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Author Topic: Lightweight fiberglass technique  (Read 911 times)

Offline Shorts,David

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Lightweight fiberglass technique
« on: November 23, 2021, 11:50:32 PM »
Hi All,
I'm going to fiberglass the middle of my wing to smooth out and reinforce some repairs. What is the lightest technique. Resin? Epoxy thinned with acetone? Epoxy thinned with acetone filled with micro balloons? I just don't want to add too much weight.
Thanks

Online Brett Buck

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Re: Lightweight fiberglass technique
« Reply #1 on: November 24, 2021, 12:20:32 AM »
Hi All,
I'm going to fiberglass the middle of my wing to smooth out and reinforce some repairs. What is the lightest technique. Resin? Epoxy thinned with acetone? Epoxy thinned with acetone filled with micro balloons? I just don't want to add too much weight.
Thanks

    Just like (1/2 ounce) fiberglass and finishing epoxy, which is already thin. Apply with a disposable brush and make sure you plenty of it everywhere. Then, take a roll of toilet paper, and roll it (in the direction it doesn't unwind) across the puddle, several times, unrolling enough to get back to clean tissue, a few time. The tissue will absorb the excess and make sure it get pressed down everywhere. Let it cure, finish over it.

      Brett

Offline Dennis Toth

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Re: Lightweight fiberglass technique
« Reply #2 on: November 24, 2021, 06:27:31 AM »
The technique Brett described is pretty much what is also done on flaps to stiffen them. One thing that is done after applying the epoxy liberally to the surface, take a playing card or business card and scrap off the excess then use the toilet paper to smooth the final surface as Brett described. Works great and gives a light hard surface to sand smooth for finishing.

Best,   DennisT

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Re: Lightweight fiberglass technique
« Reply #3 on: November 24, 2021, 07:19:30 AM »
The technique Brett described is pretty much what is also done on flaps to stiffen them. One thing that is done after applying the epoxy liberally to the surface, take a playing card or business card and scrap off the excess then use the toilet paper to smooth the final surface as Brett described. Works great and gives a light hard surface to sand smooth for finishing.

Best,   DennisT

Den,

I guess you forgot I explained this toilet tissue thing back in 2013, with photos?

Here's the link to the technique with photos and plenty of text. Only difference is "we" all, that is, the R/C pattern guys, used the lightest laminating resin available. Polyester Resin. Not as easy to work with but it's already thin and designed for laminating layers.  Available from Sig, so people are still using it.

https://stunthanger.com/smf/cfc-graphics/'mig-3-reconnaissance-aircraft-and-warbird!'/500/

Post #525.

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Offline Mike Alimov

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Re: Lightweight fiberglass technique
« Reply #4 on: November 24, 2021, 07:58:53 AM »
I would recommend EZ Lam 30 minute epoxy from ACP Composites in Livermore CA (store.acpsales.com).  Great product, wets out fabric better than some more expensive epoxies, and is available in smaller quantities more suitable for modelers.  If you also order some Cabosil thickening filler (no, not microballoons, they reduce strength), you will be able to use the rest of the epoxy as general purpose adhesive (adjusting the ratio until desired viscosity is achieved), and it will be many times stronger than the Bob Smith Industries 1:1 ratio epoxy that we all get from hobby shops.

Offline Shorts,David

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Re: Lightweight fiberglass technique
« Reply #5 on: November 24, 2021, 09:17:42 AM »
Okay, dumb sounding follow up question. But is fiberglass resin (which I do have-I think it's bondo brand from the hardware store), the same as finishing epoxy? Or, I can order one of the finishing epoxy products you all recommend.

Online Brett Buck

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Re: Lightweight fiberglass technique
« Reply #6 on: November 24, 2021, 09:49:47 AM »
Okay, dumb sounding follow up question. But is fiberglass resin (which I do have-I think it's bondo brand from the hardware store), the same as finishing epoxy? Or, I can order one of the finishing epoxy products you all recommend.

