Humungotron
Jr Member
Ahh, bondo. Nothing beats the smell of cracking a fresh can. Even now it gives me a headache.
Notice its not Bondo. Marson, the company that makes this, also makes bondo. This is better.
Herein, I will explain, to the best of my abilities, everything you need to know about plastic body filler, its uses, abuses, and the fastest and easiest way to get it to do what you want.
- History. (feel free to skip this part).
Before plastic body filler was invented, any time you wanted to do bodywork on a car, lead was used. typically in a 70/30 ratio with tin. Yes, Lead. the stuff in your car battery.
The problem with lead is that it's applied at approx 350-ish degrees. I dont know the exact temp, I just know by feel when applying it. and it sucks. Once you have the lead on the car, you have to file about half of it off. It kicks out lead dust, and you will typically burn yourself alot. But I digress.
As far as I know, and don't quote me on this, plastic body filler came out in the mid 50's, about the time that fiberglass became prevalent. the two technologies came into existence hand in hand. Seeing as they both utilize the same resin and catalyst mixes, its not that far of a draw to figure out why. Obviously, they suck far less now than they used to.
-and frankly, thats probably more history than you care to know. I know more, but to you its useless.
- Types of body filler.
There are quite a few different brands, many of which belong in a trash can. I've used alot of various products, and I'll try to steer you away from the ones that suck.
The biggest one that sucks? Bondo.
The problem with Bondo is that because its produced in such massive quantities, the quality control on it has gone out the window. Also, plastic body filler has a shelf life, and because it's produced in such quantities, the people who are most typically going to stock it (checker, autozone, the like) dont understand that fact, it'll go stale on you. That, and most people hang on to it waaaay too long. its got a 6 month shelf life after opened, tops. Unless you're hanging on to it for a show and tell project, toss the can. No, seriously. THROW IT AWAY.
I know, you're saying something along the lines of 'shelf life? wtf?'. Seriously. It does. Ever opened a can of bondo that had the consistency of peanut butter? That can is toast. A fresh can of body filler has the consistency of pancake batter. thick, but easy to stir. Anything else has bled off the plasticizers and resin in the form of vapor, and while still usable, is going to make you job alot more difficult. Not only is it a pain to spread, but you can't be sure when or if it's going to kick off.
Bondo is poop, pure and simple.
USC and Marson make some decent products that are comparable in price and quality. If you're going to be using alot of it, you can get a gallon can. Personally, I like Marson platinum. look familiar?
Granted, you're probably only going to need a gallon if you're doing a full suit, but this was a 3 second google search. It's also available in quart sizes.
For those of you familiar with spot putty, its a little thicker, but its got a very consistent kick time, is vacuum made (no bubbles), doesn't shrink (yes, bondo will shrink), sands quite nice, and you don't have to worry about gas-out (some body fillers will continue to catalyze, kicking off fumes for what seems like forever. This stuff doesn't).
Second on my list is the USC line of products. USC's base/clear
Yes, it's a little more expensive, but it sets up harder than the platinum does. It's tougher to sand, but ideal for use on something thats going to take alot of abuse.
There are other types of fillers out there, but these are the two brands I prefer, and I've used just about all of them. You may have found something that works better for you, maybe not. These are worth giving a try.
Another thing you should know about, and I've yet to see it mentioned here, is kitty hair, or Duraglass.
Duraglass is basically chopped fiberglass added to plastic body filler (from here out, referred to as PBF. I'm not calling it bondo. Bondo is to PBF what bottom shelf vodka is to grey goose). Typically, when you're applying PBF, the maximum thickness you're looking for is 1/8th inch. anything over that is likely to crack out because of improper gas-out. Also, the additional thickness can cause heat buildup, and may screw you in the long run, as PBF gets chalky when it gets hot.
So, say you're building a chest piece, and you want to curve out the suit. Build it up close with Duraglass, then clean up the details with PBF. This will not only strengthen your armor, but it'll make it last longer in the long run.
