Two-part modelling putties are mixed from two components and harden by chemical reaction throughout their volume. Against fillers that merely dry, they bring two clear advantages: they do not shrink, so a filled spot never sinks later, and they can replace genuine material rather than just a groove. The category holds kneadable epoxy compounds in several shades and two-part paste fillers that cut, sand and take a scribed line much like styrene once cured.
It is the material for jobs a drying filler cannot handle: a missing section of a cowling, a detail the kit never carried, a void under a resin part, a transition into diorama groundwork. Because the reaction runs through the whole volume, one generous application can be enough — and the dimension stays, so the spot can be worked to a measurement.
Measure the components as the pack states and knead until the colour is uniform with no streaks. From that moment the working time is running — minutes with some compounds, tens of minutes with others. Mix no more than you will use; the rest cures on the palette.
Most kneadable compounds smooth under a damp tool or fingertip, water keeping them from sticking. Detail is cut in with tools from sculpting tools, and texture can be pressed in with tape or fine mesh. The advantage is that until it begins to set you can keep trying the shape and correcting it.
Cured compound behaves like a harder plastic. Take the rough excess off with a file, level with abrasive, and if the spot needs it, carry a panel line across using tools from scribing and panel lines. Some compounds drill cleanly too, which helps where a pin has to be seated.
These compounds come in several colours and that is not decoration. A dark compound reads clearly on light styrene and a pale one on dark, so while sanding you know exactly when you have reached the level of the surrounding material. Shades also differ in hardness and grain, which changes how well they hold a sharp edge and how thin they can be drawn out.
For the small blemishes left after shaping, a liquid filler from fillers is the quickest answer.
