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Glue and varnish

Posted: Mon Nov 05, 2018 10:02 am
by Brian Amato
This has probably been beaten to death before but I'm not finding what I'm looking for in the archives section so....
Glue: Lots of guys are using T-88 with good luck and I have too in the past. But then I started reading about guys using Titebond-3 with great luck too.
Squeeze it right out of the bottle, water clean-up, water proof when dry, no mixing, cheap and you get the same "the wood lets loose before the glue fails" kind of break test. I bought some and did that test. It's true.
So I've built this whole rack of ribs with Titebond-3. What say you experts out there?

Varnish: When I built the Corben Jr. Ace, I used the entire line of products from Ray Stits including his varnish. Never gave it another thought. Poly-tak stuck to it like crazy and there was never any kind of funky interaction.
Now, on the Piet I'm thinking of using a good quality spar varnish like you can buy from the boat shops. Lots of guys are reporting good coverage and easy enough to work with. My only question is: will polly-tak (or any of the other covering systems glue....I haven't decided which yet) attack spar varnish?
Does it have to be some sort of super special voodoo aircraft varnish or I'm going to fall out of the sky?
OK....I'll sit back now, shut up and let you guys talk.

Re: Glue and varnish

Posted: Mon Nov 05, 2018 12:28 pm
by Clay Hammond
Won't speak to the glue. That's a very personal decision. Are you carrying pax? Which glue should you trust their life too...your considerations should come second to theirs.

Poly-Tak will absolutely attack the spar varnish and inhibit adhesion. The two-part epoxy varnish from Poly-Fiber is the best thing to have between your wood and the fabric. That being said many will build up their varnish protection using single-stage from the hardware store for cost savings, and then only put a single coat of the Poly-Fiber two-stage on top to act as barrier. Whatever floats your boat.

Re: Glue and varnish

Posted: Mon Nov 05, 2018 12:32 pm
by Brian Amato
Thanks much for the reply

Re: Glue and varnish

Posted: Mon Nov 05, 2018 1:35 pm
by Terry Hand

I spoke to the tech guy at Poly Fiber a few weeks ago about this same subject of varnishes to use. He said that there is definitely an issue, as Clay said, with Polyfiber products reacting with products like spar varnish. He did say, though that if you have already used spar varnish (like me), you can apply Polyfiber's 2-part epoxy varnish directly over the spar varnish with no issues at all, where the fabric would come in contact with varnish. He suggested a minimum of 2 coats of the epoxy varnish over the spar varnish, and preferably 3 coats.

Re: Glue and varnish

Posted: Mon Nov 05, 2018 2:33 pm
by Brian Amato
Thanks Terry.
And...Navy here :)

Re: Glue and varnish

Posted: Tue Nov 06, 2018 6:41 am
by Brian Amato
One more thing about the glue:
Just so nobody thinks I'd risk safety over cost let me say this:
The difference between using something like T-88 over Titebond-3 can't be 5 cents a rib. No...what I am trying to do is keep the build as close to the spirit of it, as Berny would have it, as I can.
Bernie recommended Casein glue in all his plans and writings. I've used that to build wooden boats with. It's essentially Weldwood brown powder glue. Mix with cold water and away you go.
I researched what the modern day equivalent to casein glue is and it turns out, it's Titebond-3 waterproof glue; only it now comes in a bottle, premixed so all you have to do is squeeze it out. I figured if Berny's casein glue was good enough for him and dozens of's good enough today.
It's only been in the past 15 years or so guys have gotten all fixated on using "Two part wood glue". What happened to Berny using casein? It somehow isn't any good anymore?
Anybody....please jump in here on this subject.

Re: Glue and varnish

Posted: Tue Nov 06, 2018 10:16 am
by Clay Hammond
I think it's two part. The body of knowledge is greatly improved today versus '29. Casein did/does have the possibility of letting go in places if the airplane is poorly stored and/or overall ambient climate is wet. Will Titebond 3 perform better? Who's to say. You'd have to run your own tests. Hot, cold, wet, dry...compression, tension. All that stuff.

