cjensen

cjensen

Well Known Member
I've had good results with the canopy fairing so far, but I feel like I'm not doing it right. When I mix flox in to the epoxy/hardener, it works great...for a short time. Then it gets SO HOT (and smokes), I can't hold on to the mixing cup. Is this normal?

Am I supposed to put hardener in with the epoxy and flox? Or is it just epoxy and flox?

What I've been doing is working great, but right after the heat buildup, it hardens within a few minutes, and at that "heat" point, I know it's unusable.

I haven't used microballoons yet, but will be for the finish filling on the canopy fairing...

What's up with this stuff?:confused:

Here's a pic of my current status with it-
7-21-08-004w.jpg


That shows two layers of epoxy/flox, then seven layers of 'glass, sanded one time...
 
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Hey Chad,

Yep you're doing it right. Mix the epoxy / hardener thoroughly then add the flox. Epoxy curing is an exothermic reaction--it gives off heat. If it's getting hot enough to smoke mix, less epoxy at one time and/or use a slower hardener.

The bigger the batch of epoxy you mix, the hotter it will get and the faster it will start to cure. That's because it's heating iself. It's better to mix several small batches than one big one, since a small batch can more effectively pass its heat off to the surfoundings than a big one.
 
Guy Prevost said:
Hey Chad,

Yep you're doing it right. Mix the epoxy / hardener thoroughly then add the flox. Epoxy curing is an exothermic reaction--it gives off heat. If it's getting hot enough to smoke mix, less epoxy at one time and/or use a slower hardener.

The bigger the batch of epoxy you mix, the hotter it will get and the faster it will start to cure. That's because it's heating iself. It's better to mix several small batches than one big one, since a small batch can more effectively pass its heat off to the surfoundings than a big one.
Click to expand...

Guy has it right on.

Depending on what brand of epoxy you are using, there may be a slower setting hardener----you need to check with the mfg.
 
there are several things you can do to prevent the mixture from exotherming

exotherming is a self heating reaction, where the heat causes the epoxy to cure faster, which produces more heat, which makes it chemically react faster, which makes it heat up more and become unusable pretty fast.

you can get a slower hardner, lancair sells fast (15 minutes or so) and fast (1 hr +) I don't know what brand you are using, lancair sells jeffco.

all reactions happen slower at lower tempuratures. If you are having problems with exo. turn the air conditioning lower or start your mixing early in the morning with the lowest temps. avoid lights that introduce heat (halogen mostly)

and as soon as you mix the flox in and have it mixed well enough to use, spread it out flat on something inert so that the heat dissapates. the closer you have your mix to a sphere shape (small dixie cup) the faster it will exo. spread it flat really fast on the surface you are working on, then make it look pretty after you have it all spread out.


edit- be very careful mixing less hardner than recommended. at some point the epoxy will not cure properly.
 
Chad,
If you're using the West System pump setup, 1 pump of each is about all you can get away with at a time, at least if you use the normal hardener. Anytime I tried two pumps at a time it started smoking on me.
Good luck.
 
Chad-
Use a wider cup to mix the epoxy - if you use a little dixie sized cup on a hot day, the epoxy will over heat. The wider container will keep it from getting too hot. I would be very weary of any epoxy that smokes as you may experience a weaker bond due to the extreme heat it experienced during mixing.

If it is 90F+ use slow hardener, a wide and shallow cup, mix for 30 seconds, then add filler to the consitancy needed. If you do it this winter - fast hardener and smaller cup, mix for 60 seconds, then add filler.

Chris
 
Epoxy resins are not like polyester resins. You should only use the appropriate ratio of hardener to resin - with the West system pumps that is one stroke of each (or two or three but an equal number). If you want to use a smaller quantity of epoxy you can measure it out by weight using some kitchen scales - you know the little digital type which will happily measure 5 or 10 grams (sorry I work in metric) but remember that you are now working in weight not volume so you need to adjust the ratio appropriately (5:1 for West I think I remember ). Alternatively get some small syringes and quills and do it by volume.

