Working with Bondo


Mic Pro

Jr Hunter
OK, I made rough-built gauntlet pieces out of the WOF templates using paper and filled with expanding foam (for rigidity). I'm about to cover the pieces with Bondo to even/smooth out the edges and any bulges caused by the foam (kind of a good idea/bad idea thing).

I've never used Bondo and I'd like to spread it reasonably thin on the pieces. My dad recommends doing it in several coats.

Any suggestions/pointers?
 

Shinobi Fett

Active Hunter
The first warning is that you might want to stay away from expanding foam. Regardless of what it lists as a cure time, it will continue to expand (and in some cases contract) depending on temperature. If you have it sealed up in bondo or other material, you might get bulging cracks over time. Just a word of caution...
 

Mic Pro

Jr Hunter
OK, I've foregone the foam and decided to resculpt the top parts with styrofoam (they came out nice and took no time at all). And Now I'm just going to Bondo on top of them and sand it down to where I want it. I'm up in Northern Ontario so hot/cold indoor & outdoor transfers are definitely happening this fall (we already had a snowfall the other day!) so the idea of the foam expanding and contracting didn't appeal to me once you guys mentioned it.
 

Heatshock

Hunter
general idea with bondo is less is more. I would go with thin layers and build em up. the harderner ratio isnt precise - but u got abt 8-10 min I would say before it goes almost crumbly solid, then solid. watch out for the smell as well!

tbh - I love the stuff. and its sands to oh-so-smooth smoothness!

piccies would be nice - just cos I am interested!

Nate
 

Stormrider

Well-Known Hunter
If your object is solid, no flex. use bondo creme. As long as your doing thin coats. Fill the major holes with bondo, then use the creme in 3 paper thickness layers or less to get a fast drying easy easy sandable surface.

A shot of good primer between coats hardens the creme and bonds to it.
 

stormtrooperguy

Sr Hunter
i also like water based wood filler for minor stuff... smooths on with your finger and can be feathered out with a little water. often i don't need to sand it at all.

i usually do 1 round of bondo, sand it out, then use wood filler for the little bits that still need love.

on the hardener note, you get to know by color how fast it will cure. make sure to use colored hardender - i've got a couple of tubes of white, and it's near impossible to tell if it's mixed well. gray with a pea sized drop of white still looks gray.

the redder the bondo when its mixed, the faster it will cook. so i play with that, and sometimes add a lot more hardener than i should for instant gratification.
 

BOBA PHAT

Active Hunter
BTW Bondo will eat styrofoam. I'm pretty sure that the blue/pink insulation foam is solvent resistant, but don't take my word on that.

If you do go and use expanding foam and paper, I'd recommend Hilti over Great Stuff. With Hilti, spritz your part with water before adding the foam. Then add just enough to cover the inside of your form, and then spritz the foam again. It will expand, but as long as it has the bottom of the form to expand out of, you should be fine. The water will help it adhere to the paper, and should speed up the cure time. Just go back and cut out the excess.

Good Luck!

-Ryan
 

Mic Pro

Jr Hunter
I bought a pint of Bondo Body Filler:

http://www.3m.com/US/auto_marine_aero/Bondo/catalog_item96ec.html?itemNbr=176

261.jpg


Is this the stuff that eats styrofoam? What if I coat it with primer first, then Bondo it? The paper molds with the expanding foam looks fine, it just bulged out in certain spots. I still have the pieces but there's more work involved than if I were to just go ahead with the styrofoam. I made a test piece before doing it and I took that piece and put it in the freezer. I took it out this morning and I didn't notice much difference contraction-wise.

Edit: Would Bondo eat through masking tape overtop the styrofoam?

DOES BONDO EAT THROUGH SINTRA?! I need to shape my knee pads!
 
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tbone9600

Active Hunter
I use the bondo fiberglass resin jelly on sintra all the time and it does well. Like the regular bondo though, it will "eat" styrofoam. As far as the masking tape... I don't know.
 

Mic Pro

Jr Hunter
I did a preliminary test this morning on styrofoam and sintra. The styrofoam, has suffered some breakdown on contact. The Sintra looks okay. Which is great, cuz I have to Bondo and shape my knee pads and codpiece tonight.
 

BOBA PHAT

Active Hunter
Sintra is a PVC material and works very well with Bondo. Masking tape might work, or brush on several layers of a shellac primer.
 

Mic Pro

Jr Hunter
Sorry, I meant spraycan primer on masking tape. I've gone back to my paper molds filled with Mono expanding foam. I've reshaped the pieces where the foam made it bulge, so it's like, 85% cardstock and about 15% exposed foam.

I was planning on covering the exposed pieces with masking tape (painter's mate) and then primering, then Bondo.
 
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Mic Pro

Jr Hunter
Well I covered the piece with Bondo right over top the tape and it seems to be holding fine. Everything looks good so far. I sand and shape tomorrow. Tonight I only have a few hours before I have to play a gig (drums in a blues band). Really wish I had all night to work on this!
 
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