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Plastic peel ply


John Slade

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The following are my recent posts to the CA-mail list concerning plastic peel ply. Some of the text below "didn't make it" to the public posting.

 

> Unless there is something else being used that is new, better or

> different, the term "plastic" in this dialogue, may simply be a generic

> term. I suspect it's still Dacron or some other similar material.

No. What Bulent and I are talking about here is the use of clear 6 ml plastic sheeting, as found in home depot, on top of the finished layup and any standard cloth peel ply. The technique has been described as "poor mans vacuum bagging". The plastic sticks to the wet epoxy and shows up bubbles very well. Squeege over the plastic with a little help from a hair dryer and you can watch the bubbles run along in front of you're squeege and out the edge. Wet the squeege with epoxy for a better slide over the plastic. The air can't get back in because of the seal caused by the plastic. Lots of excess epoxy can be removed this way for a very tight, compact and lightweight result. Do not press too hard because air can be sucked back into the layup through the foam - you'll see this when it happens because the area goes dark when you squeege it, then goes white again. If this happens lift the plastic and add more epoxy. After cure the plastic comes off in an instant and you have a very smooth, almost moldlike finish. I describe this in detail in my web page "tips and tricks" section. http://kgarden.com/cozy I first saw this at Bulent's shop 3 years ago after finishing my fuselage sides. I've used it ever since. The airframe is now finished and in gloss. The only place I saw pin holes was in the parts I did BP (before plastic).

Try it once. You'll never go back.

 

> I'm sure John Slade would jump in but... The technique is to use

> your basic

> peel ply and then cover that with a plastic sheet - 3mil plastic

> drop sheets

> at Agent Orange (Builders Depot) or equiv. (see

> http://kgarden.com/cozy for a

> more in depth explanation).

 

Actually, I find the 3mil too thin. 6 Mil works better. Doesnt wrinkle up as much.

The 15% reduction was in the weight of the layup. I subtracted the weight of the foam in each case.

 

> (created by getting all of the air out) would actually pull the

> layup off of the foam.

Hmmm. I never heard of (or saw) anything like that.

 

> so do some test layups and destroy them with a spring guage

> in shear, torsion and tension (I couldn't find a difference).

Wouldnt hurt, just to make you feel better.

 

> I suspect I am missing something that makes your process worthwhile. Can

> you explain it again for me please? Thanks

Yes, Art. What I think you are missing is that significant compression DOES take place. With the squeege sliding on plastic the fibers are squeezed. Air can't get back in, so they stay squeezed. Its hard to get a dry layup this way, and its very obvious when you do. The color change from light to dark as the squeege passes tells you everything. Air bubbles are being displaced. The gloss finish is very easily scuffed up for bond since there is no weave to deal with. I think we had the best suggestion earlier - try it on some test pieces and do structural tests. Prove (or disprove) the technique with practical experiment rather than theoretical science.

 

> You are the one who has been quoted as having reduced your part weight by

> 15% using this method, not me.

 

Wrong. I said:

"The 15% reduction was in the weight of the LAYUP."

 

You said:

"Vacuum Bagging ...they consistently reduce the weight of PARTS

made that way by 25%."

 

Apples and oranges, even at grade school level.

 

>I am telling you that if you use those parts in your airplane, you are

>risking creating a great deal of pain and sadness for those who love you!

 

Ahha! the old scare tactic, commonly used to assert the status quo when innovation rears its ugly head. Usually indicates the end of a discussion.

 

The plane is almost finished, Art. I'll "drop in" and give you a demo one day.

 

Note: See my web page, http://kgarden.com/cozy/chap20.htm for pictures and discussion of this method.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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  • 1 year later...

ok john, i can't let things go in my head, 2+2 always has to = 4, our sides were deemed just enough epoxy by our teck advisor, we used plastic on the sides and bottom and some other parts but it was thinnnnn plastic wrap, very hard to get the bubles out. if i wasn't near completion, i would switch to your method.

