I think scale modeling – whether it’s kits, dioramas, bases, scratchbuilding, whatever – can be split into three distinct sections: building, painting and weathering. Each one in turn can be split into a number of steps. In this tutorial, I’ll focus on the most fundamental part of building – sticking stuff together. Or, more precisely, the glue we use to attach parts to each other.
Different Types of Glue
I say ‘glue’, but really there are tons of different types, each with its own uses. In addition, we have some auxiliary products worth knowing. Let’s break it down, one by one!
This type of glue works by literally melting the plastic. Pushing the parts together with a bit of cement in between will effectively weld them into one. It works fast and does a great job holding the pieces together. In addition, its ability to melt the plastic makes it excellent at removing seam lines, as I’ve detailed in one of my other tutorials. You can also mix it with polystyrene to create your own putty, a great filler for minor imperfections.
‘Polystyrene’ is the key word here, as most cements will only work with this type of plastic. That said, there are some which also work on ABS and potentially other types – like Plastic Magic by Deluxe Materials. None of them work on resin kits though, so keep that in mind.
While we’re at it, let’s mention some other plastic cement variants. There is extra thin type, which allows it to flow into the gaps by capillary action. Most notable example is Tamiya Extra Thin Cement, glue of choice for many modelers worldwide. There is also quick setting / quick dry variant, though it’s not all that useful, as it often dries way too fast. Finally, we have limonene cement, which replaces the chemical stink with a nice, fruity aroma.
One area plastic cement falls short though is gluing big pieces – think 2x3cm and up – as the solvent in the center has nowhere to evaporate to, leaving it as a gunky mess for a long, long time. For this kind of work it’s better to use CA glue.
Methyl Ethyl Ketone (MEK), also known as Butanone, is a chemical compound which melts polystyrene. It’s included many types of plastic cement, but it also works well on its own. You can easily buy it from Ebay or online store stocking chemical supplies.
Why would you want to do so? Well, mainly the price. A 250ml bottle of pure MEK is cheaper than 40ml bottle of plastic cement.
There is one caveat though – Butanone is much stronger than typical plastic cement. If you’re not careful when applying it, you can easily damage the pieces you’re working on.
A solution to this is creating your own mix. Personally I use a 50/50 mix of MEK and Tamiya Extra Thin as my go-to glue and it works wonderfully. It also saves me some money, since each Extra Thin bottle lasts me twice as long.
Some brands come with applicators of their own. Small brushes on Tamiya or Mr.Hobby bottle caps work great. They’re convenient and allow a fair amount of precision when applying glue. Others, like Revell Contacta, come with needle applicators – great for reaching tight areas. They don’t allow as much control over the amount we apply as the brushes do though. Sometimes dried glue can also clog the needle, but it’s quite easy to clean.
Other options include precision applicators – basically a tiny needle at the end of a glass tube. These work nicely, though usually only with extra thin type, as they use capillary action to get the glue flowing. Needle itself is also somewhat fragile.
We can also use cheap paint brushes. Since those come in dozens of shapes and sizes, you can easily find one which will work for the area you’re working with – whether a flat surface or a tight corner. Another alternative are microbrushes – basically tiny cotton buds on a plastic handle. They work alright for some small spaces, though I rarely need them.
CA stands for cyanoacrylate, but you probably know it as instant glue, Super Glue, Krazy Glue or one of a million other brand names. This type of glue works extremely quick and bonds most materials – plastic, resin, metal parts, metal songs, your fingers and broken hearts.
It’s close second when it comes to most used adhesives in scale modeling and for a good reason. In addition to working very fast, it bonds materials plastic cement can’t deal with – resin, photoetched parts, metal details, wires, some types of rubber and so on. We can also use it as gap filler – just drop a bead of glue on top, let it dry and sand it down. The consistency will usually be similar to plastic, so it works well for fixing scribing mistakes for example. Brushing some over loose joints easily fixes those as well. Just, you know, let it dry first, unless you want to turn loose joint into no joint.
