Bondo 801 "Professional Glazing & Spot Putty"

[Ace-Garageguy]

                                                                                

 

Recently, I've seen a few people mention they're not having good results with this stuff. There is a little learning curve, but once you get the hang of it, you can do heavy fills with no waiting for it to shrink like you'll have on old-style lacquer putties. You will still most likely need several applications to get a perfect shape and surface, but it goes a WHOLE LOT FASTER than the old-school stuff...and it doesn't crack and fall off years later.

I've been doing high-end bodywork on real cars for decades, and I got pretty familiar with using 2-part catalyzed fillers.

Using this stuff on a model is a lot like using bondo on a real car, but there are some differences, too.

Here's a list of tricks that might make it easier for new users. This may all sound like it's a real PITA, but after working with the stuff a few times, it will seem easy, and eventually become second nature. And there's no limit to the kind of custom stuff you can do with it. 

1) Whatever you're trying to stick it to needs to be clean, and sanded thoroughly, so that no shiny spots remain. For the 2-part putties, I like a 180-grit sanded surface for best adhesion on models. And very often, adhesion to primer isn't very good.

2) There is most definitely a sweet-spot for mixing, and thorough mixing is very important. This can be a pain in hot weather, as the stuff starts to kick pretty fast, and you literally have only a couple of minutes to spread it.

3) Once it's started to kick, stop trying to spread it any more. It won't stick properly.

4) Even though it starts to kick pretty quick, it can take 20 minutes to an hour before it's ready to sand. It's kinda counter-intuitive, but the stuff sticks better the longer you leave it alone. It's tempting to start shaping when it's still a little soft, but that will invariably pull up edges rather than allow a nice feather. I sometimes get in a hurry to this day, though I have a pretty good idea of what I can get away with. Every now and then, I'll still pull up an edge because I started shaping too soon.

5) If you buy the Bondo "professional" in the metal tube, don't squeeze the tube. Because the stuff separates while it's on the shelf, if you squeeze the tube, you'll probably get some runny resin and some dryer inert filler on your mixing board, instead of a nice creamy gray mass. The best way to remix it is with a piece of 1/8 welding rod, or a bamboo skewer, etc. Just stick it down in the tube and pump up and down. After a few strokes, it will be a nice consistent color again, with the liquid back in suspension.

6) The catalyst will separate too. Best way to fix it is to carefully remove the cap (with the opening up), gently squeeze the air out, put the cap back on tightly, and then gently knead the tube for a few minutes.

7) Instead of squeezing the putty tube to get material out, I have come to prefer something like a wooden coffee stir-stick to dip a little out, and scrape it off on a mixing board. Keep a place to lay the gooey stick so you don't get it all over your fingers and everywhere else.

? The same method works best with the catalyst too. For that, a metal axle or a piece of 1/16" brass stock works well. DO NOT get your sticks mixed up. Just a little catalyst in the resin tube can ruin the whole batch.

9) You want your mixed material to be a medium pink. Dark pink has too much catalyst and may stay rubbery, and peel up instead of feathering. Too far towards the gray side, the stuff may just never cure at all.

10) Experiment until you can get a good mix every time, and make sure it feathers...BEFORE you try to use it on a model.

11) For mixing and spreading, small paddles or spatulas made from .020" -.040" styrene work well. You can cut different widths and even shapes; for instance if you're doing the curved top of a fender, you can cut the curve you want to achieve into the spreader.

12) If you don't want to waste good styrene stock, I've found these plastic bread ties work very well, are easily trimmed, and can be scraped clean and used several times. And if they come on the bread you like, they're free.

                                                                   

Here's a thread that illustrates the kind of work you can do with it...

 

Edited September 13, 2019 by Ace-Garageguy

[porschercr]

Great information, thank you.

[High octane]

Thanks Ace.

[89AKurt]

Thank you for the very detailed tutorial.  But I still have a dumb question, picture of one tube, but you talk about mixing two parts?

[Ace-Garageguy]

3 minutes ago, 89AKurt said:

... picture of one tube, but you talk about mixing two parts?

Yup. It's a 2-part polyester product. The tube of hardener comes in the package, and is behind the tube you can see.

[TarheelRick]

I have been using the stuff that comes in one tube and notice it has the same tendency to separate.  Thanks for the advice on mixing it.  I have a question concerning one issue I had recently.  I was trying to build up a flat surface and spread it really thin over the surface.  As it dried it began to  split, sorry I didn't take a picture, but this has happened once before.  After final sanding it came out all right, but I am concerned about trying to build up a surface with it.  Also does using a dehydrator have any good or bad effects on this stuff?

[Modlguy]

I save key cards from hotels and expired credit cards. They can be cut with scissors and used to spread putty. McDonald's used to have coffee stirrers with a little paddle at the end but I haven't seen these in some time. Thanks for this, Ace. It's good tip. 