 

does the plasyic come on rolls without folds/creases to mess with?

 

enjoy the build

 

mike

maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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Ok, I've been wondering about this for a little while and would like to clarify it.

 

You wrote:

"the gloss finish is very easily scuffed up for bond since there is no weave to deal with"

 

So am I understanding it right that parts made with plastic peel ply still need to be sanded? Do you use Dacron where a structural joint will be or is sanding adequate?

 

Thanks

Drew Chaplin (aka the Foam Whisperer)

---

www.Cozy1200.com - I'm a builder now! :cool:

---

Brace for impact...

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So am I understanding it right that parts made with plastic peel ply still need to be sanded? Do you use Dacron where a structural joint will be or is sanding adequate?

 

Correct. The surface is too smooth to get a good bond. In areas where peel ply is called out in the plans I added the dacron, then used the plastic on top of that. Just sanding it would probably be ok, but I used the dacron to be sure.

 

By the way, I picked up the folowing source for rolled plastic from the Cozy list, compliments of Joe Hull. I never had much of a problem with the creases myself because warming with a hair dryer usually eliminates them, but no creases at all might be a bit easier.....

 

Trinity Packaging (www.tripack.com)

1358 Charlestown Ind. Dr.

St. Charles

Missouri, 63303

 

Phone: 800-873-4610

Fax: 636-724-1801

 

Part No: CF404C 4ft x 100ft x 4.0mil Clear Poly Sheeting

Specify rolled with NO CREASE.

 

It was about $20 a roll.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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I guess this must be an Canadian/American thing because 6 mil poly in 4 ft. rolls (actually, its 8 ft. wide with a single crease) is available by the bucket load at any home improvement store up here. It's normally used as a vapour barrier that goes on over top of the insulation in home construction. I would think that it would be available at such stores in the northern states at least.

 

I have about 20 ft. of it left over from building my shop.

Rui Lopes

Cozy MkIV S/N: 1121

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Hello fellas:

 

Using plastic or peel ply should not be confused with the need for prep sanding.

 

No matter if you're using plastic or peel ply, do yourself a very big favor and prep sand all areas prior to glassing in the next layup. Prep sanding helps to "wake up the molecules" and helps get rid of contaminants from the oils on your fingers and from the surface finish from most epoxy systems.

 

...Wayne Hicks

Wayne Hicks

Cozy IV Plans #678

http://www.ez.org/pages/waynehicks

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So does some sanding still need to be done before proceeding [after dacron peel ply]

 

Theoretically no, but it sure can't hurt provided you dont overdo it and damage the threads. Especially if the area has been exposed to the air and/or potential contaminates (like you're fingers) since you took the peel ply off.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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Since we are on the topic of surface prep.. What are you all doing AFTER sanding the area.. I have been using the shop vac to get up the dust, then using a bit of dish soap and Hot water on a clean towel, then rinsing the same area with another towel with hot water again. After that, drying the area with hair dryer or space heater and make sure it is good and dry before commencing the next layup. All this done, just prior to doing the layup so the area will not be contaminated..

 

What other Techniques have you been using?

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I'd say you're overdoing it, John. I used to sand with 60 grit, then just blow the area off with an air hose. Sanding removes contaminates, and a few particles of DUST will tend to just go disappear into the epoxy and form part of the layup.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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Stop washing, the plane is made out of dust, micro and flox.

 

Just vacuum well, keep oils and silicones out of your shop and your hands clean and you are there

 

enjoy the build

 

mike

maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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I knew I read it some where about surface prep washing....

Last paragraph

 

 

 

 

Basic Composite Construction

Sport Aviation 8/99

By Ron Alexander

 

Over the past few months we have discussed most aspects of building a composite airplane. This article will focus on a few specific items that require explanation such as proper preparation of parts prior to bonding, post-curing, blushing problems, etc.