It’s worth remembering that CA is not a single product, but rather a family of glues and each of them can be fine-tuned for a specific purpose. Consistency varies from watery liquid, which easily penetrates through gaps in material, to a thick gel, which stays in place where it was applied, rather than spreading over the surface. Standard, medium-thick liquid tends to be most easily available and works well for most modeling purposes though.
Another variable is cure time, which ranges from couple seconds to minutes. That is when bonding two surfaces, when you just brush it over a joint, it’ll take much longer – sometimes up to 24 hours.
One disadvantage of CA is the fogging. While drying, it tends to release vapors, leaving a white residue on the surface. Using CA for painted parts is inadvisable, unless it’s a specific, odorless kind.
Most common one is the kicker, or accelerator, which massively speeds up the curing time. Whether it’s already holding two pieces, or it’s just spread out on a surface, using kicker will turn CA rock hard within a second. Keep in mind though that accelerated CA will be much harder and slightly more brittle than if it cured naturally – not the best option for gap filling, especially when scribing.
Speaking of – next up is filler powder. Mixing it with CA will pretty much create instant putty. It works best by dropping some powder on a surface, then adding extra-thin CA (like Deluxe Materials Roket Hot) on top. Liquid CA will quickly spread throughout the powder and bond it to a surface within seconds. There are some branded filler powders, but save your cash. Cheap alternatives like baking soda, cornstarch or baby powder work just as well. Once again though – this kind of filler is too hard to be used when scribing.
Next up, we have adhesion promoter, sometimes also called CA primer. This chemical is intended to go over difficult materials – like polycaps – and allow them to be bonded by CA glue. It’s neat when it works, but it can be somewhat unreliable and require multiple applications. Polycaps are tricky.
Finally we have the debonder – a chemical which dissolves cured CA and allows the pieces to be separated. More often than not ‘pieces’ will be your fingers. Worth having.
As far as CA applicators go, 95% of the time I just use toothpicks. You can buy a nice, reusable applicator that’s shaped to better hold the glue and made of metal – so you can burn off cured CA – but it doesn’t offer much extra value for the price. You can also get brass toothpicks, because one paint company actually makes them, but for the price of 3 I’d rather get a backpack full of wooden ones. Better value. Easier to chew on too.
You can also get precision applicators – basically extra cap with a length of rubber tube attached to it. These work pretty well with thin to medium CA, giving you better control of where you pour it on.
Last type of glue you might want to use on your model is two-part epoxy resin.
As with standard resin or epoxy putty, it consists of two ingredients – resin and hardener – both of which are inert until mixed together. Once mixed in 1:1 ratio, you’ll have a certain amount of working time before it starts to cure. Usually 5 to 30 minutes, depending on the type. I like 5 minute kind – more than enough time to place and align the elements, plus less waiting around afterwards.
You probably don’t see the epoxy resin mentioned often, as it’s extremely situational. It really excels in those few situations though.
This type of glue creates a very strong bond, but it also retains some flex once cured. This property makes it perfect for load-bearing parts, like landing gear on an airplane. As for Gunpla, it’s great for fixing broken pegs or adding ball joints you’ll be popping in and out. If you want to modify Gunpla hands with some wrist bend, epoxy resin is what you should be using when gluing ball joint back on.
As for application – usually it’ll be a toothpick or some kind of sculpting tool. Probably whatever you used to mix it – because convenience.
Make sure to use gloves while working with it, as it can cause skin irritation.
PVA (polyvinyl acetate) Glue is also known as wood glue, white glue or Elmer’s Glue (mostly in the USA, though it’s just one of many, many brands producing it). It’s been a couple decades since it was phased out as model glue, though it remains extremely useful for diorama builders.
PVA dries rather slow – taking up to 24 hours for a full cure – which allows plenty of working time. Once cured it’s completely transparent. It might be somewhat glossy, though some brands, like Mod Podge, also make matte variant.
There are two main ways to use PVA. It can be applied neat on a surface, followed by elements we want to add, like rocks, static grass, other kinds of greenery, wooden/plastic constructions, figures and so on. You can also apply it on top of resin water and spread it randomly with a blast of air from an airbrush to create a nice ripple effect. Luke Towan, a great diorama builder, often uses this particular technique.
