davidfee

Lee,
Your C114 fuse looks great! I think Ed cleared up what I was trying to say, which was just that using a slower hardener will offset the increase in curing rate you see when you heat the epoxy. The result is that you have a lower viscosity for better wet-out, and you still have plenty of time to do the work.

FWIW, I did have one "negative" experience when thinning with alcohol to apply light FG over a balsa-skinned wing. Not knowing any better, I picked up "denatured alcohol" from the drug store. I didn't read the label because I figured the stuff would be what I wanted. It turns out that the denaturing agent, rather than being some other alcohol ethyl/methyl, was some form of petrolium distillate. This resulted in a rubbery finished product. I actually experimented with this, once I realized what had happened. I tried using the "denatured alcohol" as a plasticizer to make some flexible FG props. That actually worked fairly well, but the strength seemed to be reduced considerably as compared to props made with un-thinned epoxy.

-David

Ed Smith

This is a Direct quote from the West Systems user manual.

Thinning Epoxy

There are epoxy-based products specifically designed to penetrate and reinforce rotted wood. These products, basically an epoxy thinned with solvents, do a good job of penetrating the wood. But the solvents compromise the strength and moisture barrier properties of the epoxy. WEST SYSTEMS epoxy can be thinned with solvents for greater penetration, but not without the same compromise in strength and moisture resistance. Acetone, toluene or MEK have been used to to thin WEST SYSTEM epoxy and duplicate these penetrating epoxies with about the same effectiveness. If you choose to thin epoxy, keep in mind that the strength and moisture protection of the epoxy are lost in proportion to the amount of solvent added.

There is a better solution to get good wood penetration without losing strength or moisture resistance. We recommend moderate heating of the repair area and the epoxy with a heat gun or heat lamp. The epoxy will have a lower viscosity and penetrate more deeply when it is warmed and contacts the warmed wood cavities and pores. Although the working life of the epoxy will be considerably shortened, slower hardeners (206, 207, 209) will have a longer working life and should penetrate more than 205 hardener before they begin to gel. When the epoxy cures it will retain all of its strength and effectiveness as a moisture barrier, which we feel more than offsets any advantages gained by adding solvents to the epoxy.

Ed S

Newflee

Thanks for the advice guys. Just a note, the alcohol I use is isopropyl rubbing alcohol 99%. It is my understanding that alcohol can not be held at anything higher than 96% due to its attraction to moisture. This I know from my other distilling hobby. Therefore your warnings about moisture contamination are quite valid. I'm sure that moisture is drawn into the mixture and then even if the alcohol is evaporated off the moisture remains.

I have heard quite a lot of good things about the MGS resins but their website doesn't offer much info on sources. Does anyone know if it is available in Canada?


Lee

Ed Smith

The distributor in Canada is:-

Airheart Distributing,
55 Lancing Drive,
Unit 1.
Hamilton,
ON. L8W 2Z9

They should be able to help with sources.

Ed S

Newflee

Great thanks Ed.

Lee

sticks-RCU

My Feedback: (23)

MGS rules, I have been using it for a couple of years now and love it. If I am working on a large project I will use their slow hardner that gives you a few hour pot life and it wets out great. If I am working on something smaller, I will use their faster hardner. I just hate it when I am trying to lay something up and the epoxy gets all sticky.

gluedoc

A minor correction Lee. Isopropyl alcohol at 99% will stay pretty close to 99% if you keep it in a sealed container. The 96% content that you are talking about is the vapor-liquid equilibrium azeotrope for ethyl alcohol, which prevents you from distilling the ethanol to more than 96% purity. However, this azeotrope can be broke with the addition of a cosolvent (benzene or octane work well), and the ethanol can then be distilled to near 100% purity. This product is perfectly stable with respect to moisture absorbtion, and is what is known as denatured alcohol. In addition, the azeotrope can be broked using liquid-solid extractions, but that is too far afield to discuss here.

Matt

gluedoc

Let me provide some minor contributions here.

First, thinning epoxy resins is certainly permissible, and a very necessary thing. Usually, this is done for the purposes of spraying the epoxy (e.g. paint) where most of the solvent will volatilize during the aerosol process. However, there has been some work performed in the commercial and military aerospace industry regarding the use of structural spray epoxies. Largely, the key to their success is the COMPLETE removal of volatiles prior to cure. In this case, these are heat cured materials, so degassing is possible. In the case of room temperature cure epoxies, this is never completely possible. Those of you who are thinning your epoxies are introducing voids in your laminates at around 5-20%. This can significantly weaken the laminates, but composites used in models are so overdesigned that it doesn't matter much.

The solution to this problem is to use a less viscous epoxy to begin with. The five and thirty minute varieties use a fairly viscous epoxy as their primary ingredient in both the part A and B. When a less viscous material is used (for RTM or VaRTM applications), a thinner epoxy is blended in to the mixture (such as an aliphatic epoxy). In addition, the use of elevated temperature cure catalysts allow the resin to flow significantly as it is heated, providing a more uniform surface.

