Putties and Fillers

Q: There are so many fillers today, and I hear about so many other things and techniques people use for filler. What should I use?
A: The statement that there are many fillers today is quite accurate. As with everything in modeling, there is no one answer as to which to use. It partly depends on what it is you want to fill. Is it a small nick or sinkhole in the model, is it a large seam, or did you do a conversion and need to fill a large area? The answer to this question partly determines what you should use. Also it also boils down to a matter of personal preference. The best way to answer is to tell what is available, give some of the characteristics of each, and some recommendations as to the situations that they work best in. There are those products that are intended as model fillers, those that are fillers for other things, and others. Let's take a look at each type. Here is a partial listing of some of the available putties and other fillers:

Lets look at each kind, and some of their characteristics.

Model Putties:
The most commonly used products are the model specific filler putties. I personally don't recommend the Testor Contour Putty. It was the first that I ever used many years ago. Maybe things have changed with it since, but it shrank quite a bit, and was not based on a solvent that bonded to the plastic. It was also somewhat brittle and tended to flake off of the model if even slightly flexed. Dr. Microtools and Squadron putties are quite similar in performance. They both are based on a solvent, toluene if I am not mistaken, thus they bond with the plastic. They fill gaps well and are easy to sand. They do have some disadvantages though. They both shrink if large amounts of filling are needed, like if you are doing a conversion and have very large areas to fill. They should be applied in thin layers when you have large areas to fill. This helps some in solving the shrinkage problem, but not completely. It also prevents the problem of too much solvent damaging the plastic (I'm almost ashamed to admit this one, but back when I was in high school beginning modeling, I decided Squadron Green Putty would be good to fix some weights into the nose of an F-14. Well, the nose radome collapsed from too much solvent). Another problem is that when sanded, these putties invariably will have small pinhole bubbles in them.

Other model fillers:
One of the best products to come around in a long time for the modeler is a product caller Mr. Surfacer produced by Gunze Sangyo. In my opinion, and in the opinion of several of my fellow modelers in our local club, this is almost a miracle product. "What is Mr. Surfacer?" you may ask. Well, I guess the best way to describe it is that it is a thin filler, almost the consistency of paint. It is the best filler for small gaps, seams, scratches and the like. It can be applied with a paint brush, toothpick, or whatever you like. It dries fairly fast. It dries without bubbles and is very smooth, and sands very well. It comes in bottles in two grades, #500 (a thicker variety) and #1000. It also makes a GREAT primer. It can be thinned with Gunze Sangyo thinner, or as I have used, Dio Sol, and airbrushed. If you don't have an airbrush, it also comes in a spray can variety. Using it as a primer the first time (or any time for that matter) is an interesting experience. Unlike other paints, you spray the Mr. Surfacer on fairly thick. It will look like you have filled every scribed line and obscured every detail on the model, but when you put it aside, go away, let it dry and come back, it will "suck down" tight and every detail will show, and any small sanding scratches or the like will be gone. This brings me to the only disadvantages. It isn't intended for large gaps, but if you layer it, it can be used even for large areas needing filling. It also, since it is so thin compared to putties, shrinks much more. However it's lack of bubbles and quicker drying time more than make up for this.

Super glues:
Super glues also make very good gap fillers. Thin superglues work well for small gaps and scratches. For gaps along seams, put a drop of superglue on a sheet of wax paper, and use a #11 hobby knife blade as the applicator. Put the tip of the blade in the superglue, and run the point along the seam like you were cutting, but don't apply too much pressure. For larger gaps, you can also use superglue combined with baking soda. Put some baking soda in the gap, and apply the superglue to the baking soda. The baking soda will add some bulk giving more filling capacity, and the baking soda acts as an accelerator for the superglue. Thick gel type superglues work very well for larger gaps. I usually use a toothpick, needle, or #11 blade as the applicator. As fillers, superglues have advantages over hobby fillers in that they don't have bubbles when they set. They also shrink very little if any. They also set very rapidly, so can be sanded much sooner. Their primary disadvantage is that they are harder than plastic, so if you are using building a model that uses a particularly soft styrene, the plastic and superglue may not sand evenly if you don't take care to make sure that they do. Probably the best way to guarantee this is to use a sanding block. Also, don't spread the superglue with your finger. For more information on superglues, refer to the section covering superglues in the glues section of this FAQ.

Non model specific fillers:
There are a number of fillers that are not intended for models, but can be used. Most of these are auto body fillers. There are many different ones available. I have not tried any, but others have and have had good luck. One that was recommended was Bondo. It is solvent based, and will bond to the plastic. It also gets harder the longer it sets. It gets very hard, and can be difficult to sand if left to set too long.

Epoxies:
Two part epoxies can also be used for filler. Either the thin, molasses consistency ones or the putties can be used. There are many different epoxies, the long set varieties all the way to the 5 minute varieties. In general, the shorter the set time, the softer the epoxy when it is set. Some of these are even softer than the plastic. Also, most of the putties are not very hard setting either. One of the harder setting epoxies that I know of is JB Weld. It's not too hard to sand, but it is harder than plastic. The advantages of epoxies are that they do not shrink. They do not attack the plastic. Their disadvantage stems from this, in that they do not really bond with the plastic like solvent based fillers. IMHO, epoxies are the least desirable for most filling applications.

Tipp-Ex for small gaps. Soft but paints well.

Milliput for larger jobs. Can be built up rather thickly, and softened during application by mixing in small amounts of water.

Home made putty made from plastic shavings and Ethylacetate. Unfortunately dries very quickly, so you have to make it as you use it.

I prefer Dr. Microtools and Gunze Sangyo "Mr. Surfacer". Use rubbing alcohol to remove thinner from unwanted areas before it sets. Don't try to use fuller to close open areas. Fill these with scrap plastic first.