TCraft Lover

My Feedback: (1)

Can it be assumed that30-50-60 minute epoxy is stronger when cured than5-6-10 minute epoxy? Is this true? If so, why?

outdoorhunting

Yes. & It has more time to bond!!!!

jaka

Hi!
Strange question when already 5min epoxy is so strong it can lift a car that weights more than a ton.

AH1G

As I understand it, the longer cure time allows the epoxy to "soak" further into the material to be bonded. It also maybe that when it takes longer to cure the chemical reaction creates less heat and components of the epoxy make a stronger adhesive.
Anyone have a better explanation?

GaryHarris

If that is true, then a thinner epoxy would soak in deeper than a longer curing time epoxy would. Like thin CA would be over thick?

FWIW, I don't buy into the slow epoxy hype that a longer curing one is stronger over the other. However, it's nice to have 30 minutes or so to get those tail feathers just right before the hardener sets in.

Jacque

My Feedback: (22)

the 30 min and longer allows the epoxys to penetrate the wood much deeper than the 5 min. therfore it makes a stonger joint. would you really let someone lift your car with 5min. I sure would not.

BarracudaHockey

My Feedback: (11)

For our purposes, 5 minute epoxy is more than strong enough.............

BUT if you're sheeting or doing stuff that requires some time to get into position and weighting down, 30 minute is the ticket.

If you want to try something that mixes up like vasaline and stays where you put it, get you some Epo-Grip epoxy, awesome stuff. You can mix that stuff, take a bolt, coat it with WD40 and put it in the epoxy, when its dry, unthread it and its near about as strong as metal.

Revy

My Feedback: (1)

My theory on this is that 5 min is thinned out (although same consistency as) 30 min using the same amount of hardener. Its like fiberglass resin when you thin it. It becomes weaker. More or less hardener will cure it at different times.

My general rule as instructed by a quality focused master builder, is initial construction, load bearing and structural, 30 min. as to give you some time to work with the pieces your putting together as previously mentioned. Everything else that isn't under major stress is 5 min.

Alex7403

A. Epoxy is a polymer
B. Regardless of minutes on the bottle Epoxy starting to cure immediately when mixed
C. The actual working time is much shorter than whats written on the bottle, 2 min when written 6 and 6~12 when written 30
D. you can slow the curing time by placing the mixture cup in icy water.

with 30 min epoxy you have more time to position things in place before the polymer chains being too long, if you move them then the part will not be attached so well.
I'm using only 30 min epoxy.

soarrich

My Feedback: (98)

I once read that the 5 minute epoxy was more brittle than the 30 minute. I thought about that and it seams as if the mix has longer to form long chains that would make it less brittle.

Rodney

The strength is a function of the length of the polymer chains. The slower the epoxy, the longer the chains thus the higher strength of the slower cures, a chemical process, not a penetration process. As for strength, non of the epoxies reach full strength for several hours, even 5 minute does not reach full strength for quite a few hours. Up to a point, the higher the temperatures, the faster the cure.

OldScaleGuy

My Feedback: (2)

I have nevered worried too much with the strength of the epoxy be it 5 minute or 30 minute. For me, the 30 minute (which usually takes about 2 hours to cure) gives me more time to get what ever it is i am gluing in the correct position. I only use 5 minute for smaller parts. Doing it this way is a lot easier on my nerves too.

Warbirdguy

Being in the "business" molding and mold building, I have found over the years by my own experiences the following.

5 min epoxy is great for quick fixes. What I have observed from my own experience is that the fast cure epoxies seem to remain flexible. Even after a year, if your in a warm enviroment, you can usually put steady pressure on a 5 min exposy glue joint and it may hold but it will eventually bend.

I use laminating resin. Its rated to cure at room temp in about 1 hour. That means you can still work with it but its not "cured" At room temp it takes it all night to be able to pull a part from the mold. I can speed this up by using a heat source of say 130 to 150 deg. To have the full properties of the epoxy, it generally takes about 5 days to fully cure.

To thickin up any epoxy to get that gel like consistancey, I use silica. Its a white powdery substance that basically has no weight to it at all. But it will turn a rather thin resin to toothpaste if need be and not mess with the chemical reaction of the hardner or resin. Great for filling in corners and gaps.

I have to say, and I have about 20 years experience to back up my observations, that the slower curing epoxies are thinner and yes they do penetrate the surface of wood better than 5 min epoxy. Check with some of the wood canoe builders. They use laminating ( slow cure ) epoxy exclusively to seal the wood and apply cloth to their canoes just for that reason.

