Joining and gap filling diecast metal. Anybody try Gap filler and super glue?

[tedd60]

Joining and gap filling diecast metal.  Anybody try Gap filler and/or thick super glue?

I've got a couple 1/18 diecast projects on my bench and I'm trying to come up with a way to fill some panel lines and other gaps.  I read that epoxy type body filler won't work because it doesn't stick to die cast metal, and no matter how hard you try, you at least get a thin crack in the paint.  

 

Edited October 5, 2018 by tedd60

[Snake45]

I'm about to try some work like this and I'm planning to use J-B Weld, an epoxy that's VERY easy to mix and use. Ask for it by name. (I think it now comes in a 5-minute formula. Don't get that. You want the original stuff.) 

I think a superglue gel might work for diecasts, too. I've had the best luck with LocTite brand--it's notably superior to the no-name stuff. 

[Pete J.]

Go down to your local auto paint store and buy a pouch of this stuff.  It is a two part epoxy and works amazingly well.  Get the thin stuff if they have it.  It hardens to sandable in about 20 minutes.  Open time is about 5 minutes.  It is designed to work with metal so it expands and contracts without cracking.  The thin version feathers out beautifully so you have no putty lines.  Also works amazingly well on plastic.  It is my go to putty.  I am very happy they started putting it in pouches because it keeps much better with the air squeezed out.  It is also dirt cheap compared to all the "hobby" putties.  If I recall I paid under $12 for it.  

One other thing, the catalyst needs to be kept in a small old paint jar.  The Tamiya jars are great for it.  Since there is enough to last several thousand models, the catalyst will cause the tube to crack over time.  Also, in the amounts we use, you just need the tip of a toothpick full of catalyst so it is easier than trying to squeeze it out of the tube.  

 

 

 

[tedd60]

I got curious so this is a test without any filler ... I just wire brushed off the paint, brushed a couple coats of Crazy Glue into the seam for the left side trafficator semaphore, sanded off the excess and primed it to see what's up.  I left the right side untouched.

The stuff at the bottom of the L/side panel is paint too tough to brush off, NOT Crazy glue.   I guess over time I will see if it cracks ... but for now, I will put it in a freezer for a couple days, and then outside in the Georgia sun.

 

FWIW, Crazy Glue seems to sand as easy as any filler I've ever used.

Edited October 5, 2018 by tedd60

[ibj40]

1 hour ago, Snake45 said:

I'm about to try some work like this and I'm planning to use J-B Weld, an epoxy that's VERY easy to mix and use. Ask for it by name. (I think it now comes in a 5-minute formula. Don't get that. You want the original stuff.) 

I think a superglue gel might work for diecasts, too. I've had the best luck with LocTite brand--it's notably superior to the no-name stuff. 

JB Weld is what I use, as well.  I created this custom Mustang hood from a combination of a Camaro Z28 hood, and JB Weld bonding it to the original Mustang hood.

Edited October 5, 2018 by ibj40

[Ace-Garageguy]

3 hours ago, Pete J. said:

Go down to your local auto paint store and buy a pouch of this stuff.  It is a two part epoxy and works amazingly well. 

 

 

Actually, it's NOT epoxy, and states as such on the label..."polyester".

Polyester fillers in general have very little STRUCTURAL strength, and don't make good adhesives, especially when used on thin bond lines. They'll crack.

People get in trouble trying to use "bondo" type products (polyester) to fill large gaps in die-cast parts, and when they try to glue two die-cast parts together with the stuff.

Polyester filler IS a very good filler, though, and as Pete says, feathers well, resists shrinking, takes primer well, etc.

BUT...epoxy and polyester are two entirely different chemistries.

JB Weld IS epoxy, and has additives to enhance it's strength when used as an adhesive.

A FURTHER NOTE: SOME die-casts have significant impurities that make them VERY difficult to bond to with ANYTHING, and may also cause them to literally self-destruct overtime.

 

Edited October 5, 2018 by Ace-Garageguy

[tedd60]

OK Ace, but what of cyanoacrylate? ... or maybe cyanoacrylate mixed with a polyester filler?

[Ace-Garageguy]

18 minutes ago, tedd60 said:

OK Ace, but what of cyanoacrylate? ... or maybe cyanoacrylate mixed with a polyester filler?

I can't honestly say I've tried CA on die-cast. 

One thing I DID try was CA mixed with baking soda, as a quick-setting substitute for epoxy on some metal fixtures I had to make fast (not die-cast metal, however).

It's very tough and tenacious, but will chip off in one piece if stressed or flexed to its limit.

Without actually experimenting on the exact metal you're working with, I'd hesitate to make any recommendation.

 

[tedd60]

13 minutes ago, Ace-Garageguy said:

I can't honestly say I've tried CA on die-cast. 