Finally, we get to spot putty. While alot of you guys are touting the benefits of how well it spreads, you need to be aware that spot putty isn't really designed to be applied in large quantities or thicknesses. When I use it, its typically only to fill pinholes or scratches. THATS IT. anything over a 1/16th of an inch may crack out on you. Alot of the better PBF's will spread just as nicely as spot putty does. But if you really really want to use spot putty, use standard PBF and add 'glass resin to it. Its the exact same stuff. In fact, you can get PBF thinner at any specialty supply shop, or on-line, like here.
If you insist on using the resin mixed with the PBF, go with the thinner. It's cheaper than the resin, and is designed to work with body filler, meaning it won't make it brittle. Plus, that leaves more resin for your glasswork. Nothing's worse than running out of resin halfway through a project.
-Mixing
And this is where everyone starts to argue.
I've lived in 5 states in the last 2 years. I've been from northern Washington to Arizona. I know what I'm talking about.
COLD AND HOT WILL CHANGE HOW YOUR MIX KICKS OFF. Period.
When PBF is mixed with hardener, it creates an exothermic (heat generating) reaction. Humidity and ambient air temperature will change how quickly it kicks off.
For example: While in northern Oregon, in the middle of December, approximately 300 yards from the Columbia river, I was working in a body shop, and freezing my ass off. I mixed up some PBF to fix a small spot on a fender. Using a glob about the size of a racquetball, I added half a tube of hardener to it. Yes, one half tube, for what would normally require about a 1 1/2 inch ribbon.
It took 20 minutes to set up.
Last week, here in Phoenix, I was mixing up some of the exact same product (marson platinum) to do a spot fill to hold together an MDF dash thats being made to create a 'glass mold for a car.
I mixed it a little hot. For a glob the same size, racquetball-ish, I used about an inch of hardener.
It was about 90 degrees out, and dry as hell. This is the desert, after all.
It took 2 minutes to set up.
Other things that can effect how quickly or slowly your mix kicks off are the age of the PBF and hardener, and you mixing board. No, seriously.
If you can help it, try not to mix on cardboard. the paper will soak up the resin and catalyst from your mix, and change the speed of the reaction. And unfortunately, there's no way to tell how. Grab a chunk of sheet metal, a cheap plastic cutting board, a cheap mixing board from a paint shop; anything non-absorbent. If you must use cardboard, mix up a test batch to get an idea of how your particular brand spreads, and coat the cardboard. Let it kick off (till it's rock hard), sand it flat, and use that as your mixing board. Trust me, it'll save you some headache.
Most cans list the following ideal ratio: for a golf ball sized blob of PBF, use a one inch ribbon of hardener.
Thats great, if you're in a lab, with a constant air temp of 70-ish degrees.
So, that being said, how much do you mix?
Well, thats a bugger. Aside from experience, the only way to tell, really, is to mix it up and see what it does.
My personal experience is that for every 10 to 15 degrees above or below that ideal air temp, change the ratio by a quarter inch accordingly. colder, add more hardener. Hotter, take it away. The only problem with me giving you this advice is that this is based on where I live, what I use, and how I use it. I can skim coat an entire side of a car in one pass, and to do so typically can take a quarter can of PBF. I can mix up that much at one time and not worry about ratios, air temp, etc, because I've been doing it for years. If you're just starting out, it gets a little tougher.
Ideally, you should have enough hardener in the batch you're mixing to give you 10 minutes or so of work time. And that is going to vary according to the humidity outside (rain does factor in, keep it in mind) the air temp, and the product you're using, so work in small batches till you get the hang of it. I'd recommend starting off with something smaller, like boots, hand guards, or extremities (arms, legs, the like). Don't go full gusto on the detail pieces until you've got a hang of it. Nothing would be worse than having to sand a hot batch off of a detail or inset corner on a helmet. Theres a term used in the industry to describe this process. Its finger f**king. And its not as fun as it sounds.
Try doing this for a day. Then go home and cover your fingers in bandaids.
Now you're ready to mix. So what?
Before I start rambling again, a word on spreaders.
There's two types, plastic and metal. metal spreaders are great for big flat panels. plastic spreaders are great for complex curves, and also great for flat panels. as I work on cars, I use mostly metal spreaders, but I have several plastic ones sitting around, because when you need one, nothing else will do.
