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Apr 03, 2019, 05:53 PM
Registered User
Thread OP
Question

Help needed with covering with fiberglass


Hi guys,
I'm sure this question has been beat to death in the past, but I'm in need of help covering with 'glass. My first attempt was a disaster, heavy as a brick. Second attempt was better, but I feel still too heavy to fly. So I have never attempted to launch it. Too pretty. So now I'm about to start building a large seaplane that will need to be 'glassed to keep water out. It's the Parkscale Models Albatross in 1/12 scale. There is an old build thread here on the waterplanes forum. Anyway, most have either glassed the whole fuselage or at least the bottom half. What's be best way to cover this monster? And then paint? Failure is not an option on this expensive build.
Thanks,
Jay
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Apr 04, 2019, 02:10 AM
Registered User
mhodgson's Avatar
There are several methods and everyone will have their preffered methods.
My method and I don't claim it is the best/ correct/ only way but because it has worked for me and produced a light, tough and strong surface on my gliders- is as follows.

Sand, fill and sand the surface until it is smooth. The time spent doing this is very important. The better the base, the better the finish.
I do not seal the balsa, the one time I did showed no benefit (personal experience, others will have their own view).
Spray the model lightly with a spray glue, such as 3M77, and lay the glass on. I find it drapes better if the weave is at 45 degrees to the part length. Press it down so it covers the model. Up to you how much you do in one go, one side/whole model etc.
Now mix up epoxy ( a good ratio is to weigh the glass you use and that is how much epoxy you need- again this is what worked for me). I use 24 hour cure.
Now pour epoxy onto the glass and start spreading it with a plastic spreader (old credit card is good). Start in the middle of your glass area and work to edges.
As the epoxy soaks in you can scrape around to cover the glass. I apply quite a lot of pressure to scrape the epoxy about. You leave very little epoxy behind and the scrapping ensures the glass is pressed onto the surface and enough soaks in to bond the balsa but not too much.
Once all the glass is wet out, you know because it goes clear, I then go over again scrapping to the edges.
And no, the weave does not get stretched by the scraping (do make sure the card edge is smooth and corners rounded).
Any wet patches that don't scrape out can be dabbed with paper towel to soak up ( I find this step is rarely needed if the scrapping is done properly).
You should be able to touch the surface and the tissue come away dry.
Leave to cure a 24hours.
Sand off the edges and do the next panel, if any to do.
Once all is glassed I leave for a couple of days to a week to finish curing.
A light sand (light because otherwise you will cut into the glass and ruin the strength of the finish) and it is ready for finishing.
For a water plane I would add another epoxy coat to ensure it is waterproof. On my gliders I use varnish to fill the weave as it easy to cut back. If painting then a filler/primer would be good.
Where strength is important I never thin epoxy.
A little thinning can help on very curved surfaces or, my preffered way, WARM the epoxy up with heat gun as you spread it. In tight corners, or inside motor cowls a brush is obviously the better tool for spreading.

As said that is how I do it, others will have theirs. It has proven easy to apply, minimum tools and mess, and above all light. It has worked well on my gliders.
Apr 04, 2019, 10:54 AM
The Junk Man
I do much as the above poster.

The REALLY important thing is to keep down the resin to cloth ratio. Never use a brush to apply epoxy. The credit card scraper method makes sure you don't leave excess epoxy in the fabric weave. You literally cannot scrape off too much, the resin remains in the weave.

I always bias cut the glass cloth. Makes it MUCH easier to conform to curves.

If you have the equipment, vacuum bagging is the easiest way to get light parts, but this is not an option for some things like complex fuselage shapes.

