Cozy

Introduction

Which Epoxy?

Which epoxy to use is an early and important decision. Nat said in a newsletter that, if he built another plane he'd use MGS, so I decided to use it. Nat later confirmed this opinion in May '99 mailist message. MGS is fine once you get used to it. I haven't worked with anything else, but I like the way MGS wets out if the temp is 75 or better. I started with all slow hardner - took two days to cure at 70 degrees. Now I'm using a 50 - 50 mix and it cures overnight at 65 - 70. In the FL winter I learned to do my layups in the middle of the day. If I can get the layup done before the temp drops the cure might take all night, but the part weights low. If I let the temp get below 75 and try to do a large layup I'm in trouble. The epoxy thickens up as it cools from the hot box temp and it takes twice as much to wet up. I've started scheduling things. Layup at lunch time, layup early evening, flox work and cutting in the evening. In the FL summer the schedule is much different. Layup early morning, layup early evening. Knife trim time varys greatly with temp. I just keep checking the edges for stiffness. If I miss the time I can always heat the edge with a hair dryer and trim. One evening the sun was going down, and shining right into my patio. It hit a pot of mixed epoxy and in a couple of minutes I experienced my first exotherm. Crackle, pop, smoke. Quite dramatic. I mixed new epoxy and hid it from the sun.

There has been a lot of discussion about need for post cure and "tg" temperatures. I've done some research on this and come to the conclusion that, while all epoxy systems will benefit from a post cure, its not essential. This is evidenced by the hundreds of canards out there which were not post cured. The MGS stuff has a higher tg at room temperature cure than EZ-Poxy, and goes much higher still with a post cure. Add to this that its entirely odor free and is supposed to be low in allergy causing ingredients. (See above comments below under allergy). The need for post cure or otherwise is not, in my understanding, a valid reason for choosing one epoxy over another. MGS have been very helpful in answering my questions. (later I asked MGS by email for advise about a yellowish batch of resin. They took a week to respond, then sent me 14 pages of german language technical text to my voice number. They put the fax on repeat, so the only way to get them off the line was to hook up the fax and bring my company to a standstill for 1/2 hour. I was not pleased.)

I ordered the recommended five gallons for Chapters 4 - 7. At the end of Chap 7 I had 1 1/2 gallons left. My initial order lasted until half way through chapter 9. I ordered 2 more gallons and this ran out at the end of chapter 14. I also noticed that my bulkheads are 10% lighter than the average in Marc's table. Either the high Florida temperatures, or the low viscosity MGS resin are helping me build light. The savings in resin also bring the slightly higher price of MGS into line with the other stuff.

There seems to be something of a battle going on between MGS and "the old standard". There are arguments on both sides. This was well documented in various email correspondence earlier this year.

My subjective report: Since starting my project I have been visited by two builders who have used other epoxy systems extensively. Both were amazed at the wetting out capabilities of MGS, the lack of odor and the apparant ease of use. One, an A&P formally trained in composite construction, was dumbfounded when I proceeded to wet out three plys of BID at once in about 30 seconds. He said that this would have been unthinkable using the "brown stuff". He had never seen epoxy of the consistancy I was using. He checked the resulting part after cure and was much impressed with the look of the layup, saying that the lack of air bubbles was very impressive. For me this was no big deal and certainly not a skill issue. When working on large layups at his shop it was considered "essential" for one person to be squeeging, another pouring and another mixing. When I calmly took a cigarette break and a quick swim between plys he thought I'd gone mad!

He said that large air bubbles appear "by themselves" in their layups, perhaps because the epoxy is much closer to a gel. They have to work very hard to get rid of them, and always have a few left. He watched me lightly brush the epoxy on to a single first ply and achieve full wet out as I went along. He is used to the pour and squeege method. Brushing simply would not work, he says.

I think that what we need here is objective scientific comparisons. Maybe at the next Sun & Fun we should have an epoxy "shoot out" where we have four or five experienced users of each system do the same layup in public view. After cure the layups could be weighed and scientifically strength / lamination tested and the results published. Meanwhile I'll stick very happily with my choice.

Concerns about allergic reaction to epoxy

There has been a great deal of hysterics about this in the mail lists. Unfortunately, none of the hysterics has been backed up by statistical evidence. Granted, there are bad things in epoxy. Granted they can cause bad reactions. Granted there is risk. When considering risk, I like to know the likelyhood of danger. Must be the scientist in me. I suspect that the risk with MGS is small and, while avoiding direct contact, IMHO there's no need to get fanatical about it to the extent of wearing a space suit.

I guess these fresh air systems, thick gloves, masks, NASA space suits and other protective measures people are recommending can't hurt, but they must make building very uncomfortable. I read all this stuff when I started my project and wondered if it was really necessary. I couldn't find any statistics anywhere. MGS state in their literature that they have made efforts to reduce the allergic impact in their products. (they still recommend heavy protection). I wondered if the nasty smell of EZ Poxy was linked to the allergy causing content.

So... by default, I tested the issue with respect to myself and MSG 335. I started using ply-9 gel, but would often forget it. For large lay-ups I used thin neoprene surgical gloves and found them excellent. However, there have been MANY MANY times when I have not used gloves or any sort of protection. I have never used a face mask except during the worst sanding. For small lay-ups I often dont bother using gloves. I occasionally smooth out micro or flox with my bare fingers. I got the stuff on my hands and arms and into cuts many times. (it stings a bit). Call me crazy if you wish. (many have, for all sorts of other reasons)

Anyway, the bottom line I haven't been all that careful to avoid contact with the MGS epoxy, and after 2 years building and all major layups done, I can report only very minor signs of allergy. Either I'm not very allergenic, or the MGS stuff is not very allergy causing. I now find that, if I'm lazy or forget to wear the latex gloves, and I get epoxy into a cut, then next day I'll find that my hands, arms and eye lids are a bit itchy. If I get a lot of epoxy on me and into cuts, then I'll get a bit of a rash on my lower forearms that clears up in two or three days.

How much time did I save? I don't know. Quite a bit, I suspect. I certainly avoided a lot of inconvenience. How much risk did I take? I don't know. Perhaps less than driving without an airbag, and many of us do that every day. My point is that there is no hard evidence to say that the likelihood of getting nasty allergies to any particular epoxy brand is 1 in 10, 1 in 100 or 1 in 10 trillion. Issues like this sometimes get built way out of proportion, especially in mail lists. For me it was a non issue. On the other hand I met a guy who had to stop building because of his allergic reaction (EZ Poxy in this case). His hands and face were a REAL MESS.

Everyone must make their own decision on this. I'm not recommending that people don't practice "safe glassing". But, I wonder if you're less likely to "fly what you build" if you wear a space suit and take 10 years to build it, than if you do it naked and finish it in 6 months.

I posted the above in the canard aviators mail list and was answered by hysterical scare tactics and a request to the moderator for censorship. Hmmm. I guess when you've just spend 5 years in a sweaty space suit it must be hard to accept that it wasn't necessary. Then, on the other hand, maybe it was.

Just so there's no misunderstanding, I am not recommending that anyone ignore the possible harmful effects of epoxy.

  • 1. There is no doubt that the stuff can be harmful to you're health.
  • 2. It makes sense to protect yourself from direct contact at all times.
  • 3. Suggesting that people put their bare hands in epoxy is like promoting smoking. I've done it, but I know its not a good idea.
  • 4. I fully advocate "safe glassing", but that doesn't extend to wearing a condom over your head.

    My 2c.