When it comes time to mix the two together, for the love of sweet infant baby jeebus DO NOT MIX IT LIKE ITS CAKE BATTER!!!!!
All this does is introduce air into the batch, making for bubbles and pinholes in your final product, which means more work.
What you want to do is scrape up the hardener with the spreader (most spreaders look like spatulas without handles) and smush it into the PBF. smear it out, scrape up the semi-mixed pile at a 90 degree angle from the smear you just took, and repeat. Its kind of hard to explain, so watch this -
Matt mixing. Ignore the radio. -Video
(You'll notice he's using blue hardener. It comes in several colors - red, blue, green, yellow, and white are the ones I most commonly see. They all do the exact same thing. You can also use all of the various colors for duraglass, and, in a pinch, for fiberglass. No, I'm not lying.)
You're looking for an even color, with no streaks. Shouldn't take but 2 or 3 minutes of mixing to get a good even blend.
-Spreading
If you've ever made a cake, and put frosting on it, you're ready to go. Its not that hard of a concept. There are a lot of little tricks to it, but its going to be about angles and the like. If you're not very comfortable with the idea of just smearing it on, try this.
Go to harbor freight, or a grocery store, or home despot, etc etc. You're looking for either a chip brush, or a basting brush. The basting brush is a little wider than I prefer, but it'll do the trick in a pinch.
this will be your friend.
Using said brush, paint the PBF where you want it. this will let you get it on with less mess, less sanding, and makes for a much faster application. Once you've got it where you want it (or the bondo starts to kick off), swish it out in a cup with a little acetone in it, and you can use it again for the next batch.
heres an example. Ignore Dave. -video (sorry about the quality, my camera battery died. This is from my phone.)
this is after less than 5 minutes of sanding (brought it home so I could charge my phone and get a decent pic):
How do you know when the PBF is kicking off? it'll start to get a little thicker. then it'll start getting grainy, kinda the same texture as cream of wheat that's been left in the pan. Then it'll start to crumble. The surface will stay tacky while the reaction is taking place, so thats probably going to be your best bet as to how to judge when you can start sanding on it.
fully kicked... still soft enough to scrape off though.
I've heard alot of people say they've had varying success with applying PBF coats over each other without sanding. Personally, is the first coat is still tacky to the touch, I can feather out the edge of my new batch without any worries. However, I've been doing this for a long time, so I know the limits of what can and can't be done. If you're just starting out, I'd recommend waiting until the first layer has kicked off completely, then hit it with some 36 grit paper before you put on the next coat. This will give the second application some mechanical bite, something to hold on to. Theres nothing worse than having to sand or scrape a fresh coat of PBF off a car because you know it's going to flake off. Any PBF applied over a fully cured coat of PBF will, in my experience, flake off. And that is a pain in the ass.
-Sanding
Most body shops have a certain procedure for how they sand the car, depending on the repair, etc. The cars I work on are typically in the 50 to 100 thousand dollar range. As such, the paint on these cars is super flat, extra shiny, and thicker than you think.
Thats great and all, but why do you care?
Because I'm going off the assumption that you want a nice paint job on your armor. As such, I recommend going in this order (this is the same order we use in my shop):
[this is after all your resin and 'glass work is finished]
1. Sand everything. nothing too hardcore, you're looking for something for the PBF to stick to. if you have air tools, this goes alot quicker. if not, you're gonna have to suck it up. You're just going for a quick pass with 36 grit. kill any shiny spots.
2. Prime. This isn't necessary, but it gives you a good base to see where you're gonna need to do more work. The color or type of primer is unimportant, just a nice even coat.
2b. Quick sand again, after the primer has gone dull. Again, its not necessary if you chose to not prime your armor pieces. 36 or 80 grit is fine.
3. Duraglass. build up anything thats gonna require a large amount of filler. This would be an ideal time to get any curves formed in your helmet, chest piece, etc.