 

Preparation of Composite Parts

In the last issue, I outlined a brief procedure for preparing composite parts prior to bonding. This step is most important and needs to be amplified. The quality of a bond is directly affected by the preparation of the two parts being joined together. If contamination exists on either part, the bond may be weakened even to the point of subsequent failure. Let me emphasize that you should follow the directions found in the kit manufacturer's manual regarding proper cleaning techniques. However, the preparation procedure is important enough to warrant more detailed discussion.

 

First of all, when bonding to an outside mold surface (such as many of the parts you receive from the kit manufacturer) cleaning and sanding of the parts is always required. When aircraft parts are molded, a release agent is applied to the inside of the mold itself allowing the part to be removed when cured. This mold release agent must be removed prior to any bonding activity. The agent is barely visible. Water will usually remove this agent. After removal of the agent and any contaminants, sanding is then accomplished.

 

Any surface that is smooth because of being next to a mold must be sanded prior to bonding. Any primer that may be present must also be removed. Sanding is generally the accepted way to prepare the surface. Opinions vary on the proper grit of sandpaper to be used. Usually 80 grit to 180 grit is recommended. Our workshop experience has shown that 180 grit sandpaper is usually satisfactory to prepare the surface. Use of 180 grit will ensure the underlying fibers are not damaged or cut. The surface should be thoroughly abraded (roughed) to completely remove any glossy areas.

 

Abaris Training, located in Reno, Nevada, instructs the military, airlines and aerospace industry on composite construction and repair. I consult with Mike Hoke, the President of Abaris, regularly concerning composite construction. His company is considered to be one of the leading composite training companies in the United States. The following quote was taken directly from their training manual regarding surface preparation. "High surface energy is the goal, not mechanical roughness. One must shear up the top layer of molecules on the surface, creating many broken bonds, without damaging or breaking underlying fibers. A water break test can be used to determine surface energy. If surface energy is high, clean distilled water will spread out in a thin uniform film on the surface, and will not break into beads. If a water break free surface can be maintained for 30 seconds, one has achieved a clean, high energy surface suitable for bonding. If the surface is contaminated or at low energy, the water will break into rivulets and bead up. "Note that tap water will not work. It is dirty enough to contaminate the surface itself, and one will never pass a water break test using it. "It is important to note that the 'high energy"'condition, once achieved, is short-lived. Within about 2-4 hours the effect is lost. In composites, one should therefore wait as late as possible in the process before surface abrasion is performed, so that all else is ready and the adhesive can be quickly applied."

 

Dry the water off of the laminate with a hair dryer prior to applying the adhesive. If it is wiped with a cloth it will likely contaminate the area again. Do not use a heat gun for this process. The heat is too intense and may damage the cured resin. This process also applies to peel ply surfaces. Even though a peel ply surface fractures the top layer of resin, it leaves a glossy, low energy surface in the weave pattern of woven cloth. This must be abraded for proper bonding.

 

So, how should you clean parts prior to bonding? The best procedure is to simply sand the surface, as discussed, and follow by a thorough cleaning with soap and water. If you are using solvents, use them initially to remove contaminants and then abrade the surface. Follow by soap and water and then immediately dry using a hair dryer. Remember to begin the bonding process within a few hours after preparing the surface.

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OK ron teaches this stuff, but this is not specific to faom and fiberglass construction.

 

we have been warned by Nat previously on the use of solvents, they can disolve the foam underneath and cause delamination, etc.!

 

"If you are using solvents, use them initially to remove contaminants and then abrade the surface. "

 

Nats plans, i would bet my bottom dollar on burts plans do NOT call for soap and water in this method of construction.

 

Now the post talks about purchased parts, who knows what they did to them in thier shop??? the only item we purchase that might qualify for this treatment whold be the landing gear strut and the front nose gear cover, no foam there, wash away. Nothing else would need this, in my opinion, radical treatment.

 

you are washing fiberglass/foam, are you contaminating the foam with moisture that you are not noticing??

