Opinions Sought: Mylar film or Peel Ply for glassing tubes

[Zbench]

I'm looking for opinions on which method is best for fiberglassing tubes. I have experience with using mylar film and a credit card to get a smooth surface when smoothing out epoxy on a glassed tube. Its not a perfect process as trapped air bubbles can be a bear to get out to the ends.

I've read about peel ply, some other type of impervious film with holes to allow air to escape. I have almost bought it 3X, but would like to know if its any better? Seems like its designed for use with a vacuum bag, but how does it fair when used in the manner of mylar film? Is the air easier to get out? Leave less voids on the surface that need filled? My concern is you can't see through it like Mylar so perhaps there are just as many air voids after because you cant see them.

Interested in the collective wisdom. And thanks in advance for the notion of "Just use fiberglass tube", but I have a lot of projects requiring glassed cardboard.

 

[John Kemker]

Look at Soller Composites ( https://sollercompositesllc.com/shrink-tubing/ ) and their heat-shrink clear tubes. No vacuum needed.

 

[rharshberger]

I'm looking for opinions on which method is best for fiberglassing tubes. I have experience with using mylar film and a credit card to get a smooth surface when smoothing out epoxy on a glassed tube. Its not a perfect process as trapped air bubbles can be a bear to get out to the ends.

I've read about peel ply, some other type of impervious film with holes to allow air to escape. I have almost bought it 3X, but would like to know if its any better? Seems like its designed for use with a vacuum bag, but how does it fair when used in the manner of mylar film? Is the air easier to get out? Leave less voids on the surface that need filled? My concern is you can't see through it like Mylar so perhaps there are just as many air voids after because you cant see them.

Interested in the collective wisdom. And thanks in advance for the notion of "Just use fiberglass tube", but I have a lot of projects requiring glassed cardboard.

You can get clear Mylar, Duralar is a type of mylar used for drafting.

 

[Zbench]

The shrink wrap type is intriguing. As I noted above, I have and use clear mylar. Looking for opinions if clear mylar is better or not as good as peel ply. Anyone?

 

[tfish]

The paint is to thick to fill the tiny holes. You can fill those pin holes by rubbing in either epoxy of automotive primer into them...with a gloved finger.. I like using sandable automotive primer..Rustoleum..spray on..until paint is runny..work paint into pinholes. Sand between filling coats. It's pretty quick to do and the primer is easy to wet sand.
I normally thin the heck out my epoxy before adding the peel ply..that helps prevent most of them.

Tony

 

[rharshberger]

The shrink wrap type is intriguing. As I noted above, I have and use clear mylar. Looking for opinions if clear mylar is better or not as good as peel ply. Anyone?

IMO peel ply is better as is forms to the tube better and I get fewer air pockets, when using mylar I have gotten some fairly good sized air pockets that required filling. I use permiable peel ply and sand after cure, the reason is I know that I have gotten good wet out of the glass underneath.

 

[rokit]

Surprised no one's mentioned this yet:

"The Jarvis Illustrated Guide to Carbon Fiber Construction" and "Part 2 of The Jarvis Illustrated Guide to Carbon Fiber", both by Jim Jarvis.

Probably a lot more than what you were looking for, but he uses peel ply and has lots of photos.

Is what you're referring to actually peel ply, or a perforated release film?

 

[JohnCoker]

Release fabrics can be used without a bag. I like the Teflon-coated release fabric; it leaves a light grid surface, rather than a smooth surface though. The thin plastic peel ply with little holes which leaves a smoother surface. They also make non-porous Teflon-coated fabric.
https://www.aircraftspruce.com/catalog/cmpages/vb7025.php
https://www.aircraftspruce.com/catalog/cmpages/vb7039.php

Obviously, Mylar is too stiff to be used in a bag.

 

[Zbench]

John, thanks for opining. Does the use of either of these make the removal of air pockets easier than by endlessly manipulating the surface with a credit card to get out trapped air bubbles? That’s the main goal and the reason for the inquiry.

 

[Banzai88]

I've used both mylar and porus peel ply as a wrap for fiberglassing tubes several times, as well as the shrink tube once.

Will never, ever use mylar ever again.

 

[rharshberger]

John, thanks for opining. Does the use of either of these make the removal of air pockets easier than by endlessly manipulating the surface with a credit card to get out trapped air bubbles? That’s the main goal and the reason for the inquiry.

