old glue joints

Very many of our glues are all variants of solids... man made or organic... thinned with some sort of solvent

The solids were ground or chemically disintegrated and added to the solvents that when exposed to warm air, dried out leaving the solid....some inflexible and some with a little elastic quality

The reason doping over old glues usually works is the solvent in the dope...mostly MEK (Methyl Ethel Keytone)/Toluene/or Xylene.. and many times a mix of each and other VOCs...is very similar to the original solvent in the glue

These will soften the original solid enough to let it re-flow and cross-link some before drying and become a solid again...although not quite as efficiently as the original fully suspended solid in the solvent

Also Dope Is really a glue...in as much as the solvents all dry out and the base solid binds with whatever it is in contact with

I have not tried it but I tend to think a 30+ year old UNCOVERED built up airframe could be Sprayed with a very heavy dose of 80%(thinner)20% Dope and set to dry for a while and be as strong as when first built with very little weight gain

I'll definitely heed the advice I've been given; to pay extra attention to the bellcrank-mounts in these old models. I have plenty of plywood around my shop.. even if it means laminating thin stock, to get the thickness required. I'd actually rather do that.. than go with an old mount that "looks" ok. The plywood that was supplied in many old kits was really sub-standard. Actually much of it was more of a "luan-type" with voids/pockets in it's core. Not too bad for nose-doublers.. but not for a bellcrank-mount. There was generally one die-smashed sheet for all the ply-parts.. including control-horns. Fortunately none of my models were built with plywood control-horns.. but there's many left-over in some old kit-boxes that I have.

 

Along those lines, the adhesive that holds the plies together on most plywoods does not allow easy gassing of the solvents in Ambroid or any other "cement" type adhesives nor air for drying of white glues. (It takes a loooooong time to dry.) For ply joints Epoxy is much better.

George

Fred, that was an excellent explanation!

George

Unfortunately, the cement shrinks back so far it's rather useless and must be re glued. No rejuvenating process is going to make the glue joint sound. It must be removed and re glued. Nine out of ten times the entire piece just picks right off. When things are at this stage which is essentially what Roddie's Streak appears to be, the parts can easily be dismantled, sanded a bit and glued up again. This is the safest and most practical way to go about repairing it. I recently spent months restoring a Sterling Skylark with this same problem. Between the tedious silkspan removal and all of the glue joints, I could've built a new one. In the end I still have a POS Sterling kit that's just structurally sound. Ken

I think Ken is correct, now that I think some more on just doping over a very old glue joint

If The model to be rejuvenated is a heirloom, or has some significance, I would do the process the right way as tedious as it may be

If it was just some old beater plane I had fun with in the 70s... I might give the dope process a shot and Hope the new covering added some of the lost strength and when the whole thing folded I would most likely shake my head and giggle as it re-kitted

Ken Cook wrote:Unfortunately, the cement shrinks back so far it's rather useless and must be re glued. No rejuvenating process is going to make the glue joint sound. It must be removed and re glued. Nine out of ten times the entire piece just picks right off. When things are at this stage which is essentially what Roddie's Streak appears to be, the parts can easily be dismantled, sanded a bit and glued up again. This is the safest and most practical way to go about repairing it. I recently spent months restoring a Sterling Skylark with this same problem. Between the tedious silkspan removal and all of the glue joints, I could've built a new one. In the end I still have a POS Sterling kit that's just structurally sound. Ken

Yikes.. (regarding the Skylark..) Had you built it originally? I'm guessing "no".. unless it wasn't flown much. What did you use when re-gluing.. and what did you re-cover it with?

Is there a current adhesive.. or combination of adhesive/filler that's lightweight, sands as easily as Ambroid does.. which holds up better over the course of time?

I've never used (and don't have any..) "micro-balloons" filler, but wonder if it can be added to certain glues for lighter-weight glue-joints? How about mixing balsa-dust with glue? Are these materials only recommended for "fillets"?