Microfibres or Flox mixed into epoxy exotherms because the resin is concentrated in a small volume unlike microballoons which displace resin. You can tell that this is what happens because you can pull a smoking lump of gelled epoxy out of the smoking mixture - its cooler at the edges and so doesn't go off so quickly. As Danny says, best to spread it out over a large surface so the heat can dissipate. If it goes off and smokes just dump it. I wouldn't keep mixed resin in the refrigerator until I needed it as it really ought to remain above 15 deg C. If you store the components at cooler temperatures it begins to crystallize.

In cooler weather (like in England) exotherm is not so much of a problem as the ambient temperature isn't high enough to trigger the exothermic reaction.

You can also use slow hardener in warm weather but don't use less hardener as the ratio will the be wrong.

Also remember that the temp needs to stay above 15deg C while curing or it won't go off properly and you will have a nasty waxy mess that needs to be cleaned off so you can start again. Some styrofoam and a small light bulb work well at providing the right conditions, tho' it sounds like heat isn't your problem right now!

I've discovered all these things in the usual fashion......

Cheers,

Chris

RV8 - working on windshield fairing and baffles
 
Thanks everyone! I am using West Systems, and am mixing in their large mixing bowl...

7-21-08-001w.jpg


I understand now how it the stuff works...less pumps (been using anywhere from 3 to 5 pumps...obviously too much) will equal better usable times.

MUCH appreciated!! I just didn't have a clue about the heat and smoke, and when it did that the other day, I thought I did something wrong.

:cool:
 
Chad - just one other thing that occurred to me while I was driving home - if you build up too much thickness of resin/glass/flox on the airplane it can exotherm in situ - I've seen a hapless dinghy sailor blow a hole in the back of his (expensive) racing dinghy trying to add extra weight to get it up to limits - he just poured a load of the stuff in, smoke started pouring out and three minutes later there was a puddle of slag under a 6 inch diameter hole. How we laughed.

Probably not a real problem for building the fairing but worth avoiding a big thickness of the stuff - better to work slowly anyway. Wait until the first layer is just tacky before putting the next layer on - that way avoids the need for sanding until the job is finished. If you do need to sand between layers wet sand with wet and dry paper, it gets the any wax byproduct off better and also reduces any heat build up from the friction of your rubbing which softens the epoxy layer.

C
 
<<I understand now how it the stuff works...less pumps (been using anywhere from 3 to 5 pumps...obviously too much) will equal better usable times.>>

You can mix as much as you want.....but you must get it out of the cup so it doesn't exotherm. In some applications you might mix a quart in one batch, but you dump the whole pot on the work and and spread it thin as soon as possible. When spread thin, you get normal pot life, more or less.

"Pot Life" is the working time for a 100 gram batch of neat epoxy (no fillers) in a standard container. Micro, flox, or other solid additives serve as insulators; they reduce pot life and make exotherm worse because they slow heat transfer from the core of the mixed batch to the surface of the cup.

When spread thin, with or without fillers, the working time is longer than the pot life, and it won't exotherm at all.
 
chris mitchell said:
If you do need to sand between layers wet sand with wet and dry paper, it gets the any wax byproduct off better and also reduces any heat build up from the friction of your rubbing which softens the epoxy layer.

C
Click to expand...


Hi Chris,

I am not doubting this advice but its new to me. When building my Vari-Eze all the instructions said was to sand with coarse paper to give a mechanical bond. Nothing mentioned about waxy byproduct on the epoxy. You do not need to sand enough to produce heat, only enough to rough up the surface so no gloss remains and without cutting excessively into the weave. From memory, epoxy can absorb water so I am not sure about wet sanding on Epoxy unless it is fully cured?? Not trying to be critical, just want to make sure we all have the correct information. Anyone else like to chime in?

Fin
9A
Vari-Eze
 
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Oh, man, cjensen, you couldn't have picked a better time to start this thread.

Anyway, I noticed the same thing (I've been doing the tips to get use to fiberglass). I had purchased the "fast" hardener because I thought I would (and will) work in cooler temps when I bought it. I bought the "slow" hardener and I don't get quite the same heat.

but, yeah, I had a pot life of about 8 minutes on a hot day the other day, but I didn't want to throw the little dixie cup of stuff in the trash because I figure it'd light that trash on fire... so I stuck it outside.

Crazy cool to watch happen, tho.
 