One thing I DID try was CA mixed with baking soda, as a quick-setting substitute for epoxy on some metal fixtures I had to make fast (not die-cast metal, however).

It's very tough and tenacious, but will chip off in one piece if stressed or flexed to its limit.

Without actually experimenting on the exact metal you're working with, I'd hesitate to make any recommendation.

 

Me neither.  I have some junkers to practice on ... I'd love it if it would bond 2 pieces together.  I have tops I'd like to chop, among other things.  Even paint chips so I'm not to troubled by that.  Seeing as I'm going on 68 none of this has to last more than about 10 years.

Why did you try baking soda (aka... bicarbonate of soda) as a binder?

[Ace-Garageguy]

20 minutes ago, tedd60 said:

...Why did you try baking soda (aka... bicarbonate of soda) as a binder?

It kicks off very fast, and is tough up to its ultimate yield strength. It fills large gaps in things, has good compressive strength, and is usable in about 20 hours less than the solid-filled high-strength epoxy I usually use for similar (but permanent) applications.

This video is pretty convincing.

NOTE: Another thought about die-cast: low quality die-cast "pot metal" can often be very porous and contaminated with a wide variety of things. I've seen people try to weld or solder the stuff with what should have been the correct materials and techniques, only to have it spit and pop and outgas as contaminates boiled out of it.

These same contaminates can make some pot-metal die-cast very difficult to bond to with adhesives as well. A very thorough cleaning with 90% isopropyl alcohol, and a careful roughening of the surfaces to be bonded or filled will go a long way towards getting a successful result.

 

Edited October 5, 2018 by Ace-Garageguy

[Ace-Garageguy]

This demo gives you a little more idea of what to expect in general. This is pretty much what I found using it. It's pretty tough.

 

Edited October 5, 2018 by Ace-Garageguy

[Pete J.]

Bill, your distinguishing between polyester and epoxy was interesting and made me do a little research.  I always assumed that epoxy was anything that required a catalyst to harden.  A little more research revealed that the term is used somewhat loosely with regards to adhesives and other commercial products, which is probably what cause my confusion. The scientific definition seems to be "a class of synthetic thermosetting polymers containing epoxide groups". By definition, because polyester resins do not belong to this group they are not epoxys.  But both are thermosetting.  Apparently the catalyst creates the heat in both to set them. I will not make that mistake again and am glad to know the difference.  

On the same subject, I also always thought that baking soda was strictly a filler and added no strength to CA glue when mixed.  I was also wrong on that.  Here is what the materials lab as Swarthmore College had to say on the subject.  All very interesting.

A monomer, such as methylcyanoacrylate (the substance in super glue), with two electron -withdrawing substituents can be polymerized with very mild nucleophiles such as Br, CN, amines or OH. The monomer polymerizes on contact with many surfaces. Most often it is initialized by the presence of water (the OH ions from water). If you have sodium bicarbonte present, traces of water (from the surface or air) will react and make NaOH. The reaction is the following:

NaHCO₃ + H₂O -----> NaOH + H₂CO₃NaOH

is a very good starter of the polymerization reaction. It will make the reaction go very fast. Since this is an exothermic reaction (energy gets released) the H₂CO₃ will break up into H₂O and CO₂ . The water will evaporate and that should be the fume you have noticed. You should also see the CO₂.

So apparently baking soda and CA do have a chemical reaction which causes the CA to set faster.  Interesting. 

[Snake45]

Over in Model Airplane World, I've heard stories of guys who used CA and baking soda as a filler back in the '80s and '90s, and things were fine for years and years--and then after some long period of time, something goes wrong with it, and it starts bubbling up, or cracking, or falling out, or something. I forget exactly what the problem is, but when it happens, it's severe and pretty much unfixable without major rework. 

[SfanGoch]

Better than JB Weld:

Lab-metal

 

 

[Ace-Garageguy]

1 hour ago, Snake45 said:

Over in Model Airplane World, I've heard stories of guys who used CA and baking soda as a filler back in the '80s and '90s, and things were fine for years and years--and then after some long period of time, something goes wrong with it, and it starts bubbling up, or cracking, or falling out, or something. I forget exactly what the problem is, but when it happens, it's severe and pretty much unfixable without major rework. 

Without studying the problem and the chemistry, my first GUESS would be that unreacted baking soda absorbs atmospheric moisture over time, leading to eventual swelling and failure. Like I said, that's an off the cuff GUESS.