4. Rough the shape out. You're not going for perfection, you're looking to get it to the shape you want. ignore getting perfect curves, super smooth faces, etc. get it to where you can stand back 5 feet or so, and it looks right. 36 grit is your friend here.
5. using 80 grit sandpaper, go back in and even out your shape. you're looking for the 3 foot appearance, meaning you can step back 2 or 3 feet, and it looks right.
6. PBF. NOW you're trying to get everything exactly where you want it. The chip brush is your friend.
7. Knock out any rough spots with 36, then fine tune with 80 again.
8. Now you're on to 120, cleaning up any details that you may have missed.
-keep in mind at this point that you may end up sanding through your primer. that doesn't matter, as long as the shape is satisfactory. This pic demonstrates this, as this has been primed twice, and still wasn't right. It is now, though.
9. Prime everything. by now, you're probably looking at several different shades of the same color, as no batch of PBF mixes the same. Its hard as hell to see what you're doing, so a good coat of primer will help you find the details you missed.
10. Refine. By now, you've probably come across pin holes, parts that look off, etc etc. take your time here, and use PBF sparingly, even swap over to spot putty. If you hurried in the last steps, this is your chance to fix your mess-ups.
11. Reprime. by now, you should be looking at a primed piece, ready to paint. HA! no it's not.
11a. Guide coat. all you're trying to do with this is put a dry light coat over the primer with a contrasting color. This will help you know what you're missing when you start to do your final sanding.
12. Because you get to sand some more. I'd leave the primed piece to dry overnight, even 2 days if you're not trying to rush things. there's gonna be 3 steps in this sand -180, 220, 340 or 400 (depending on what's available). The second and third passes are simply to remove the scratches from the previous grits. When you're done, the surface should look a little shiny if you view it at an angle.
13. Paint!
Don't think that you have to go out and buy sanding blocks. there's no block out there that will work for every application, and in some instances, I've had to make blocks. This is a small sample of the various blocks we use:
Yes, this is a long and involved process. Yes, it looks awesome when you're done. If you're going for a look thats a little less refined, you can skip a few steps. Again, thats up to you.
finished car we did, using the process above:
-cleanup
Acetone will clean PBF off of spreaders and brushes. If you're using plastic spreaders, and you've got a thin, rock hard layer on it, mix up a little and spread it thick on the spreader. after it kicks off, flex the spreader and it'll pull off the stuff you couldn't get off with acetone or a fingernail. If you leave it to harden on the brush, you now have a stick. Congrats.
If you get it on your skin, you can typically flake it off. Anything thats worked its way into your skin (typically around the knuckles and such) will come off in the shower with a little elbow grease.
Any PBF that gets on your clothes is now a permanent addition to that article of clothing. This is especially true of cotton/poly blends, as the PBF will basically melt into the poly as is cures. Even on an all cotton article, it'll be there for a few washes, if not more. Wear something that you have no problems messing up.
Any questions, please. Ask. For the love of the FSM.
I could have been a jackass, and posted pics after my project was done, but I came into the forums, lurked for a few weeks, and saw alot of questions pop up that no one could answer, but which I knew the answer to. PLEASE DON'T FLOOD MY PM BOX. I've been on a lot of forums, and I'm sure I have full PM's on more than one or two. Granted, I get pop-ups here, which makes it easier, but please. If I don't answer in this thread, THEN pm me.
My fingers hurt, and I have a headache. consequentially, if you see something here that you disagree with, let me know. I will either clarify, or edit as needed.
I intentionally put in only a few pics. The videos cover either things I've seen here that weren't done right/well (no offense, but I'm anal retentive) or haven't been here before. Please keep in mind the phrase 'JFGI'. If you don't know what that means, I recommend using google to find out.
There are a million people out there who know how to do this a million different ways. I went to school for this, sadly enough, and this isn't even close to what I was taught. As such, keep in mind that this is what works for me. Find what works for you and go for it. I'm just trying to pass along a few tips.
That said, have fun!
-edit: I really need to use the preview post button.
-2nd edit: pics and vids added. Ignore the guy who sounds like a retard in the chip brush video. His name is Dave, and although he's damned good with fiberglass, he's an idiot (proof of this? He never wears a respirator when doing fiberglass).