   You *can* use polyester resin, but there are some finishes that cause it not to cure if there is any underneath it. Bare wood, OK.  Similar technique to epoxy, the problem being that the polyester resin tends to "go off" much faster, meaning you need to work it much more quickly. Reducing the amount of hardener will make it go slower, but don't go less than, maybe, 80% of the recommended, and stir it very well.

   I also recommend EZ-Lam (30 or 60 minute - both have far more than enough working time) but any epoxy intended for finishing should work about the same. You can use any slow-cure epozy (30-minute or longer), just warm it up with a heat gun. Warm, not heat, just get a bit warm to thin it out right before you roll it.

    Using epoxy, this time of year, you need to make sure that it stays warm enough to cure, over 70 degrees for sure.

     Brett

Online Brett Buck

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Re: Lightweight fiberglass technique
« Reply #7 on: November 24, 2021, 10:54:38 AM »
I guess you forgot I explained this toilet tissue thing back in 2013, with photos?

   Oh, so you took that technique that was old news in 1975 when I first heard of it, repeated many times since, and then in the 21st century you made a thread about it, implying that you invented it?

    Brett

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Re: Lightweight fiberglass technique
« Reply #8 on: November 24, 2021, 12:46:06 PM »
You can invent something that someone else has invented if you didn't know about it. Happened to me a couple of times lol.

Some of that Bondo stuff has fiberglass fibers in it so make sure what you have. Clear Polyester resin is thicker than Zap Zpoxy finishing resin. I've never had any luck with 2 part polyester myself.


Motorman 8)

Polyester resin isn't for everyone. There's a learning curve which comes from use and application.

We mixed a quality brand of acetone with the first coat, 50%-50%. This coat was just to be brushed over the bare balsa wood to soak in. Next coat was for the glass application using toilet tissue. A quality primer came after this. I've mention this before.

Some guys used a third coat which required more sanding. I never used a third coat.
You really have to make sure your glass cloth is saturated so it adheres well.

I no longer use the product. Deft Wood Lacquer sealer and silk or Minwax is what I've used on recently finished models. Speed dry with a hobbyists heat gun. Open bays I use clear dope.



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Re: Lightweight fiberglass technique
« Reply #9 on: November 24, 2021, 12:56:57 PM »
   Oh, so you took that technique that was old news in 1975 when I first heard of it, repeated many times since, and then in the 21st century you made a thread about it, implying that you invented it?

    Brett

Why are you such a jerk? I mentioned all us R/C pattern guys used it back in the day.

Besides, you said yourself the stuff was junk when I first mentioned the use of Polyester resin at Stupid Stint years ago.

Maybe you remember the model? Or are you trying to forget it?  LL~ LL~

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Re: Lightweight fiberglass technique
« Reply #10 on: November 24, 2021, 01:04:31 PM »
Den,

I guess you forgot I explained this toilet tissue thing back in 2013, with photos?

Post #525.

How could we ever forget?

Bob Hunt explained this as early as the 70's.

Keith

Offline Shorts,David

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Re: Lightweight fiberglass technique
« Reply #11 on: November 24, 2021, 02:18:22 PM »
Okay, I ordered some finishing epoxy. Not going to use the fiberglass resin. I've used it before and it worked fine for what I was doing, but always game for trying something better.

Thanks
David

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Re: Lightweight fiberglass technique
« Reply #12 on: November 24, 2021, 02:24:04 PM »
How could we ever forget?

Bob Hunt explained this as early as the 70's.

Keith

Where did you explain this, or are you just "name dropping?"

Sad actually, all the "name dropping which goes on in the Forum.
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Re: Lightweight fiberglass technique
« Reply #13 on: November 24, 2021, 02:28:42 PM »
Okay, I ordered some finishing epoxy. Not going to use the fiberglass resin. I've used it before and it worked fine for what I was doing, but always game for trying something better.

Thanks
David

Yes, you're better off using a product which is easier to work with.

As I said, I no longer use it, but I don't use Finishing Epoxy either.

I'd like to see a test of both materials to compare weight.

