It's been mentioned several times about the max. thickness that one should apply bondo. If the bondo is( too thick) in a area after it's sanded and prepped it may be prone to cracking .Is there any rule-of -thumb as to the max thickness where you are still safe? Gene
You'll get a bunch of different opinions on that. If you can almost read thru it you'll have absolutely no worries, that's pretty unanimous. It's a way better job to bump the metal closer than to pave over the unevenness. The problem is once you start and start blocking then find the high spots you missed that make the low spots even thicker & it's a really ****ing hard thing to do and start over, however that's probably what you should do. Remember it the high spots that ruin your day because everything needs to come up to those.
It's the other way around. I have seen 30 or 40 year old bondo peel off a rusty fender if it was 1/8" to 1/4" thick. Have never seen thicker bondo peel or fall off, except due to accident crash damage. And I have seen it up to 2" and 3" deep. This is based on 50 years experience working on cars in the rust belt, not some theory I saw in a magazine or on the internet.
I work for a filler company and we recommend nothing thicker that 1/4". The biggest cause of filler cracking is too much hardener. Filler becomes very brittle when it is over catalysed.
There you go, different opinions. I guess if the mud never feathers you just make your car 4-6" bigger
The label should state the max thickness. There may be a product information sheet for the product as well.
So in 50 years I bet a fella does a lot of cars, I gotta ask how many are you responsible for in the bondo abuse thread. 2-3" deep ? A hammer is cheaper than a gallon of mud
1/8" max is the general rule. Either over clean bare metal with a good scratch pattern or epoxy primer sanded with 80 on a da. Sometimes its hard to tell how thick the filler will be, on low crown panels a straightedge will show any low and high spots, on higher crown panels a profile gauge works good. An old school way that works great for highlighting highs and lows is a vixen file, but for beginners its best to use a long sanding block to avoid removing too much metal. That being said i have seen a couple cars with over an inch that lasted a long time. prep of the surface beforehand is key, filler doesnt bond well to old paint or rust. I worked on one car with really good metalwork that had 1/8" or less but the filler was cracking all over. The reason it was cracking is the metal had been sanded so fine that there was no grinder marks for the filler to bite into. It looks cool to polish up the metal nice after the metalwork stage, but before i go to put filler on anything i always go over it again with a grinder and 80 grit to put a nice scratch pattern in, then wipe it down with an automotive wax and grease remover.
It's kinda like making a peanut ****er sandwich. You can spread it on an inch thick but you won't feel good about it afterwards. I vote for 1/4" on a daily and 1/8" on something I'm proud of.
I've seen a lot of guys put bondo on metal that has not been etched with a body disc. This is trouble down the line. I use a 80 grit disc cut in a hexagon and lightly grind the area to give the bondo something to bond to. I always grind the metal fresh before bondo as the metal will start to oxidise and resist touching it after grinding. I'm not a believer in this bondo on primer bs.
I have been doing polyester filler over primer for 25-years. No issues. Never over 1/8". Hammer and dolly, or stud gun, are your friends.
Better today as their more flexible,laying it down is no easy task,it takes practice,maybe checkout y/tube for ideas,Gaz!
Watched this guy, Ian Roussel on the TV show Full Custom Garage chop the top on a Packard, he stated he used "2" gallons of bondo on that roof. WOW. http://www.fullcustomgarage.com/videos/
I bet, have any idea how much faster it is to spouge out 2 gallons of mud that to make the metal right.
I dread to think how much filler I used in my C Cab, but then it's all resin anyhow so no compatibility issues. Never go overboard on the hardener is all I can say. I sometimes make up my own filler using resin and microballoon powder, then I can control the ratio of resin to powder for consistency that suits the job.
If you think it's hard to find quality work, it's even harder to find a customer who will pay for it. I remember a 68 Camaro that had the vinyl top go bad. If you have never seen that happen the roof was a m*** of rust under the vinyl. The customer would not pay to have a new roof welded on and would not pay to have it fixed properly. I peeled off the vinyl top, ground off the rust and glue as best I could, dumped a whole gallon of bondo on the roof and smoothed it out. When it dried I sanded it smooth with an orbital sander and 40 grit, then sprayed it with stoneguard and a coat of black primer to make a cheap vinyl top. The customer was happy, the boss was happy, and I got a pay check that week. I wasn't working in heaven, or some car magazine or internet fantasy. I get a laugh out of guys who know how to criticize everything but they never worked in a shop in their life.
