Will bondo stick to a surface that is treated with POR15? I would do the three step POR15 treatment. I'm trying to patch up an area the size of a half dollar. Would bondo even work for an area that big? I would use the bondo that has the fiberglass hairs in it.

 

I have seen bondo fill some massive holes and hold for a long time.

 

Yes it will hold you might have to apply it a few times to fill it all but dont just put it on cut all the rust out or it will just come back soon......

 

Bondo will hold to anything that is keyed. By that i mean scratches surface either with sandpaper or scrub cloth. Be aware though that different bondo is rated for differnt things. Some are rated for over painted surfaces and some for on bare metal. Be sure to check the can first. a dent the size of a half dollar wont need the fiber filling bondo just regular. Fibre is strong but will be a bitch to get flat for painting in that size unless your filling a hole. if your filling a hole( rust hole) put something behind the panel to give the bondo something to stick too. Chicken wire .... aluminum foil... paper ... something otherwise it will just fall out. Sorry bout the long winded thing but dont want to see you do it and have to redo it again the following week

Ok with the POR15 yes it will but again needs to be keyed. Be warned... once rust has started it will continue to grow no matter what is covering it. The coating is doing what it says... placing a rock hard coating over it but the panel underneath will continue to rust due to mositure in the metal.

If budget is tight go to Tractor supply or Home Depot and pick up some 20 guage sheet steel. Roughly form it to the shape you need then cut out the old rust with an angle grinder and pop rivet the new panel in with some seem sealer. Then bondo over that.

 

Why not email POR 15. They have given me great customer service in the past.

jamie

 

After looking through their products a bit, I found this:
http://www.por15.com/STRAIGHTLINE/productinfo/STL20/
Kinda answers my questions. Thanks guys! I'll be sure to post my results

 

Actually, the POR15 is non-porous, so whatevers underneath it will cease to rust entirely due to the lack of oxygen.

The best way to fill that hole would be to just weld a new piece of steel onto it.. it doesnt look like it would be that hard.. Then, you could throw the bondo-putty over it to fill in the pitting.

 

I don't have access to any welding equipment. Thinking about it now, I want to remove the rust with naval jelly then apply the por15. Maybe get the hole welded up after that? How much do you think a shop would charge to weld it? What about painting that section?

 

well, if you know anybody with a welder you could have them weld it on.
I dont know if a welding shop would do something that small but idk.