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Online Mark wood

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Re: Lightweight fiberglass technique
« Reply #14 on: November 24, 2021, 05:11:36 PM »
I'm a fan of west systems or epon and ink rollers myself. I am going to give the EZ Lam epoxy a go though for the 30 minute applications Bob smith and Devcon just don't always cure nicely IMO. Especially if they've been thinned. I use on ink roller to spread the resin as I find it does a better job and doesn't drag the fabric around. Of course there's limitations as well. When that happens I resort to the scraper method.  I don't find the need for the TP method which is good due to the volatility of the TP market these days. Instead I always mix my epoxy by weight 1.1:1, epoxy : fabric. Doing that, there is not not much to spare if any.

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Online Brett Buck

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Re: Lightweight fiberglass technique
« Reply #15 on: November 24, 2021, 07:22:13 PM »
I'm a fan of west systems or epon and ink rollers myself. I am going to give the EZ Lam epoxy a go though for the 30 minute applications Bob smith and Devcon just don't always cure nicely IMO.

    The really outstanding feature of EZ-Lam is the near complete lack of self-heating, which means you get the full working time if you mix it in a cup.

    Brett

Offline Astropuppy

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Re: Lightweight fiberglass technique
« Reply #16 on: November 24, 2021, 07:36:23 PM »
For me the biggest big down side of "polyester resin" is it stinks, I mean really stinks. When epoxy finishing resins came to be, I and most of my buddies never looked back.
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Re: Lightweight fiberglass technique
« Reply #17 on: November 25, 2021, 08:22:53 AM »
Gentlemen,

I'm a first time moldmaker/caster...

So I read this whole thread and have a few questions regarding Bob Smith epoxy (it is all I have, so I need to use it). I now know I need to heat the garage-based build closet up above 70 degrees. I plan on bringing the two bottles into the main house and warm them in cups full of very warm water (Hobby Closet is too cold for storing/mixing).

This for my first attempt at molding a fiberglass cover (Southeridge CNC Hyper Viper forward fuse and engine cover). The shape appears to be fairly easy to work, as the original balsa "buck" came out of the mold quite easily.

Am I headed in the wrong direction with BSI epoxy? If not, more questions.

I won't be able to tissue roll the cavity, so I plan on using gloves fingers and tissue to mush the epoxy/matt down. I expext to use a hit air gun to keep the epoxy warm and flowing.

Can I thin the epoxy enough so that I can invert the mold and allow gravity to pull excess epoxy out of the mold?

How thin can I go with BSI and what is the best thinner? I have acetone, methanol, and lacquer thinner on hand.

I still need to read the thread Charles alluded to, but it sounds like the TP is to blot off the excess while ensuring the matt stays in place.

Or am I way off target?

TIA


Online Mark wood

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Re: Lightweight fiberglass technique
« Reply #18 on: November 25, 2021, 08:55:53 AM »
Gentlemen,

I'm a first time moldmaker/caster...

So I read this whole thread and have a few questions regarding Bob Smith epoxy (it is all I have, so I need to use it). I now know I need to heat the garage-based build closet up above 70 degrees. I plan on bringing the two bottles into the main house and warm them in cups full of very warm water (Hobby Closet is too cold for storing/mixing).

This for my first attempt at molding a fiberglass cover (Southeridge CNC Hyper Viper forward fuse and engine cover). The shape appears to be fairly easy to work, as the original balsa "buck" came out of the mold quite easily.

Am I headed in the wrong direction with BSI epoxy? If not, more questions.

I won't be able to tissue roll the cavity, so I plan on using gloves fingers and tissue to mush the epoxy/matt down. I expext to use a hit air gun to keep the epoxy warm and flowing.

Can I thin the epoxy enough so that I can invert the mold and allow gravity to pull excess epoxy out of the mold?

How thin can I go with BSI and what is the best thinner? I have acetone, methanol, and lacquer thinner on hand.

I still need to read the thread Charles alluded to, but it sounds like the TP is to blot off the excess while ensuring the matt stays in place.