The second part is that safety in operation is much more of a bugaboo today than it was back then. Our representing body and association for EXP aircraft and homebuilders is committing funds and resources to actively campaign and educate for better, safer homebuilt aircraft so that the accident numbers can be brought down. The design of the AirCamper is proven safe...its the builder that is the variable. Is Titebond 3 safe...maybe. Is T-88 or Resorcinol proven...yes. (Resorcinol has been a go-to glue for at least 75 years now, using it would still be in the spirit and it is proven, takes more skill in terms of requiring closer tolerances) The builder should endeavor to build the safest contraption he possibly can. Is their a standard available? In a way yes...we can use the same basic regs and recommendations that standard certificated antiques use for maintenance and repair. AC 43.13 is the best start for that.

Because that's essentially what we are doing. Building an antique. That's an oxymoron but it absolutely applies. Do our mechanics and shops that do work on vintage aircraft use casein glue, Grade A cotton, 1020 steel, cardboard...etc anymore? No...with the exception of the Cotton sometimes. Mostly because from a regulatory standpoint they have moved to newer methods and materials based on experience and knowledge gained by the aviation body over the past century. Doesn't mean the old airplane in question loses any of its soul, and it does mean that it is a safer, longer lasting airplane.

As a body, we owe it to ourselves to be as safe and conscientious as we can...if for no other reason than if we are carrying unsuspecting/innocent passengers (their not having been complicit in the build), don't we owe them to hold to some minimum standard? Do I want to establish that standard, or is it easier to use an already established standard that is VERY attainable.

And I don't mean to sound or come across like I'm pontificating. Its just the thought process of one guy (me) who has spent his whole life so far flying and working on standard category, new and antique...who is starting to contemplate doing his own homebuild. I have flown homebuilts over the years...but I've never carried a passenger in one that I can remember. And I never built it. To build one means I have to think all this through so that I can sleep easy.

Re: Glue and varnish

Posted: Tue Nov 06, 2018 10:23 am
by taildrags
There are numerous glue tests and comparisons out there, most of them from woodworking sites. One such example is "The Great Glue Test" by James Wright, posted on the Popular Woodworking site and quite current (2018). The caution he has about Titebond II and III is that they are not good in exterior conditions. You can be the judge of what constitutes "exterior", but to me an airplane flying through the sky is in an "exterior" environment, while a dining table or a bed frame is not. The test data that Wright gathered is a huge body of information, but I'll give you the snip from his conclusions, attached.

Re: Glue and varnish

Posted: Tue Nov 06, 2018 10:50 am
by Brian Amato
Really don't mean for this to be a can of worms...but the more we all learn, the better I'd say.
Exterior? Here's the word from the folks who make the stuff:

Titebond III Ultimate Wood Glue is the first one-part, water cleanup wood glue ever offered that is proven waterproof. The waterproof formula passes the ANSI/HPVA Type I water-resistance specification and offers superior bond strength, longer open assembly time and lower application temperature. Titebond III is non-toxic, solvent free and cleans up with water - safer to use than traditional waterproof wood glues. It provides strong initial tack, sands easily without softening and is FDA approved for indirect food contact (cutting boards). The ultimate in wood glues - ideal for both interior and exterior applications.

Re: Glue and varnish

Posted: Tue Nov 06, 2018 3:14 pm
by taildrags
I have no dog in the fight...

Re: Glue and varnish

Posted: Tue Nov 06, 2018 4:13 pm
by Clay Hammond
Me neither. Do whats best for you.

Re: Glue and varnish

Posted: Tue Nov 06, 2018 5:08 pm
by EAB4
I would kind of expect Titebond to say they have the best thing out there, and while they are good glues, I have had Titebond II and III fail in exterior projects.
Ca glues will also make the wood fail before the glue joint, and they are faster and easier to use than Titebond but I'm not building my Piet with them.

I don't understand why, if you've had success with epoxy in the past, you don't stay with that, and I agree with Clay, that if you want to stay with the spirit of the project, then Resorcinol might be your choice.
But building a safe aircraft is also in the spirit of the project (and a responsibility of the builder) and going with a known quantity as far as glue goes, is one less thing to worry about.

