Body Filler- What to use?

Let's talk putties, shall we? No matter how well molded a kit may be, there might be a few areas that need attention. Specifically, body work. Maybe it's a nasty seam between two parts, and there's no seam there on the actual car. Or a sink mark along the quarter panel. Or maybe you've done a few body modifications and you need to cover up the scars. While there are several ways to deal with these problems, we will focus on the putty option this time around.

There are basically two types of filler putty you can buy. The first is the single-part, solvent based putty. This is covers most of the well-known hobby fillers on the market- Testors Contour Putty, Squadron Putty (no matter what color), or even the Bondo Spot Putty, which is meant for 1:1 bodywork but can be used on scale models as well. The second is two-part catalyzed putty, which is mixed in a certain proportion of filler to hardener.

I prefer the two-part fillers, and use them almost exclusively. While both types of putties have their place, it's generally a good idea to go with two-part putties for the majority of jobs where it's required.

Here's why. Single part putty dries (or "cures") as the solvents evaporate out of it. As the solvent "gasses out", some volume is lost. This means shrinkage- the putty will shrink as it dries out, even in the short term. Depending on how thickly it is applied, this can create even more problems, as the solvents continue to dissipate. Your model may look great now, but in a few years you may find sags, cracks, ripples, and splits in the paint caused by the single-part solvent putty's continued shrinkage.

By and large, there's no set rule as to when a solvent-based putty is truly cured. It could be 45 mintes or 4.5 years. Do you really want to gamble? Yes, single-part putty may be okay for smaller blemishes and such, but for bigger jobs it isn't worth the risk if you want your finished model to look as good as it does now in ten years time.

Catalyzed (two-part) putties work differently. When the two components (putty and hardener) are mixed, the putty cures not by way of evaporating solvents, but from a chemical reaction taking place between the two components. There will be no shrinkage, cracking, or anything like that over time (barring improper application or any type of outside damage), because once the chemical reaction does it's thing- that's it. The putty is chemically set.

Not only is two-part putty more stable over time, but it also dries much more quickly- in some cases, you can realistically expect to begin sanding it within an hour. With single-part putties, the stuff might still be tacky 48 hours from now. That's because, again, when a two-part putty is set, it's set. The single-part putty may be degassing for years to come.

That being said, the single part is convenient if you have a small, shallow imperfection you need to fill, because you don't need to mix it- just apply it to the model and wait for it to cure. When used in razor-thin "skim" coats, drying time isn't as much of an issue, and neither are shrinkage or cracking over time.

Every modeler has their favorite filler, mine is the Bondo Glazing and Spot Putty , along with the corresponding red hardener cream. This stuff is meant for use on 1:1 vehicles, so it should be more than sturdy enough for a scale model. It's also pretty easy to find, and the price isn't too horrifying... as shown, you're looking at about six bucks per tube, though there is a package which includes the 4.5oz tube of putty along with a smaller tube of hardener for about nine bucks (last time I saw them). Unless you go through it rather quickly, smaller amounts might be a good idea- this stuff does have a shelf life, and will go bad eventually once the seal is broken. My last 4.50z tube lasted almost a year, but it was starting to get a little "chunky" toward the end.

Pay close attention to the labels...

The Bondo Glazing and Spot Putty is the single-part, solvent based kind, and is reddish-brown in color.

The PROFESSIONAL Glazing and Spot Putty is two part, meant to be used with the included red hardener cream. The Professional puty is white in color.

The hardener comes in a plain white plastic tube. The hardener itself is reddish brown, similar in color to the single part Bondo putty

The Bondo is my personal preference, but there are other brands. I know many a modeler who swears by the Evercoat line of of filler putty. The bottom line is to look for a two-part catalyzed putty. Feel free to try a few different ones, to see if a particular one works better for you.

Just read, and more importantly FOLLOW, the directions included with the product and you should be alright. The Bondo stuff is mixed in a 4:1 ratio (putty/hardener), but it differs depending on who's product you use.

One disadvantage two-part putties have going for them (and this is about the only real disadvantage) is that you do need to work quickly- once the two parts are mixed, it's setting, so you need to get it where it's needed before it sets up. Single part putties generally give you more time to apply.

A few tips for working with putty.

1. Mix the smallest amount you can realistically get away with, but an amount that you think will be slightly more than what you'll actually need. This takes some practice, but once you get good with putty you can generally "eyeball" the job and make a pretty good educated guess as to how much you'll need.

2. Don't try to putty every area that needs attention at one time, break it up into individual areas when you apply it. One area at a time! If you try to apply putty everywhere at one time, you'll end up with a half-puttied model and half a pile of cured putty still on the mixing board.

3. Pretty much anything can be used as a mixing board- index cards, folded instruction sheets, or those old "Blueprinter" subscription sheets you'll find in pretty much any AMT kit from the '90's.

4. I use a toothpick to mix the putty and catalyst. I use scraps of thin (.020" or .030") plastic strip to spread and apply it to the model. Some of the reissued AMT kits (the '66 T-Bird comes to mind) actually come with tools for applying putty.

5. Always, always, always read and follow the manufacturers directions to the letter! This goes for the practical instructions, and anything regarding your safety.

6. Never mix brands of filler and hardener. If you use Bondo putty, and run out of Bondo hardener, get more Bondo hardener. Don't get Evercoat hardener and try to mix it with the Bondo putty, or vice versa. If you do, don't expect good results. The no-name parts store brand red hardener might work with Bondo... or it might not. Trust me, I'm speaking from experience on that last one!

7. Always apply putty over a primed substrate- putty will not adhere to raw plastic.