I am christening a new series focusing on modelling chemistry and tips associated therewith for both beginners and advanced modellers. We will guide you through the world of chemistry as it pertains to model technology from basic construction to surface treatment all the way through to finishing and weathering. We will assume the use of readily available materials with a certain amount of emphasis on Mr. Hobby (Gunze) products.
The first volume of this series is dedicated to adhesives.
The question of with what and exactly how to glue plastic models together is as old as the hobby itself. The answers change with the passage of time as technologies develop and along with them, trends. Currently, we find four types of adhesives that are front and centre in plastic model relevance:
- Solvent based adhesives
- Instant glues
- Dispersion adhesives
- Epoxy cements
The method and range of use varies and it can generally be said that each of these types has their usefulness. It is essential to use the right adhesive for the right job. Here, we’ll focus on Solvent based adhesives, and so that the situation isn’t too simple, even they have their specific differences from brand to brand, despite our general focus on Mr. Hobby products. Solvent based adhesives have no minimum film-forming temperature (as do dispersion types) and so no coalescence process will be observed. After the application of the solvent, and its subsequent evaporation, signs of its presence will be left behind in the form of the polymer film. It is this polymer film that, thanks to its adhesive properties, is responsible for the bonding of parts together. Another type-specific effect of solvents on plastic is the etching of its surface. After the solvent component evaporates, we are left with a very solid and stable bond. The chemical process at work here leads to a cold weld, and it is necessary to use these adhesives on materials that the adhesive is able to etch. In other words, they are able to chemically etch the material being glued. Solvent type adhesives are not effective on materials such as resins (polyurethanes) from cast or 3D printed items, metals, wood or paper. So now we’ll take a closer look at specific products and the differences between them. Solvent type adhesives can be categorized into two groups, universal and weld type.
All of the solvent based adhesives described in this article come in sturdy glass containers with a screw type lid with an integrated brush applicator.
UNIVERSLA ADHESIVES (BASIC)
MC127 – Mr. Cement Deluxe
Mr Cement Deluxe (or Mr. Cement, the same product in a smaller packaging) hails from the Mr. Hobby product line and is their best for gluing together large surfaces but is still useful for small detail items, too. It is a low viscosity liquid, meaning it flows easily and the time the solvent takes to evaporate is a little longer than that of Extra Thin types. Mr. Cement and Mr. Cement Deluxe (MC124/MC127) are applied to the contact surfaces of the components to be joined. The longer evaporation time of the solvent allows the larger components being joined to be cantered properly. For the joining of smaller parts, the same quality allows us to apply small quantities of the cement to the contact surface in preparation for placing the part in its final spot. This operation never takes more than a couple of seconds and the glue is ready to be applied throughout.
WELDING SOLVENTS (BRUSH ON)
MC129 – Mr. Cement S
Mr. Cement S is an extra thin ‘Brush On’ type material which obviously refers to its method of application. This involves the joining of the two components together and running along the joint with the solvent using the brush applicator. The solvent evaporates very quickly from the surface (the speed of which is comparable to acetone), but it remains within the joint long enough to optimally act ont the surfaces of contact to form a solid bond. Personally, I think that Mr. Cement S as the premiere extra thin product, which I would recommend among these types of products.
MC131 – Mr. Cement SP
Another member of the extra thin family of cements from Mr. Hobby is Mr. Cement SP. The SP stands for ‘Super Power’. This is a product that has the same roots as Mr. Cement S, but with a new recipe which yields a higher rate of drying and a correspondingly increased bond strength. It is well suited for stressed joints where we may want a faster bonding between parts and a higher strength to reduce the probability of a failure. This product is ideal for wing to fuselage joints or for leading edges of the wings. The quicker evaporation time, though, requires the modeller to be efficient in the process as a whole, more so than with the use of MC129 – Mr. Cement S.
MC 132 – Mr. Cement SP B
The last type of Mr. Hobby extra thin cement is Mr. Cement SP Black that directly comes from Mr. Cement SP. It is characterized by a very rapid drying time and high strength between joined parts. On top of that, it contains a black pigment which serves as a consistency indicator for greater application control. In recessed panel lines and joints, it can map out crevices and scratches and provides an excellent opportunity to assess the surface quality of the model, indispensible for the fixup of details. I do not recommend the use of this product on white, or light, coloured surfaces because the adhesive may remain visible on the surface.
From the manufacturer:
Technical Aspects of Solvent Based Adhesive Application
The technical aspects of these types of glues are pretty simple in and of themselves, with respect to their application. They can be separated into two methods, based on the type used.
Thin glues (slightly higher viscosity, or thicker, than the extra thin variety with a longer solvent evaporation time) require glue application to the join surface and then attach the parts together and, if necessary, press the parts together.
Extra thin glues differ in that the parts are first attached and the join is then glue applied. If we aim to seal the joint between the parts with the use of our extra thin (such as fuselage half joining, leading edges of wings, etc.) then there should be a small gap left between the parts. The glue is then applied and after about five seconds, the parts are pressed together. The pressing together will squeeze out redundant plastic which is then allowed to harden for 24 hours until it can be sanded smooth. This creates an excellent connection of the parts and the join line will be invisible on the kit.
The biggest advantage to using solvent based glues is the strength of the joint and the neat join line that they provide with proper use. They are great for modern kits with a high level of precision of molding, where the fit of parts is to a very high tolerance. Use of any other types of glues, notably cyanoacrylate types, could lead to problematic misalignment of parts, even if to a small degree.
Solvent type adhesives are irreplaceable in the role that they fulfill in plastic modelling and should be at the disposal of every modeller, at least in the thin variety as well as the extra thin, or ‘basic’ and ‘brush on’, and in greater versions as we have discussed here.
Main Advantages to Mr. Hobby Solvent Based Adhesives
- Bond strength
- Clean joints
- Application brush generally included
- Speed of bonding
- Use repetition
- Low volume usage per application
- Easy and precise application
- Sturdy packaging
- Long shelf life
- Easy storage with no special requirements
Main Disadvantages and Risks of Mr Hobby Solvent based Adhesives
- Significant odor
- Longer through and through curing time
- Risk of failure of joint if too much is applied
- Risk of surface etching where no adhesive is desired as a result of poor application
Winner of international IPMS competitions in Master categories and multiple Czech Republic IPMS champion. Author of articles in international magazines with worldwide reach (Military Illustrated Modeller, Cocardes International, ModellFan, Modelář). Co-author of modeling startup Plastic Invasion.