TheNeedForZ Posted August 10, 2005 Share Posted August 10, 2005 A bad and crazy day, long story short : There are some steel patches welded on my 260Z body shell. Generally speaking the welds are not very skillfully done(these were done before I got the car). Now that my car is media-blasted from head to toe, there are tiny holes(about 0.010"~0.030" in diameter) along the welding seams that you can see thru. The paintshop owner told me that no matter what I use to protect bare metal, when bondo is applied on the seams full of tiny holes like on my car, bondo will bubble up in monthes. My plan is to spray the entire car with Rust Bullet which is like POR15(but more user friendly, UV resistant, less finicky with topcoat)and can seal metal totally. After sealing metal with the special paint, the surface is basically a chemically inert surface with tiny holes. Then Bondo will be applied to that inert surface. The paintshop owner(he's an ole'timer with 20+year experience in this industry) insists that bondo will bubble up no matter what I do to the surface. I don't understand why would bondo bubble up even if the metal is totally coated and inert. If a piece of inert material has tiny holes on them, will bondo bubble up monthes after applied to the inert surface? What do you think? Thanks a lot Quote Link to comment Share on other sites More sharing options...
Hypertek Posted August 10, 2005 Share Posted August 10, 2005 One of the local "import shops" told me that they patch holes with JB Weld, then sand or grind em down.. I actually did this to my 240sx. I hear bad things about Bondo brand, so use Evercoat. I used a drill type body puller. But hey its my first time learning body work. Before http://img.photobucket.com/albums/v72/streetphase/DSC00552.jpg After http://img.photobucket.com/albums/v72/streetphase/100_0420.jpg As of today http://img.photobucket.com/albums/v72/streetphase/100_0537.jpg http://img.photobucket.com/albums/v72/streetphase/100_0536.jpg *Flat spot is from the fender pulling to fit wider wheels* Anyways, well Im not too worried, as long as the body filler does its wear and tear before I paint it, its ok. But probably not as bad as a 30+ year old car... Quote Link to comment Share on other sites More sharing options...
Dom Posted August 10, 2005 Share Posted August 10, 2005 Can't you just weld the holes? Quote Link to comment Share on other sites More sharing options...
innerware Posted August 10, 2005 Share Posted August 10, 2005 Once bondo is cured or any polyester resin type material is cured, it is cured. There will be no bubbling at all. Concrete can't bubble after it is cured right? What he is probably refering to is when applying the bondo over a hole there is a chance you smooth in an air bubble or pocket, thus leaving material that is not soo dense in spots. A good way to get material into holes is to inject them with a plastic syringe. You could also squeegie the material in from the back. Either way cured resin is cured. Just make sure there is ample surface texture for it to grip etc. Quote Link to comment Share on other sites More sharing options...
Jeff Posted August 10, 2005 Share Posted August 10, 2005 Bondo is porous even after it is cured. Since you won't be painting the back side the bondo will be exposed to moisture where it has filled the pin holes. Moisture can then get into the bondo and cause rust and/or the paint to blister. I don't think it would happen within a matter of months but it will eventually cause a problem. Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted August 10, 2005 Author Share Posted August 10, 2005 Bondo is porous even after it is cured. Since you won't be painting the back side the bondo will be exposed to moisture where it has filled the pin holes. Moisture can then get into the bondo and cause rust and/or the paint to blister. I don't think it would happen within a matter of months but it will eventually cause a problem. Actually I'll be(they'll be) painting the car everywhere. Quote Link to comment Share on other sites More sharing options...
DemonZ Posted August 11, 2005 Share Posted August 11, 2005 I agree with Jeff,... I believe what causes the bubbling is that most fillers are made of talc and is porous. Like a sponge, the bondo/filler will soak up water from the atmosphere, or from direct rain exposure. The process is, the bondo/filler gets baked by the car sitting in the sun, and the water inside the bondo turns to vapor that cannot escape fast enough through the entry point (paint chip, pin hole, exposed back side, etc...). The resulting water vapor causes the bubbling. If the underlying metal is unprotected, it's even worse, as the metal underneath the bondo will rust, and will pop off from the forces of the rusting metal. So what I do whenever I can is use fiberglass bondo/filler as the base/sealer coat, then follow up with easier sanding/lighter bondo later. That way, water cannot get at the metal as easy. I can't remember the name of the product, but you can buy it at the automotive refinishing store, or a boating store. Basically what you want is a water impervious bondo. Also, if you don't let the bondo fully cure before topcoating, the great vapor escape process also applies. Quote Link to comment Share on other sites More sharing options...
Guest 305240 Posted August 12, 2005 Share Posted August 12, 2005 I also have to agree with Jeff. Bondo applied over any bare metal not properly treated will bubble up after awhile. The small holes only invite moisture. Bondo is like a spunge, it will soak up moisture. Old school here...If at all possable, grind the back side of the panel, treat it with a product called "Ospho". It's an acid that will stop any rust dead. POR 15 will work great also. Apply a thin layer of Bondo to the back side...let dry good. Then use any type of paint to cover and seal the bondo. I use products called "All metal, or Aluma lead" to do this when I can get it. Now go to the outside surface. Lightly grind the surface before you apply the bondo. NOTE: This is importent. Use a propane torch and flash the moisture off the bare metal. You will see it run before the flame. Then apply the Bondo. Any ammount of moisture trapped between the metal and bondo WILL bubble up...Guarenteed. Throw your DA and air files away. Use a paint stick wraped in sandpaper. Sand smooth using the following grits...80....200....300. Then lightly flash the bare metal spots again. Use a heavy fill primer such as Ditzler Condor. Water sand the primer with a paint stick wraped in 400, then to 600. You will have to hit it with more primer a few times to get it smooth with out and metal showing. If you do this, the primer will be as smooth as glass. I'll guarentee you can look down the side of the car and not get sea sick. Quote Link to comment Share on other sites More sharing options...
innerware Posted August 12, 2005 Share Posted August 12, 2005 OK so we all agree if not prepped right bondo will absorb moisture. But if prepped correctly it is fine. I have never seen a problem with moisture causing bubbles on a properly prepped area. Mix it right, let it cure right, prep area correctly, and paint over it with a barrier paint (non spray can primer) and you should be ok. If the area has a hole make sure you seal the back of it, or paint the back once bondo'ed. Is this safe to say? Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted August 12, 2005 Author Share Posted August 12, 2005 Can Rust Bullet (again, a rust proofing paint like POR15) be used to seal the bondo? The process now becomes : 1. paint rust bullet on bare metal(both sides) 2. apply body filler 3. after shaping and curing, apply rust bullet to completely cover bondo area. should this be able to seal bondo? Quote Link to comment Share on other sites More sharing options...
pdinnell Posted August 13, 2005 Share Posted August 13, 2005 I'm using short strand kitty hair to fill my moulding holes, made by evercoat. It's not porous, after that a skim of bondo and it will never bubble. Quote Link to comment Share on other sites More sharing options...
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