Putty suggestions?

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Posted (edited) · Report post

Well I need to figure out what type of putty to use for model building with SEVERE modifications. Like mixing two different things and they have a large size gap

Edited by Kyle Krueger

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Posted · Report post

I'd suggest a two part polyester filler. Evercoat makes some good products.

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Posted · Report post

Squadron Putty (either green or white, they seem to be the same except for color) works great for me.

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Posted · Report post

Severe like really laying on the putty? Bondo. Other than that, I like the Squadron line of putties.

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Posted (edited) · Report post

Use a 2 part putty. Evercoat makes it and somebody else but I can't think of the name right now - professional something that comes in a tube. Make sure it's professional so you get the smaller tube of hardener also. Maybe it's Bondo Professional?? The Evercoat comes in a big can and is a waste of my money.

I use the green and/or white Squadron putty for very minor work.

Edited by crazyjim

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Posted · Report post

The kinds of putty that you apply directly, by squeezing it out of a tube like toothpaste, dry or harden via evaporation of the solvent (the liquid part), leaving behind the actual hardened putty. Since these putties all dry the same way (by evaporation), by definition they lose a part of their volume (the solvent part) as they harden. Or in plain English, they shrink as they dry.

Putties like that ("one part" putties) are really only suitable for very minor work like filling small imperfections and scratches. They are not meant to be used for any kind of major body work or reshaping. If you lay them on too thick, they will not only shrink, but also probably crack as they dry.

What you always want to use whenever you plan on laying it on fairly thick are "two part" putties... the kind where you have to mix the putty with a small amount of hardener. These two-part putties do not "dry" or harden via evaporation, they set via a chemical reaction between the putty and the hardener... the same way epoxy chemically sets when you mix the 2 parts together.

Because two-part putties do not dry via evaporation, they do not lose volume as they harden... so they do not shrink. Also, once the chemical reaction has happened, the putty is hard, period, unlike one-part putties that can take a long time to fully dry. In fact, it's not uncommon for people to use a one-part putty, do all their sanding and painting, then weeks or months later see depressions on the model, because the putty continued to dry after the paint was applied and the model was finished!

Do yourself a favor and stick with two-part putties. Your best bet is Bondo "Professional" glazing and spot putty, which comes in a small tube along with a separate tube of hardener. It can be found at most auto parts stores and sells for about $8 or so.

bondo-1.jpg

Also... before you apply the putty to the body, sand the area with some fairly rough grit sandpaper. You want to rough up the smooth surface of the plastic so that the putty has something to "grip" onto. If you apply the putty over a smooth surface, there's a chance it might snap off if you twist the body.

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Posted · Report post

HEED HARRY'S ADVICE !!! He's absolutely right. I sand bare plastic with 180 grit to insure adhesion...and don't just lightly pass over it...get ALL the shine off any area there may be filler.

Also it's IMPORTANT to learn how to mix the 2-part putty correctly. Many folks have adhesion problems, or gooey putty simply because they either use too much catalyst or too little. There needs to be a pretty close relationship of putty to catalyst, no matter what you may hear from 'experts'. It's polyester based, and it's usually 1% to 1.75% catalyst to resin, which isn't much latitude, really. If you just slop in any old amount, you WILL have problems. READ the mixing directions on the material and experiment with it to get a feel for how it works.

Too little catalyst and it won't harden at all, and you can't sand it. Just right and it should be good to sand in about 20 minutes. If it's right, it will feather-edge nicely and sand to a fine powder. Too much catalyst and it will get hot, harden rapidly, and may be rubbery and not adhere well.

This may sound like a royal pain, but a lot of us use it constantly and get excellent results. There IS a learning curve, so don't expect your very first attempt to be perfect, and don't experiment on a model that's really important to you.

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Posted · Report post

There is another option, if you want to get a little more technical. I'm currently using microballoon and epoxy resin for filler on some more extreme mods. I'm using the West System epoxy (made for boats, and used in non-structural applications on the 1:1 aircraft I work on). Well stocked hobby stores sell dry micro-balloons as a thickener for epoxy resin on RC model planes. You mix the epoxy as per the label directions (again, get the ratios CORRECT or you WILL have problems) and then thicken it to the consistency of putty with the micro. If you use the 15 or 30 minute epoxies for RC planes, you'll have plenty of working time and your filler will stick WAY better than the polyester stuff mentioned above, and can be used really thick.

BE SURE TO WEAR A GOOD DUST MASK or RESPIRATOR when you sand ANY OF THIS STUFF.

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Posted · Report post

Another tip is to make sure you don't use the Bondo to fill in a gap that could be filled with plastic strip or styrene. Much like a 1:1 car, you shouldn't use Bondo to fill the whole, use it to smooth out your bodywork.

Harry is correct on the tube putties- I have had to go back over some models and re-do them because of my mistakes.

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Posted · Report post

If you have large gaps, you first want to fill them with styrene and crazy glue. No putty, whether it's one or two part, is made for filling large gaps. As for putty, I have never had a problem with using Squadron's white putty. I've filled stuff that was 3/16 of an inch deep and built entire fenderwell arches with it. I've filled holes that were all the way through the body on a resin kit that were close to 1/4 of an inch in diameter. I recently made a set of head light buckets with it on a '37 Ford. No idea of how thick those actually are. It does dry by evaporation, but shrinkage is so minimal (if any) that it isn't even worth mentioning in my experience with it. Unless of course, you apply it about a 1/4 inch thick and how many people do that? The best parts: no mixing or having to worry if you have it mixed right and no waste. Another thing about Squadron putty is that it actually bonds into the plastic. You don't have to rough up whatever you're working on to get it to stick because it literally melts into the plastic.

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