How To Use Bondo Body Repair Kit
At that place is not a more maligned automotive product than "bondo". Plastic body filler is nigh often referred to by the brand proper name "Bondo" (fabricated by 3M), and its bad reputation comes from decades of poor application and misuse. Nearly every loftier-end custom car or restoration has some corporeality body filler on it. Using information technology on your daily commuter or projection is not a bad affair, as long every bit you use it the right way. Learning how to use Bondo the right way isn't equally hard as you think.
History of Bondo
Like well-nigh plastic body fillers, Bondo is a lightweight polyester-based plastic body filler that was originally developed equally an alternative to lead body solder. One-time school body shop techs used to melt strips of lead with a torch to fill up body imperfections and joints. The Bondo brand name was created in 1955 by Robert M. Spink, just a few years after the use of pb body solder began to be prohibited. Many bodyshop men of that age were non sold on the idea of using plastic body fillers, but over time, it became apparent that the lightweight, piece of cake to utilise nature of body filler was a benefit over lead. Not to mention that lead body solder is very unsafe to work with given the demand for a torch to oestrus it, pb fumes, and even lead dust from sanding. In comparing to working with molten lead using plastic body filler but made sense.
Bondo Abuse
Where the bad reputation comes from is misuse and incorrect application. Nosotros've probably all seen a machine in the parking lot that looked similar someone slathered on trunk filler with a trowel. Don't do that. Plastic body fillers are intended for minor dings and smoothing out warped panels, non a major repair itself. It was never intended to fill large dents, rust, or other major body damage. Information technology does not move or or behave like a metal body console. Why would yous waste material fourth dimension laying downward a gorgeous paint task if you lot know the gigantic hulk of plastic body filler behind information technology could actually pop off in the future?
You can really bank check whether a car has besides much trunk filler by using a refrigerator magnet. Put a piece of paper betwixt the steel body panel and the magnet (to protect the paint), and so see if the magnet sticks to the car. If a magnet won't stick to a steel body console, it may be loaded with plastic body filler.
Working With Bondo The Right Style
Now that you know a piddling more about plastic trunk filler, you can start working with it the right way. But there are a few fundamental points that you lot should know before working with body filler:
Thickness Matters
At that place is no minimum thickness for Bondo, but at that place is absolutely a maximum. Y'all do non want to utilize body filler to anything that is thicker than about a 1/4". That does not mean information technology can't be done, but the repair volition not last as long. Eventually the filler will shrink and perchance crevice, or even popular off! The general rule of pollex is that if the paring it deeper than ane/eight" you demand to do metal work offset. Call back, your nice paint job depends on a solid foundation. Simply troweling on the filler may expect like the easy button, but that slab of filler may determine to fall off some twenty-four hour period (we've seen it happen).
Fix The Foundation
What you are working with needs to be properly prepped BEFORE y'all apply any body filler. Do not slap Bondo onto a smoothen painted surface, it is non going to stick very well. The paint should be sanded off, to the bare metal, and then apply the filler. A 36-grit to 180-dust surface is platonic for body filler application so that the filler has a good rough surface to grip.
Non For Every Location
Don't use body filler on full gas tanks, or anywhere that gets hot. Bondo is resistant to fuel, just but after it is cured. If you are smoothing out a gas tank, that is great, it you are trying to set a rusted out gas tank, this is not going to do a proficient chore. Don't misfile Bondo with JB Weld, the two are not the same.
It Won't Magically Fix Rust
Body filler is not skillful for rust repairs. Y'all cannot slather some Bondo over rust and expect it to stop the rust or stick to it for that matter. For rust repairs, y'all must first remove any rust scale from the metal. If in that location are holes in the metal, you are much better off cut it all out, patching it with new metal, and then working the body filler from there. Whatever rust left under the filler volition continue to grow, and so don't be surprised if a small repair turns into a bigger problem down the road. If y'all absolutely must use body filler to make the repair, then you should remove all the rust scale, add a backup screen to cover the holes from the back side, and then use Bondo Bondo-Drinking glass over the rusted area, sand and cease out with regular Bondo body filler for a stronger repair.
Pay Attending To The Mixing Ratio
The mix is crucial. Nearly of this comes from experience, but you tin get close to the optimum mix with this tip- use 1:one ratio of inch bore of filler to inch-length of hardener. A 4-inch diameter of raw filler needs a four-inch ribbon of hardener at room temperature. If it is hotter (above 85 degrees), utilize slightly less, if is colder (beneath 65 degrees), apply slightly more than. If your filler hardens too fast, you used also much, if it takes too long, yous didn't use enough. Y'all only desire to mix what you can utilise in almost x minutes. Properly mixed, torso filler will brainstorm to thicken in 10-15 minutes, and be fully cured in 30. Until you get the hang of mixing it is wise to buy a chip more than plastic trunk filler than your project needs so you lot have room to endeavour again without running dorsum to the store.
Do not whip the torso filler while mixing information technology. This will incorporate a lot of bubbles in the filler, which means more pinholes to set later. Apply a slow and deliberate figure-X design, wiping the filler across itself.
Awarding Technique Is Key
You can use plastic or metal spreaders, choice is up to your personal preference. Metal spreaders last longer and provide a more than divers edge, simply plastic spreaders are cheap and tin be custom cut to match shapes. Apply the filler to the console, pushing the filler into whatsoever crevices. Wipe the filler equally shine and level every bit possible, but leave plenty of extra filler above the surface level to sand the repair smooth. Improve to take a little too much filler and sand it off, than have to mix up another batch of filler for a low spot.
Get Ready To Sand…A Lot
There are two schools of thought on when to sand filler. If you are doing general bodywork, leveling wavy panels, fixing small dings, etc, then wait until the filler is fully cured, about 20-xxx minutes. If you are using a lot of filler or doing some shaping with the filler, you can use 36-grit sandpaper when the filler is in the "light-green" phase, this is solid, slightly rubbery, just not fully hardened. Using low-cal force per unit area, you can knock off large amounts of filler to rough-in the shape needed earlier the filler hardens, making sanding more labor-intensive. And don't forget the respirator and safety glasses, fine filler dust tend to get everywhere when sanding.
The cardinal to a quality body panel repair is seamless filler piece of work. The edges of the filler should feather out to the existing panel. Y'all should not be able to feel where the metal stops and the filler begins. Any defect you see or feel in the filler will be amplified when the paint is on the trunk, then check the console repeatedly. Big repairs crave actress try, as y'all can easily get waves and ripples in the bodywork when working a big area. Never sand in straight lines, instead use a criss-cross pattern, up and down, side to side. This eliminates waves and results in a much ameliorate repair.
Bodywork is a slow, slow task that takes time to master, simply is piece of cake to learn. Don't be agape to use Bondo, equally it is a skilful quality product that is a must-have for whatsoever body repair project. And don't worry if you screw up, you lot tin can ever sand it off and start over.
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Jefferson Bryant View All
A life-long gearhead, Jefferson Bryant spends more than time in the shop than anywhere else. His career began in the car sound industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Arts and crafts, Hot Rod, Rod & Custom, Truckin', Mopar Muscle, and many more. Jefferson has as well written 4 books and produced endless videos. Jefferson operates Red Clay Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.
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