Epoxy curing temperatures
 

Hello all,
I was just ready to mix some epoxy and thin it out with denatured alchol to fuel proof my engine/firewall area and read on the epoxy bottle "Must be cured above 70 degrees F). I don't even keep my house above 70 degrees, never mind my basement workshop. With this said how do you resolve this issue? I would like to build in the winter. If I can't use epoxy to fuel proof what other products have you used that would serve the purpose? Is polyurethane any good?
Thanks for you input,
Pat

The cooler temps just slow down the cure. It will still cure but may take a bit longer. You can use something like a heat lamp to help it cure.

Yes for a full cure and for the epoxy to reach full strength it must be cured above 70 degrees. At work we cure all epoxies at 160 degrees or higher ( I'm a composites tech by trade ). For your application as long as you get enough cure to keep fuel from invading the molecular structure of the epoxy you will be fine. After initial application warm it up with a hair dryer and continue to do so one every hour until the epoxy is tack free. If you are building in a cold environment your glue joints will not be as strong as they would be had the epoxy been cured at a higher temp. Not to worry, the elevated temps of being transported in your car and sitting in the pits will take care of that and actually perform a post cure of sorts.

As others have said, you will probably be fine for your fuel-proofing application.

I have the same situation with a relatively cold basement workshop. When building in the winter, after putting together an epoxy joint, I usually bring the assembly upstairs and put it on top of a bookcase (heat rises) to cure overnight.

Thank you all for all your prompt input. I applied the epoxy then used a heat gun on it lightly for a few minutes to brush it on easier. I have a heat lamp facing it now for the night (thanks ACERC) and hopefully that'll take care of it.
Thanks again,
Pat

You are welcome. Just don't go to bed with the heat lamp on!!!

If you ever get some epoxy that is 'sticky' when it is supposed to be cured, try putting the part in your car with the windows up and setting in the sun. Even in winter the temperature inside a car can get warm enough to complete the cure!

Especially in AZ.

Place your epoxy containers in warm water before mixing and bring them up to where they flow easy and smooth. Mix and spread quickly, in a warm room if possible. This is what I do here in the far north during winter or when the humidity is high.
Your mix should "kick" as designed.

But not so much in MA.

Yep, even here in Cali if it's going to be below 60 degrees in the shop over nite and I'm vacuum bagging a part I will wrap it up in an electric blanket.

Epoxy can get kind of thick in the bottles if it has been sitting a long time or in the winter. I put the bottles in the microwave oven for about 20 sec. or so and they get right back to normal. Been doing this for years with only good results. I have been doing some building in the garage this winter with temps in the 50's. Usually after applying the epoxy I'll take the parts into the house to harden just for peace of mind. The left over mix seems to harden hard as a rock in the garage though, but does take a little longer to harden. This is with 30 minute (or less) epoxy. When I used to vacuum bag wing skins using West System 24 hour epoxy, there was a strong belief with the sailplane pilots that if the room temperature was not up to specs or close enough, that this 24 hour epoxy would NEVER really cure. I didn't want to find out. When mixing micro balloons or milled glass when epoxy, I know you want to thoroughly mix the epoxy before adding the filler. Yes, clear polyurethane works great for painting the tank and firewall area with. Might even be easier than mixing and thinning epoxy.

I'm going to disagree with you on some points of your post:
1) for a full cure and for the epoxy to reach full strength it must be cured above 70 degrees
2) If you are building in a cold environment your glue joints will not be as strong as they would be had the epoxy been cured at a higher temp
Per the West Systems website:
Each hardener has an ideal temperature cure range. At any given temperature, each resin/hardener combination will go through the same cure stages, but at different rates. Select the hardener that gives you adequate working time for the job you are doing at the temperature and conditions you are working under. The product guide and container labels describe hardener pot lives and cure times.
At no time does the manufacturer make any reference to strength and heat being inter-related. In fact, the website actually states:
CAUTION! Heating epoxy that has not gelled will lower its viscosity, allowing the epoxy to run or sag more easily on vertical surfaces. In addition, heating epoxy applied to a porous substrate (softwood or low-density core material) may cause the substrate to "out-gas" and form bubbles in the epoxy coating. To avoid out-gassing, wait until the epoxy coating has gelled before warming it. Never heat mixed epoxy in a liquid state over 120°F (49°C).
In a commercial manufacturing application, the chemical makeup of the epoxies used are different than what we as consumers and modelers will have access to through common sources. Years ago, I was working at Hexcel where we used pre-preg materials with varying epoxy compounds in the fabrication of aircraft parts. To increase strength and decrease cure time, the parts were vacuum bagged to 29" of vacuum and baked in an oven slightly hotter than you indicated. The vacuum bagging was what increased the strength, compressing the fabrics more tightly together and removing almost all of the air in and between the plys. The heat only decreased cure time and melted the epoxy coating so that it could flow between the fibers and actually "grab" the fabric plies, holding them together and filling the weave to make a solid, windproof surface.