Peel ply is a porous coated polyester or nylon material that allows excess epoxy to wick through it so that when you peel it off it leaves a slightly sand like surface (very fine) the advantage to peel ply IMO is that it allows you to apply the epoxy heavy then squeegee off the excess through the peel ply material, which when fully wet out changes color typically (at least the ones I have used do) allowing me to see areas not fully wet-out. It is still possible to remove too much epoxy through the peel ply though causing small pin holes, one nice thing about the peel ply finish is I can go back and coat the whole tube with a thin layer of epoxy and get the smooth finish I want or l can sand it lightly and prime then paint. The perforated teflon release films work better than mylars but I have not had as good of luck getting nice finisheds with them unless I am vacuum bagging flat surface like fins.

 

[JohnCoker]

Does the use of either of these make the removal of air pockets easier than by endlessly manipulating the surface with a credit card to get out trapped air bubbles? That’s the main goal and the reason for the inquiry.

Release fabrics are more flexible than Mylar and porous fabrics allow the air and excess resin to pass through. However, I have not done this for surface finishing. (The usual reasons to use release film and vacuum bagging are to produce an optimal layup and leave a matte surface for further bonding.) The Mylar preserves the excess epoxy and creates a smooth surface over most of the tube (aside from the inevitable bubbles).

Your original idea of trying "peel ply" (thin plastic film with punched holes) is definitely worth trying.

 

[Zbench]

So we are giving this a go. I bought some sleeve material from Soller composites and created some hubs on a piece of 1/2” steel conduit.

I applied a liberal layer of Silvertip once the sleeve was stretched on the 3” tube. I applied it with a Harbor Freight 2” chip brush. This is my first time using the fiberglass tube and I have to say it’s a joy to use compared to regular fiberglass fabric. No loose edges or other defects to worry about.

After the whole assembly was wetted out I layed a piece of the teflon coated release film on and carefully smoothed it on the wet tube. It was pretty wild the epoxy wicked through the fabric and it was also translucent so I could see the tube underneath. Using latex gloves I worked it all the way around and I noticed that the excess epoxy wicked through all around.

It’s curing now. Here is a closeup of a section of the tube. Excited to see the result. There is a splice in the tube which you can see below.

 

[SolarYellow]

I'll defer to Jarvis, if he has it all detailed out in his PDFs. But just to summarize the clarifications in terminology that have been made in this thread, as I understand them:

"peel ply" is the textile cloth that is meant to go directly against the layup. When it is peeled off after cure, it leaves a rough, textured surface that promotes adhesion of whatever comes next. There's more to it, but that's at a very high level.

"release film" is the perforated sheet that is an impermeable sheet with holes punched in it. These holes allow air and some amount of resin to flow through during a vacuum bag process. The size and number of holes may be important for regulating how much resin flows through, but that's beyond any decisionmaking I've been involved in. I'm sort of speculating there; I haven't seen the hole density used as a layup variable, but I have pretty limited experience with this stuff in industry. The epoxy or other matrix resin cannot stick to the release film, and it peels away from the cured layup easily, leaving a smooth and shiny surface on the outside of the peel ply. The holes are generally small enough that the "glue rivet" passing through them fractures when unbagging the layup. There is occasionally some extra trouble with the glue rivets wanting to hold together and tear the release film as it is removed.

"breather" is a layer that goes between the release film and the vacuum bag. It allows air to move around the part, preventing the bag from prematurely sealing areas that become a bubble. Air passes through the peel ply, then through a hole in the release film, and then through the breather layer to get to the vacuum fitting point on the bag.

One could, perhaps, use a breather layer directly against the peel ply, but it would likely absorb too much resin out of the matrix, starving the structure. In addition, the breather would become excessively saturated and be very stiff and difficult to separate from the layup. Would it peel off the peel ply, or would it pull the peel ply off the part prematurely? Or a messy combination of both?

Ideally, vacuum bagging a layup not only compresses the fiber plies and makes the layup thinner and smoother, it also regulates the resin matrix to a near-optimum percentage of the composite material, maximizing the efficiency of the structure.

Vacuum bagging with just peel ply to vacuum bag film will generally give a nicely compressed layup with smooth surfaces, but at least on larger layups, it still risks capturing bubbles. And because excess resin would have to flow through the sheet of the layup, it's probably not going to be squeezed out. It will just be smooth, but you can still end up with too much resin. Adding the release layer and breather layer ensures that both air and resin can be separated from the layup as required for an optimized result.

If you're not bagging it, you almost certainly are choosing between excess porosity due to not enough resin and too much resin for optimum strength in order to get a smooth surface.

 

[Zbench]

I used this release film as recommended by John:

The results are really good and I had some key learnings:

1) apply more that what you think is enough epoxy. I knew this from work with regular fabric and put on what I thought was more than enough. I used 215g of total epoxy for the 425 square inches I needed to cover. .5 gram per square inch is a good benchmark. I only had a few places that I could see the twill after the release film was pulled.

