This article will deal with the various types of glue available to modellers, explaining their characteristics, advantages and disadvantages. It does not cover the techniques of applying adhesives which are explained in the article ‘Joining Parts Together’ .
In the early days of the hobby, there was one type of glue that was almost universally used and that was thick polystyrene cement that came in a tube. Today, there are numerous types to choose from which reflects in part the fact that high quality scale models may be made from a variety of materials – traditional styrene plastic; polyurethane resin; various metals; rubber and soft vinyl. Getting the right glue for the right job is very important, so modellers need to know what is available. Although this article will cover the main types of glue, the huge variety of glues from so many manufacturers means that you should always pay attention to the instructions on the particular product you are using.
Types of Glue
The main types of glue that a modeller will need in their armoury are;
- Polystyrene cement
- Cyano acetate (‘super glue’)
- Epoxy Resin
- Clear ‘canopy’ glue
- Gloss varnish
- Clear rubber/silicone cement
- PVA adhesive
- White glue/woodworkers glue
1. Polystyrene Cement
|The fumes from polystyrene cement are toxic. Use only in a well ventilated area.|
|Polystyrene cement dissolves plastic. Use minimum amounts only and do not use it in an enclosed space on a model where it will take a long time to dry.|
Polystyrene (poly) cement is only suitable for rigid polystyrene plastic which is the type used for injection molded kits. It works by dissolving the surface of the plastic which then re-hardens. If a bead of poly cement is put between two pieces of plastic, then both faces of the plastic dissolve and meld together so that when they harden they have formed a solid joint. In effect, the two pieces have been welded together, so a very good bond is formed that is as strong as the plastic.
The drying time will vary mainly depending on how much is applied and the viscocity (thickness) of the glue. Very thin formulas will normally dry in seconds, but the very thick tube glue might take a few hours. Note that even when a bond has formed the plastic may not have fully re-hardened so should be treated with care for a time.
The major disadvantage of poly cement is that if too much is used, then it will completely dissolve through the material being glued and damage it. Also, if any glue is dropped or smeared on the surface of the model it will damage any surface detail. For this reason, it does have to be used with care and the minimum amount should be used. Furthermore, glue should not be placed into holes and cavities that are not exposed to the air, because it will not be able to dry and will slowly dissolve the surrounding plastic.
Poly cement is normally only available from modelling suppliers and it comes in three types according to how viscous it is:
Thick Tube Cement
When scale modelling first became popular, this was used almost exclusively. It comes in metal tubes similar to toothpaste and is quite thick. The thickness of the glue means that it needs to be used sparingly to avoid damaging the model. Some brands also have a tendency to be ‘stringy’ and leave a thin thread of glue behind which can be annoying.
Although tube cement has lost popularity over the years, it does still have its uses. It is easy to precisely apply a very small drop and the slow drying time gives the modeller plenty of time to position the parts correctly.
Medium viscous cement
This normally comes in plastic bottles that have a long thin hollow tube to apply the glue. It is more user-friendly than the thick glue, being less likely to dissolve away the part being glued. It also dries much faster than the tube cement, whilst still giving the modeller enough time to position the parts.
Ultra-thin or liquid poly cement
This normally comes in a small glass bottle with a brush applicator fitted into the screw top and it looks like water. Some modelllers find the brush supplied too large for many purposes, but it can be cut down or an old small paintbrush can be used for detailed application. The glue does not seem stick the paintbrush bristles together even when the cement dries on them. The bristles will go hard, but can be easily softened with gentle rubbing.
One thing to be aware of with liquid poly cement is that although it always looks the same, the amount of solvent in it varies from one manufacturer to another. Therefore when using a bottle from a manufacturer you are not familiar with, first try a few tests on scrap plastic to get a feel for how strong it is.
The fast drying time of this type of glue means that it is vey unlikely to damage parts unless some is accidentally dropped on a visible surface. One disadvantage with this glue is that there is only a very limited time to assemble the parts after applying it. There must also be a good contact between the surfaces to be joined as this is definately not a gap-filler.