The bottom line on this issue is that pinholes in the surface don't affect structural integrity, but require rework and lead to added weight to get a smooth surface. Voids on the interior of a laminate can lead to delaminations and component failure. A good way to prevent both is to edge bleed a wet laminate, and make sure that you don't suffer from bridging or resin pooling because your vacuum distribution medium isn't adequate.

Matt

chelapa

well. ok guys. i love your write ups. esp the last one on this thread. Now, i hear mgs is good. How good. what is the mix ratio in weight. and, i need something that i only have to pay about 40-50 per gal. if less then that would be even better. I cant spend to much money here. got any links??!?!?!

davidfee

MGS H285/L285/L287 is marketed for use in the aviation industry (has been a standard product for 20 years). For that reason, it must meet strict quality standards and have fully explored chemical and physical data. Full scale aircraft must be certified, so they must be made with quality stuff. If you read the data sheets for MGS, you find that the manufacturer specifies a post-cure at elevated temperature to complete the cure and stabilize the part. For most hobby applications, the post-cure is not actually needed.

The MGS resin and hardener are low-viscosity (600-900 cps for resin, 50-100 cps for hardener), so they wet out fabrics quickly. The mix ratio is 100:40 by weight and 100:50 by volume.

In the US, MGS is about $80/gallon for the resin only... and another $40 or so for the hardener. Is it worth it? Perhaps not for every application. However, I love the stuff.

-David

davidfee

Thanks for your contributions. Care to elaborate on this a bit? How is ~100% ethanol moisture-stable (i.e. not hygroscopic)? Also, denaturing typically refers to the "adulteration" of ethanol with some small percentage of methanol, does it not?

thanks,
-David

gluedoc

We are way off topic here, and you all have a very adoit understanding of this, just seem to be missing a few of the details. If you leave nearly any substance exposed to humid air, it will pick up water. This has to do with vapor/liquid or vapor/solid equilibria. If you want anything to stay absolutely moisture free, then you have to store it in packed in an inert gas. Yes, denatured alcohol, or even non-denatured pure ethanol will pick up environmental moisture. However, if the purity of the alcohol is above the azeotrope, it will never pick up more than 4% water (from the atmosphere), the nature of the azeotrope works both ways. Technically, this does not make the material hygroscopic (as that refers to an acceleration of condensation or a scavenging of water vapor), but your point is the same.

As for the term denatured, you are correct. It does refer to the addition of a second substance to the ethanol. This substance can be added for the express purpose of making the alcohol non-potable (and thus, tax free for industrial purposes), but it can also be added to break the azeotrope and obtain pure ethanol. The second process is needed to make pure ethanol for blending with gasoline, and iso-octane is often used in that case to break the azeotrope.

Matt

davidfee

Thanks, Matt.

I do have an M.S. in physical chemistry, so this is not mysterious to me. I just simply wanted a bit of clarification because I wasn't sure if we were on the same page about these things.

-David

branded

My Feedback: (9)

I think you need to seperate your argument of thinning epoxy by it's application. It's perfectly acceptable to thin epoxy, whether it be West System or other, with Alcohol for purposes of covering a model with glass. If the application is structural, such as in laminating, or reinforcing firewalls, etc. then it's not advisable to thin.

Epoxy has long been used as a filler for glass on models. When used in this way the epoxy is thinned just to the consistancy of milk using alcohol. It is used to apply the glass to the surface. What I and others have taken to in the past few years is that following the application of the glass (using thinned epoxy) is to complete the remainder of the substrate with WBP until the weave is filled. I also use talcum or other filler on the last couple of coats of WBP .

Why use epoxy for the application of the glass? Epoxy has better adhesion and "tack" when applying glass. I found that trying to apply glass to compound surfaces, such as on fuslages, that the glass will pull away from the surface of its own weight when saturated with WBP. It's advisable to do the attacment, or the application with a thinned coat of epoxy and when cured do the remainder of the surface with WBP.

The primary purpose of glassing a model is not structural strength but rather to create a smooth substrate by which to paint. No more, no less.

davidfee

Branded,
Check post #26 above, where I discuss my experience thinning epoxy (Jeffco 1310 L-6 / 3102) with "denatured alcohol" from the drug store. I was glassing a balsa-skinned foam core wing with 0.6oz fabric. The solvent did not evaporate quickly enough and, in my case, the epoxy stayed gummy for several weeks, so sanding and filling was greatly hindered.

-David

branded

My Feedback: (9)

Firstly, you do not get "Denatured Alcohol" from the drugstore you get ISOPROPOL alcohol which has water in it......Denatured does not. Never use ISO alccohol to thin epoxy!

To thin epoxy with Denatured Alcohol do the following.

Mix the epoxy as always (if West Systems use the same 2:1 mixture using the pumps).

After mixing part A and B thoroughly, then thin with DENATURED ALCOHOL , the type which you would would get from the Home Depot or LOWES, MENARDS, etc.


Hope this helps.......

Ed Smith

I would suggest you separate your arguments. There are different reasons for glassing models. In my case I am looking for strength in the wing. I glass the centre section at the same time as the rest of the wing. My top wing skin is also the aileron hinge. As is the top skin on the horizontal tail and one side on the vertical fin. The hard surface is just an added advantage to the structure.