When Ambroid is applied properly to a joint.. (as noted; a penetrating-application to both surfaces, then a second application once dry and prior to assembly) how long approximately.. and under ideal conditions; can it be expected to hold-up before the joint is at risk of failing? Five.. ten, twenty years? Would environmental conditions play a part in this?

 I'm just a naturally curious person.. We all store our models somewhere.. and I'd imagine that a temperature/humidity-controlled environment must be better than subjecting them to temperature/humidity extremes. My models have all unfortunately run the gamut of environmental conditions in storage over the years. Not much that I could do about then and even now. My worst case scenario is with the large models that have been hanging in my shed for the last 5 years. All the other models are in the basement. It's a dry basement though.. and the temperature only fluctuates 10-15 degrees throughout the year. When I had my apartment for ten years.. the models were all stored in the attic.. which had extreme fluctuations in temperature. Surely my old models were negatively affected by those conditions.

I recently saw some models built in the 60s using Humbrol Balsa Cement (similar to Ambroid and smells the same!) and Araldite (the original epoxy resin that took 48 hours to completely cure). The air frames were still sound but the coverings - dope and tissue - nylon and dope - had gone brittle. The dope would have been what we knew as Humbrol Nitro Cellulose.

These were, however, stored in a spare bedroom. The chap who had them also had some he built in the 90s using PVA and many of the joints had given way but the old PVA glue was never waterproof.

The aliphatic resins are pretty odourless and easily sanded but I don't know about longevity. I have no really old models - they keep crashing!

I have seen models stored in unheated garages subject to temperature extremes - cold and damp/ hot and humid that have been shot the following season.

The chaps with the models has restored a few but the process of stripping of the covering weakened the glue. He used thinner to soften the dope and painstakingly removed the covering but then he used a large plastic bag - put one of the models in it - sprayed MEK in there - sealed the bag and the next morning he had a kit of parts in a bag! He used heat to remove the epoxy resin.

He only did this treatment once! By the time he had finally cleaned everything up for reassembly - he could have cut out the parts ten times over!

The other models he lived with the less than perfect covering removal.

Roddie, the newer Ambroid was very poor compared to the old stuff. If you happen to look at a old Ambroid joint, you will note that it's built up to almost 3/16". You could never do this with the newer stuff. The color of the new stuff was more yellowy and very very thin. The second you opened the tube, it would need the sides squeezed to stop it from flowing out all over the place. Just like everything else that was old and good, formulations changed and certain chemicals that allowed it's superiority were removed. Over the pas 15 years, the models I used Ambroid on haven't seemed to redeem any failing qualities. My models though aren't exposed to heat other than the field which by itself can do some serious damage alone. I have had doped planes blister from the sun.

         I haven't been able to source a place for Ambroid in over 4 years. I don't believe it's even in production. In addition, I found Sig-Ment to work equally well and is readily available through Sig.  I typically purchase it when I purchase fuel from them. I used Duco cement in the past but I haven't tried it currently. I have noticed that they don't offer large size tubes. I mainly used solvent based cements for sheeting and laminating due to it's sanding qualities.

             As for the Skylark, I used what was essentially left of my Ambroid and basically anything on hand. CA doesn't work well on old wood . Ribs, spars, doublers were all glued with carpenter's yellow glue. The less you use, the better it works. I don't get carried away with glue joints . The entire wing and fuse was  getting silkspanned and doped which is what really holds things together. I completed the model a few months ago and while it was on top of my to do list, It went to a fellow club member who almost has it completed. In my model trashing and smashing venue recently, it was one of the bigguns that was just taking up too much real estate inside. This particular Skylark was a NATS winning plane in the 70's. It had a beautiful finish on it, it was heavy as all heck and the controls were just plain worn out. I had to do a shotgun blast of the control system. The bearers were also redrilled for a OS FP.40. I removed wood anywhere I could on the model. To my surpise, I had the plane down to 40 oz's with engine, tank wheels no covering.

