Profil 2,0 x 3,2 mm

A 2.0 x 3.2 mm strip

A rectangular section, the most universal shape in the whole range. You can build a frame, a stiffener, a beam under a floor or a ledge under a sill out of it, and because two of the sides differ, the same piece can be turned and behave like two different dimensions. White polystyrene, a 35 cm length, sold singly.

Sanding leaves a mark that paint will not hide

After an end is trued up or an edge is thinned, the strip is left with a place whose surface differs from its surroundings. It does not show on white plastic, but once painted it leaps to the eye at once: a sanded area is more matte, soaks up more strongly and looks half a tone darker in shade. Evening the surface out is therefore work that comes before painting, not after it.

The simplest way is to sand the whole part with the same grit so that it is uniform. The second stage is to lay down a primer coat, let it dry and go over the surface with a very fine sponge, which levels even microscopic differences. Where the sandpaper has hollowed out a dip, a drop of thin filler and a fresh sanding will help.

• Step the grit up; do not jump from coarse straight to polishing.
• Sand with a backing block, because fingers create a wave.
• Wash the dust off rather than blow it onto the rest of the part.
• Check under sharp side light.

It remains to add that a strip is the ideal practice material for exactly this: it can be sacrificed without regret, it has flat faces and a mistake on it spoils no model.

Before you cut the length up, think through which side the parts will lie face up. A change of orientation in the middle of a frame shows, and it can only be put right by replacing the whole piece.