Varnish: Spar varnish can be used with the Stewart System of covering with no problems

Re: Glue and varnish

Posted: Tue Nov 06, 2018 7:07 pm
by DHeal
Great discussion about glues. Out of curiosity, what glues are currently being used to build FAA-certificated Standard category aircraft such as the new Wacos, Great Lakes, etc? One might assume that such glues are in a sense "FAA-accepted".

Re: Glue and varnish

Posted: Tue Nov 06, 2018 7:41 pm
by Clay Hammond
Resorcinol and two-part epoxy. Technically Resorcinol is the only approved glue for repair on standard category wood structures. Many though read the regs to allow two part epoxy for repair also based on later produced documentation.

Manufacturers who are building and certifying the aircraft on a production line can get any glue process approved that they want, if they prove to their ACO that it is proven. Same goes for covering or anything else for that matter...the Polyfiber STC is not followed to the letter by at least one tube and fabric manufacturer that I know of. Not by a long shot.

Re: Glue and varnish

Posted: Thu Nov 08, 2018 11:11 am
by Lownslow
I don't have a dog in this "fight" either but I feel compelled to put my two cents in anyways. First of all let me mention that I am a retired coatings chemist and product development chemist. I have been a technical director for multiple international companies over the past 45 years. Normally when I see discussions like this I don't bother to respond because so much is based on hearsay and opinion without any science behind it. In this case I do need to chime in.

Now on to the facts.....Casein glue is certified as is Resorcinol but they are not the same animal. Titebond III is also completely different. The only thing these 3 glues have in common is they use water as the carrier.

The FAR AC43-13 states “Casein adhesives should be considered obsolete for all repairs.” so if you use casein glue on your Pietenpol you probably cant legally get it certified.

If you use Titebond III you would have to prove to the FAA that your glue joints conform to AC43.13-1B which states “Adhesives meeting the requirements of a Mil Spec, Aerospace Material Specification, or Technical Standard Order (TSO) for wooden aircraft structures are satisfactory providing they are found to be compatible with existing structural materials in the aircraft and the fabrication methods to be used in the repair.” Does Titebond III pass muster with this? Maybe it does, but the proof will be up to the builder before you can get certification on your aircraft. This would be an involved process and not worth the effort unless there was some monetary gain.

How about a 2-part epoxy like T-88. While it may not be formally approved by the FAA, there is plenty of prior use examples. Approval for certification is typically not a problem.

Now for the bottom line...I would be very leery of flying a plane built with Titeond III, I certainly would not purchase one. I think the resale value would be nil.

At this point in time why not use epoxy. Its easy, relatively cheap and has great characteristics.

Re: Glue and varnish

Posted: Thu Nov 08, 2018 3:16 pm
by Brian Amato
Fair enough Lownslow. I like your argument.
But one last question: If Titebond-3 is not formally recognized by the FAA.....but neither is T-88, what is it that makes the FAA "like" T-88 better then?
Just because a bunch of guys have already used it so it has "history" we have to assume, when you tell the FAA you built your Piet using T-88 they say "oh, well, we haven't seen any joint failures coming from that stuff, so....OK you're approved". Is that pretty much it?
I'll switch to T-88 from this rib forward and everything else about to be glued.
PS...I have YOUR airplane as my computer's Desktop Background. Lovely ship.

Re: Glue and varnish

Posted: Sat Nov 10, 2018 9:40 pm
by taildrags
Well, I decided to wait a while before posting a response to the continuation of this thread but having not seen any other responses, I guess I'll step in it. EAA Tech Counselors, FAA inspectors, DARs, anybody else who disagrees- please weigh in. It is my understanding that our aircraft (experimental, amateur-built) are not required to comply with the requirements for FAA type certification, nor are we bound to follow AC43-13 in any of its iterations... it is "advisory", not "mandatory". We can use non-certified automobile engines, hand-carved propellers, motorcycle wheels and tires, house paint, hardware from the hardware store, wood that we judge to be adequate for our purposes... and adhesives that we wish like to include as part of our experimentation in building and flying out own aircraft under that specific airworthiness certification.