Now that we've addressed several of the issues here, my recommendation for BONDING die-cast parts together, or for FILLING LARGE GAPS, would be a relatively high-strength epoxy, thickened with cotton flock. (Finish fill with polyester putty) Cotton-fiber-filled epoxy material is used for structural bonding in aircraft, and is as permanent an adhesive as there is. By "relatively high strength", I mean an epoxy that takes AT LEAST a couple of hours to cure. Generally, the LONGER AN EPOXY TAKES TO CURE, THE STRONGER IT IS. The stuff I use, leftovers from aircraft work (but past its legal use-by date) has to be mixed on a gram-scale, takes several hours to gel, overnight to set up to handle, and an additional 24-hour post cure at elevated temperature to reach maximum strength. It's beyond overkill for most model applications, but it allows me to produce extremely thin parts that are far stronger than styrene.

On something like a chopped top, I'd further reinforce the bonded joints with fine fiberglass cloth on the backsides, as I do on styrene models.

There's nothing so maddening as being in the middle of the last phase of polishing paint, and having a crack appear in an insufficiently strong joint.

That's why I tend towards overkill.   

 

[Art Anderson]

8 minutes ago, Ace-Garageguy said:

Without studying the problem and the chemistry, my first GUESS would be that unreacted baking soda absorbs atmospheric moisture over time, leading to eventual swelling and failure. Like I said, that's an off the cuff GUESS.

Now that we've addressed several of the issues here, my recommendation for BONDING die-cast parts together, or for FILLING LARGE GAPS, would be a relatively high-strength epoxy, thickened with cotton flock. (Finish fill with polyester putty) Cotton-fiber-filled epoxy material is used for structural bonding in aircraft, and is as permanent an adhesive as there is. By "relatively high strength", I mean an epoxy that takes AT LEAST a couple of hours to cure. Generally, the LONGER AN EPOXY TAKES TO CURE, THE STRONGER IT IS. The stuff I use, leftovers from aircraft work (but past its legal use-by date) has to be mixed on a gram-scale, takes several hours to gel, overnight to set up to handle, and an additional 24-hour post cure at elevated temperature to reach maximum strength. It's beyond overkill for most model applications, but it allows me to produce extremely thin parts that are far stronger than styrene.

On something like a chopped top, I'd further reinforce the bonded joints with fine fiberglass cloth on the backsides, as I do on styrene models.

There's nothing so maddening as being in the middle of the last phase of polishing paint, and having a crack appear in an insufficiently strong joint.

That's why I tend towards overkill.   

 

Excellent, Bill, and I concur!   For everyone else here, CA glues simply lack the ability to truly adhere to metals, and that includes diecast.  For assembly work on a metal kit, I strongly urge epoxy, and for filling, catalyzed polyester body putty.

Art

[Pete J.]

Well, I'm glad we have that all worked out.  I recall reading some time ago that the issue with CA is that in most formats it is very brittle.  If you have parts expanding and contracting at different rates it doesn't have the flexibility to withstand the shear stresses.  That is why one of the old tips for breaking a CA bond is to put the part in the freezer and then run hot tap water over it.  

Actually the best way I have found for bonding diecast is to solder it with roses metal.  However that is beyond the skill level and equipment available to most modelers as it requires precise temperature control.  Most diecast metals have a melting point at or near the temperature of normal solder around 400 degrees so using a normal soldering iron or torch would be very risky.   I have done this with  a resistance soldering unit and a bit of experimentation to find an amperage that will bring the diecast just below the melting point.  That point is most likely above the 200+ degrees needed to melt roses metal. Once that balance is attained then the rest is rather easy as long as you give the metal a good key with sandpaper.   I would still use two part polyester putty to fill and smooth over the top. 

[tedd60]

8 hours ago, Pete J. said:

Well, I'm glad we have that all worked out.  I recall reading some time ago that the issue with CA is that in most formats it is very brittle.  If you have parts expanding and contracting at different rates it doesn't have the flexibility to withstand the shear stresses.  That is why one of the old tips for breaking a CA bond is to put the part in the freezer and then run hot tap water over it.  

 

Now I found that interesting.  As I mentioned above, I planned on testing CA as a filler by both putting it in a freezer then setting it in the hot sun.  My part sat in the freezer (15 degrees F.) overnight with no damage.  I set it in the sun this AM and now the part is over 60 degrees F with no sign of cracking.

My hope was to see if the CA expanded and contracted at the same or a different rate than the diecast and would show a crack in the primer.  So far it shows no harm.

After this test cycle has concluded, I'm going to sand it and spray on a coat or two of paint ... then repeat the test to see if the CA filler shows crack lines.

