How do you use bondo?

Egon Spengler

Sr Member
I need to fill in some areas and make a costume piece more solid.

I know it can't be that complicated, but how do you use bondo to smooth over pieces and to fill in cracks/gaps?

Is bondo strong enough to be used on a finished piece or do you need to do more ?



Sr Member
Bondo is a filler, and won't "bond" pieces together, so if the crack is flexable, the bondo may fill it, but if it flexes, the bondo will split down the crack. Bondo is pretty durable, so you can prime it, and paint right over it.
Basically, you mix part a+b and you have about 5-10 min to work with the stuff. You want to make sure you don't use too much of the accelerator (red stuff in the tube) or the bondo will cure too quickly. You final mix should be very light pink in color.. like a tanish pink. Usually it will come wil a little plastic spreader, that is the approximate color you want to achive in your mix. Once you have it mixed, just spread it on.

If the crack is deep, a few thin layers is better. You can slop it on, and waite for it to "gel" and trim off some of the excess with a razor or exacto blade befor it fully cures.

Depending on the material it is applied to, be careful sanding, because the bondo will be eaten away much more quickly then the surrounding area, and if you are too agressive, you may be left with dimples, or a crease that you would need to refill.


Well-Known Member
Also, bondo goes through several 'stages' as it cures. Right when you mix it together, bondo is like toothpaste consistency. This is the time you need to smear it on like cake iceing. Wear rubber gloves, and try to get as smooth a surface as you can. Wait 2-3 minutes, and the bondo will start to firm up. It will be like hard cheese. You can even grate it with a shur-form tool, rasp or other coarse file. After about 5 minutes, it sets to very hard. Much like that of MDF or poplar wood. Now, you sand.

It its important to 'work' the bondo at it's various stages, save a lot of effort.

Don't just mix up a batch, blob it on, walk off, and have supper, then come back expecting it sand it down. Save your arm.

Wear a dust mask, and work in a well vented area. Bondo smells pretty bad.

For a faster set, use more of the pink tube hardener. Also, invest in those 'spreaders'.

No real strenght in bondo, as it is not intended to be an adhesive. Does make a good sculpting medium, though.

division 6

Master Member
If the piece your putting it on flexes it will pop off ot peel at the edge.

An epoxy 2 part putty would work better.

The more catalist you use the weeker it becomes also the hotter it gets and quicker it kicks.

I've had small amounts kick before I was able to use it. :angry



Well-Known Member
If you're filling cracks forgo bondo.

Using baking soda and water thin superglue will achieve better results. After you sand the area, let the "sand dust" stay in the cracks and add more superglue. Let this set and sand again. If you have small telegraph seam lines once this is done, then add bondo to cover up the patched area.

The superglue/baking soda will actually bond the areas around the crack together like a weld will metal.

Use the bondo as a filler to cover up the patched area.


New Member
Hmmm I was planning on converting a Boba helmet into a Jango. I was going to use Bondo to fill in the dent. Is this recommended? Also where can you buy the stuff?


Sr Member
if the helmet is fiberglass or rigid.. Bondo would work fine.. if it's a dp or vinyl..something stickier with more flex like the epoxy suggestion would do..
Hansicle & Jimbo wrote the basics, but one tip for working with Bondo, or two part fillers is instead of squirting the hardener directly into your blob of filler, is to place your two parts seperately on a "pallette" ( piece of flat scrap wood etc) and then combine the red hardener into the grey filler a little at a time, working quickly to achieve the set-time and hardness that you want. too little accelerant & the mix will not set up and be a sticky mess..too much and the mix will dry fast, but brittle.. might do a practice run to test if you've not worked with it before, so you don't mess up a helmet or costume.
Bondo takes primer & paint very well. & you can use a very fine sandpaper on it..
Another tip is to use those annoying fake credit cards you get in junk mail as spreaders ..:) Good luck..


Well-Known Member
Originally posted by Starkiller@Jan 18 2006, 10:01 PM
Hmmm I was planning on converting a Boba helmet into a Jango.  I was going to use Bondo to fill in the dent.  Is this recommended?  Also where can you buy the stuff?
you can.

I would personally use baking soda and superglue for a job like that though. Little baking soda, shoot it with glue. More baking soda, shoot it with glue, etc. etc. building in layers (it won't take much).

The results will be stronger then bondo and be able to withstand the abuse and flexing better.

Egon Spengler

Sr Member
Thanks everyone. The helmet does flex a little so maybe bondo isn't the best idea for what I want to do. Hm. Now I have used baking soda and superglue before, but really, for large gaps, im going to need a lot of superglue. There a place you can buy big packs of the stuff, and I mean big.

The normal sized tubes just aren't cutting it.


Well-Known Member
You may want to look into epoxy putty for large gaps. I am a big fan of QuikSteel steel reinforced epoxy putty. There are also puttys specifically for plastic repair that should have more flex to them.

If you want to stay with superglue, I think hobby shops have some larger than usual superglue containers. They are around 1.5"x1.5"x0.5" if memory serves me correctly. Home Depot may even have them with all the other adhesives.


Well-Known Member
If you use superglue, don't use the crap you can get at the hardware store.

Don't use the thick stuff either. You want water thin.