Last, make sure you are using the right cloth. The best supplier I have found (and happily used for years) is Thayercraft. All prices include shipping and he ships rolled, not folded. I use the 0.73 ounce stuff a LOT.

https://www.thayercraft.com/fiberglass-for-models.html

Tom
Apr 04, 2019, 05:36 PM
Registered User
Thread OP
Thanks guys. Nothing I've never heard before except for the spray glue and cutting on a bias. I did thin my last project and it turned out much better, lighter. I'm always afraid of breaking the balsa sheet by pushing too hard scraping. I did use tissue to soak up lots of excess epoxy. But it still turned out so heavy I'm afraid to fly it. Probably have a glide ratio of a brick!
Has anyone had success getting film covering to stick to epoxy?
Apr 05, 2019, 10:54 AM
Registered User
Try this tutorial
Fiberglassing Tutorial (17 min 20 sec)
Apr 05, 2019, 07:16 PM
Registered User
Thread OP
That's a good video. But nothing I haven't tried before. Lol! I think it still came out heavy. I'm excited about starting this build, but I don't have a large enough building bench. I think just the fuselage is 63", and the wing is 96"! I may have to use the dining room table and that may lead to divorce! I may end up buying an interior door to build on, leave the car in the barn, and build in the garage. Still waiting for motorcycle season in Indiana...
jay
Last edited by flying jeep; Apr 05, 2019 at 07:46 PM.
Apr 05, 2019, 07:31 PM
The Junk Man
Actually, it's not.

For several reasons.

First, he is using a low quality epoxy glue formulation as laminating resin.

In order to make the thick glue work at all, he then compounds his error by thinning it to 'water" consistency. EVERY SINGLE MANUFACTURER of epoxy resin recommends against thinning at all and if really pressed will sometimes say that if it absolutely HAS to be thinned, never thin more than 5%.

Next he holds up a small balsa wing and says he put THREE COATS of epoxy on it. Wow. You can tell he is building model boats with no regard to weight instead of aircraft right there.

Next, you don't need brand new scissors to cut cloth. A pair can be "fiberglass cloth" sharpened in seconds on a belt sander. I have several pair that have been in use for literally decades. A quick touch on a belt sander and they cut cloth like butter with their now micro serrated blades.

Next, he slathers on epoxy with a brush.

After that, I just quit watching. That is just about the worst epoxy application video for model aircraft i have ever seen.

Tom
Apr 06, 2019, 01:19 PM
Dinosaur
Twodor's Avatar
I concur with Tom. The method shown above might be fine for boats, models or full size but an aircraft covered as shown will weight about half again what it should have weighed.

I never thinned my resin but I did remove much of what I put on by using the old tried and true, 'Toilet Paper' method. Worked well for me for many years. It makes sure the cloth is adhered to the surface being covered and absorbs the extra, un-needed resin reducing the weight. A second light resin coat might be needed to fill the cloth weave but most of that will get sanded off if you do it right. Just do not sand into the cloth weave.

Tom
Last edited by Twodor; Apr 06, 2019 at 01:26 PM.
Apr 12, 2019, 11:56 AM
Play that funky music right
kenh3497's Avatar
I agree 100% using the credit card and scraping the epoxy around. Toilet paper or paper towel if you have a little excess to get rid of. I personally have never use any spray adhesive to "tack" the cloth down with and for me see no reason to do so.

I cover using glass in the same manner as I would if using plastic film. Wings, trailing edge where the ailerons go, bottom, then top. The fuse gets the bottom, sides, then the top unless it makes sense to include the top and sides as one.

Ken
Apr 14, 2019, 09:10 AM
Registered User
mhodgson's Avatar
Spray glue.
Should have mentioned I don't use it when covering wings and tails.
With fuselages however I do. I find I can completely cover the fus, often in one piece of glass with the seam on the bottom and then apply the resin. Where there are 2+ layers of glass I warm the epoxy and might use a short brush to stiple the resin into the cloth but then the card to scrape off the excess and spread.
Nov 19, 2019, 10:43 AM
Registered User
seiser01's Avatar

Fiberglass methods


Quote:
Originally Posted by T_om
Actually, it's not.

