I prep for painting flexible plastic parts (delrin plastic) or any plastic part that has a shiny finish by blasting them with baking soda. This creates a dull/satin finish that allows the paint to “bite” into the surface better.
The instrument for applying the media is a Paasche Air Eraser; basically a miniature spray gun the size of an airbrush. The Air Eraser came with a jar of aluminium oxide which works very well even on metal, but I am personally not comfortable with using this for health reasons. I use baking soda (Arm & Hammer) instead. This works very well for dulling plastic surfaces and removing paint and lettering. It is not very effective in dulling metal surfaces.
As can be imagined, this would be a very messy job if the basting media is not somehow contained. It built a blasting box as follows:
In the view above, the box is made from 11mm birch plywood on five sides screwed together with no 6 wood screws and a hinged plexiglass (.093″) lid. I added four 1×2 gussets to the opening for stiffness (these are the triangular shapes at the top). Foam weatherstrip tape seals the opening and the interior is painted white, although in retrospect, a light grey might have been better for seeing the baking soda. The Air Eraser sits inside with a hole just large enough to get the hose outside. Being right-handed, I placed it on that side. When I finish blasting, I vacuum the contents of the box.
The rubber gloves are from the grocery store. They are cloth lined. They are not so much for protection, but as a means for sealing the box while manipulating the Air Eraser. The gloves are held in place with octagonal retainers made from .060″ styrene sheet with button head screws and washers. Each glove was just pierced by the screws as the retainer was installed. Handles make carrying the box easy. The black squares on the gussets are Velcro pads to keep the lid shut.
On the opposite end, another piece of Velcro stapled to the box holds the hose when not in use. I use my Iwata air compressor at 60-80 psi for blasting with soda. I added four peel-n-stick flexible button feet on the underside of the box to keep it from sliding on the table.
My current project: NYC Class H6a Mikado (Broadway Limited Imports). These tender trucks were dismantled and blasted with soda. I’ll remove the wheels again prior to painting them by airbrush.
Why do I do this? Well it’s more a case of insurance. I’ll never know how well the paint would stick to the trucks if I had not blasted them. I have gotten away with it before (not blasting and the paint did not peel/chip off). But with the amount of time I put into any model, I feel better about it if I at least blast the trucks to give the paint a better chance for adhesion.