J.B. Weld vs. Epoxy

[karatekicker271]

I wanted to use J.B. Weld for my Polecats Thumper (for extra reassurance). My dad asked me if J.B. Weld was accualy better than epoxy. Not price wise, but its quality.

 

[cls]

dude, don't even consider anything but a top quality epoxy like WEST or G3. you're putting a lot of time and money on the rocket, what are you saving?!??

 

[r1dermon]

JB weld is awesome stuff no doubt...makes for really great smooth fillets too. but i've had better luck with epoxy...plus, setup time for jb is really long.

 

[rstaff3]

Use regular epoxy. Save the JBWeld for the AeroPack retainer.

 

[karatekicker271]

Ok, I get the drift I think I would prbably end up using epoxy anyways, considering I am broke! Thanks guys!

 

[Hospital_Rocket]

I'm not sure if most of you are aware of this but JBWeld is an epoxy. It's special feature is the iron powder it uses as a filler.

A

 

[Mad Rocketeer]

I voted Personal Preference. I'm building an LOC/Precision Graduator, and I opted to use J.B. Weld for the joints that touch the motor mount tube and 30-minute epoxy (Bob Smith stuff) for the rest. My theory was to use the J.B. Weld where heat would be more of an issue. I know the 1:1 ratio epoxies, like the Bob Smith, have more filler and aren't the top of the line, but I could have some for less than a $50+ investment in quart cans and pumps.

The J.B. Weld has worked fine as far as I can tell, with one exception that's my fault. [See my thread on the Mid-Power forum for my woes and what I'm looking to do to fix it.] I timed my fin work to the 2 hour setup-to-handling strength of the 30-minute epoxy rather than the longer J.B. Weld figure. When I left the rocket to set up overnight with the second fin vertical, the first (which I had thought fully firmed) drooped a little. I should have given it 6 hours before rotating to the next fin. Had I done so, I'd be a very happy camper. The J.B. Weld should be very strong and is gooey enough to help hold things in place as it cures, as long as you keep the fin vertical.

One guy suggested tacking the fin with CA gel then doing the fillets (all six, counting the internal ones) in epoxy of one form or the other. At first, I thought that would leave the fin weaker than all epoxy, but in retrospect I think he's right that the fillets have so much area that it will hold just as well and be easier to do. It's worth thinking about.

Next time around, I'll probably do it the same way I did it this time, except I'll use masking tape to help keep the fins in position while they cure, and I'll give the J.B. Weld overnight to cure for each fin.

By the way, don't use a Q-tip or similar for J.B. Weld. It's so tarry and sticky that it will pull the cotton fibers into a rope, making it tough to be neat.

 

[DynaSoar]

Originally posted by karatekicker271
I wanted to use J.B. Weld for my Polecats Thumper (for extra reassurance). My dad asked me if J.B. Weld was accualy better than epoxy. Not price wise, but its quality.

JB Weld actually is stronger, but not enough to make it worth it.

It's very hard to get smooth. It's nigh impossible to finish well.

Definitely use it on anything that's glued to the motor tube or anywhere else exposed to high heat. But for everything else regular epoxy is already so much stronger than your materials you're gluing, the difference would never be noticed.

Early on I used "slow" epoxies, then switched to 5 minute. I've had plenty of wrecks. Nothing happened with the 5 minute epoxy that didn't also happen with the slow epoxy, and that was stress fractures at the edge of the fillet where the epoxy held together but the body and fillet separated -- the paper peeled at the surface.

Of course it all depends on you preparing your materials and using your glue properly. That can make far more difference than the difference between glues.

 

[urbanek]

When I built my level 1 Graduator, I used 100% RAKA epoxy. https://www.raka.com Their epoxy is meant for boat building. It's a great fiberglassing epoxy. The 2:1 mix is easy to use.

It's like buying epoxy from Costco or Sam's Club. You pay more up front, but you get great big containers and the cost per serving is lower.

At first I used ketchup/mustard dispencers that you can buy at a grocery store for the resin and hardener. I used small measuring spoons to measure.

Now I have a pair of pump lotion dispencers that I got from Target or Wallmart. I figure if it can pump hand lotion, it can pump epoxy resin and I was right.

For attaching things to other things, I used filler to thicken the epoxy. Maple flour works great and is cheap. I thickened to peanut butter consistency for attaching stuff, mayonaise for fillets, unfilled for laying up fiberglass. Made for a very strong rocket because the thin epoxy penetrated well.

OTOH, it took forevery to build that rocket because it took hours for the epoxy to set up. I'd put on one fin a day.

That Graduator is still flying. It's survived a forward closure failure, a number of flat spin recoveries and a few hard landings on the Bonneville Salt Flats (like landing on concrete). I'm going back to that technique with my Level 3 rocket. I think that this boat building epoxy is superior in strength and flexibility to anything you can buy in the hobby store and ouce for ounce, it's cheaper. I can get 1 1/2 gallons (192 oz) for $76.00. So, I it's costing me $3.56 for 9 oz of epoxy, which is about 1/2 price for the hobby store stuff.

For speed, though, I'll still use the 5 minute Bob Smith epoxy.

urbanek

 

[Stones]

Personally, I'm sold on West Systems epoxy. I use a couple of small squeeze bottles and have become pretty good at mixing small amounts at a 5:1 ratio. For fillets and the like, I mix in micro-balloons to the desired thickness.

