Using Epoxy and also Microballons Question

Might as well double up here

On what areas do you most use epoxy? Control horns, fuse doublers, motor mounts etc. Where else? Do you epoxy the engine/tank compartment too? It needs to be fuel proof but I'm not sure on how to best do this.

Microballons...

Pardon my infinite ignorance, but what exactly do I mix them with? I'll want a sandable filler to use before I start offical sanding.

Thanks for the tips as always guys!

LAST EDITED ON May-13-04 AT 12:45 PM (CDT)
 
>Might as well double up here :7
>
>On what areas do you most use epoxy? Control horns, fuse
>doublers, motor mounts etc. Where else? Do you epoxy the
>engine/tank compartment too? It needs to be fuel proof but
>I'm not sure on how to best do this.
>
>Microballons...
>
>Pardon my infinite ignorance, but what exactly do I mix them
>with? I'll want a sandable filler to use before I start
>offical sanding.
>
>Thanks for the tips as always guys!

Ron B.
F4Fguy

I use epoxy for laminating carbon,glass,and kevlar,to themselves and to balsa,foam etc.I seldom use it for other applications.The exception is fuel proofing engine/tank compartments.For this application I thin 30min. epoxy at least 50/50 with acetone(after mixing the epoxy and hardener).This gives a thin,watery mix which penetrates well,and goes on very thin.The acetone is evaporated well before the epoxy begins to set and the result is a light,totally fuel proof interior.For all other gluing I use thinned Sigment,DUCO,or Ambroid,or thinned aliphatic resin glues.I've just recently tried some polyurethane resin glue.It appears to have some interesting properties,for,say,laminating doublers,but my jury's still out.

Microballoons can be mixed with almost any vehicle.Unfortunately,most won't carry enough in suspension to make a useful one coat fillet.Epoxy is the usual carrier for fillets as it will hold almost it's own weight in microballoons.The down side is that to get really high filler content requires long mixing times,as only small amounts at a time will go into suspension.If the filler content is too low,the resulting fillet is VERY hard to sand.I use mostly balsa fillets,but if I do use epoxy,I use West's slow epoxy with the slowest hardener and mix in (phenolic)micrballoons until no more will wet.What I find better yet,but a little more difficult to mix,is Aeropoxy.I highly recommend it,but,be extremely careful to mix per instructions,by WEIGHT,NOT by volume.Yet another usable product is SIG Epoxolite,with 50/50 microballoons added by volume.Add the microballons after the two part Epoxolite is mixed.This gives a much more sandable,and also much lighter fillet than straight Epoxolite.

Note the recommendation to mix epoxy before adding fillers.If you add before,or during mixing,the epoxy and hardener will not have enough mass to initiate the hardening process.This will cause extremely long hardening time,or in extreme cases,no full cure.

One other note,epoxy is HEAVY.Use it sparingly,and only where nothing else will do the job.

In using epoxy to fuelproof compartments, I simply mix the epoxy (slow setting is easiest to work with) and use one of the disposible epoxy brushes to smear it all around. The I use my hairdryer to heat it up. The epoxy will become quite fluid when heated, and any air present in the wood will expand and come out as bubbles. Heat until there are no more bubbles. Then take a paper towel and wipe away any excess epoxy. Epoxy is thigmatrophic and penetrates into voids and cracks (better than thin CyA, according to some). The slow-setting epoxy stays fluid longer and thus penetrates more.

I have read that when you use acetone, alcohol, etc. to thin epoxy the result is the thinner, on evaporating, leaves micro channels through the epoxy, thus weakening it and allowing fuel, etc. to move through later. I don't know if there is any truth to this, however.

>
>I have read that when you use acetone, alcohol, etc. to thin
>epoxy the result is the thinner, on evaporating, leaves
>micro channels through the epoxy, thus weakening it and
>allowing fuel, etc. to move through later. I don't know if
>there is any truth to this, however.
>
>Jim
>
>

Ron B.
F4Fguy

Thats the reason for using acetone rather than alchohol.Acetone is such a "fast" solvent that it's long gone before the epoxy begins to harden.This is aided by the latent heat of evaporation of the acetone which retards the reaction time of the epoxy.

Ron,

What are you thinning the aliphatic resin with? What ratio? Have you noticed any reduction in strength? Are you using this as a penetrating or fillet bonding adhesive?

Dave
LA_Flyer
"Pukey Profile Pilot"

LAST EDITED ON May-14-04 AT 01:25 PM (CDT)
 
>Ron,
>
>What are you thinning the aliphatic resin with? What ratio?
>Have you noticed any reduction in strength? Are you using
>this as a penetrating or fillet bonding adhesive?
>
>Dave
>LA_Flyer
>"Pukey Profile Pilot"

Ron B.
F4Fguy

I thin aliphatic with water about 10%,sometimes more,up to 20%if I'm looking for long open time or large area coverage.I use this mix more for indoor rubber models than U.C..The main use(by me)in other models is laminating doublers on profiles.It's as strong as is needed,is fuel proof,and weighs less than epoxy.I haven't seen any noticable decline in joint strength with thinning,but it does become a little more difficult to apply. A brush or an old fashioned glue stick* is almost mandatory. I still prefer the solvent glues for most model work.
*A bamboo skewer sharpened on one end and rounded on the other,to allow exact amounts to be transferred to the joint.

For fillets,as I said above,I usually use carved or molded balsa.When I use microballoons(phenolic,not glass),I use epoxy or,better,SIG Epoxolite or,better yet,Aeropoxy without any additions.

While it's true you can mix microballoons with almost any vehicle,shrinkage becomes a real problem with most of them.The only really practical ones are the non-evaporative cure ones.For practcal purposes that pretty much limits it to two part epoxies and polyesters.