If you really understood what speed was saying, you would realize that he simply meant they post cure all epoxies @ 160 degrees without spelling it out for you, plain and simple.

The caution label from West Systems is really for the unknowing hobby types because there are many manufacturing applications that require heating epoxy resins well over 120 degrees as part of the processing.

You have stated heat is only used as a processing means to decrease the cure time when utilizing pre-pregs as your manufacturing media. You might consider staying away from entering into disagreements on a subject you have clearly illustrated you possess limited knowledge of.

Bob

Back in the 70's I had curing problems with the model epoxies used at that time. It was common practice to use epoxy to both fill and get an initial "finish" on pattern models.
In one case, I had to just let a model sit for almost a year before the epoxy finally completely hardened. (Yes, it was mixed per the instructions.)
The problems were due to initial application/use in lower than normal temperatures, and possibly low humidity.

The company I worked for at the time used a great deal of potting compounds and various epoxies,
The area reserved for this use was temperature and humidity controlled, with a temperature at 77-80F, and a higher than average humidity.
Epoxy and potting compounds were "out-gassed" before and after mixing. The finished products were designed for use at high voltages and ~40-50 thousand feet altitudes.

Mix, apply, wait, fly. We ain't building rocket ships or stealth bombers:rolleyes:

A mistake many make that causes slow or poor cure of epoxy is to mix it in a waxed container such as a paper cup or bowl. The wax can even prevent it from ever properly curing.

The West System is designed to work in less than ideal conditions. I use it exclusively with the 105 and 106 hardener depending on which cure times I need. In fact I use their whole system glass beads, milled fibers etc. It’s what I used when I was clunking around in wooden boats. Canoes built 20 years ago are still being used on a regular basis. The West System in my book is the best out there for ease of application and finishing.

Dennis

Well, there are builders and then there are builders, aren't there...:rolleyes:

We ain't building rocket ships or stealth bombers.

Some of us aren't, but then again some of us actually are and some of us have been in the business of designing and developing things just like you mentioned for decades, with that said, some of us try to pass on our years of experience only to have some cowboy with just enough knowledge on a subject to be nothing short of dangerous, then enters into a thread with their opening statement of (I AM GOING TO DISAGREE WITH YOU ON SOME POINTS), and begins to spout out with complete rooky nonsense that has absolutely no validity to it whatsoever...

Bob

I use the West System because I am very familiar with it from building stripper canoes and repairing a few older wooden boats. By no means an expert. Being familiar with a product makes the construction so much easier. That being said I have many friends and acquaintances that use nothing but the hobby epoxies and get great results. We indeed are most fortunate to have so many options. We don’t put our butts in these things so insisting on certified epoxy and techniques is a bit much. If your doing what the plans/instructions call out and its working your doing it correct no mater what the experts say. It’s a hobby, experts and their opinions are sometimes way over kill.

Dennis

Dennis, this sort of thing comes up all the time. As in this thread a specific question was asked. A couple of us whom do composites for a living gave the correct answer. Yes it could have been considered overkill as far as some peoples expectations but the answers were correct none the less. Some guys want to learn new and better techniques and build better airplanes, some don't and that is fine. What bothers myself and Sensi is when we share information that has taken us years to gather just to be called wrong or as in your case disregarded. It would be my wish that someone would at least give something a shot before tossing aside. You in fact may have a future issue that could have been solved by our advise.

Sorry I’m entitled to my opinion and I will express it. I think you are wrong overloading most modelers with information that they will never use. You may work and be an expert in the composite field but the average guy works in an environment so far removed from what you describe, the information becomes irrelevant because he has no hope or want to duplicate it.

The places I have built canoes and worked on wooden boats have been with little or no heat, open to the elements, at times fluctuating temperatures and humidity we had little control over and we never had problems with the epoxy curing or its final strength. The West System has a whole section on cold weather bonding http://www.westsystem.com/ss/cold-temperature-bonding/

How come neither one of you bothered to warn of the exposure to epoxy. To me this is the most important bit of information you could pass on to a hobbyist. After all many of the modeling areas are small and have limited ventilation.

Regardless of the brand you use check out the West System web site. There is tons of information that the hobby user can access. The information is applicable to most epoxies.
http://www.westsystem.com/ss/


Dennis

Yes you are entitled to your opinion just as I am entitled to express mine in the level of advise I offer. Before I was in the composites industry I was an R/C hobbiest, my building methods were pretty much run of the mill. When I started gaining knowledge of composites I would incorporate this knowledge into my airplanes thus building better and safer airplanes. Should I not share this knowledge willingly because of your entitled opinion that it's not nesessary? I'm happy that your canoe was a success, when you start putting flight loads on it let me know.

