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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

acerc

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.

speedracerntrixie

My Feedback: (29)

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.

aymodeler

My Feedback: (3)

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.

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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

acerc

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

tailskid

My Feedback: (34)

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!

speedracerntrixie

My Feedback: (29)

Especially in AZ.

Gizmo-RCU

My Feedback: (27)

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.

TomCrump

But not so much in MA.

speedracerntrixie

My Feedback: (29)

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.

Ernie Misner

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.

Hydro Junkie

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.

sensei

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

chuckk2

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.

raptureboy

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

Rodney

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.

Propworn

My Feedback: (3)

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

sensei

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

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

Propworn

My Feedback: (3)

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

speedracerntrixie

My Feedback: (29)

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.

Propworn

My Feedback: (3)

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

speedracerntrixie

My Feedback: (29)

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.

Hydro Junkie

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

Rodney

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.