Putties and modeling compounds are among the materials that often seem optional to beginners, but in practice, they prove to be key elements of modeling technology. They allow for correcting form imperfections, eliminating gaps created during assembly, and restoring surface continuity where glue alone is insufficient. Whether we're dealing with a simple plastic model, an advanced resin conversion, or a wooden structure, modeling putty serves as an intermediate material between rough assembly and the final finish.
Technologically, putties are not "hole fillers," but precisely designed masses with specific viscosity, setting time, shrinkage, and reaction with the substrate. Differences between individual types result from the type of binder, the solvent used, and the curing mechanism. Understanding these differences is crucial to consciously selecting the right putty for your model and avoiding problems that only become apparent during the painting stage.
What are putties and modeling compounds and how do they work?
Modeling putty is a semi-solid material designed to fill voids, crevices, and surface irregularities of a model. After application, this mass hardens – through solvent evaporation, a chemical reaction, or a mechanical bonding process – creating a surface suitable for further processing, primarily sanding and re-engraving.
A key parameter of any putty is the way it bonds to the substrate. Some compounds operate solely through mechanical adhesion, while others have limited chemical interaction with the plastic or primer. This determines not only adhesion but also the risk of cracking, shrinkage, or joints "bouncing" after paint application.
In modeling, we encounter classic solvent-based putties , epoxy resins , water-based acrylic putties , and intermediate products such as surfacers and liquid putties . Each of these groups has different properties and optimal applications.
Types of modeling putties and their characteristics
Solvent-based putties (nitro)
This is the most classic form of modeling putty , known from brands such as Tamiya, Revell, Humbrol, AK Interactive, Ammo of Mig, Mr. Hobby, Trumpeter, and Wamod. Its operation is based on the evaporation of a solvent, which gradually evaporates after application, leaving a hardened mass.
The advantage of this type of putty is its good adhesion to polystyrene plastic and the ability to be easily sanded after it has fully dried. However, it's important to remember that the solvent affects the model's surface – thinner elements or too thick application can result in local softening of the plastic and loss of detail.
Solvent-based putties also exhibit volumetric shrinkage, meaning deeper cavities often require application in several thin layers rather than a single thick one.
Acrylic putties (water-based)
Acrylic modeling compounds —represented by brands such as Vallejo, AK Interactive, Ammo of Mig, and Mr. Finishing—are based on acrylic binders and water as a carrier. Chemically, they are much gentler on the modeling material, making them attractive to beginners.
Their greatest advantage is their lack of aggressive action on plastic, resin, and wood. This allows them to be used in sensitive areas without the risk of deformation. Their disadvantages include lower hardness after curing and weaker adhesion compared to solvent-based putties.
Acrylic putties are best for minor surface corrections, micro-cracks and finishing work, especially where control and cleanliness are important.
Epoxy masses (two-component)
Epoxy resins , such as Milliput and Amazing Art products, are a completely different technological category. They consist of two components that, when mixed, enter into a chemical reaction leading to permanent hardening.
Their greatest advantage is their lack of shrinkage and very high mechanical strength. These compounds do not evaporate but bond structurally, making them ideal for rebuilding missing parts, sculpting details, or working with metal and resin elements.
On the other hand, they require greater precision, planning, and experience. Working time is limited, and post-curing processing can be more difficult than with traditional putties.
Liquid putties and surfacers
Products like Mr. Surfacer , Mr. Dissolved Putty , and Gunze Mr. White represent a cross between putty and primer. These are very thin compounds that are perfect for filling micro-scratches, parting lines, or subtle surface defects.
They work by creating a thin layer that simultaneously evens the surface and prepares it for painting. A surfacer doesn't replace a traditional putty knife for larger gaps, but it's indispensable during the finishing stage.
Selecting the putty for the model material
The choice of which putty to use should always take into account the base material and the nature of the defect.
Solvent-based putties and surfacers work best for polystyrene plastic , offering good adhesion and cohesion with the material. Acrylics can be used as a guide for minor corrections, while epoxy resins are suitable for larger reconstructions.
Resin requires caution – aggressive solvents can cause micro-cracks. In this case, water-based acrylic fillers and epoxy resins, which do not react with the material, are safe choices.
Metal practically does not react with classic solvent-based putties, so the best results are achieved by using epoxy masses or thin layers of surfacer on a properly primed surface.
Wood , found in models such as Artesania Latina and Woodland Scenic, works best with acrylic masses and dedicated wood masses, which compensate for its natural workability and absorbency.
How to work with putty - technological basics
Working with modeling putty involves controlled surface leveling, not mechanically "sealing" gaps. Substrate preparation, the thickness of the applied layer, and curing time are crucial.
The surface to be filled should be clean and degreased. For plastic, lightly sanding the surface will improve adhesion. Resin and metal require more thorough cleaning, as even minor contamination can weaken the bond.
Modeling putties are designed for thin-layer work. Deep cavities should be filled gradually, applying several thin layers instead of one thick one. This reduces shrinkage, cracking, and the risk of the putty collapsing.
Curing time is often underestimated. Touch-dry putty is not always fully cured, especially with solvent-based putties . Sanding too early can lead to pinholes and visible joint lines after painting.
Sanding should be done gradually, using fine-grained sandpaper. The final step in surface inspection is to apply a thin layer of surfacer , which reveals micro-irregularities invisible to the naked eye.
FAQ – putties and modeling compounds
What is the difference between modeling putty and surfacer?
Putty is used to fill holes and crevices of actual depth, while surfacer is a leveling material designed to eliminate micro-scratches and minor irregularities. Surfacer does not replace putty for larger gaps.
Which modeling putty should I choose to start with?
For beginners, the best choices are acrylic modeling putty or classic solvent-based putty applied in thin layers. They are predictable and easy to work with.
Can putty be applied directly to plastic?
Yes, most fillers are designed to be applied directly to plastic. However, avoid thick layers and always allow the putty to fully cure before further processing.
Why are the joint lines still visible after painting?
The most common cause is shrinkage of the filler or insufficient curing time before painting. The problem may only become apparent after the paint, especially varnish, has been applied.
Can epoxy compounds be sanded?
Yes, but they are much harder than classic putties. The best results are achieved when applied partially cured or using fine-grained paper.
Is one putty enough for the entire model?
In practice, no. Different stages of the work require different materials – from epoxy resins for reconstruction, through classic fillers for gaps, to surfacers for final surface leveling.
Are acrylic putties always better for resin?
They are chemically safer, but not always mechanically durable enough. For larger defects, epoxy resins are a better choice.
Can you apply paint directly to the putty?
Technically, yes, but it's recommended to use a primer or surfacer. This ensures uniform adhesion and reveals any imperfections before painting.