Notice its not Bondo. Marson, the company that makes this, also makes bondo. This is better.
Herein, I will explain, to the best of my abilities, everything you need to know about plastic body filler, its uses, abuses, and the fastest and easiest way to get it to do what you want.
- History. (feel free to skip this part).
Before plastic body filler was invented, any time you wanted to do bodywork on a car, lead was used. typically in a 70/30 ratio with tin. Yes, Lead. the stuff in your car battery.
The problem with lead is that it's applied at approx 350-ish degrees. I dont know the exact temp, I just know by feel when applying it. and it sucks. Once you have the lead on the car, you have to file about half of it off. It kicks out lead dust, and you will typically burn yourself alot. But I digress.
As far as I know, and don't quote me on this, plastic body filler came out in the mid 50's, about the time that fiberglass became prevalent. the two technologies came into existence hand in hand. Seeing as they both utilize the same resin and catalyst mixes, its not that far of a draw to figure out why. Obviously, they suck far less now than they used to.
-and frankly, thats probably more history than you care to know. I know more, but to you its useless.
- Types of body filler.
There are quite a few different brands, many of which belong in a trash can. I've used alot of various products, and I'll try to steer you away from the ones that suck.
The biggest one that sucks? Bondo.
The problem with Bondo is that because its produced in such massive quantities, the quality control on it has gone out the window. Also, plastic body filler has a shelf life, and because it's produced in such quantities, the people who are most typically going to stock it (checker, autozone, the like) dont understand that fact, it'll go stale on you. That, and most people hang on to it waaaay too long. its got a 6 month shelf life after opened, tops. Unless you're hanging on to it for a show and tell project, toss the can. No, seriously. THROW IT AWAY.
I know, you're saying something along the lines of 'shelf life? wtf?'. Seriously. It does. Ever opened a can of bondo that had the consistency of peanut butter? That can is toast. A fresh can of body filler has the consistency of pancake batter. thick, but easy to stir. Anything else has bled off the plasticizers and resin in the form of vapor, and while still usable, is going to make you job alot more difficult. Not only is it a pain to spread, but you can't be sure when or if it's going to kick off.
Bondo is poop, pure and simple.
USC and Marson make some decent products that are comparable in price and quality. If you're going to be using alot of it, you can get a gallon can. Personally, I like Marson platinum. look familiar?
Granted, you're probably only going to need a gallon if you're doing a full suit, but this was a 3 second google search. It's also available in quart sizes.
For those of you familiar with spot putty, its a little thicker, but its got a very consistent kick time, is vacuum made (no bubbles), doesn't shrink (yes, bondo will shrink), sands quite nice, and you don't have to worry about gas-out (some body fillers will continue to catalyze, kicking off fumes for what seems like forever. This stuff doesn't).
Second on my list is the USC line of products. USC's base/clear
Yes, it's a little more expensive, but it sets up harder than the platinum does. It's tougher to sand, but ideal for use on something thats going to take alot of abuse.
There are other types of fillers out there, but these are the two brands I prefer, and I've used just about all of them. You may have found something that works better for you, maybe not. These are worth giving a try.
Another thing you should know about, and I've yet to see it mentioned here, is kitty hair, or Duraglass.
Duraglass is basically chopped fiberglass added to plastic body filler (from here out, referred to as PBF. I'm not calling it bondo. Bondo is to PBF what bottom shelf vodka is to grey goose). Typically, when you're applying PBF, the maximum thickness you're looking for is 1/8th inch. anything over that is likely to crack out because of improper gas-out. Also, the additional thickness can cause heat buildup, and may screw you in the long run, as PBF gets chalky when it gets hot.
So, say you're building a chest piece, and you want to curve out the suit. Build it up close with Duraglass, then clean up the details with PBF. This will not only strengthen your armor, but it'll make it last longer in the long run.
