers all.