Bondo strength?

[MYX]

I have used bondo a lot on cabinet repair. It is great in situations where there is water damage or things like that. But I need to make something that I can squirt into a mold and it is something that I think will take some abuse. How strong is bondo as a stand alone structure. I figure it will be about half an inch thick and about 2 inches wide and 5 inches long.
Or is there something better I could use? I do not want to pay a ridiculous amount and I already have bondo (which is why I was asking.)

[Texasmame]

What are you casting?  What will it be used for?  Bondo is pretty strong stuff but if you wanna get real good strength for molding some part, try using some of that "steel putty."  Mold it, let it dry *at least* 24 hours (don't fiddle with it prior to that).  Should be fine.

[Tailgunner]

Sounds like a job for Alumicast, but if you want something you can get locally I'd suggest "tiger hair". It's basically bondo with strands of fiberglass mixed in to give it reinforcement.

[spooky]

Do not use Bondo as a structure. Its made for filling and is only good for a quarter inch.After that it gets brittle. Kitty hair type bondo is stronger and has some fiberglass resin mixed in usually but still not what I would use to build something. If you could give more insight in to what you are doing I may be able to help you further. I am a paint and body man so I know a little bit about that good 'ole Bondo.

[daywane]

I used to work at Arizona rentals , years ago
we used to fix risers ( stage's for bands) with bondo
I am talking the hole coner.
we would put in a thin sheet of metal under the riser (the missing section)
fill with bondo. dry, sand and paint.
Pink Floyd used our stage .
the news casters used our rised at basketball games.
never a problem

I think alot of things here use WAY OVER KILL.

[_) (V) (-)]

Not too sure about squirting bondo into a mold, how would you plan to get the air bubbles out?

Strength is also dependent on the guts of the item you are making, if you use an inner structure it would fair much better.

[jace055]

I would try fiberglass and fiberglass resin.  You might be able to get away with just the resin but a little glass in there wouldn't hurt.  For something that thick and large I would want to use a little more hardner in the resin than usual.  You will have a shorter working time but without it the object may never dry and set-up.

[shardian]

Ask pinewood princess what she is using for her molds.

[luckyfold]

http://www.smooth-on.com/liqplas.htm

They make some kick ass two part plastics [mix part a with part b and watch it harden] that I have used - really strong stuff.  Of course you will need to obtain or build a pressure pot so that you can put it in a mold - then into the pot - kill all the air bubbles.

It sets up really fast.

[RandyT]

I would avoid regular Bondo.  Not designed for the job.

Go to the local home store and get some of the Bondo resin designed for structural repairs (they keep it in the caulk/adhesive department area at Home Depot).  It's kind of translucent brown in color and smells bad, but it is strong.  It's also very inexpensive at about $18 a gallon, IIRC, and it includes the hardener.  You might want to pick up an extra hardener while you are there.

Thick parts will experience some shrinkage, and a vacuum chamber would be best to get the bubbles out. But if a bubble-free finish isn't important, it shouldn't be a big deal.  Again, it depends on the part.

RandyT

[MYX]

I can say that it will be a handle. So anything with fiber glass will probably cause an itch correct? I got the idea the other day and I am thinking stongly about trying it. I will avoid bondo. Figure the strength of a joystick handle (actually where I got the idea). But I do not know if my widget will get that kind of abuse or not. But I figured I would try.

Randy I have seen that. Is it fiberglass or will it become a plastic?

[Derf00]

I think someone else mentioned this already but Alumilite is a cast resin that would work very well. Bondo works great as a filler but that's it. Fiber filled bondo works with bigger holes but again, not ideal for the job.

[jace055]

I can say that it will be a handle. So anything with fiber glass will probably cause an itch correct?

The fiber in its raw state, like attic insulation, will itch before it is mixed with a resin.  Afterwards,  It can be sanded to shape with a dremel or sandpaper then use a light skim coat of bondo to even the surface.  Then paint or use the plasti-dip stuff for tool handles to put a rubber like coat on it. 

In my experience with auto repair and computer case modding,  fiberglass is great for this kind of thing.  Bondo cracks in thinkness over 1/8 inch or so with stress. 

[RandyT]

I can say that it will be a handle. So anything with fiber glass will probably cause an itch correct? I got the idea the other day and I am thinking stongly about trying it. I will avoid bondo. Figure the strength of a joystick handle (actually where I got the idea). But I do not know if my widget will get that kind of abuse or not. But I figured I would try.

Randy I have seen that. Is it fiberglass or will it become a plastic?

The stuff I am talking about is technically a polyester resin.  So it gets very hard and becomes a plastic.  I made some balls from it once as an experiment and then threw one against a concrete floor as hard as I could.  After it bounced off of a 15' high ceiling I examined it and found that the impact with the floor marred the surface but it didn't crack or break.

For extra strength, like for boat or auto body repairs, you can use it with fiberglass cloth or loose fibers.  As long as you don't have very thin walls, you should be able to skip those and use the resin alone as an inexpensive casting material.  Other than the price, the availability can't be beat.  Just understand that very thick castings will generate a lot of heat and there will be some shrinkage (normal for a fair number of casting compounds.)  As long as you account for these in your molds, you should be fine.

Also, you can use the dispersed dyes from the craft store to tint it.  These are usually found by the crystal clear casting resins...which you should avoid due to the difficulties they present from the omission of a particular component in order to make them clear.  You won't get much of a color range, but if the translucent brown is too ugly, you can at least change it to a muddy green

RandyT

[MYX]

Yeah, Wow, that sounds great. I will look for some this weekend. Can it be dyed Black?
Which casting compounds shrink least?

So it gets very hard and becomes a plastic.  I made some balls from it once as an experiment

Just understand that very thick castings will generate a lot of heat and there will be some shrinkage (normal for a fair number of casting compounds.)

RandyT

So... Randy has plastic balls that when exposed to certain temperatures, may shrink?

Sorry, it was there.

But thank you. I will try to put this together this weekend. How long does that stuff take to set? Is it thin enough to inject into a mold? Any ideas where to buy a syringe for injection? I have seen a number of folks mention air bubbles. How do I avoid them?
Are Air bubbles a bad thing if it is an opaque structure?