Tutorial: Using Bondo for Detailing

So when I first started i didnt really have any idea how to use bondo, now that I do, i figured I'd make this tut for you all incase some noob like me rolls around with the same question!

How to mix bondo body filler:

Get a FLAT clean surface made of plastic or metal (plywood is not acceptable).

Scoop a 4" diameter dollop of filler onto the surface.

Squeeze out a 1-3" line of hardener. A 1" line is what is called mixing the putty "cold". This means you will have more time to work with it, but it takes considerably longer to dry. If you use too little hardener it will never dry and will always be sticky. If you use a full 3" line of hardener you will be mixing it "hot" This will give you quick drying times and a very hard finish. Unfortunately it will be more brittle than mixing it cold. 2" is the median and is what I would recommend.

Using a putty knife, fold the hardener vigorously into the putty so that it is mixed evenly. Don't take too long doing this or the filler will begin to harden while you are mixing.

Now carefully apply a generous amount of putty to the area you are trying to fill or shape.

When the putty is hard but can still be dented by your fingernail use a small Sureform file to roughly shape the putty. You can also use some 80 grit sandpaper for this.

Now allow the putty to cure completely. When cured it will be hard like plastic, and will be giving off no heat.

Now do your final forming with some 360 grit sandpaper, elbow grease and finish it up with 1200 grit for painting.

hope this helps someone!

A good Black and Decker mouse helps when working with bondo like you wouldn't believe


http://www.blackanddecker.com/ProductGuide...cPath=2516.2518



If I remember right, I only paid around 35 dollars or so for mine at home depot, and I could not live without it.

thanks i was wondering what the filler was for when i bought it

can someone pin this

is filler difficult to use, like it is hard to place it exactly were u want it cause u cant use your hands?

Its certainly not hard to use, just use a dog poop sized pile, add little Cream, a little dab will do ya!

irvinelax said:

is filler difficult to use, like it is hard to place it exactly were u want it cause u cant use your hands?

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i actually do use my hands sometimes, when i really need to... for those areas i just can't get at well enough with a spatula. I just wear quite thick gloves kind of like the rubber gloves some people wear when they wash dishes.

I've never had a problem with it like eating through them or anything getting to my bare skin, since the work time of the body filler is so quick.

Should using bondo be the last step before painting, or can you applay another coat of resin ontop of the bondo?

I just finished fiberglassing my pep helmet, and am doing my first sanding. The helmet is not exactly symetrical, and there are som spots where the fiberglass did not touch the cardstock so there are some small dimples on the helmet. Can I just apply bondo and then paint the helmet, or should I apply another coat of resin?

parabus said:

Should using bondo be the last step before painting, or can you applay another coat of resin ontop of the bondo?

I just finished fiberglassing my pep helmet, and am doing my first sanding. The helmet is not exactly symetrical, and there are som spots where the fiberglass did not touch the cardstock so there are some small dimples on the helmet. Can I just apply bondo and then paint the helmet, or should I apply another coat of resin?

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usually bondo it untill its the shape you want, with all the detail you want, bondo is the last step before primer and paint..

you want to sand it untill satisfied, then go right to primer(Make sure u wipe it down first so theres no dust left from sanding the bondo)


**EDIT** and about using ur hands, i dont suggest it, but ive use bare fingers for pain in the ass places and i used a little gasonline to clean em off, i had no problems...

TwistedCory said:

usually bondo it untill its the shape you want, with all the detail you want, bondo is the last step before primer and paint..

you want to sand it untill satisfied, then go right to primer(Make sure u wipe it down first so theres no dust left from sanding the bondo)
**EDIT** and about using ur hands, i dont suggest it, but ive use bare fingers for pain in the ass places and i used a little gasonline to clean em off, i had no problems...

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if you leave it thick enough on your finger, just wait till it hardens then peel it right off easily. That's what I do. Bondo doesn't stick very well to skin

How hot does bondo get? And also how long do you have to work with it when you make it cold, im slow and a perfectionist so I need some time to work.

Thanks for this post, every bit of info is helpful. I don't get much time off to work on my hobbies and right now I am in the research and building the pepakura armor.

joshua61991 said:

How hot does bondo get? And also how long do you have to work with it when you make it cold, im slow and a perfectionist so I need some time to work.