Smoking Glass

Cut up some old cardboard boxes into 6X8 or so flat pieces. After you mix your resin and flox or other filler, spread it out into a thin layer around the cardboard sort of like a painters palette. Thinning it out helps to disperse the heat and slow the set long enough to get a decent working time. Just scrape up small amounts at a time with a plastic spreader and make like a painter. You should be able to get pretty good working time this way.
 
All has been good advice so far. I'll add that we put our chemistries in the fridge to cool them down before mixing. The same amount of heat is released in the reaction but doesn't become hot as fast and is dissipated over a longer time stretching your actual pot life. The hints about spreading your material out on something is good but would be better to just use less and spread it out on the work sooner. If you’re doing any work with glass cloth always work from a wet edge esp. with Polystyrene materials never work an edge that's "kicking off". Epoxy is a little more forgiving about the wet edge treatment but it’s a good habit not to let the edge kick off none the less. Epoxy doesn't have wax added to it but polystyrene plastics do. The reason for the added wax is that oxygen in the air prevents the surface from completing it's reaction. Think of it as plastic tendrils not being able to connect because of something getting in the way. Wax is put in the finishing resin to prevent oxygen from contacting the surface of styrene plastics thus allowing the reaction to complete. That’s where the terms laminating resin and finishing resin come from.
 
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So far so good... if someone already didn't mention these might be usable: don't warm the epoxy with your hands so try to keep pot so that you are not warming it. When not using mixed epoxy, put the pot to the ground/floor (there is cooler than at table). When you stop put the pot on the floor level again but in the place where it won't start fire if it flammables...

And to underline Chris's comment about the hardeners: With epoxy resins the reaction time is set with appropriate hardener (different hardener for different timing). With polyester resins the reaction time is set with amount of hardener (single hardener).
 
There's lots of infomation on using West epoxy here:

http://www.westsystem.com/. Its worth the read to understand what is happening with this stuff.

Fin - so far as wet sanding goes, the relevant bit is quoted below -the waxy byproduct, technically called amine blush, is seen in cooler, humid conditions. The waxy problem becomes really prominent if the reaction proceeds at too cool a temperature. The main reason I prefer wet sanding is that the paper won't clog. The other problem I have found is that the friction from vigorous sanding can be enough to soften the epoxy and degrade the surface. Yes I do sand dry with 80 but only gently, and not if I can avoid it because I prefer to use wet lay-ups (ie previous layer is not fully cured) where the bond is chemical.

"Surface preparation.

Cured epoxy - Amine blush can appear as a wax-like film on cured epoxy surfaces. It is a by-product of the curing process and may be more noticeable in cool, moist conditions. Amine blush can clog sandpaper and inhibit subsequent bonding, but it can easily be removed. It's a good idea to assume it has formed on any cured epoxy surface.

To remove the blush, wash the surface with clean water (not solvent) and an abrasive pad, such as Scotch-brite(TM) 7447 General Purpose Hand Pads. Dry the surface with paper towels to remove the dissolved blush before it dries on the surface. Sand any remaining glossy areas with 80-grit sandpaper. Wet-sanding will also remove the amine blush. If a release fabric is applied over the surface of fresh epoxy, amine blush will be removed when the release fabric is peeled from the cured epoxy and no additional sanding is required."

Bob - different fillers - microballoons, flox, colloidal silica, carbon, whatever, all fulfill different functions depending on what you are trying to achieve - the West System site gives guidance on whats appropriate, albeit in boat building terms. For example, if I was filling around rivet heads I'd use microballoons or microlight - its easy to sand and will take paint well. If you inadvertently use filleting blend, its a pain in the neck to sand off. Also most people don't add enough filler and have a mixture that is too runny - again the West site gives really useful advice.

Just to provide an example, when I built the windshield fillet for the -8, as recommended in the Vans instructions I first made a small fillet using filleting blend (nice strong fillet) to hold the base of the screen and make sure that the glass tape couldn't migrate through a small gap. Then I used the requisite pieces of tape, starting 1/2" wide and working up in 1/4" increments with unfilled resin, waiting till the previous layer was tacky before adding the next one. Then I added a layer of a stiff microballoon mixture and let that go off completely, sanded it gently to the final shape and added odd bits of microballoon mix to fill the low spots. You could of course finish the final layer with glass with some peel-ply over it and then sand that smooth but I prefer to finish with microballoons and shape that.