[Ace-Garageguy]

2 hours ago, TarheelRick said:

I have been using the stuff that comes in one tube and notice it has the same tendency to separate.  Thanks for the advice on mixing it.  I have a question concerning one issue I had recently.  I was trying to build up a flat surface and spread it really thin over the surface.  As it dried it began to  split, sorry I didn't take a picture, but this has happened once before.  After final sanding it came out all right, but I am concerned about trying to build up a surface with it.  Also does using a dehydrator have any good or bad effects on this stuff?

I can't recommend the one-part stuff, especially for heavy fills. It dries by evaporation and shrinks a LOT in the process. It also requires many coats to do a decent job of filling anything deep, because once the top surface "skins", the interior can take a week or more to dry thoroughly if you put it on thick. Too thick, it will crack, or as you noticed, split.

The one-part stuff is old-school lacquer putty, really only appropriate these days for filling pinholes and very minor imperfections...and if you need something to do that, something like Tamiya white (one-part) is much better.

Because the one-part stuff cures by evaporation, a dehydrator should help it along...if you just insist on using it.

Because the 2-part stuff cures by a chemical reaction, it "dries" all the way through (assuming it's mixed correctly), and shrinks very little. A dehydrator won't have much, if any effect.

Edited September 13, 2019 by Ace-Garageguy

[Codi]

I love this stuff and have used it for some time as well.  The mixing tips are very helpful and I'll print this out for future reference.  One "trick" I stumbled upon when using this bondo is that when I'm done sanding it down and getting it pretty much where I want it, I take Zap a Gap "THIN" glue in the pink bottle and "seal" the bondo with the glue with a simple applicator. Not a lot btw.  Just enough to seal it and make it appear semi-glossy.   Then I go back with 800 / 1000 grit sandpaper to knock it down a bit and to a perfectly smooth surface.  I started doing it as a way to eliminate any "ghosting" effects wherein the bondo will be visible underneath.  If I have a spot that's not quite right still, I'll just sand it down a little bit, re-apply the zap a gap and follow the same steps.  I've done several models with body work (some was extensive) and none of them have experienced the ghosting that can / might appear occasionally.  Hope this helps others in some way.   Again, great product !!   cheers, tim

[TarheelRick]

Thanks for the tips.  I was just down at my bench a couple hours ago and noticed I do have the two-part hanging on my pegboard, still in its blister pack.  Will be digging it out when I get back to doing some more bodywork.

[Draggon]

Ha, I thought I was the only one that used those plastic bread ties 

[Ace-Garageguy]

5 minutes ago, Draggon said:

Ha, I thought I was the only one that used those plastic bread ties 

Great minds..., as they say.

[Ace-Garageguy]

On 9/13/2019 at 10:47 AM, Codi said:

  One "trick" I stumbled upon when using this bondo is that when I'm done sanding it down and getting it pretty much where I want it, I take Zap a Gap "THIN" glue in the pink bottle and "seal" the bondo with the glue with a simple applicator. Not a lot btw.  Just enough to seal it and make it appear semi-glossy.   Then I go back with 800 / 1000 grit sandpaper to knock it down a bit and to a perfectly smooth surface.  I started doing it as a way to eliminate any "ghosting" effects wherein the bondo will be visible underneath.  If I have a spot that's not quite right still, I'll just sand it down a little bit, re-apply the zap a gap and follow the same steps.  I've done several models with body work (some was extensive) and none of them have experienced the ghosting that can / might appear occasionally.  Hope this helps others in some way....

I'll have to try that. The stuff does indeed really suck up thin primers like Duplicolor sandable, and it can take several applications and sanding to kill it...which can be detrimental to surrounding details if you're not careful. Your trick may save my bacon on a couple of jobs. Thanks. 

[Bainford]

On ‎13‎/‎09‎/‎2019 at 11:47 AM, Codi said:

I love this stuff and have used it for some time as well.  The mixing tips are very helpful and I'll print this out for future reference.  One "trick" I stumbled upon when using this bondo is that when I'm done sanding it down and getting it pretty much where I want it, I take Zap a Gap "THIN" glue in the pink bottle and "seal" the bondo with the glue with a simple applicator. Not a lot btw.  Just enough to seal it and make it appear semi-glossy.   Then I go back with 800 / 1000 grit sandpaper to knock it down a bit and to a perfectly smooth surface.  I started doing it as a way to eliminate any "ghosting" effects wherein the bondo will be visible underneath.  If I have a spot that's not quite right still, I'll just sand it down a little bit, re-apply the zap a gap and follow the same steps.  I've done several models with body work (some was extensive) and none of them have experienced the ghosting that can / might appear occasionally.  Hope this helps others in some way.   Again, great product !!   cheers, tim

I do something similar, but I brush on some Gunze Mr Surfacer (1000 or 1500) to coat over the final sanded filler. The Mr Surfacer seals everything up nicely, and it feathers out very well.