Just for reference, polyester resin does not bond as well as epoxy when dealing with wood. I could cut and paste an article about this and will if yall are not satisfied with my explaination

This and a dollar will get you a cup of coffee. Just sharing what I have learned over the years. Good luck and have fun

Rodney

A word of caution, the stated speed of epoxy is not the time to cure, it is roughly the time to become tack free, not cure. It takes hours to cure, even 5 minute epoxy does not gain full strength for several hours. Also, when you stick things together with epoxy, it is a molecular bond between the epoxy and the elements being bonded to whether it be wood, glass, or ????. The idea of "soaking in" for bond strength is a fallacy. If it depended on penetration, how do you think you ever bond to metal, glass, etc?

SCALECRAFT

My Feedback: (13)

With all due respect...........but

Your question is not specific enough.

Do you mean bonding or stiffness by stronger?

As bonding, place some 5 min on a small sheet of balsa, and some 20-30 min along side. Peel off and see results. The viscosity of the resin does play a role in the bond. The 5 min stays on top.

Then there is post curing in composite fabrication.


Steve

Steve Steinbring

Interesting thread! A lot of good information has come forward about epoxies in this discussion.

As a prior owner of an epoxy adhesive company having dealt with adhesives for over 35 years I have some experience with this subject.

Basically with epoxies the longer the cure the stronger the bond. However, a great deal of that statement depends upon what you are bonding and often gets down to a matter of varying degrees.

For instance if you are bonding a porous woods like pine, fur, poplar, or balsa the fast set epoxies exceed the fiber shear strength of what is being bonded which is the case in modeling. So in effect it really becomes academic if the adhesive exceeds the strength of what is being glued or bonded.

The other side of the story is bonding dense or non porous materials. Rule of thumb..... the longer the cure time the stronger the bond.

WHY? Because the longer the cure or the chemical reaction takes the greater the dwell time for the "wetting agents" to penetrate the substrate creating a stronger bond. Most generally the shear strengths of slower cured epoxies significantly exceed the faster cure adhesives. So if you are bonding glass, metal, stone, brick, a slow setting epoxy will yield best results.

There are basically only two things that effect the cure of an epoxy other than the design chemistry of the hardeners and resins used to formulate the product.

One is temperature, the other is mass !

If you will note most adhesive manufacturers give suggested working temperatures for best results and consistent cure times. In our manufacturing we used 77 degrees F as a bench mark for our products. If the ambient temperature is higher than the benchmark temp the "potlife" or working time of the material is shortened (potlife is not the cure time, its the time the product is still workable). You can shorten cure times by the addition of a heat lamp just remember it shortens dwell time and possibly compromising some strength. Cooler temperatures will lengthen the potlife and cure time of the product.

A thicker layer of material will cure faster than a thin layer because it has more "mass" and thereby generating more heat in the reaction. So if you pile your adhesive up on you mixing board its going to cure faster than if it is spread out over the mix surface. Bottomline a thick joint will cure faster than a thin one!

You can slow the cure time of an epoxy by thinning it with a compatible thinner like acetone. Be aware acetone is highly flammable. Essentially the acetone evaporates from the epoxy allowing the chemical reaction to continue after application is made. Be sure to induct the epoxy first before thinning for best results. Thinning too much will cause problems generally 10-15% is all that is needed.

The addition of thickening materials like micro balloons where the consistency of the end product is driven to a clay type product weakens the strength of the bond because the wetting agents not able to adsorb freely enough into the microscopic profile to ensure a strong bond ( product is too dry). For example the clay "tootsie roll" type clays generally have a greatly reduced shear value depending upon the product around 500 psi between blasted steel in a hydrolic press. The same clay products base resin and hardners shear without the fillers would be perhaps 2500 psi or higher depending. To make a paste materials the addition of Aero-sil or Cabo-sil works well without compromising strength to any great extent. The addition of Micro balloons is great for making a fillet material as it sands well.

Hope this helps some. Have any questions PM me!


Check out Epo-Grip Adhesives in the hobby section their products exceed most all modeling needs.

www.epogrip.com

1800-888-2467

Warbirdguy

Well put Steve, and if you read between the lines of my post, I said exactly the same thing :P LOL I just dumbed it down some. I remember the very first layup job I did and I found out ...in about 15 mins...you dont let a cup full of epoxy set for very long. Smoke will start to form and if your using a plastic cup, like I did, it begins to melt down lol. If your gonna take a while in putting the epoxy on, I use a pie pan to pour my epoxy in after I mix it. Gives you longer pot life to work with.

Bed time for me and tomorrow, I have some resin to mix and parts to make.

nite nite all