Finally, we get to spot putty. While alot of you guys are touting the benefits of how well it spreads, you need to be aware that spot putty isn't really designed to be applied in large quantities or thicknesses. When I use it, its typically only to fill pinholes or scratches. THATS IT. anything over a 1/16th of an inch may crack out on you. Alot of the better PBF's will spread just as nicely as spot putty does. But if you really really want to use spot putty, use standard PBF and add 'glass resin to it. Its the exact same stuff. In fact, you can get PBF thinner at any specialty supply shop, or on-line, like here.
If you insist on using the resin mixed with the PBF, go with the thinner. It's cheaper than the resin, and is designed to work with body filler, meaning it won't make it brittle. Plus, that leaves more resin for your glasswork. Nothing's worse than running out of resin halfway through a project.
-Mixing
And this is where everyone starts to argue.
I've lived in 5 states in the last 2 years. I've been from northern Washington to Arizona. I know what I'm talking about.
COLD AND HOT WILL CHANGE HOW YOUR MIX KICKS OFF. Period.
When PBF is mixed with hardener, it creates an exothermic (heat generating) reaction. Humidity and ambient air temperature will change how quickly it kicks off.
For example: While in northern Oregon, in the middle of December, approximately 300 yards from the Columbia river, I was working in a body shop, and freezing my ass off. I mixed up some PBF to fix a small spot on a fender. Using a glob about the size of a racquetball, I added half a tube of hardener to it. Yes, one half tube, for what would normally require about a 1 1/2 inch ribbon.
It took 20 minutes to set up.
Last week, here in Phoenix, I was mixing up some of the exact same product (marson platinum) to do a spot fill to hold together an MDF dash thats being made to create a 'glass mold for a car.
I mixed it a little hot. For a glob the same size, racquetball-ish, I used about an inch of hardener.
It was about 90 degrees out, and dry as hell. This is the desert, after all.
It took 2 minutes to set up.
Other things that can effect how quickly or slowly your mix kicks off are the age of the PBF and hardener, and you mixing board. No, seriously.
If you can help it, try not to mix on cardboard. the paper will soak up the resin and catalyst from your mix, and change the speed of the reaction. And unfortunately, there's no way to tell how. Grab a chunk of sheet metal, a cheap plastic cutting board, a cheap mixing board from a paint shop; anything non-absorbent. If you must use cardboard, mix up a test batch to get an idea of how your particular brand spreads, and coat the cardboard. Let it kick off (till it's rock hard), sand it flat, and use that as your mixing board. Trust me, it'll save you some headache.
Most cans list the following ideal ratio: for a golf ball sized blob of PBF, use a one inch ribbon of hardener.
Thats great, if you're in a lab, with a constant air temp of 70-ish degrees.
So, that being said, how much do you mix?
Well, thats a bugger. Aside from experience, the only way to tell, really, is to mix it up and see what it does.
My personal experience is that for every 10 to 15 degrees above or below that ideal air temp, change the ratio by a quarter inch accordingly. colder, add more hardener. Hotter, take it away. The only problem with me giving you this advice is that this is based on where I live, what I use, and how I use it. I can skim coat an entire side of a car in one pass, and to do so typically can take a quarter can of PBF. I can mix up that much at one time and not worry about ratios, air temp, etc, because I've been doing it for years. If you're just starting out, it gets a little tougher.
Ideally, you should have enough hardener in the batch you're mixing to give you 10 minutes or so of work time. And that is going to vary according to the humidity outside (rain does factor in, keep it in mind) the air temp, and the product you're using, so work in small batches till you get the hang of it. I'd recommend starting off with something smaller, like boots, hand guards, or extremities (arms, legs, the like). Don't go full gusto on the detail pieces until you've got a hang of it. Nothing would be worse than having to sand a hot batch off of a detail or inset corner on a helmet. Theres a term used in the industry to describe this process. Its finger f**king. And its not as fun as it sounds.
Try doing this for a day. Then go home and cover your fingers in bandaids.
Now you're ready to mix. So what?
Before I start rambling again, a word on spreaders.
There's two types, plastic and metal. metal spreaders are great for big flat panels. plastic spreaders are great for complex curves, and also great for flat panels. as I work on cars, I use mostly metal spreaders, but I have several plastic ones sitting around, because when you need one, nothing else will do.