Or am I way off target?

TIA

Well, this is a wide open ask for a thousand opinions. The bottom line is that BSI epoxy works for many things and is the staple of modelers world wide. It will do what you are asking it to do but is not the best option. For your first efforts it is perfect because you have it on hand and you have lessons to learn which it will suffice for that mission just fine. However, the end product using BSI is not going to be the best. In all of these threads, I always post the same thing, I am a fan of West Systems epoxy. This is the result of making parts for 40 plus years. There are other systems that work equally well, one which I used to use is the Aerosystems epoxy. It isn't as well supported as the WS. The only "complaint" I have with WS is the curing time which is longer than my patience for gluing parts together with.


I won't be able to tissue roll the cavity, so I plan on using gloves fingers and tissue to mush the epoxy/matt down. I expext to use a hit air gun to keep the epoxy warm and flowing.

Don't do it that way. Here's how I do it. First, I mix my epoxy by weight which requires a scale, I use either my beam balance or my reloading grain scale. The ratio of epoxy to fiber should 1.1 or 1.2 to 1 epoxy to fiber. CF needs a little bit more than glass. I cut my fiber to the rough shape of the mold. Use a piece of paper pushed in to the mold to create a template. Then cut and weigh your resulting fiber. I then take a piece of a 5 mil drop polypropylene drop cloth (the thick kind) and tape it down to the  table. I lay my fiber on that. I then mix the epoxy necessary to fill that fiber to the correct ratio. Pour the epoxy out on to the fiber and spread it thin. I use an ink roller to spread but a scraper works too but it will be tough to get the epoxy  everywhere that way. By inky roller I mean a small hard or rubbery roller. I made mine. A this point if you used more epoxy than needed you could blot the excess away. I never have to do that. We're, in essence making prepreg on the spot. The whole shebang, can be easily lifted off of the work bench and cut to the necessary size for the mold. Separate the epoxy laden fiber and work in to the mold. In an ideal situation you would have the other necessary materials to vacuum bag but as long as your mold doesn't have any tough corners you should be fine.

Can I thin the epoxy enough so that I can invert the mold and allow gravity to pull excess epoxy out of the mold?
How thin can I go with BSI and what is the best thinner? I have acetone, methanol, and lacquer thinner on hand.

I have used all of those with BSI and they will make it thinner. They also impact the cure and and sometime the epoxy never fully hardens. I don't thin any epoxy if I can avoid it. That is likely a result of the water that gets in to the solvent. I have different epoxies for different applications on hand. West Systems being my go to for almost everything including gluing parts together that structurally count. The thickness of the epoxy can be modified by having micro balloons, milled glass, silicate, milled carbon and balsa dust on hand.

Or am I way off target?

No, just in a steep learning curve phase.
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Online Avaiojet

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Re: Lightweight fiberglass technique
« Reply #19 on: November 25, 2021, 09:10:50 AM »
Quote
I still need to read the thread Charles alluded to, but it sounds like the TP is to blot off the excess while ensuring the matt stays in place.

Or am I way off target?

Jim,

Correct, but the second and final coat adds to this.

Clearly I stated a few times I no longer use this method. The Mig-3 was the last model I used Polyester Resin on with glass cloth on the control surfaces, only because I had the stuff. I still have a good deal of silk.

The Polyester resin and TP application could be the quickest and possibly the lightest method? I don't know this as fact.

I'm now using silk everywhere, and I'll bet many others are also. Tests would have to be done to determine which method, material and resin, or whatever product, yields the best results, which is the lightest and stiffer. I have little interest in flying, so I'll never do the test.

I do know from the models I've built and covered with silk, using clear dope, Deft Wood Lacquer Sealer or Minwax, and CA for open bay models, it's just as easy, quick, even quicker if you force dry like I do, and the results last.

I never use Nitrate for anything, It's not even in my shop.

Sure, you could view the Mig-3 and look at the TP method, which has been around longer than some have been flying CL, but it's not for everyone, especially the use of Polyester resin. I only dod what all the R/C guys did back then, and it worked well. Auto primer over the second sanded coat.

