On Model M1911, it is important to get a smooth surface prior to painting.
The previous step was the completion of the larger details.
Commonly referred to as “Bondo,” this is a trade name for a class of fillers utilizing the chemistry of polyester resin and fillers that create a paste. This paste is catalyzed prior to it being spread onto a surface. Bonding is important, and that is why the surface is sanded thoroughly with 40 or 80 grit sandpaper.
The bondo filler is easy to sand, shape, and provides a surface on which to apply primer and paint.
The Bondo has a short working time, requiring batch mixing. The Bondo is applied to specific areas and sanded after it is cured. Then another layer is added, sanded, and the process repeats until a satisfactory surface results.
Sanding blocks can be used to make sure the surface is flat or curved in the desired areas. Most of this work was accomplished with 80-grit sandpaper. Air-powered tools can be used, but have drawbacks. The author’s experience is that they kick up too much dust, can easily sand too much, and dont make the surface as straight as manual sanding.
Surfacing primer can be applied via spraygun over the Bondo. The author chose a 2 part Urethane primer surfacer by Dupont. This primer creates a thick build that can be sanded smooth. It will fill scratches and pinholes left from the Bondo surface.
The author chose to sand the primer with 320 grit sandpaper followed by 400 grit sandpaper. The picture above shows the use of filler putty. This is best described as primer in a tube, and fills holes and scratches that the primer didn’t cover.