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bondo doesnt get hot as in it will burn you, it gets warm.

working time depends on how much hardener you use.. the more, the faster it hardens, the less, the slower.. just make sure you put enough or it will never harden. try a test batch, take a bit of bondo, and then test how long it takes to harden how much hardener you used.

bdw, if your not that pushed about getting a perfectly smooth surface you can use polyfiller, not sure what you guy call it in America but its used for fixing holes in walls or the like, is surprisingly light, soluble with water until dried and is very easy to work afterwards cuz its relatively soft but it can be varnished with floor varnish or glue and its sealed. actually depending on what paint you use it might seal it for you.

p.s. you can get a nice smooth surface if you wet a piece of plastic and drag it over the surface before its dryed. you cant get the really shiny surface that you can with bondo but its as smooth as you'd need unless you an absoloooooot protectionist. also v fast to apply and work afterwards.

after the suit is built in cardboard could cover the whole thing in polyfiller, then sand it down to make it smooth
then paint however you want and finally coat it with sealant

i know it would be a big job but wonder if it could work

Am I able to use a plastic knife to use as a putty knife?

Hi. Im new here and am slowly making progress on my own armor but ive read many things that i believe need clarifying in terms of using filler (bondo) and paint.

Once your piece is fiberglassed and trimmed and ready for your filler, sand the fiberglass with 80 grit sandpaper and then with 150 grit sandpaper (you can just start with 150 if you want but it will take longer). This will help the filler to grab onto the fiberglass and provide a much stronger bond. As for mixing it make sure you dont add too much hardener. Too much hardner will cause stress cracks from the heat generated by the chemical reaction. Add as much filler as needed and wait until hardened before sanding and detailing. At this point carve all the detail you want into the piece as the filler creates a very suitable material for detail work. The filler can be sanded with as low as 40 grit to knock out the rough spots and then work up to 150 or 180 grit. Filler does not need to be sanded any higher than that. Your piece should be detailed at this point and ready for paint.

Once sanded, use a can of "primer filler" or "primer surfacer." They are the same thing just labeled differently. This type of primer can be sprayed directly onto the filler (just make sure its clean obviously). Primer filler is made of a high solid material, meaning it will lay on thick. Apply 3 wet coats of primer filler waiting for it to dry between coats (5-10 min depending on temp). After your third coat let it dry completely. wait 2-3 hours to be safe.

Now you want to use whats called a guide coat. Just get a cheap can of spraypaint of a contrasting color and apply a VERY light mist over the entire piece. You're not going for coverage here just enough to contrast the surface. Wait a few minutes to let the guide coat dry then start sanding with 320 grit paper. Sand just until the guide coat is gone. The guide coat will show low spots this way and make it visible where there might be small imperfections and allow you to sand them out. Once the guide coat is completely gone the entire piece will be sanded in 320 grit and you know you didnt miss anything. (if you missed a spot the guide coat would still be on there)

Now apply another very light guide coat and let it dry. Do the same thing but this time sand it with 600 grit paper. Once the guide coat is gone you're ready for your "primer sealer." Obviously clean the peice really good before proceeding.

DO NOT WORRY IF YOU SANDED THROUGH THE PRIMER FILLER IN SOME AREAS. This is normal, especially on edges.

Primer sealer is your last coat before color. Its basically a fresh unsanded coat of primer for the paint to stick to. You could go without the sealer and spray right over the filler, but i wouldnt recommend it. You only really need one or 2 coats of sealer as its not needed to fill anything since it was all sanded out. Spray your sealer and let it "flash off" (not reflective or wet anymore). Now you're ready for your color.

Spray your color coats as needed to get complete coverage, waiting for the paint to flash off between coats. From here you can either call it quits or move on to a clear coat if desired. The clear coat can be applied right over the color after it has flashed off. If you wait until the color has cured you will need to sand the color with 600 grit paper before applying the clear.

Hope this helped you guys. Ill be showing off how my project is coming along as i get more done. maybe ill take some pictures to go along with this and post a tutorial

BTW i work in an auto body repair shop and have been going to school for a year for auto body repair. What i explained here is basically the steps used to paint your car (minus a few steps needed to paint bare metal). If you have any questions feel free to ask me

Can I primer BEFORE i bondo? and then just primer again? because I would like to primer for the first sanding and then I will only use bondo in specific areas

you could but i wouldnt. just use the bondo in those areas and then do what you have to do. Then apply your primer filler over the whole piece. Primer fille is only going to give you maybe anywhere from 3-6 mils of thickness depending on how much you put on (more of course if you add like 10 coats). Thats not very much, its only used for final smoothing before paint

For smaller detailing or filling dents or spots a bit too deep to sand out, got to a hobby shop and get some Squadron Green Putty,(also known to model builders as 'Green Stuff' since that was its original name.) here's what the tube looks like http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXFP27 It's cheaper and eaiser to use than bondo for smaller details since it air dries. It's very sandable when dry, but be advised, the more you use in one spot, the longer it takes to dry so building up in layers is best.
It can be drilled when conpletely hard, but don't expect any real strength when screwed into plain putty (it ain't that strong ) also comes in white.