Can You Apply Bondo to Bare Metal "Bmw"
In that location is not a more maligned automotive product than "bondo". Plastic body filler is well-nigh often referred to by the brand name "Bondo" (fabricated by 3M), and its bad reputation comes from decades of poor awarding and misuse. Every loftier-end custom automobile or restoration has trunk filler on it. Using it on your daily driver or projection is not a bad thing, as long every bit you use it the right way.
Like most plastic body fillers, Bondo is a lightweight polyester-based plastic body filler that was originally developed equally an alternative to lead body solder. Erstwhile school body shop techs used to cook strips of lead with a torch to fill body imperfections and joints. The Bondo brand name was created in 1955, merely a few years after the utilise of pb body solder began to be prohibited. Many bodyshop men of that age were non sold on the thought of using plastic torso fillers, but over time, information technology became credible that the lightweight, easy to use nature of body filler was a benefit over pb. Non to mention that lead body solder is very dangerous to work with given the need for a torch to rut it, pb fumes, and even pb dust from sanding.
Where the bad reputation comes from is misuse and wrong application. Plastic body fillers are intended for small dings and smoothing out warped panels. It was never intended to fill up large dents, rust, or other major body damage. There are a few key points that you should know before working with body filler:
Thickness Matters
There is no minimum thickness for Bondo, but in that location is admittedly a maximum. You exercise not want to utilize body filler to anything that is thicker than nearly a 1/4". That does not mean information technology can't be done, just the repair will not final as long. Eventually the filler will shrink and possibly crack, or even popular off! The general rule of thumb is that if the dent it deeper than 1/8" you need to practice metal piece of work first. Call back, your nice paint job depends on a solid foundation. Simply troweling on the filler may look similar the easy button, just that slab of filler may decide to autumn off some day (nosotros've seen it happen).
Prepare The Foundation
What you lot are working with needs to be properly prepped BEFORE y'all employ whatever body filler. Do not slap Bondo onto a smooth painted surface, it is not going to stick very well. The paint should be sanded off, to the blank metallic, and then utilize the filler. A 36-grit to 180-grit surface is ideal for body filler application and so that the filler has a good rough surface to grip.
Not For Every Location
Don't use body filler on full gas tanks, or anywhere that gets hot. Bondo is resistant to fuel, but only after it is cured. If you are smoothing out a gas tank, that is bang-up, it you are trying to fix a rusted out gas tank, this is not going to do a good task. Don't confuse Bondo with JB Weld, the two are not the same.
It Won't Magically Fix Rust
Body filler is not good for rust repairs. You cannot slather some Bondo over rust and look it to end the rust or stick to it for that matter. For rust repairs, yous must first remove any scale from the metal. If there are holes in the metal, you are much better off cut it all out, patching it with new metal, and so working the body filler from there. Any rust left nether the filler will keep to grow, and then don't exist surprised if a small repair turns into a bigger problem down the road. If you absolutely must use body filler to make the repair, and so you should remove all the scale, add a backup screen to cover the holes from the dorsum side, then use Bondo Bondo-Glass over the rusted expanse, sand and cease out with regular Bondo body filler for a stronger repair.
Pay Attention To The Mixing Ratio
The mix is crucial. Almost of this comes from experience, but you lot can become shut to the optimum mix with this tip- use 1:1 ratio of inch bore of filler to inch-length of hardener. A 4-inch bore of raw filler needs a 4-inch ribbon of hardener at room temperature. If it is hotter (above 85 degrees), use slightly less, if is colder (below 65 degrees), use slightly more. If your filler hardens also fast, you used likewise much, if information technology takes too long, you didn't use enough. You just want to mix what you can use in near 10 minutes. Properly mixed, body filler will brainstorm to thicken in ten-15 minutes, and be fully cured in 30.
Do not whip the body filler while mixing it. This volition incorporate a lot of bubbles in the filler, which means more pinholes to fix later. Employ a boring and deliberate figure-X pattern, wiping the filler across itself.
Application Technique Is Cardinal
Yous can use plastic or metallic spreaders, your pick. Metallic spreaders last longer and provide a more defined edge, simply plastic spreaders are inexpensive and tin exist cut to match shapes. Apply the filler to the panel, pushing the filler into whatsoever crevices. Wipe the filler as shine and level equally possible, only leave plenty of extra filler to a higher place the surface level to sand the repair polish. Better to have 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 2 schools of thought on when to sand filler. If yous are doing general bodywork, leveling wavy panels, fixing small dings, etc, then await until the filler is fully cured, most xx-thirty minutes. If you are using a lot of filler or doing some shaping with the filler, you can utilize 36-grit sandpaper when the filler is in the "green" stage, this is solid, slightly rubbery, but not fully hardened. Using light pressure, you can knock off large amounts of filler to rough-in the shape needed before the filler hardens, making sanding more labor-intensive. And don't forget the respirator and safety glasses, filler grit tend to get everywhere when sanding.
The key to a quality repair is seamless filler piece of work. The edges of the filler should feather out to the existing console. You should not be able to feel where the metallic stops and the filler begins. Whatsoever defect you meet or feel in the filler volition exist amplified when the paint is on the body, and then check the panel repeatedly. Large repairs require extra effort, as you lot tin hands get waves and ripples in the bodywork when working a large area. Never sand in directly lines, instead use a criss-cross pattern, upwards and down, side to side. This eliminates waves and results in a much better repair.
Bodywork is a slow, tedious task that takes fourth dimension to chief, but is like shooting fish in a barrel to larn. Don't be afraid to apply Bondo, as information technology is a good quality product that is a must-accept for any trunk repair project. And don't worry if you screw up, you can always sand it off and get-go over.
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Jefferson Bryant View All
A life-long gearhead, Jefferson Bryant spends more fourth dimension in the shop than anywhere else. His career began in the automobile sound manufacture as a store director, eventually working his way into a position at Rockford Fosgate as a production designer. In 2003, he began writing tech articles for magazines, and has been working equally an automotive journalist ever since. His piece of work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin', Mopar Muscle, and many more. Jefferson has besides written 4 books and produced countless videos. Jefferson operates Carmine Clay Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.
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