Do a sample or two. My guess is you'll gravitate towards the silk and Deft Wood Lacquer sealer as I have.

Also keep in mind, I no longer use Polyspan or Silkspan for good reasons. One being they tare so easily and I've found they both need more coats to fill than silk. But that's me. Others have experienced different results.

"Choose wisely"

BTW. Everything I've talked about here is for surface prep before primer.

CB

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Offline Dave Hull

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Re: Lightweight fiberglass technique
« Reply #20 on: November 25, 2021, 11:37:56 PM »
A few more comments to peruse and cherry pick thru that might apply to your situation:


1. An epoxy finishing resin should have a non-1:1 mix ratio, and should be thinner. (They make stuff 1:1 for mixing convenience by adding filler. This is fine for gluing operations but not helpful for cloth layups.) This helps a lot with wet-out on lighter weight cloth. Ez-Lam 30 minute has always worked great for me for a variety of jobs and down into 1/2 oz cloth. Using filled epoxy for laminating causes issues because of the (much) higher viscosity. Guys try to get around this by adding thinners. That is a poor substitute. Sure, I've done it and learned it is (much) more work and doesn't always turn out good. In particular, using isopropyl alcohol is a terrible idea. You are trapping water in the resin. If you combine this with colder air temps you can easily create a situation where it never does completely cure. The advantage of West Systems is that since they developed it for boatyards--in unheated boatsheds--they formulate for lower cure temps.

2. You can avoid stress risers in a wing center by using two layers of cloth, such as 1/2 oz. per sq. yard or 3/4 oz. One patch/reinforcement is larger, the other smaller. The edges should not line up. Pick your druthers about which should go on the outside. You will "float the cloth" if you put the larger one on top and likely have a void at the edge of the underlying cloth if the layup isn't awfully wet, or if you don't press the layup with a peel-ply and foam pad technique. You can put the two layers down at different angles and improve the overall strength. You didn't say if you cut the wing out to do this repair or not, or even if it was a full fuse job or a profile, but depending on what you have to work with, you can adapt the reinforcement. Do not run a glass patch clear across the center section planking LE to TE and then terminate at the edge. That focuses--even more than most construction methods--all of the bending stress there, where if you doink it again it will more easily break.

3. For an in-situ wet layup, especially a repair job where things can be bulky/awkward, just paint on the epoxy resin, drape the cloth and do the TP roll method if that is your preference. It works.

4. For a wet layup where maybe you are reinforcing a wing or a fuse--or anything else, for that matter--but especially as part of a normal build, cut all your layers beforehand and lay them out on a table where they won't get snagged or warped (pulled out of square). If you have good access to the whole part, and aren't trying to fold the glass over a small radius, you can just paint on a shiny coat, and drape the layer on. There are techniques to getting it right where you need it. You don't want to be pulling the glass around or it will lose it's shape. If you are doing a second layer, best to lay that on the bench and wet it out on top of a piece of MonoKote backing plastic. Then drape it and the plastic over the area and squeegie with a credit card. (You can wet out all the layers on the bench, stacked one on top of the other, and then drape just once. If your resin control is not real good, this lets you get the excess out before it ever touches the plane.) Leave the plastic on until it cures. If you are going to press it between upholstery foam blocks you can do that next and get a bit of weight on the stack so the glass stays as close to the wood as possible. The idea here is that if you painted on just the right amount, it will leave a very smooth finish on the outside where it was up against the plastic and you won't have much sanding or filling to do. Even more important, you minimize the pinhole problem if you plan on painting. If you sand into the glass fiber during the prime/fill process, you create places where, despite the Volan treatment of the glass, the paint doesn't want to go. Pinholes create more work in final finishing than the entire process combined--if you get them. Be sure to use plastic backer that does not have wrinkles or you will replicate them in your finish. And, be sure that what you use will peel off the epoxy once cured. You can buy peel-ply from ACP, but the MonoKote backer works well.