              Micro balloons, I wouldn't use it to thin out any cements other than epoxy. It greatly compromises the strength and it doesn't allow epoxy to retain it's structural integrity. No joint that's being called upon for strength should have micro balloons added to it. While it lightens epoxy, it also accelerates it's kick off time. Epoxy joints are little to no value if the epoxy doesn't soak  into the wood. The slower the cure, the stronger the joint. It works great for additional strength as a fillet to a rudder, stab or side of fuse fillet.

             Adding baking soda sprinkled over a CA joint can bridge huge gaps. I would tend to believe that micro balloons in CA would do the same. Baking soda kicks CA off instantly. It makes for a very crude bubbly glue joint however. But, if you have that front end that's so busted up that you can't find the wood through the CA, baking soda could be you best friend here when added to thick CA.


One thing I forgot to add when posting was epoxy. When I was repairing the old Skylark which was very oil soaked, I used the last of my K2R spot lifter. This worked quite well for oil soaked balsa. It took an entire can to wick out the oil. So to glue things back after this grueling treatment, I used T-88 epoxy which when applied was immediately heated with a heat gun. It would run down alongside of plywood and balsa firewalls not to mention the engine crutch. T-88 has the ability to stick to oily woods wuch as teak, and ipe. I used it when I felt the glue joint was compromised due to my acetone wash following the K2R.

Thanks for the valuable advice Ken. My full tube of Ambroid was purchased many years ago.. possibly close to twenty. It's likely the "good ol' formula".. I hope. It says made in Taunton, MA like my other older tubes.

Here's a close-up of an interesting tube of Ambroid that I found at a railroad-salvage outlet (Building 19) back in the early-90's..



As much as I can tell.. the product that was made in Swanzey, NH was the last known source.. and probably the new formula that doesn't work as well.



but it was also made in Lowell, MA... I assume just before the move to NH.



but was "originally made in Boston (proper), MA.. (check out this old ad!)



You'll notice that the tube-graphics are inverted on all the web-images of the tubes made in NH

Most of the aliphatic resin type glues suffer a similar fate as Ambroid. I like it though and this can really aid in taking a model apart if needed. One yellow glue that seemed to have a quality above the rest for me was Sig-bond. I have used this in both a white and yellow version. Anymore seeing I get it by the gallons is Titebond. While I'm not a fan of Titebond II, I found it to remain real flexible over time instead of drying out. The oldest flying model I have on hand currently was built 5/23/69. It was the first .35 size plane I learned to fly built by my father and we still fly it today and just laugh about it. That was built entirely using Ambroid. The fuse and stab was doped with Aero Gloss silvaire aluminum and the wings were Monokote. It crashed in 1984 due to a line break and my father repaired it changing the entire paint scheme. Surprisingly , it still flies well although heavy.

Ken Cook wrote:          Most of the aliphatic resin type glues suffer a similar fate as Ambroid. I like it though and this can really aid in taking a model apart if needed. One yellow glue that seemed to have a quality above the rest for me was Sig-bond. I have used this in both a white and yellow version. Anymore seeing I get it by the gallons is Titebond. While I'm not a fan of Titebond II, I found it to remain real flexible over time instead of drying out. The oldest flying model I have on hand currently was built 5/23/69. It was the first .35 size plane I learned to fly built by my father and we still fly it today and just laugh about it. That was built entirely using Ambroid. The fuse and stab was doped with Aero Gloss silvaire aluminum and the wings were Monokote. It crashed in 1984 due to a line break and my father repaired it changing the entire paint scheme. Surprisingly , it still flies well although heavy.

Ken, thanks again for sharing your experience. I appreciate your taking the time to write, and I've saved our conversation as a word doc. under "adhesives/glues" in my modeling files.

As to "which" products to use; seems to depend on a lot of variables. It boils down to everything (including ourselves..) having a useful lifespan.. IMHO. With model airplanes that are or were great flyer's.. we want to keep flying them indefinitely.. but there inevitably comes a point to where they need to retire.