texasaggie72

I am in the final stages for completing a Sig Senior Kadet, and I am looking for the best way to seal the firewall. I am considering either clear dope or epoxy. I really prefer the epoxy, but I know that I will need to thin it a little so that I can brush it.
What is the best method? Can I thin epoxy with acetone (laquer thinner)? or is there something better with which to thin? or is there a better material?

Thanks,
texasaggie72

Russmall

Denatured alcohol works well. (Don't use rubbing alcohol)..........RS

hogbilly

Finishing epoxy works well to. cant remember what brand I use and Im at work now. but says 20 minute epoxy and comes in larger bottles

texasaggie72

thanks for the reply...

Regards,
texasaggie72

Roger Hill

My Feedback: (2)

The easy way is to first get out your heat gun. Mix the epoxy full strength, sprread several globs in the various firewall areas, then hit it with the heat gun. Reduces it to water viscosity. Spread QUICKLY with an epoxy brush. It cures very rapidly after the heat.

Roger Hill

scale buff

My Feedback: (24)

I've used acetone for years, and it has always worked great for me.

Frank T.

damifino

Acetone or denatured alcohol added to your epoxy is OK but no more than 5%. The most effective way to thin epoxies according to West Systems literature is with heat. Pre-heat the epoxy components to no more than 110-115 degrees before mixing (hot tap water in a pan is perfect), heat the area to be coated and have at it. The heat will cure the epoxy really fast so you should use some 1 hour epoxy at the least or preferably 3 hour so it will drain off or brush off to leave a thin coating to save weight. Pre-heating the area to be protected is the preferred way according to West Systems. Epoxy, unlike paint, does not get lighter as it cures because it has no solvents to evaporate. West Systems literature has everything you will ever need to know about epoxies and most of the info can be applied to any brand.

dabigboy

Hmmm, I guess I need to work on my building skills and knowledge....when I fuel-proofed the firewall and fuel tank compartment on my last model, I just mixed up epoxy normally (without thinning) and slopped it on with a scrap of ply.

But that was about 5 years ago, and only my third complete kit, so it's reasonable, right?

-Matt Bailey

Donnie7

I've used rubbing alcohol for years to thin epoxy. Whats the problem???
Donnie

Ed Smith

Actualy you do not. You are the only one here that did it right. Epoxy resin is easily brushable, how else could we lay any thing up with it? Whereas it might not make a lot of difference sealing a firewall, thinning epoxy is bad practice. Thinned epoxy does not have the same integrity as the full strength. Some of them do not cure completely when cthinned.

Ed S

MinnFlyer

My Feedback: (4)

Thinning epoxy for structural bonding is not a good idea.

But if all you're doing is fuel proofing an area, virtually any of the described methods will work well. I not only use plane ol' rubbing alcohol, I have even used some that I got for free that had mint added for a pleasing aroma.

It's not there for strength, it's just keeping the fuel out of the wood.

damifino

Right on Minnflyer. For structural bonding thinning with a solvent is a no-no. For fuel proofing a little thinning won't hurt anything.

leftnut

My Feedback: (1)

yeah...what's the problem with using rubbing alcohol ?
i had just fiberglass a wing joint with expoxy and rubbing alcohol.
was that a no..no..?

damifino

In our little world of toy airplanes it probably doesn't make a s**t. But people who make epoxies sell it to homebuilt airplane builders, boat builders, construction industry and any number of users who build things that must not break or someone may die. My information comes from the source and I feel good about how I apply it.

dr_wogz

My Feedback: (3)

As for the 'why not' questions:

Rubbing alcohol contains water. As much as 30% of the bottle can be water. Water dosen't evaporate to well when mixed with epoxy, so you'll get little 'pockets / bubbles'. Also, thinning epoxy too much will also leave little 'pockets / bubbles' in the epoxy, and it'll be like foam, waiting and wanting to soak up any oils.. Also, it can greatly increase the cure time, causing a 'rubbery / gummy' coating that never seems to fully cure..

Methyl Hydrate or Denatureds Alcohol evaporates at a high rate (and contains virtually no water). And you only need a few drops per ounce of mixed epoxy. (I remember erading about someone using a 50/50 mix of alcohol to epoxy.. Big no-no!)

Heating is and always will be the best way to thin epoxy. heating the bottles in the nuker for seconds has worked (so I've read..) and the bottles in cups of hot water work teh best (known from experinece) but use long cure times for the reasons stated above!!

Plan to 'fuel proof' outside on really hot days! This time of year is perfect! PArk teh bottles in the sun for a bit, and the plane, then go at it!

(I learnt my lesson when glueing in my hinges, they seemd to cure prematurely. I was installing them on a really hot summer day! +30°C. On day , I'll pull off the offending aileron, and re-hinge it..)

Donnie7

Why not use rubbing alcohol,,,,, I was just talking about fuel proofing only. Not structural value. There is nothing wrong with using standard rubbing alcohol for fuel proofing. I wouldn't thin it for anything else. Hope this clears my statement.
Donnie

damifino

OK you're cleared. But, try the heat thing, all you need is a heat gun or a hair dryer. If you have not 'thinned' epoxy this way you'll surprised at how much better it works than 'watering' it down.

Donnie7

I have a 1/3 spacewalker up next. I'll give it a try,,,,,thanks for the info
Donnie

PlaneKrazee

My Feedback: (14)

As stated, rubbing alcohol should not be used because it contains up to 30% water. Water, if trapped in epoxy will not evaporate. It can cause bubbles and pin holes in your fuel proofing making it not truely fuel proof. At that point dope would work as well so would CA glue so long as you don't use high nitro.

leftnut

My Feedback: (1)

it's a good thing i re-enforced that wing.lol
a secondary spar built of berch..
all spar joints was expoxy wihtout additives.
it's not life and death...but it's still a $300 investment.lol

yep...the epoxy with rubbing alcohol was gummie at certain area.
took longer to cure. i'm not sure how stronge the bone is ?
3" wide fiber glass..using CA was always a mess or big air pockets
under the glass....so i went epoxy and read in the past you can
can thin it with alcohol.....but that dude wasn't clear on what type.[sm=spinnyeyes.gif]

Rumple

dr_wogz and skypilot_one are right, its the water in the rubbing alcohol thats bad. Epoxy resins and most amine curing agents (hardeners) are not miscible with the water. So you get 2 phases, like oil + water. Not good for a fuel barrier, since the water phase can wind up yielding pin holes in the epoxy which let the fuel right through.

The immiscibility reveals itself as a cloudy (milky) mixture. If your epoxy is is truly miscible with whatever solvent you choose, the mixture should turn clear after being well mixed in your mixing cup.

Kurt

BasinBum

My Feedback: (2)

I fuel proof all my planes with epoxy thinned with denatured alcohol at about 50-50 and do it back as far as I think fuel would go if the tank ruptured. I use acid brushes because you can bend them at a 90 degree angle to get at hard to reach areas and wear disposable gloves. Let it dry overnight and it works great. Most hardware stores sell denatured alcohol cheap and while you are there get some acetone and lighter fluid.

damifino

As already discussed before: Just because some people do it that way doesn't make it right.
**Parts don't fail, people do**