Another way of using PVA is watering it down and adding a tiny amount of dishwashing soap, creating what is sometimes called ‘Scenic Glue’. In this form it can be applied with a pipette or spray bottle to glue down ground cover – sand, flocks and so on – since it can flow into the gaps between grains, making them stick to each other as well as the surface they’re on, ensuring good adhesion all around. It’s often preceded by spraying down some IPA (isopropyl alcohol), to further break down surface tension and ensure it flows nicely. It’s also used as a sealer before moving on to the next stage of the build.
Uncured PVA can be easily cleaned with a damp cloth.
And, obviously, you can also use it to build your workshop organizers.
Still with me? We’re about halfway through. From now on we’ll be moving on to more situational stuff though.
‘Polymer’ glue can describe any number of products, though in this case we’re talking about generic, off-brand ‘universal’ glue. This type is usually clear, dries clear and creates decently strong, slightly flexible bond. It can join a number of materials, including styrofoam, wood and plaster. Those three are the main uses we’re interested in here.
Polymer glue works very well for gluing together layers of styrofoam or XPS while constructing a diorama. You can also use it to stick plaster rocks to the foam or add a wooden frame around the scene. It can also bond plastic with the above.
As with PVA, damp cloth should be enough to clean up any excess.
Its main advantage is speed, making it great for quickly building up diorama elements – like a rock face. You can also use it to securely install LEDs, if there’s enough space for it. That’s one disadvantage – you need quite a lot of it for a really secure bond. Another good use is creating smoke effects – for example sticking cotton wool to a skewer to add some flair to a rocket fired from Zaku’s bazooka. You can probably find couple dozen other uses for it.
One of the most creative ones I’ve seen is using it to create transparent thruster effects, kinda like Freedom’s wings of light. Keep in mind cheap glue usually turns milky white once cured though.
Speaking of curing, here’s a neat trick: turn compressed air can upside down and blast freshly applied glue. It’ll set pretty much instantly.
At this point though, we’re mostly covering the alternatives to the things I already mentioned. Silicone creates a strong, slightly flexible bond and works quite well for adding rocks or a frame to a diorama.
Why transparent kind? Well, that’s because you can also use it to get your Point Break on and create some water effects, including decently sized waves. It doesn’t take paint very well though, so you might have trouble imitating foam or rapid flow. Another disadvantage? It stinks like rotten eggs.
Spray adhesive is… well… glue in a spray can. It bonds wood, fabric, polystyrene and a fair amount of other materials. I suppose it’s more useful for cosplay, but it still can come in handy. Since you can easily apply it in thin, even layers, it works well when working with big surfaces. For example, laminating big pieces of pla-plate for a base.
Another use is creating simple trees for a diorama. Spray the branches, then sprinkle some flock on them (or just dip the whole armature in) and voilà – instant tree. Maybe not a mind-blowing one, but often good enough.
Our final entry is something you’ll rarely see or use, as this type of glue is mostly used for woodworking and furniture construction.
That said, it can be be useful for diorama building – especially sticking together layers of XPS or adding wooden/plastic frames. Unlike others though, this one really needs to be clamped or weighed down.
Like polyurethane insulation foam, this glue absorbs moisture from the environment to expand many times beyond its initial volume. If it has nowhere to expand to, it’ll push apart the surfaces its meant to bond. We can use this property to our advantage though. In fact, it’s why I bought it in the first place. Story time!
When constructing diorama for my Barbatos, I decided to add a plastic frame around the terrain to make it look neat. Problem was, the XPS foam on the edges was very uneven, with 0.5-1cm gap between it and the plastic (which was already neatly glued to the wooden picture frame I used as base). Rather than filling it up with a ton of plaster, I simply poured in a little polyurethane glue all around. Couple hours later – presto – gaps filled, with a solid bond between the surfaces. Only thing left to do was to trim the excess which poured out and blend it in.