I hope that's helpful. I hasten to add that I'm a novice aircraft builder. My experience of polyester, vinyl ester and epoxy resins has been for boat-building.

Chris
 
Clarification of terms please

Rivethead,

As a novice working with fiberglass, perhaps you could define for me what you mean by "wet edge" and "kicking off." I have a lot to learn in a short time as I am just starting the fiberglass work.

'If you?re doing any work with glass cloth always work from a wet edge esp. with Polystyrene materials never work an edge that's "kicking off".'

Thanks,
greg
 
West System has a number of publications (for a fee) that go into "advanced" techniques, mostly in the boat building / repair area.

However, there is one good publication that is free, called "West Systems User Manual". It is also available as a download from the West System web site.

I have picked up several copy's from my local Boating Marine store that also carries the West Systems products. It was free there too.

ACS also carries this pub, (free from them also) and the ACS p/n
is 01-08750.

Note: this document is only intended for the West Systems line of products, and only for their epoxy brands of resins and hardeners.

I found this free material was all I needed to understand the processes involved. I am happy with the results.
 
Greg sure thing, I didn't mean to confuse. First term “kicking off” is anytime after the material starts becoming a solid (becomes set). With Polyesters it is an unrecoverable state but with epoxy what I have found is that epoxy will flow back out and allow some manipulation of material even after it begins to set. However, adding fresh epoxy to an already setting edge of epoxy will shorten the set time of the fresh epoxy to some degree.


Second term wet edge. Lets say you have a dinning room table that for some reason you wanted to cover with fiberglass. You cut a sheet of glass cloth and begin laminating it. Somewhere through the job you run out of resin. Part of the glass is wetted and sticking but another part of it is dry and so far is just glass laying on a table. The wet edge is the border between the resin and none resin filled glass. If polyester begins to set along this edge the newly wetted glass (newly wetted because you just went and mixed a new batch of resin and started applying it) along that edge will not lay down correctly. With epoxy you can get the resin to thin back and save that edge with fresh epoxy to a point. However even though you can save an epoxy edge there will be a shortening in the set time of the epoxy that's been mixed with the old setting resin. Probably not a big problem since the idea is to have it set anyway. Something I always do in my shop is not to mix fresh epoxy in a pot that has epoxy already setting in it. I always wait until my waste epoxy (even if it's just a smear) has fully set before reusing anything I mix epoxy in. Usually I prefer to throw away my mix pot after one use but that can get pretty wasteful.
 
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Amine Blush

Apparently, there is an epoxy system that doesn't produce a blush called MAS. I don't know if anyone has used this system, but just putting it out there for reference. No experience with it as yet, but if I can get to my boat project (sump/keel repair on a J24) I'll let everyone know how it goes. Supposed to be really nice to work with, if that can be said of epoxies.
 
Use EZ Poxy instead!

Holy cow you guys.... you should be using EZ Poxy (formally Safety Poxy), available from Aircraft Spruce. This epoxy gives you an easy 30 min pot life with tack out time of about 4-6 hrs at room temp.

Having just a few minutes of time to spread flox and wet out cloth is rediculous. As a Long-EZ builder, trust me, go this route!!!
 
I agree with Mike (except I do not use EZ poxy for reasons not covered in this thread). You can use EZ, Aeropoxy or MGS all available at spruce. MGS is the most expensive but you can get up to 4 hrs (2 realistically) with the slow hardner. Remember this is POT life. If you mix a bunch of epoxy, seperate it out into multiple containers to prevent the exotherms described before.

Ryan
 
MAS epoxy

I've been using MAS to glass a wooden kayak. It works very well and won't blush with slow hardener. However, some of the boat building guys say it is possible for MAS to blush if you use the fast hardener. They suggest warm water and a sponge to remove blush.
 
Rivethead said:
I always wait until my waste epoxy (even if it's just a smear) has fully set before reusing anything I mix epoxy in. Usually I prefer to throw away my mix pot after one use but that can get pretty wasteful.
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get little dixie cups without the wax to mix with. even with one pump of the mixer they are cheap enough to use once and toss. i can mix four pumps in the cups, they are just about right for mixing most anything.
 
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