2) The film is porous but not endlessly so. I only had trapped air where the film overlapped at the seam. I suspect the double layer of film at the seam didn’t allow all the trapped air to diffuse out of the assembly. Next time I’ll minimize this as much as possible. An inch should be plenty.

All that said, I consider the results a success. Much less areas to fill than when using Mylar and next time i would expect the results to
Be near perfect.

Below is a shot of the film as it’s being pulled from the assembly and the resulting surface finish. Hope this helps someone who wants to try this approach. It’s a worthy endeavor.

 

[Banzai88]

I used this release film as recommended by John:

The results are really good and I had some key learnings:

1) apply more that what you think is enough epoxy. I knew this from work with regular fabric and put on what I thought was more than enough. I used 215g of total epoxy for the 425 square inches I needed to cover. .5 gram per square inch is a good benchmark. I only had a few places that I could see the twill after the release film was pulled.

2) The film is porous but not endlessly so. I only had trapped air where the film overlapped at the seam. I suspect the double layer of film at the seam didn’t allow all the trapped air to diffuse out of the assembly. Next time I’ll minimize this as much as possible. An inch should be plenty.

All that said, I consider the results a success. Much less areas to fill than when using Mylar and next time i would expect the results to
Be near perfect.

Below is a shot of the film as it’s being pulled from the assembly and the resulting surface finish. Hope this helps someone who wants to try this approach. It’s a worthy endeavor.

View attachment 633521

Yup, that's it in a nutshell. Pic and description looks like every tube I've done since switching to peel ply, and I'm much happier over using mylar.

 

[cls]

Nothing like facts to end an argument!

 

[jderimig]

I have used them all. Peel fabric, perforated mylar film both with vacuum, and perforated shrink tape and heat gun. If i were doing anything but a round tube I'd use the traditional peel ply. For tubes, perforated shrink tape is the way to go.

 

[Zbench]

I have used them all. Peel fabric, perforated mylar film both with vacuum, and perforated shrink tape and heat gun. If i were doing anything but a round tube I'd use the traditional peel ply. For tubes, perforated shrink tape is the way to go.

Never heard of perforated shrink tape. Care to tell more and share a source?

 

[jderimig]

Never heard of perforated shrink tape. Care to tell more and share a source?

I got mine from Robert DeHate. Here is a company that makes it. Let me see if I can find a retail source.
https://www.shrinktape.com/resources/news/perforated-tape-sticking-to-the-facts/

Edit: However I don't think you need the perforations, the excess resin will ooze out between the layers. I use it because it seems I have a lifetime supply of it.

 

[John Kemker]

I got mine from Robert DeHate. Here is a company that makes it. Let me see if I can find a retail source.
https://www.shrinktape.com/resources/news/perforated-tape-sticking-to-the-facts/

Edit: However I don't think you need the perforations, the excess resin will ooze out between the layers. I use it because it seems I have a lifetime supply of it.

Found a retail soruce source

https://compositeenvisions.com/product/hi-shrink-tape-100-yards-release-coated-220r/

 

[John Kemker]

Wow. Lots of sources. FiberGlast has it, as well:

https://www.fibreglast.com/product/Shrink-Tape

 

[jderimig]

Wow. Lots of sources. FiberGlast has it, as well:

https://www.fibreglast.com/product/Shrink-Tape

I don't think that one is perforated. Again I not sure the perforations are need but it lets gases out.

 

[tfish]

but it lets gases out.

...and unwanted/needed epoxy.

Tony

 

[JimJarvis50]

If anyone is interested, here are links to the process I use. There is a Part 1, Part 2 and then an Addendum to the things I would now do differently.





A few years back, I got some tutoring from Mick Kelly on the mylar method that he used for making tubes (some really nice ones). I was not able to make it work for me, but obviously he did. It's attached.

Jim

 

[John Kemker]

but it lets gases out.

So does pulling my finger. [grin]

 

[tfish]

I've been following John Coker and Mick for a few years. I've gotten fairly good at laying up tubes. I've done 29mm to 6". You get better with each tube. I work with a local high school's rocket STEM program and usually each year, one group wants to build a 54mm min dia rocket.
My normal layup is... 1-2 layers of thin mylar on the mandrel..only tape the ends of the at the ends. No tape under the layup. 4-6 layers of 6(ish) oz glass. 2 layers of pourus Teflon peel ply. Raka Boat epoxy HP 900 632 hardner...thin with denatured alcohol as needed. Make sure the last layer is pretty sloppy wet..to prevent voids or pin holes.
The last photo shows how wet..drippy coming through the peel ply.
You can add art work under the last layers of glass. The 'NASA rocket' was part of NASA grant outreach/internship thing. It was built at a city park..7 - 2 hour sessions..

Tony