5. If you decide you have to put another layer of glass down, or want to fill with epoxy resin, then you need to get the gummy surface film off of the prior coat of epoxy. This is the amine blush that bleeds out during curing. Wiping down with lacquer thinner works.

6. There are a lot of reasons that epoxy is preferred over polyester resin. Right at the top of the list to keep in mind is that the polyester catalyst is really dangerous. Sloppy handling leading to contact with the eyes is said to cause near-instantaneous blindness. It is also easy to end up with a "hot" batch when mixed in small quantities which means that your finished part may be brittle. And so on.

7. Guys always are tempted to use epoxy paint to lay something up. I've never seen that work well. (Two cases where club guys tried it and reported their results.) It isn't glue and it isn't laminating resin.

Hope these comments might be of use somewhere along the line

Offline pmackenzie

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Re: Lightweight fiberglass technique
« Reply #21 on: November 26, 2021, 02:06:35 PM »
Polyester resin is fast, and cure speed can be adjusted by how much catalyst is added.
Beyond those advantages, it is basically useless for building aircraft, model or full scale.

- stinks to high heaven
- much more brittle than epoxy resins
- Once cured nothing sticks to it, not even additional polyester resin. Only mechanical bonding is possible.
- Oxygen prevents it from curing. That is why there is "surfacing resin", which has wax in it that floats to the surface to seal it from the oxygen.
    This wax only makes worse the bonding issue.
- Does not properly wet out many composites
- Shrinks when cured, which will warp parts.

Great stuff for doing boat hulls, bondo repairs and hot tubs. Not so much for anything else.

https://www.aeromarineproducts.com/polyester-resin-vs-epoxy-resin/
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Online Brett Buck

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Re: Lightweight fiberglass technique
« Reply #22 on: November 26, 2021, 02:48:04 PM »
As is normal, a lot of this is techncially accurate, but somewhat beside the point. For what David is doing, any epoxy that doesn't set up while he is applying and sopping it up will be good enough. Even .5 ounce glass/epoxy or glass/polyester resin will add tremendously to the strength, far stronger than the original material.

   In fact, you could probably do just about as well with Ambroid or even dope brushed through the cloth, good enough.

    Any port in a storm, just grab whatever you can get your hands on in a few minutes, use good workmanship, it will be fine.

       Brett

Online Mark wood

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Re: Lightweight fiberglass technique
« Reply #23 on: November 26, 2021, 04:44:17 PM »
As is normal, a lot of this is techncially accurate, but somewhat beside the point. For what David is doing, any epoxy that doesn't set up while he is applying and sopping it up will be good enough. Even .5 ounce glass/epoxy or glass/polyester resin will add tremendously to the strength, far stronger than the original material.

   In fact, you could probably do just about as well with Ambroid or even dope brushed through the cloth, good enough.

    Any port in a storm, just grab whatever you can get your hands on in a few minutes, use good workmanship, it will be fine.

       Brett

Yup...
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Why do we fly? We are practicing, you might say, what it means to be alive...  -Richard Bach
The aerobatic airplane is a tool, a pencil, a paintbrush the artist uses to paint their aero art onto the tapestry air with. That art is the combined elements of figures drawn in space and time.  - M. Wood

Offline Shorts,David

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Re: Lightweight fiberglass technique
« Reply #24 on: December 05, 2021, 06:07:38 PM »
Thanks for all the advice. I went with the zpoxy 30 min because Amazon had it. I didn't thin it with anything and maybe should've, but brushed it on, got it all smoothed down, then rolled the toilet paper many times. A little worried about weight gain. I'll have to weigh the wing but I don't want anyone fainting.

Online Mark wood

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Re: Lightweight fiberglass technique
« Reply #25 on: December 05, 2021, 06:27:22 PM »
Thanks for all the advice. I went with the zpoxy 30 min because Amazon had it. I didn't thin it with anything and maybe should've, but brushed it on, got it all smoothed down, then rolled the toilet paper many times. A little worried about weight gain. I'll have to weigh the wing but I don't want anyone fainting.