For several reasons.

First, he is using a low quality epoxy glue formulation as laminating resin.

In order to make the thick glue work at all, he then compounds his error by thinning it to 'water" consistency. EVERY SINGLE MANUFACTURER of epoxy resin recommends against thinning at all and if really pressed will sometimes say that if it absolutely HAS to be thinned, never thin more than 5%.

Next he holds up a small balsa wing and says he put THREE COATS of epoxy on it. Wow. You can tell he is building model boats with no regard to weight instead of aircraft right there.

Next, you don't need brand new scissors to cut cloth. A pair can be "fiberglass cloth" sharpened in seconds on a belt sander. I have several pair that have been in use for literally decades. A quick touch on a belt sander and they cut cloth like butter with their now micro serrated blades.

Next, he slathers on epoxy with a brush.

After that, I just quit watching. That is just about the worst epoxy application video for model aircraft i have ever seen.

Tom
Tom,

While we all appreciate different points of view and advice, I personally don't when it takes on a tone of judgment.

That being said, it is widely known that the strength of epoxies is reduced by thinning with alcohol. However, the resin is being used in an application that does not require great strength. Further, the thinning, in this case, reduces the amount of resin that is actually applied making the structure lighter. It also affords the builder the luxury of applying the resin with a brush since it now auto-leveling due to the reduced viscosity. Self-leveling is greatly desired especially since it minimizes sanding and promotes a naturally smooth finish.

In addition, the thinning allows the resin to permeate the balsa to a greater degree thus creating a harder substrate to back up the now-laminated cloth.

In the end, we all will have a preferred method of fiberglass application and that is a preference. Whichever method we use is fine as long as it does the job that we want it to. If the finish achieves the goals of the modeler, then it is a good finish regardless of the method used to obtain it.

Also, I appreciate the time and effort put forth by individuals who make videos and document processes to share with others so that we may benefit from their experience.
Nov 19, 2019, 11:18 AM
The Junk Man
Quote:
Originally Posted by seiser01
Tom,

While we all appreciate different points of view and advice, I personally don't when it takes on a tone of judgment.

That being said, it is widely known that the strength of epoxies is reduced by thinning with alcohol. However, the resin is being used in an application that does not require great strength. Further, the thinning, in this case, reduces the amount of resin that is actually applied making the structure lighter. It also affords the builder the luxury of applying the resin with a brush since it now auto-leveling due to the reduced viscosity. Self-leveling is greatly desired especially since it minimizes sanding and promotes a naturally smooth finish.

In addition, the thinning allows the resin to permeate the balsa to a greater degree thus creating a harder substrate to back up the now-laminated cloth.

In the end, we all will have a preferred method of fiberglass application and that is a preference. Whichever method we use is fine as long as it does the job that we want it to. If the finish achieves the goals of the modeler, then it is a good finish regardless of the method used to obtain it.

Also, I appreciate the time and effort put forth by individuals who make videos and document processes to share with others so that we may benefit from their experience.
Your appreciation of my "tone" matters much less to me than you apparently think. And who, exactly, is the "we" you speak of in that statement, a mouse in your pocket?

I don't care if he hired Cecil B. DeMille's grandson to shoot the video, his "experience" is apparently directed at furthering poor glassing methods. Just because someone makes a video doesn't mean the video demonstrates correct technique or methodology. The video is still promoting VERY POOR fiberglass composites techniques.

And saying "If the finish achieves the goals of the modeler, then it is a good finish regardless of the method used to obtain it." is patently ridiculous when the stated result of the instructions claim to be PROPER composite methodology to achieve the best result for model aircraft. The "modeler" should adjust his/her "goals" if they settle for what they will get from that video. They can do better.