Im also fully aware of West Systems solution to cold bonding as it was developed for marine usage where getting the work into a heated environment is not usually possible.

Sensei and Speed, I was not saying anywhere that you are wrong and, as I said, there are applications where HEAT CAN BE REQUIRED as when I worked at Hexcel where nose radomes, farings and other aviation parts are made with prepregs and honeycomb. What I was disagreeing on is the statement that HEAT IS REQUIRED FOR A FULL CURE. I specifically mentioned West System due to the fact that, as Propworm pointed out, it does not need heat to cure to full strength as Speed stated in an earlier post. It was, in fact, formulated for marine use on full sized boats in conditions that are far from optimum for other epoxies. I've used it in sub 60 degree environments and it not only cured, though slowly, it was stronger than the wood it was used to bond. The fact that the manufacturer's website says not to heat to over 120 in liquid form attests to the fact that heat isn't desired unless you get below the recommended heat range for the hardener being used. To take it one step further, it is a common practice in boats to heat an epoxy joint to weaken the epoxy to facilitate separation of materials bonded with it which contradicts the use of heat being needed for a proper cure. One last point, I use West Systems to build R/C hydroplanes as well as aircraft. While my boats won't be doing snap rolls and hammerheads, they are subjected to a pounding and G-loads that aircraft will never experience while running at 60+MPH. Try subjecting an aircraft fuse, R/C or full sized, to the torque and vibration of a engine running at 25,000+ RPM and the opposing torque of a spinning surface drive prop, while at the same time pulling 3+Gs across two geometrically opposed two square inch areas with the forces applied in opposite directions while slamming against the water's surface and see if it holds up. That's what my 14 pound scale boat endures every time I put it into a corner. The hull has to endure the twisting of the engine torque with the reverse torque of prop blades hitting the water while the hull also is getting pulled in opposite directions at the point the turn fin and rudder brackets are attached on the transom and sponson transom. This is what fully cured West Systems epoxy must endure during a three minute mill period and five racing laps per heat with a possible 6 heats being run in a single day while normally sitting in the sun when it's not on the water. That is a lot of stress for the epoxy to handle. One more thing, for the record, the water is never smooth

I for one appreciate the comments by speedracerntrixie and Sensi. Keep up the good work as many of us appreciate the more detailed and correct info you provide.

Thanks Rodney, I appreciate the feedback. The OP simply stated if he needs to follow the directions on his packaging and we tried to give him the answer and reasoning behind it. Unfortunately RCU is famous for guys with limited experience wanting to argue points without fully understanding the situation. West epoxies are formulated for cold cures because they are intended for boats that may still be in the water or not able to get to a warm environment. Hobbyists like it because it is user friendly and it does the job. My last race airplane would not be the same if it was not built with materials and knowledge that go beyond common hobby. It has 520 sq in of wing, weighs 6.25 lbs and is powered with a YS 115. First off the weight would be almost impossible, the engine weight is 1/3 total aircraft weight. Figure in radio gear, retracts, 16 oz fuel tank, full paint job and you can see what I mean. The fuse is laid up using a surface layer of 2.4 ox cloth followed by a layer of 6 oz cloth with 3K CF tow between the layers in the nose and wing TE. Thats not a lot of material there yet the airplane does an honest 160 mph and will do a 180 degree turn in 50' dia. That is right around 20 G's. The fuse also has no formers, not even a firewall. What makes it work is that I used Hysol 9396 resin and then post cured the fuse at 180 degrees for 2 hours following an ambient cure of 48 hours. Once you have the knowledge of composites you will find areas to use the knowledge.

All I disagreed with were the two points I listed. The rest of the post is direct from the West System web site I cannot take credit for that. As far as knowing what they are talking about I think their expertise far outstrips anything you have to offer. By the way I still disagree with those two points. His remarks were inclusive of all epoxies and that is not true as some are designed to work in less than ideal environments. It wasn’t a criticism or rebuke but an observation from my experience using the West System. Hobby epoxies tend to be similar in that they work in less than ideal conditions. Most problems occur because modelers mix improperly or use epoxy that has been sitting around for years or has been contaminated. The OP is using it for a barrier coat against fuel penetration I don’t see any reference to using it for bond or adding strength. The cure he would get in less than ideal temps would be sufficient.

As to the West System web site the manuals, videos and general information is much more informative than the self posturing and poor attempt at putting down any who would dare to offer an opinion that might run contrary to the grand Wazoo and his elf.

Dennis

The advice from a few of the other non experts like using a heat gun or putting it in a heated area is enough to address the OP’s concern. Simple but effective. Going on about how big an expert you are adds nothing as far as I am concerned of value. It seems every time someone asks what should be a simple question there are those who feel the need to convince everyone they are the true messiah of what ever is being discussed. If there are several so called experts then look out the next 30 pages of posts are spent all of them trying to out do each other with their knowledge on the subject. Meanwhile the OP has fixed his problem, moved on and most likely is out flying never to bother to return to the topic again.