2. Cyano Acetate Adhesive (‘Superglue’)
|Bonds human skin almost instantly and will cause permanent damage to the eyes.|
|The fumes from cyano glues will make clear plastic parts cloudy – do not use for windscreens and cockpit canopies etc. Special gules are available for this purpose.|
When this glue was introduced, it was advertised as instantly bonding almost anything to anything else and indeed it is very versatile. The only substances that resist it seem to be certain soft plastics. As such, it is very good for bonding hard plastics, resin and metals to each other, which makes it very useful on multi-media kits. However, it not easy to use and should perhaps be avoided by novices and children. It can be unforgiving, with the thin formulas curing in one or two seconds and often seeming to stick fingers to the kit much better than it sticks kit parts together.
Although cyano will stick most things together, the quality of the surface is far more important than when using poly cement. Any dust or grease on the surface will substantially reduce the strength of the bond. Rough surfaces stick better than smooth ones, so a light sanding of the surfaces that are to be bonded is worth considering.
If cyano accidentally gets on the wrong surface, then the excess should be immediately wiped off with a paper towel. Any residue should be left to harden and then scraped off with a sharp knife. If fingers, or other human tissue is accidentally bonded, it should be carefully separated with superglue debonder which should always be available when cyano adhesives are being used.
It is probable that only a fraction of the cyano adhesive that is bought is actually used. This is because once open, it deteriorates quickly and it very easily blocks the nozzle of the bottle which often makes it impossible to get at the remaining contents. To reduce this problem, always wipe the end of the nozzle, gently tap the bottle on a hard surface to encourage any glue on the inside of the nozzle to go back down and put the top back on straight away. If you are not going to use a bottle of superglue for some time, the shelf life can be extended by putting it in the fridge.
Like poly cement, it comes in three viscocities from ultra-thin to thick (also known as gap-filling superglue).
Thick (Gap-filling) Cyano
Gap-filling superglue can be used where two parts do not meet closely and it will bond the two pieces and fill the gap. However, it is not ideal as a filler. It can be difficult to apply just the right amount of glue to fill the gap without either leaving a depression or, having some ooze out on the model. It is also difficult to work it to the correct shape when it is drying and to sand it smooth when it has dried. There is only a short time between the glue going firm when it can be sanded and when it becomes too hard to sand down.
Thick superglue can take a long time to cure, but it is possible to buy an activator spray that hardens it almost instantly. It is also possible to buy microsopic beads which when sprinkled on to thick superglue is claimed to improve the strength of the bond.
This is probably the easiest viscosity to use. Unlike the ultra-thin variety it will not run everywhere uncontrollably and it normally has about the right drying time. When you buy superglue from a hardware store for domestic use it will probably by medium viscosity.
Care needs to be taken when using this. Unlike ultra-thin poly cement, it cannot be applied by a normal brush because it would ruin a brush with each application. Sometimes, it will come with a special applicator consisting of a thin plastic tube, but even with this it can be difficult to apply the right amount without it running everywhere. Some thin superglues come in a bottle with a brush and these may be the easiest to apply.
The advantage of the ultra-thin superglue is that parts can be assembled ‘dry’ and then the adhesive allowed to run along the edges where it is sucked in by capillary action. It bonds very fast – sometimes in only one or two seconds.
3. Epoxy Resins
These adhesives consist of two parts – the hardener and adhesive – which need to be thoroughly mixed before application. Sometimes they come in separate tubes and sometimes they come in a double syringe. The latter is the easiest to use because it is simple to get equal parts of hardener and adhesive which is important for the strength of the bond.
Like superglue, the epoxy resins glue almost anything to anything, but they also need a good clean grease free and preferably roughened surface to get the best bond.
It is possible to buy epoxies with setting times from 5 minutes to 24 hours and it is useful to keep both quick and slow setting varieties around. Theoretically, the slow drying varieties produce a stronger bond, but this is largely academic as even the quickest setting varieties will produce a very strong bond. Increasing temperature will speed the setting time.
Because of the slow drying time it will normally be necessary to support the objects being glued until the adhesive begins to harden.