Do I recommend using kindergarten craft glue to build an airplane? No, I do not. I'm just voicing my opinion concerning the over-arching principle that we are not required to use certified materials, STC'd equipment, or to strictly abide by AC43-13 when building experimental aircraft. Clearly though, it is prudent to do so because that publication is based on time-tested materials and methods that are used on certified aircraft for good reasons... safety and durability. Prudence dictates that we follow those time-tested methods and materials, but it is my opinion that we are not required to use them.

I read the applicability of Airworthiness Directives (ADs) in the same light, and so does the EAA, that ADs do not apply to experimental amateur-built aircraft or to any type-certificated parts being operated on an experimental aircraft.

You may fire at will.

Oscar Zuniga
Medford, OR

Re: Glue and varnish

Posted: Sun Nov 11, 2018 10:45 am
by Brian Amato
Thank you Oscar! You are absolutely right and good of you to remind us all of the intent of the whole concept of "Home Built Aircraft".
Having said that tho, and as you pointed out, that does not mean the FAA is going to approve of, nor should we be dumb enough to use Library Paste to stick the fabric to the airframe or mom's old bed sheets to cover the wings. Some things are just inherently too stupid to even think about.
But, I'll bet if I told my wife I was going to cover my airplane with Irish Linen and paint it with self tautening "dope" she'd take out a second policy on me.

Re: Glue and varnish

Posted: Mon Nov 12, 2018 11:00 am
by Brian Amato
Just bumped into this one on Matronics. I haven't tried it yet but thought it worth tossing out here:

The subject once again is T-88. Good stuff. One concern is thermal
resistance. Try this. Then tell me what you think: glue a piece of 1.5mm
ply to a piece of wood let it cure. Use your covering iron to get the ply
just slightly too hot to touch. The ply will peel off like a post it note.
With thousands of planes being built using T-88, obviously it works, but
should this be a concern?

Re: Glue and varnish

Posted: Mon Nov 12, 2018 9:40 pm
by taildrags
From the Systems Three web info on their T-88 epoxy product, the "heat deflection temperature" of T-88 is 119F. From the West Systems website for the definition of "heat deflection temperature", they state that that is the temperature that the epoxy will deform under constant load. From ASTM C1055 (Standard Guide for Heated System Surface Conditions That Produce Contact Burn Injuries), the average person can touch a 140F surface for up to 5 seconds without sustaining irreversible burn damage. Since you said the ply was getting just slightly too hot to touch, it may have been well above the stated heat deflection temperature of 119F and your test proved that.

I have been in many attics in the summertime where I measured the temperature to be in excess of 140F, which means T-88 under constant load might be expected to creep or let go if I subjected it to those conditions. It was HOT! I have also flown my airplane in the summertime, in direct sunlight, when the outside ambient temperature was above 100F. The hottest temperature ever recorded here in Medford Oregon where I live was 113.9F, but we see triple digits quite often in the summer months. Almost exactly the same at Laredo, Texas where I first began my flying career: 114F is the record high. In San Antonio where I've kept 41CC most of its life, 111F was the record high. I've flown my Piet in triple-digit temperatures a number of times and nothing fell off or came loose as a result of it.

If you wanted to delve further into it, calibrate the iron before you apply it to the wood or else use a thermometer or maybe even a thermoscanner to determine the actual temperature of the glue joint when the adhesive lets go. If it's 119F or higher, then you've just verified what the manufacturer of T-88 has already stated in their technical specifications for the product.

Re: Glue and varnish

Posted: Tue Nov 13, 2018 6:45 pm
by Richard Roller
Oscar. I'd have to agree with you on the glue subject. We don't have to comply with the military specs on glues. But we would be a little crazy not to consider the information available in the mil. specs. or from AC 43.13. Information from successful builders should, of course, be considered. I'm aware of several Piets under construction using System 3 or West systems epoxy. When I was still an active 767 mechanic I used to experiment with Boeing spec. epoxy that I used with composite repairs. It worked well, but would be expensive to use.

One other thing. I don't know the current opinions in the FAA about certified parts on experimental aircraft. But when I was still working on light aircraft as a living the thought at that time, at least in the Kansas City FSDO area, was that certified parts still had to comply with A.D.'s. An example, the repetitive inspection on Slick magneto impulse couplings. Does anyone have any hard information on this subject?