 

Johns method is a "tweek" to the plans method of working with foam and fiberglass, not a change.

 

thousands of planes have been built with this method, with great results, tweek is fine, total change and intrudicing other items, i feel, would be risky.

 

In our shop we keep the oils and solvents away from all glass work and as a matter of effiency the areas to be bonded are sanded just before bonding

 

enjoy the build

 

Mike

maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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Originally posted by John DiStefano

Ron Alexander wrote...One must shear up the top layer of molecules on the surface, creating many broken bonds, without damaging or breaking underlying fibers. A water break test can be used to determine surface energy. If surface energy is high, clean distilled water will spread out in a thin uniform film on the surface, and will not break into beads.

If a water break free surface can be maintained for 30 seconds, one has achieved a clean, high energy surface suitable for bonding. If the surface is contaminated or at low energy, the water will break into rivulets and bead up. "Note that tap water will not work. It is dirty enough to contaminate the surface itself, and one will never pass a water break test using it. "It is important to note that the 'high energy"'condition, once achieved, is short-lived. Within about 2-4 hours the effect is lost. In composites, one should therefore wait as late as possible in the process before surface abrasion is performed, so that all else is ready and the adhesive can be quickly applied."

 

This doesn't make sense from a chemistry standpoint. Water is comprised of polar molecules, whereas resin is non-polar (organic or carbon-based....non or ~low-polar). The hydrogen bonding that occurs between water molecules is greater than the other attractive (ie VDW) force between water and the resin organic molecules. Moreover, that the author suggests that tap water (laden presumably with ions such as flouride and calcium etc) would "foul" the silly test is even more suggestive that test is not based on genuine science. Ions if anything would disrupt the h-bond matrix of the water, making it easier to disperse atop the "high energy field."

 

Abraiding a non-polar carbon-based structure leaves a non-polar carbon-based structure. Just for how many milliseconds would these "broken bonds" stay "un-broke?" 2-4 hours?!?

 

Nat himself used solvents while building his Varieze causing real damage. This was written up in a early Canard Pusher. To suggest using a solvent on one of our composite structures is a terrible mis-informed mistake!

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  • 1 month later...

I tried this technique on my first practice layup. The surface turned out very nice. One thing that I would add is that to make sure that you don't crease the plastic too much with rough handling. Even though I put about 50 lbs of weight on it during cure the crease still showed up.

 

The part came out at 10.2 oz which is below the acceptable range (ie. 10.5 oz minimum with 11 oz ideal). I think I was just too agressive with the squeege. There is only one white area bigger then a quarter. I had forgotten about looking for dark areas while squeeging, I'll have to do that next time.

 

One other question. This method is only for flat layups, right? I tried doing it for the second practice layup but it just would work. Is there some secret of making 6 mil plastic adhere around bumps?

 

On a general note, it feels really great to actually start this. I have never worked with epoxy or fiberglass before and find that I really like it!! My latest "discovery" is the wonders of 5 minute epoxy. I used it to stick foam onto the sides of my hotbox, to apply a stiffener to the door of the hotbox (hinge side) and last night to make a clamp holder. This epoxy stuff is GREAT!

Rui Lopes

Cozy MkIV S/N: 1121

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make sure that you don't crease the plastic too much with rough handling. Even though I put about 50 lbs of weight on it during cure the crease still showed up.

Are you using a hair drier? Also, you mention 6 mil. That's too thick. I used 4 mil. Most of the creases go away when you squeege with a hair drier, but be careful - there's a fine line between warm plastic and melted plastic. :(

 

As for plastic on compound curves - sure. Just cut it and let it overlap where needed. Some parts are just too curvy for the technique to be useful, but it works on gentle curves. Also works great for BID taping when you get to that.

 

Ah - I get it - you're shooting for absolute perfection. Don't. On curves you have to accept a slight crease or a small area that isnt stuck totally to the plastic, then you'll find it works well in most layups. Still much better than not using it. Watch out for over squeeging - you should see the bubbles ahead of the squeege and the dark area behind it. If white comes back you need more epoxy and /or less pressure. Try wetting the squeege with a little excess epoxy to help it slide.

