This article explains the different types of gap filling materials available to modellers. Techniques for filling gaps are covered in the article ‘Gap Filling’ .
Nothing spoils a good model more than the sight of gaps or ridges along seams. The best paint job in the world cannot disguise or compensate for an unsightly gap. Filling gaps is one of the fundamental skills of scale modelling and needs to be mastered to get a reasonable finish on any model.
In the early days of plastic kits, modellers probably spent more time filling and sanding than anything else. The quality of the moldings was poor compared to today’s standards and it was expected that major parts would not fit well and that gaps would have to be filled.
Fortunately, those days are well behind us and the quality and precision of models released recently is generally astonishing. Sometimes, complex major parts go together perfectly. Nevertheless, most kits will still have some visible join lines that need attention. Furthermore, if the kit was orignally released a few years ago, or if the modeller is attempting some kit-bashing or a conversion there may be considerable gap filling to be done.
It should be noted that the uses for some of the products listed below go far beyond simply gap filling. Milliput, for example, can be sculpted to make all manner of accessories such as baggage, bedrolls and sandbags.
Types Of Filler
Over the years, I have heard of all manner of products being used by modeller’s who swear by their usefulness. These include plastercine, writer’s correction fluid and window putty. However, the vast majority of modellers stick to mainstream products that have proved their worth and this article will be limited to those.
|Hazardous fumes, use in well ventilated area. Potential skin irritant.|
These normally come in metal ‘toothpaste’ like tubes and are produced by a wide range of manufactuers. They are ready to use and good for most small gap-filling problems.
Most of these putties contain a solvent that dissolves styrene plastic and one of the reasons they work so well is that they bond to the plastic. However, this does mean that care is needed because using to much will damage the model as will getting some of the putty on any surface detail. These putties are best used for filling smaller gaps and if you are going to use them for building up a large area then apply it in thin layers allowing each one to dry before applying the next. These putties dry very quickly so only a small amount should be taken from the tube at a time and the cap replaced immediately.
It should be noted that the type and amount of solvent varies from brand to brand, so when trying a new brand it is advisable to test it first on scrap plastic. Perhaps the most famous of these brands is Squadron Green Putty and Squadron White Putty with the latter having milder solvent properties.
The advantages of these putties are:
- Ready to use;
- Easy to apply;
- Bonds well with the model and when dry can be sanded or shaped easily.
The disadvantages are:
- They will dissolve the plastic if too much is used;
- They can dry too quickly, forming a skin and not giving enough time to apply them carefully;
- They do not bond with resin or metal, so are best used for gaps between two styrene parts;
- They give off toxic fumes.
There are a few brands of model filler on the market that do not contain any solvent. These have the advantages that they are safer for children and there is no danger of damaging the model. Unfortunately, they do not bond with the plastic and so can come loose or crumble away when sanding. For general use I would not recommend them.
Like epoxy glue these come in two parts that have to be thoroughly mixed. It is possible to buy this product from hardware stores as they can be used general mending purposes. The most famous brands and the ones most used by modellers Milliput and Apoxie Sculpt. Both of these come in various grades and the one of most use to modellers is the superfine variety.
Milliput comes as two cylinders of fairly hard putty in a cardboard box. A ‘salami’ slice is cut off each cylinder and mixed together well. As the putty is mixed and warmed in your hand it will become softer and easier to use. You then have a clay like ball that can be molded and used to fill gaps or build up irregularities.
Milliput takes a while to set and like epoxy glue sets faster as the temperature rises. At room temperature it is normally quite hard after about an hour and will be rock hard after two but continues to strengthen for 24 hours. Epoxy putties are very difficult to sand or shape when they have been left to fully harden. It is necessary to either smooth them to shape with a little water so they do not need sanding, or to sand them when they have started to harden but have not yet achieved rock hard status.
Much of the above applies to Apoxie Sculpt except that it comes in tubs.
The advantages of epoxy putties are:
- Plenty of time to work with them;
- Can be used for large gaps, and, like plastercine or clay, can be scupted into any shape;
- Bonds well (if the surface is non-greasy), is strong and does not shrink
The disadvantages are:
- Need to mix the two parts thoroughly;
- Difficult to prepare a very small amount;
- Difficult to sand or shape when it has fully set.
Almost all modellers will have a supply of Milliput or a similar epoxy putty in their tool box. Further information about using Milliput can be found in the article ‘Using Milliput’ .
Gap Filling Superglue
This is a thick gel like version of superglue (cyano adhesive). As such it is useful for bonding together almost any substances. It’s thickness means that it will also fill any gaps between the two parts and it can be run along the inside edge of two parts to give additional strength where it will not be seen.
This is not a filler like the products above. It needs to be applied very carefully and is difficult to smooth to the right shape. It is possible to sand it, but timing is crucial because if left too long it will become very difficult to shift. Drying time can be very long so many modellers use it with a spray accelerator that makes it set almost instantly.
- Ready to use
- Fill gaps as you glue parts together
- Needs to be used with care – very unforgiving of mistakes
- Difficult to get a good finish and any sanding has to be timed well
At first glance this would not seem to be a very good filling solution and yet some modellers use it all the time in preference to other fillers, so maybe it just takes a while to get used to.
Acrylic Plastic Filler
Vallejo offer a filler that differs from most, being acrylic based. It can be used like most model fillers, but it does not give off dangerous fumes or dissolve plastic. At SMG.com we have no experience of this product (although have a very high opinion of Vallerjo products generally). Therefore, we can only quote the manufacturers description:
“A modelling paste which dries to a white, totally opaque, stone hard finish. It is used principally for rebuilding or restructuring models and miniatures, for textures and high reliefs. For extra high relief the paste should be applied in layers, allowing each to dry before applying the next. If a more flexible paste is desired, mix with Gel Medium”
There is no reason why common household interior filler cannot be used for some modelling applications. Some varieties can be quite course and they will not bond with plastic so these types are not all that useful. However, those interior fillers branded as ‘fine surface’ and aimed at filling tiny cracks in plaster may well be fine enough to use for modelling. Some dry to a texture that can be sanded and others have a formula that dries rock hard and is difficult to sand, so it is best to make a test to find which type you have before putting it on a model.
The advantage of these over the traditional fillers described above is that you can buy a big tub for very little money and you may even have some lying around in the garage or shed.