I have restored cars that were so far gone with rust no one else would touch them. All hand fabricated patch panels and minimal filler. I can also do lead fill if anyone is willing to pay for it. Not many people are.
I'm a fan of 1/8 inch or less. 1/4 inch max. If I can't get it straight enough for that. It needs to be replaced. Prep is the key. Grind your metal with a co**** grinder like 36 grit, and I like to grind to bare metal. Never leave your mud out in the weather, and sand it while it's soft. Hard mud takes to much work. I like to smear it once and sand it in 36 grit, finish it 80. I then like to put a real thin coat on and sand it in 80, finishing in 120. This makes primers job a little easier. Less scratches to shrink back on you. Posted using the Full Custom H.A.M.B. App!
never worked in a shop in their life. That's probably the key to your angst and criticism. If the boss is ok with it, you (not you but all) should be ok with it. It's the boss's name on it, it's his *** if it goes wrong and all are just chasing a pay check. I've had a few bad bosses try to teach me some bad habits and try to get me to conform to their ill thinking. Thankfully I knew the difference way before encountering them.
My "rule" is if a fridge magnet will still stick (those little thin ones that look like a decal). It seems to be the best compromise of cost and quality. On good work I get close enough for a wisp of metal glaze. Never understood the desire to mud up a whole car. Just get a fibergl*** body and be done with it. The other part of layered fills are the differences in hardness. For a 2nd coat (rarely needed) I mix in some metal glaze (finishing putty) to change the consistency. Works like a charm. I'd rather pick n file. That vixen file on the metal is the most honest tool in a body repair ****nal.
Maybe OT but I once owned a 1950 25' Roamer Cabin Cruiser ( steel, but it was not a Chris Craft ) that had burned decades ago. I stripped it to bare metal for a repaint. The heat from the fire had warped the hull sides up to 1/2" over a wide area. Yup! Someone had filled it with bondo and it held up just fine. Of course the metal was about 1/8" thick, but I am sure there was some oil canning going on with the waves on the Great Lakes. My 2 cents.
shoot for as little as possible. I like to follow the refridgerator magnet rule myself, that siad, the first time my avatar was rebuilt after the house fire the cowl top as probably an inch thick--it sunk flat and as "sculpted" by someone using mud. I left that mud in when I got the truck back in 1985 or so and it's still there today and not cracked. But I'm taking it out this time and fixing it right. BTW, the 1/2 inch or so I put in parts of the doors was still in and fine after 20 years of it running as a stiff suspension, hard mounted body rattle trap too. they didn't call me bondo boy for nothing in high school. I know better now, though.
There are 2 points I wanted to make. One is, thick bondo is not going to fail because it is thick. I have seen a lot more thin coats of bondo peeling off a car than thick coats. Anyone who has worked with old cars in the rust belt can tell you the same thing. The second thing is, lots of cars were fixed crudely in the past because the customer would not pay for good work. The bodyman knew how to do it right but the customer wanted the cheapest job possible, and the bodyman had a family to feed. So don't be too quick to condemn someone you know nothing about. For a bonus you could be philosophical and say, if my car had not got a cheap repair back when it was just another second hand car, it would probably have been s****ped. In other words it was not a choice between a cheap job and a good job, it was a cheap job or a quick trip to the junk yard. In that case you could be happy that at least it survived, and you are smart enough to fix it properly.
If you say thick bondo is crude and you prefer to metal finish to perfection I agree 100%. But that is another story.
no blanket answer to question. post pics of what you are working on. like anything, it is the basic prep work that makes for a good finished product. yes, if at all possible repair metal or replace a heavily damaged part. sometimes doing a lot metal work can cause problems within the metal itself. some parts can not easily be worked on with limited or no backside access. sometimes there is no easily obtained replacement piece. yes, even big time body guys at times have to use bondo. just like paint, prep area and put on a thin coat at a time. have to make sure that whatever products that you use are compatible with one another. a lot depends on your skill level, or that of the guy doing work for you. a deep wallet helps sometimes too but, still not a guaranty of a good finished product.
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