When it comes time to mix the two together, for the love of sweet infant baby jeebus DO NOT MIX IT LIKE ITS CAKE BATTER!!!!!
All this does is introduce air into the batch, making for bubbles and pinholes in your final product, which means more work.
What you want to do is scrape up the hardener with the spreader (most spreaders look like spatulas without handles) and smush it into the PBF. smear it out, scrape up the semi-mixed pile at a 90 degree angle from the smear you just took, and repeat. Its kind of hard to explain, so watch this -
Matt mixing. Ignore the radio. -Video
(You'll notice he's using blue hardener. It comes in several colors - red, blue, green, yellow, and white are the ones I most commonly see. They all do the exact same thing. You can also use all of the various colors for duraglass, and, in a pinch, for fiberglass. No, I'm not lying.)
You're looking for an even color, with no streaks. Shouldn't take but 2 or 3 minutes of mixing to get a good even blend.
-Spreading
If you've ever made a cake, and put frosting on it, you're ready to go. Its not that hard of a concept. There are a lot of little tricks to it, but its going to be about angles and the like. If you're not very comfortable with the idea of just smearing it on, try this.
Go to harbor freight, or a grocery store, or home despot, etc etc. You're looking for either a chip brush, or a basting brush. The basting brush is a little wider than I prefer, but it'll do the trick in a pinch.
this will be your friend.
Using said brush, paint the PBF where you want it. this will let you get it on with less mess, less sanding, and makes for a much faster application. Once you've got it where you want it (or the bondo starts to kick off), swish it out in a cup with a little acetone in it, and you can use it again for the next batch.
heres an example. Ignore Dave. -video (sorry about the quality, my camera battery died. This is from my phone.)
this is after less than 5 minutes of sanding (brought it home so I could charge my phone and get a decent pic):
How do you know when the PBF is kicking off? it'll start to get a little thicker. then it'll start getting grainy, kinda the same texture as cream of wheat that's been left in the pan. Then it'll start to crumble. The surface will stay tacky while the reaction is taking place, so thats probably going to be your best bet as to how to judge when you can start sanding on it.
fully kicked... still soft enough to scrape off though.
I've heard alot of people say they've had varying success with applying PBF coats over each other without sanding. Personally, is the first coat is still tacky to the touch, I can feather out the edge of my new batch without any worries. However, I've been doing this for a long time, so I know the limits of what can and can't be done. If you're just starting out, I'd recommend waiting until the first layer has kicked off completely, then hit it with some 36 grit paper before you put on the next coat. This will give the second application some mechanical bite, something to hold on to. Theres nothing worse than having to sand or scrape a fresh coat of PBF off a car because you know it's going to flake off. Any PBF applied over a fully cured coat of PBF will, in my experience, flake off. And that is a pain in the ass.
-Sanding
Most body shops have a certain procedure for how they sand the car, depending on the repair, etc. The cars I work on are typically in the 50 to 100 thousand dollar range. As such, the paint on these cars is super flat, extra shiny, and thicker than you think.
Thats great and all, but why do you care?
Because I'm going off the assumption that you want a nice paint job on your armor. As such, I recommend going in this order (this is the same order we use in my shop):
[this is after all your resin and 'glass work is finished]
1. Sand everything. nothing too hardcore, you're looking for something for the PBF to stick to. if you have air tools, this goes alot quicker. if not, you're gonna have to suck it up. You're just going for a quick pass with 36 grit. kill any shiny spots.
2. Prime. This isn't necessary, but it gives you a good base to see where you're gonna need to do more work. The color or type of primer is unimportant, just a nice even coat.
2b. Quick sand again, after the primer has gone dull. Again, its not necessary if you chose to not prime your armor pieces. 36 or 80 grit is fine.
3. Duraglass. build up anything thats gonna require a large amount of filler. This would be an ideal time to get any curves formed in your helmet, chest piece, etc.
4. Rough the shape out. You're not going for perfection, you're looking to get it to the shape you want. ignore getting perfect curves, super smooth faces, etc. get it to where you can stand back 5 feet or so, and it looks right. 36 grit is your friend here.