What ever happened to answering a simple question with a simple answer without all the chest pounding? It’s like a clip from the movie Spaceballs “I see your Swartz is as big as mine.”

http://www.youtube.com/watch?v=RI0i_tL-8aU

Now Dennis, you seem to be getting a little personal there bud. Tell ya what, lay up a couple piles of cloth between some mylar or plastic bag with your West Systems wonder epoxy and let it ambient cure for 24 hours. Check the flexibility. Then place in an oven set to 150 to 175 degrees for 2 hours, let cool and check the flexibility again. I don't have to guess what you will find out. I understand if you don't want to take the time to prove my point but if you choose not to then please leave the thread and let us teach something to the guys who would like to learn.


PS I love that movie........My hair, he shot my hair LOL

So it’s as I thought answering and solving the OP's question is not as important as hearing yourself from the top of the soap box telling the rest of us we are not worthy. Don't you ever get tired listening to yourself? For 99% of us the hobby shop epoxies do everything we need and more. Instructions are super simple. The West System gives more options and I use it because I am familiar with it. I don't consider myself any better or more knowledgeable than the next guy. I have nothing to prove I don't feel the need to feel superior. Your last post has nothing to do with what most modelers will expect out of an epoxy so it has little value to me or the real world of most modelers. An awful lot of expert modelers have written books and made videos on finishing models with glass cloth or laying up the odd one-of mold and using resin/glass/carbon to enhance the airframe. They explain it simply with readily available tools so that even the most basic modeler can achieve a modicum of success. On the other hand the information you throw out there has so little value for the average modeler because they don’t have the ability or want to attempt to duplicate it. That you are capable of using these techniques and have access to the equipment I think is great for you but of absolutely little value for what most expect for their applications.

For instance I have watched the university students who have no experience with epoxies, fiberglass, Kevlar or carbon fiber take the information from web sites and use that information to build a model that weighs less than 10 lbs powered with a Jett .65 that will lift 40 plus lbs in a successful flight taking off in under 200 feet and landing in 400. They design and build these things with the most basic equipment and minimum of knowledge and technique.

I hate to burst your bubble but this very exacting knowledge you think everyone must hear. Not so, try spending the time better explaining techniques that have value to the guy with no equipment and little knowledge. How to mix epoxies properly, storage, shelf life and what to look for when having problems that can be easily solved without all the bloody industrial equipment. How many people do you think own a vacuum pump? Guys are interested in how to lay the cloth so it stays in the corner. How do I make and use a one time mold for a cowl that’s no longer available. Where is a good place to buy supplies for my small needs? There are lots of topics, tips and tricks you can volunteer that many will actually make use of. Your last post, I cannot think of one modeler I know who would even have a need to attempt the process you describe. I ask what the relevance to modelers is in general when you go on about tools and techniques we will never encounter.

Dennis

Dennis, are you reading the same thread I am? Take a look at post #3. I only gave the information the OP needed. It wasn't until you came around and started talking about about a product that the OP clearly did not have. He asked if he should follow the instructions that state the cure should be done at or above 70 degrees. We told him yes. It wasn't until you came around much later that this became an issue. If you think what we have said to this point as being overcomplicated then you have no real clue about composites as we really have kept it simple to this point. It's obvious that you feel you have nothing to learn and I really can't care less about this but seriously stop being the class clown here. Rodney has already stated that he feels our information has value and that is good enough for me to continue to answer composites related questions to the best of my ability. If you don't like that may I suggest the door once again.

You guys are hilarious carry on Mcduff and may the Swartz be with you:D

You still don't get it do you I never said that there was anything wrong in what was posted I simply said it wasn't necessary for 99% of the modeling community. The type of epoxy use for most is simplistic in method and application but many times is performed incorrectly. A better service of the expertise between you two would be addressing the problems most run into rather than discussing autoclaves and advanced techniques most will never use. If it makes you feel good carry on. At least the web site I referred to attempts to take into consideration all levels of experience the customer will have from the most basic to the advanced. Don’t get your knickers in such a bunch most modelers have never used the techniques you guys flaunt and they do just fine. When I need an advanced technique I will research it then for right now I’m quite content in the knowledge I have gained being enough to satisfy my current needs.

Well its a banner day would like to keep the difference of opinion going (its the only one at this time) but I'm going flying with my F5B glider put together without any special equipment or techniques and its 4 years old ticking and still taking a licking. I think I'll take my MXS as well haven’t flown it since last fall. Taking your advice and getting out from behind a keyboard you should take your own advice might put you in a better frame of mind. LTR

Dennis