 

[Elapid]

is very heavy, but resists 500* heat while regular epoxy will turn to jelly @ that temperature.

JB Weld is simple to finish beautifully.
water is used to smooth it out to a ready-to-finish shine...
it also washes off easily in water, while epoxy needs rubbing alcohol on a gloved finger to accomplish similar results.

I love JB Weld in small amounts wehre heat will develop. The rest is epoxied.

 

[rstaff3]

I've used my share of JB, but didn't know it washed in water. (Some day I'll resort to reading the instuctions?)

 

[11bravo]

After looking at this thread last night, I took a look at the JB Weld (JBW) website; it said that you can thin it with acetone.
That would make for an easier time making it look good I would imagine.

JBW FAQ-
https://jbweld.net/faq.php#faq015

Maybe someone should use only JBW on a rocket and enjoy that nice dull grey color.

Greg

 

[Hospital_Rocket]

Might be the way to do Quantum Tube.

 

[Mad Rocketeer]

Originally posted by urbanek
When I built my level 1 Graduator, I used 100% RAKA epoxy. https://www.raka.com Their epoxy is meant for boat building. It's a great fiberglassing epoxy. The 2:1 mix is easy to use.

Good link! I'd not heard of Raka before.

Originally posted by urbanek
At first I used ketchup/mustard dispencers that you can buy at a grocery store for the resin and hardener. I used small measuring spoons to measure.

Now I have a pair of pump lotion dispencers that I got from Target or Wallmart. I figure if it can pump hand lotion, it can pump epoxy resin and I was right.

Great idea! Cheap pumps.

Originally posted by 11Bravo
After looking at this thread last night, I took a look at the JB Weld (JBW) website; it said that you can thin it with acetone.
That would make for an easier time making it look good I would imagine.

JBW FAQ-
https://jbweld.net/faq.php#faq015

Maybe someone should use only JBW on a rocket and enjoy that nice dull grey color.

Yep. I have a quart of the stuff on my shelf, but I don't think it will do anything to my already cured J-B Weld. Not sure what acetone soaked into a tube might do either.

Hmmm. Ought to be able to make a couple of card stock tubes (Think Fliskits Midnight Express.) of different diameters, cure some J-B Weld between them, then sand away the paper to have an all J-B Weld rocket. Seems rubbery enough and yet stiff enough to do without needing a kevlar or fiberglass substrate. Could also just paint a tube with the stuff. Then an acetone soaked used engine could be slid into the body tube to the right depth and removed quickly, to create a motor mount tube and a thrust ring at the same time. Hmmm. Cures slowly though, so you'd probably have to smear a motor with Vaseline and leave it in until the J-B Weld cures. Heavy, expensive, and impractical, but it could be fun as a novelty.

 

[DynaSoar]

Originally posted by 11Bravo
After looking at this thread last night, I took a look at the JB Weld (JBW) website; it said that you can thin it with acetone.
That would make for an easier time making it look good I would imagine.

JBW FAQ-
https://jbweld.net/faq.php#faq015

Maybe someone should use only JBW on a rocket and enjoy that nice dull grey color.

Greg

I've been considering something like that for the design I;m hashing over with Bob Krech in "Advanced". Mix JB Welb wil a lot of ceramic flake, and let it ablate as it hits maxQ and reaches 1000 degrees.

I forgot about smoothing it with water. Yes, that works. Washes right off the fingers too. Acetone? As long as it says it won;t weaken it, sure.

For really easy JB fillets, use the two part epoxy putty from Apogee. Fantastic stuff. Aerodynamic playdough.

 

[JDcluster]

While JB weld might be superior in strength, it won't make your joints any more so.

JB Weld is better for bonding metal than fiberglass & paper.
I'd go with epoxy , which will soak into the fiberglass & paper giving you a much stronger bond = stronger rocket.


You reserve your JB Weld for bonding hardware & metal motor retainers.


JD

Originally posted by karatekicker271
I wanted to use J.B. Weld for my Polecats Thumper (for extra reassurance). My dad asked me if J.B. Weld was accualy better than epoxy. Not price wise, but its quality.

 

[Mad Rocketeer]

Originally posted by DynaSoar
I forgot about smoothing it with water. Yes, that works. Washes right off the fingers too.

Hmmm. The J-B Weld site says J-B Weld isn't toxic but shouldn't be ingested anyway (duh). Does this mean that even though it's an epoxy it may be safer to get on one's hands than regular epoxy is?

Originally posted by DynaSoar
For really easy JB fillets, use the two part epoxy putty from Apogee. Fantastic stuff. Aerodynamic playdough.

Gotta get some of that stuff. I have my eye on some Apogee rockets too.

Originally posted by JDcluster
JB Weld is better for bonding metal than fiberglass & paper.
I'd go with epoxy , which will soak into the fiberglass & paper giving you a much stronger bond = stronger rocket.

How about fiberglass fins, which aren't porous? Is regular epoxy better there too.

Always looking to further my education.

 

[Stymye]

heck... use J.B. weld on the motor mount and epoxy on the remainder... best of both worlds

 

[Mad Rocketeer]

That was my thought too. If I do it sparingly enough, I may not need any added nose weight. Hope not, but I'll definitely add if if needed.