If any glue is squeezed out then it is best left until it begins to become firm when it can be cut away cleanly. If you try to wipe it away immediately you will invariably just smear it and make a mess.
Epoxy glues are great when a really strong bond is needed, especially between two different materials. Because it has to be mixed (and you will usually mix far more than you need) and it tends to be messy, it is not the primary glue of choice for modellers, but there will usually be a packet of it in the bottom of every modeller’s tool box.
4. Clear ‘Canopy’ Glues
Sticking clear plastic parts presents problems. The fumes given off by polystyrene cements and even cyano glues can make the clear parts become foggy. It is very difficult to use epoxy resin glues on clear parts without smearing the glue on the parts.
For this reason, a few modelling suppliers have produced their own glues specifically designed for clear plastic parts and these are sometimes called ‘canopy’ glues. They appear to be very similar to the clear adhesives described in the next section, but tend to be less viscous and so it is easier to apply them in small amounts. Not only do they not affect the clear parts but by drying completely clear any excess is almost invisible. It should be noted however, that the bond is not as strong as some of the glues in the previous sections, but it is normally quite adequate.
In addition being used as a glue some brands can also be used to create a membrane to form windows across small gaps such as in models of airliners.
5. Gloss Varnish
It may be surprising to find gloss varnish in a list of adhesives because clearly it is not intended to be used as a glue at all. However, gloss varnish is surpisingly useful for holding very small parts, such a photo etch buckles in place.
Johnson’s Future/Klear works very well because it becomes tacky in under a minute and can be handled after a few minutes. However, any gloss varnish will work. Paint a layer of varnish where the small part is to be placed and then lay the part on the wet varnish. The natural tackiness of the varnish will hold it in place and more varnish can be painted over the top for additional security.
Using a small paintbrush wet with gloss varnish is also a useful way to hold tiny parts and put them into the correct position.
6. Clear Rubber And Silicone Cements
There is a wide range of tube glues mainly intended for domestic use that are often branded as ‘All Purpose’ or ‘Universal’ glues. They generally dry clear and remain rubbery. The majority are solvent based, but there are varieties advertised as “safe for children” that do not contain any solvents.
These are not suitable for general modelling use because they are difficult to apply in small amounts, can be stringy and generally do not produce a bond as strong as any of the adhesives mentioned above. These glues only work well when there is a large surface area. However, they can be handy for special work such as:
- Small drops can temprarilly hold parts in place when doing a dry run, the glue can be pulled away later.
- Fixing model tarpaulins and other flat stowage to armoured vehicles.
- Gluing flexible materials such as rubber tyres.
- Gluing clear parts such as cockpit canopies (although glues specially made for this purpose are available).
When using a solvent based clear glue check that it will not react with the plastic before using it.
It is worth mentioning that Revell produce their own brand of ‘universal’ glue that differs from most because it is less viscous and comes in a bottle with a brush in the lid. This can be quite useful for gluing objects with a large surface area. This looks very similar to liquid poly cement so don’t get them confused when buying or using it.
7. PVA Glue
This is a thin water based white glue that dries rubbery. It has wide range of commercial and domestic uses. For example, in the construction trade it is often watered down and used to prime walls prior to painting. It is very popular in kindergartens and schools because it is ideal for sticking paper and card and safe for children to use. It can be found in building suppliers (where it is sold by the gallon) and in art shops.
The uses for PVA adhesive are the same as for clear glue in the previous section. The difference is that it is thinner and water based, so is more suitable for situations where it can be brushed on a large area. The bond will not be as strong as with clear glues. When dry it can be peeled off most surfaces.
This glue is particularly useful for dioramas when it can be watered down and painted all over the base to fix the grass, sand, pebbles and other landscaping materials into position prior to painting.
8. White Glue / Woodworkers glue
This looks very much like PVA glue, being white and water-based but it is more viscous. It has limited use for most modelling applications, but is very good at bonding wood, so may be useful when making dioramas or bases. Some modellers use it to bond clear parts such as cockpit canopies. It may dry clear or white depending on the manufacturer.