[tedd60]

8 hours ago, Pete J. said:

Actually the best way I have found for bonding diecast is to solder it with roses metal.  However that is beyond the skill level and equipment available to most modelers as it requires precise temperature control.  Most diecast metals have a melting point at or near the temperature of normal solder around 400 degrees so using a normal soldering iron or torch would be very risky.   I have done this with  a resistance soldering unit and a bit of experimentation to find an amperage that will bring the diecast just below the melting point.  That point is most likely above the 200+ degrees needed to melt roses metal. Once that balance is attained then the rest is rather easy as long as you give the metal a good key with sandpaper.   

I've not tried soldering diecast due to all the negatives I have found ... but years ago I build my own resistance soldering unit.  It's output is 8 amps @ 12 VDC and was designed for very fine work.  I don't know what kind of temp I can get a big joint up to ... but I know a way to find out.  What flux is used with rose metal?

[tedd60]

I might be wrong, but I see we are talking about 2 different applications.  1) filling and 2) bonding.  I think there are different stresses effecting both applications, although there may be some overlap.  I am very impressed with both vids that Bill shared, especially the one from Stew-Mac.

Bill offered as a guess (quote):  "Without studying the problem and the chemistry, my first GUESS would be that unreacted baking soda absorbs atmospheric moisture over time, leading to eventual swelling and failure. Like I said, that's an off the cuff GUESS."

 

In this quote I am thinking that "unreacted baking soda", i.e., in the bag before CA application may be a bit hygroscopic.  Perhaps a couple of quick blasts in a microwave or conventional over before use would dry the moisture out to prevent problems down the road.  After reacting with the CA, and coating with primer and paint I expect moisture would no longer be a problem.

 

Interesting and worthwhile conversation.  thanks.

Edited October 6, 2018 by tedd60

[Ace-Garageguy]

7 minutes ago, tedd60 said:

I might be wrong, but I see we are talking about 2 different applications.  1) filling and 2) bonding.  I think there are different stresses effecting both applications, although there may be some overlap.

Your first line: "Joining and gap filling diecast metal"...

"Joining" in this context means "bonding" or "adhering" or "attaching one thing to another thing".

Filling means filling.

Bonding two parts together, and filling large gaps are best done with a filled or toughened epoxy, as discussed above....JB Weld or something similar, or cotton-flock/epoxy, etc. (I use high-strength aircraft stuff, but it's expensive...over $200/gallon with the hardener).

Filling the areas AFTER joining, or smaller things like door lines, etc. is best done with a catalyzed polyester putty like the Evercoat product Pete mentions, as also discussed above.

[Ace-Garageguy]

1 hour ago, tedd60 said:

...In this quote I am thinking that "unreacted baking soda", i.e., in the bag before CA application may be a bit hygroscopic.  Perhaps a couple of quick blasts in a microwave or conventional over before use would dry the moisture out to prevent problems down the road.  After reacting with the CA, and coating with primer and paint I expect moisture would no longer be a problem...

What I was actually thinking is that, in my experience experimenting with the stuff, usually NOT ALL of the baking soda gets equally saturated with CA, because it starts to "kick" immediately, and forms a crust. It's my GUESS that the less-saturated baking soda may be the source of the long-term problems reported by Mr. Snake.

NOTE: Another good polyester filler that comes in MODELER FRIENDLY packaging is the Bondo Brand "Professional" catalyzed glazing putty. The much larger body-shop packages usually go bad long before the typical modeler uses them up.

These small tubes, available at most general auto parts stores, come with a small tube of the correct catalyst, too. There IS a learning curve to mixing and using it to best advantage, so don't experiment on a model you care about.

 

[Pete J.]

13 hours ago, tedd60 said:

I've not tried soldering diecast due to all the negatives I have found ... but years ago I build my own resistance soldering unit.  It's output is 8 amps @ 12 VDC and was designed for very fine work.  I don't know what kind of temp I can get a big joint up to ... but I know a way to find out.  What flux is used with rose metal?

I don't generally use flux when soldering with rose metal.  I just make sure to  hit the areas to be soldered with a new sanding stick just before soldering.  It works fine.  As to the soldering unit, I do it in small sections, less than 1/2" at a time,  and move to the next area.  It really doesn't impact the strength of the joint to remelt rose metal like silver or lead solder.  Rose metal in my experience flows out nicely.  

[tedd60]

My experiment continues.  As seen above I took a bit of scrap 1/18 Maisto VW and filled in the slots for the directional signal trafficator semaphore with CA using a brush.  then I sanded it flat and primed it.  Next i put it in a freezer for 24 hours and set it in the Georgia sun to see if the filling popped out or a hair line appeared.  No pop ... no hair.

 

So I sanded it and put on one coat of gloss black from a rattle can, let it dry then back in the freezer for 24 hours and warmed it up today ... no pop no hair ... no change. 

So far so good.

 

I think it looks great.  I'll let it sit over night and hit it with a heat gun and see what that does.

Edited October 8, 2018 by tedd60