Pass go, collect $200, be happy.
Life is good AMA 1488
Why do we fly? We are practicing, you might say, what it means to be alive...  -Richard Bach
The aerobatic airplane is a tool, a pencil, a paintbrush the artist uses to paint their aero art onto the tapestry air with. That art is the combined elements of figures drawn in space and time.  - M. Wood

Offline Shorts,David

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Re: Lightweight fiberglass technique
« Reply #26 on: December 05, 2021, 06:55:55 PM »
Pass go, collect $200, be happy.

Thanks Mark.

Offline Jerry Rauch

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Re: Lightweight fiberglass technique
« Reply #27 on: Yesterday at 10:42:43 AM »
I do not want to get into any argument on which to use, epoxy or polyester based resin, but keep in mind that epoxy based will be much much stiffer than the polyester. I have experience in seeing epoxy based resin in carbon fiber get hair line cracks after use. The polyester based resins in the carbon I never saw cracks in the 8 1/2 years I made flat sheets for parts.
Choose wisely...

Online Mark wood

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Re: Lightweight fiberglass technique
« Reply #28 on: Yesterday at 01:20:46 PM »
I do not want to get into any argument on which to use, epoxy or polyester based resin, but keep in mind that epoxy based will be much much stiffer than the polyester. I have experience in seeing epoxy based resin in carbon fiber get hair line cracks after use. The polyester based resins in the carbon I never saw cracks in the 8 1/2 years I made flat sheets for parts.
Choose wisely...

Best way to start an argument is to begin with saying I don't want to start an argument but.... Just saying... I've used both and have never experienced cracking with epoxy when using for purpose epoxy such as West Systems, Epon or Aeropoxy. Other epoxies I've seen issues which is why my go to is West Systems. I've never found polyester particularly good for making light structural parts but is great because of cost for making molds. The biggest key to making good parts is the right ratio of matrix to fiber and it sounds like that ratio isn't correct when you are seeing hairline cracks or the load is higher on the part. It's not an argument or debate, just my experience.
Life is good AMA 1488
Why do we fly? We are practicing, you might say, what it means to be alive...  -Richard Bach
The aerobatic airplane is a tool, a pencil, a paintbrush the artist uses to paint their aero art onto the tapestry air with. That art is the combined elements of figures drawn in space and time.  - M. Wood

Online Tim Wescott

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Re: Lightweight fiberglass technique
« Reply #29 on: Yesterday at 02:18:44 PM »
I didn't thin it with anything and maybe should've

No, that was the right decision.  First, you only want to thin epoxy if you're painting with it, and then only if the thinner has time to flash off from the paint before it hardens -- otherwise the thinner ends up trapped in the epoxy forever, and the epoxy never fully hardens.  In the extreme you end up with something rubbery, weak, smelly, and probably more toxic than hardened epoxy.  Second, unless you're doing something non-critical like fuel-proofing around the engine, you only want to use epoxy that's specifically made for painting (note that I violate this rule all the time -- but all I ever do with thinned epoxy is fuel-proof around the engine, so I'm following my own advise).

The BSI epoxy "finishing resin" seems to work well for me for this sort of task.  It's mixed to be thinner than epoxy glue (so no temptation to thin it), and it has a reasonable pot life.  But like has been said -- any epoxy will do.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Tim Wescott

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Re: Lightweight fiberglass technique
« Reply #30 on: Yesterday at 02:23:04 PM »
... I now know I need to heat the garage-based build closet up above 70 degrees. I plan on bringing the two bottles into the main house and warm them in cups full of very warm water (Hobby Closet is too cold for storing/mixing). ...

Your workspace doesn't need to be warm -- just the space where you cure stuff.  In the winter, when I glue something, it gets done out in the shop (brrrrr, cold), then brought into my office and put on, or hung in the vicinity of the heater, to cure.

I may or may not put the epoxy on my heater for an hour or so to get it to flow enough to dispense and mix, but that's not about curing -- that's about getting it out of the @#$% bottle.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.


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