 

Hope this helps

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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Originally posted by John Slade

Are you using a hair drier? Also, you mention 6 mil. That's too thick. I used 4 mil. Most of the creases go away when you squeege with a hair drier, but be careful - there's a fine line between warm plastic and melted plastic. :(

Actually I'm using a heat gun that I had from before. It puts out quite a bit of heat. Enough to burn the bristles off the paint brush.... I'll see if I can find some 4 mil stuff. The 6 mil stuff is standard vapour barrier material used in construction. But I really like the results so even if I don't get 4 mil, I'll just be more careful with the plastic from now on... no big deal.

 

As for plastic on compound curves - sure. Just cut it and let it overlap where needed. Some parts are just too curvy for the technique to be useful, but it works on gentle curves. Also works great for BID taping when you get to that.

Hmmm, my only experience so far has been with the confidence layup in Chapter 3. Maybe the 4mil will work better, but I didn't see any way to get the plastic to bend around the "bump" caused the foam. It certainly isn't a gentle curve...

 

I just let it cure without the plastic and it was fine. Good experience,really as I now see what its like w/o the plastic.

 

While I'm on this subject, I did use the plastic on the bottom (in place if the wax paper), so one side is smooth and the other is rough. I did the strength test and was pleased to find that it didn't break in two. But when I looked at the bottom where the pivot point touched there was some flaking. I turned it over and did the strength test again (this time by putting it on the floor and standing on it) and there was no visible damage. Have you seen this? Does using plastic peel ply make a layup more susceptible peices flaking off??

 

One thing I should point out about this is that I made my slurry too thick and I can see areas on the bottom where it didn't spread out to. So maybe there are localized weaknesses on this side of the layup. I took some pictures, but haven't set up my website yet. Hopefully I'll get that done sometime this week.

 

Ah - I get it - you're shooting for absolute perfection. Don't. On curves you have to accept a slight crease or a small area that isnt stuck totally to the plastic, then you'll find it works well in most layups. Still much better than not using it. Watch out for over squeeging - you should see the bubbles ahead of the squeege and the dark area behind it. If white comes back you need more epoxy and /or less pressure. Try wetting the squeege with a little excess epoxy to help it slide.

 

Hope this helps

Thanks for the tips!!

Rui Lopes

Cozy MkIV S/N: 1121

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i would stop using wax paper, wax paper degrades and I don't like the possibility of wax contamination. I would use the 6 or 4 mil plastic on the bench or the plastic coverred butcher paper.

 

enjoy the build

 

dust

maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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Does using plastic peel ply make a layup more susceptible peices flaking off??

Flaking off? What - pieces of cured epoxy? Pieces of the layup? This sounds very strange. I've never seen anything I'd describe as "flaking". Please elaborate.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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Well I'm not sure if I'm using the correct term, but it looks like a piece about 1/2 inch x 1/4 inch on the underside (where it was on top of the plastic, note that this may not have anything to do with the plastic peel ply method, just my poor layup technique) came off. Basically this little area is not shiny like the rest, it is rough, and there's a chunk missing. It looks like the first ply is exposed.

 

What I assumed happened is that when I did the strength test this is where the piece touched the edge of the 2x4 that I was using as a pivot (ie. instead of the broom handle mentioned in the plans). So this is probably where the compression force was highest. Note that in a previous post I said that my micro slurry was too thick and I can see some places where it didn't spread to on the underside (the top is well adhered to as I stippled the hell out of it to get the corners to be void-free). Maybe this caused a weak point which, when compressed caused the "flaking off" .

 

 

This is a case where a picture is worth a thousand words. I'll take it off my camera tonight and mail it you if you don't mind looking at it.

Rui Lopes

Cozy MkIV S/N: 1121

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