5. using 80 grit sandpaper, go back in and even out your shape. you're looking for the 3 foot appearance, meaning you can step back 2 or 3 feet, and it looks right.
6. PBF. NOW you're trying to get everything exactly where you want it. The chip brush is your friend.
7. Knock out any rough spots with 36, then fine tune with 80 again.
8. Now you're on to 120, cleaning up any details that you may have missed.
-keep in mind at this point that you may end up sanding through your primer. that doesn't matter, as long as the shape is satisfactory. This pic demonstrates this, as this has been primed twice, and still wasn't right. It is now, though.
9. Prime everything. by now, you're probably looking at several different shades of the same color, as no batch of PBF mixes the same. Its hard as hell to see what you're doing, so a good coat of primer will help you find the details you missed.
10. Refine. By now, you've probably come across pin holes, parts that look off, etc etc. take your time here, and use PBF sparingly, even swap over to spot putty. If you hurried in the last steps, this is your chance to fix your mess-ups.
11. Reprime. by now, you should be looking at a primed piece, ready to paint. HA! no it's not.
11a. Guide coat. all you're trying to do with this is put a dry light coat over the primer with a contrasting color. This will help you know what you're missing when you start to do your final sanding.
12. Because you get to sand some more. I'd leave the primed piece to dry overnight, even 2 days if you're not trying to rush things. there's gonna be 3 steps in this sand -180, 220, 340 or 400 (depending on what's available). The second and third passes are simply to remove the scratches from the previous grits. When you're done, the surface should look a little shiny if you view it at an angle.
13. Paint!
Don't think that you have to go out and buy sanding blocks. there's no block out there that will work for every application, and in some instances, I've had to make blocks. This is a small sample of the various blocks we use:
Yes, this is a long and involved process. Yes, it looks awesome when you're done. If you're going for a look thats a little less refined, you can skip a few steps. Again, thats up to you.
finished car we did, using the process above:
-cleanup
Acetone will clean PBF off of spreaders and brushes. If you're using plastic spreaders, and you've got a thin, rock hard layer on it, mix up a little and spread it thick on the spreader. after it kicks off, flex the spreader and it'll pull off the stuff you couldn't get off with acetone or a fingernail. If you leave it to harden on the brush, you now have a stick. Congrats.
If you get it on your skin, you can typically flake it off. Anything thats worked its way into your skin (typically around the knuckles and such) will come off in the shower with a little elbow grease.
Any PBF that gets on your clothes is now a permanent addition to that article of clothing. This is especially true of cotton/poly blends, as the PBF will basically melt into the poly as is cures. Even on an all cotton article, it'll be there for a few washes, if not more. Wear something that you have no problems messing up.
Any questions, please. Ask. For the love of the FSM.
I could have been a jackass, and posted pics after my project was done, but I came into the forums, lurked for a few weeks, and saw alot of questions pop up that no one could answer, but which I knew the answer to. PLEASE DON'T FLOOD MY PM BOX. I've been on a lot of forums, and I'm sure I have full PM's on more than one or two. Granted, I get pop-ups here, which makes it easier, but please. If I don't answer in this thread, THEN pm me.
My fingers hurt, and I have a headache. consequentially, if you see something here that you disagree with, let me know. I will either clarify, or edit as needed.
I intentionally put in only a few pics. The videos cover either things I've seen here that weren't done right/well (no offense, but I'm anal retentive) or haven't been here before. Please keep in mind the phrase 'JFGI'. If you don't know what that means, I recommend using google to find out.
There are a million people out there who know how to do this a million different ways. I went to school for this, sadly enough, and this isn't even close to what I was taught. As such, keep in mind that this is what works for me. Find what works for you and go for it. I'm just trying to pass along a few tips.
That said, have fun!
-edit: I really need to use the preview post button.
-2nd edit: pics and vids added. Ignore the guy who sounds like a retard in the chip brush video. His name is Dave, and although he's damned good with fiberglass, he's an idiot (proof of this? He never wears a respirator when doing fiberglass).