And one more note about how well the thinned out epoxy is "permeating" wood as you, and some others, claim. You need to read some of the technical papers published by the Gougeon Brothers (WEST System Epoxy) and other formulators concerning wood being "saturated" by epoxy. It doesn't. Same with regular old white glue watered down with tap water. The WATER will soak into the wood, but the resins in the glue will not. So, having ruined the epoxy's characteristics (the characteristics that made you pick epoxy to begin with) by using grossly excessive dilution, all you get is the alcohol soaking into the wood, NOT the actual resin. You gain nothing. And end up with rubbery, weak coatings.

And that has been shown time and time again by manufacturers and resin formulators.

So if you have any valid references for claiming the poor techniques illustrated in that video are CORRECT methods, let's see them.

Tom
Nov 20, 2019, 07:36 AM
Registered User
There are many ways to fiberglass a plane and they all work for the guy doing the job. For me, the credit card scraping method is quick, neat, and helps to keep the plane light. Watching the toilet paper method made me shudder. However; it works for that guy.

I will never thin any epoxy. I use Bob Smith Industries "Finish cure" 20 minute epoxy. This stuff is so thin it's like water. It also sands very well. I've used 45 minute epoxy and also old timey polyester finishing resin and Finish cure is vastly superior.

Carl
Nov 20, 2019, 10:04 AM
The Junk Man
Quote:
Originally Posted by carlgrover
There are many ways to fiberglass a plane and they all work for the guy doing the job. For me, the credit card scraping method is quick, neat, and helps to keep the plane light. Watching the toilet paper method made me shudder. However; it works for that guy.

I will never thin any epoxy. I use Bob Smith Industries "Finish cure" 20 minute epoxy. This stuff is so thin it's like water. It also sands very well. I've used 45 minute epoxy and also old timey polyester finishing resin and Finish cure is vastly superior.

Carl
Yep, the proper way to thin epoxy laminating resin is to use THIN laminating resin to begin with. Look at the data sheet for the epoxy you intend to use. Look for the "CPS" rating of the epoxy. CPS (sometimes just listed as CP) stands for Centipoise, the measurement unit of viscosity.

I am including a chart of common liquid viscosity measurements.

And beware epoxy companies touting their resins as "thin" with no data sheet to back up their claims, because in many cases is is pure bullsh|t sales hype.

For example, WEST System 105/205 resin/hardener series epoxy has a CPS of between 1000 and 1200. The resin I use most often, Adtech 820, has a CPS rating of 500 to 600 TWICE as thin as WEST. (The numbers vary according to the hardener used.)

System Three is about 950 CPS
MAS (who shout out how "thin" their epoxy is) is about the same as WEST, 1000 CPS. Not thin at all.
Resin Research Composites Pro resin averages about 600 CPS while their "regular" resins are about 1000 to 1500.
MGS, the superstar amongst resins in the aircraft industry, lists their resins and hardeners separately, their L285 being 600-900 with the hardeners 80 to 100, so the mixed viscosity will be in the 500 to 600 range.
WEST Pro-Set series LAM-125/129 has a mixed CPS rating of about 642

If you want thin epoxy, buy thin epoxy and get the performance you are paying for instead of trying to make a silk purse out of a sow's ear.

Tom
Last edited by T_om; Nov 22, 2019 at 10:12 AM. Reason: Added WEST Pro-Set to the list
Nov 21, 2019, 12:16 PM
Registered User
Dave Platt made a video on building and fiber glassing, which may be available on DVD. May still be available somewhere.
As to using standard modeling epoxy for such, personally I don't use it. Instead I use West Systems 105 resin/206 hardener as they are of such low viscosity, they don't need thinning. Gougeon Bros. strongly advise against thinning with alcohol or other solvents. Some people have even used rubbing alcohol, which is a foolish mistake as it contains water and a small amount of oil.
The hobby epoxies we buy are cheap and meant to be used for attaching heavy parts such as motor mounts, fire walls and dihedral braces.
The late Ron Bush, who owned Balsa USA told me they used CA even for attaching firewalls.


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