Just a hard paintable surface is easy to achieve without vacuum bagging etc etc.

WBP?? I do not speak in code.

Ed S

branded

My Feedback: (9)

WBP is Water Based Polyurethane. You have some very common misconceptions about covering an airframe, as well as a wing.

Vacuum bagging? How'd this come into this conversation? You purport to give advice about glassing models. Are we discussing glassing foam/fiberglass models or are we discussing smallish lightweight models such as gliders? I use vacuum for sheeting my foam core wings but what has this to do with this conversation? I donot use vacuum for glassing, nor is it required or needed.

I'm not sure what you're talking about, Ed.

I'm talking about mainstrem large scale aircraft constructed of foam/balsa, or framed/balsa sheeted wings.
I'm discussing balsa sheeted fuselages.

What are you talking about? Perhaps my 6 month lapse away from this hobby has left me behind?

davidfee

Branded,
I most certainly did get denatured alcohol from the drugstore. It was not isopropanol and there was no water in it. It was ethanol, denatured with petroleum distillates as I said above. I mentioned my adventure so as to make the point that one must read the label to ensure the denatured alcohol being purchased is ethanol/methanol, rather than ethanol/petroleum distillates. Regardless, the reduction in strength resulting from thinning with alcohol is well documented.

Please do not assume that I am ignorant or misinformed. Such does not make for good conversations.

-David

branded

My Feedback: (9)

Well, then you simply did not mix the epoxy correctly.

What else do you expect me to say?

I have far more experience in these matters than you. I know this to be a fact simply by virtue of the fact that you're asking the question and by virtue of the fact that I have had no problems in 25+ years of modelling.

Take my advice or nor. If not then you do not need to forward my payment.

Seriously, if you really want to be tutored by "experts" go to- http://www.rcscalebuilder.com/

Stay with it, you'll get it right though!

davidfee

Who is the one asking the questions? Did you bother to read what I wrote? Have you read the entire thread? I am a responder... not the original poster. My questions of gluedoc were merely for clarification of his responses.

The denatured alcohol I was discussing came from a Sav-On/Osco drugstore in Goleta, CA in 2000. I had no reason to assume that it was any different from the denatured alcohol available at Home Depot, Lowes, etc. ...so I bought and used it without reading the label. It was only after the epoxy did not cure properly (measured out with a digital scale with +/- 0.05g precision) that I had a look at the label and found "petroleum distillates" as the denaturing agent. I then experimented and found that the evaporation rate was too slow to be used with laminating epoxy. I doubt that I mixed the epoxy incorrectly.

Like you, I've also been modelling for 25+ years... so go easy on the insults and other inflamatory language.

-David

branded

My Feedback: (9)

Come down off your high horse.....If you, and any poster to this thread is having difficulty thinning epoxy then you cleary need assistance and tutelage.

You apparently have some latent arrogance whereby you continually state your credentials on the internet but have no solutions to the process and subsequent problems that are described in this thread. My observation is that you're perplexed by them.

Well, I'm impressed ( sort of <shrug>) but having said that I've never had a single problem thinning epoxy, EVER and wonder why it is that we're having this anal conversation, given your lofty level of experience in modeling.

Thinning epoxy is rather a mundane routine process that's intuitive to most experienced modelers.

I fail to see what your problem is? Do you say that *I* do not not know what I'm talking about?

You're the guy confused over all this, not I.............Seems pretty simple to me....Mix epoxy as usual, and afterwords mix Denatured Alcohol in to change the viscosity of the epoxy .......

What's hard to understand here?

branded

My Feedback: (9)

I have built many models, perhaps 100+, with .6 oz glass using thinned epoxy. David...you did not mix the epoxy properly or you did not use products that are compatible with this application.

I use West System epoxy (105) resin and 205 hardner. I've never had any such problems. Many experienced modelers such as myself do the same and never have any problems. We are not inventing a process here. This process has been in use for many years.

The problems you experience are obviously due to your own inexperience and ignorance. Sorry, but that's what I see here.

davidfee

You seem intent on arguing and that's fine, but you'll have to argue with someone else. This incompatibility was precisely my point when I got into the discussion about ethanol denatured with petroleum distillates vs. ethanol denatured with methanol. You will find the solutions I offered in the first page of this thread. These solutions are the ones prescribed by epoxy manufacturers, including West Systems. Conventional wisdom and personal experience are fine, but facts are facts. Volatile solvents do weaken the structure of room-temp systems. If you are using so much epoxy that this weakening is inconsequential to you then fine... but other modelers may have different results.

-David

branded

My Feedback: (9)

David. I'm not intent on arguing. I'm intent on teaching someone that has ignorance concerning a rather mundane and routine process that modelers have used for years. Yes we have been doing this process for years, Dave.........

I'm sorry that you take offense. Eventually you will understand that you're on the wrong side of this discussion.

My intent is not to debate you. Please take the time to "educate" yourself. You will feel rather foolish afterwards. This "discussion" is rather a 'no brainer' for most modelers.