The subject of this month’s tutorial was introduced simply enough, ‘How about putting together a couple of pages on case painting?’
Rather than try to cover a heap of ground that may not be of relevance to most readers, we’ve put together a work log on a common case painting scenario with methods that can be applied to other projects. The application we decided to run with is one of our pet hates – ventilation perforations. Those ugly blocks of 3 or 4mm holes along side panels that are supposed to aid the flow of cool air, but are really just an easy way for dust to enter – and noise to exit – the case. To make the ‘before’ and ‘after’ steps more obvious, we’ve only covered in a 65 x 45mm section, leaving the remainder as the ‘control’.
The first step was to glue a piece of aluminium sheet behind the holes, using a thin, even coat of five-minute epoxy resin. The plate was then clamped into place until the glue had fully set. For this exercise we had 48 holes in the side-cover that needed to be filled, undercoated and painted, however they could have just as easily been any type of surface imperfection.1
The supplies needed for this step are body filler, spray putty, a good undercoat, a 10 x 8cm cork sanding block and reams of Wet’n’Dry sandpaper in varying grades. The reasons for painting are many, but the desired outcome is the same – to create a smooth and blemish-free surface. Regardless of the starting point, the only way to achieve the perfect finish is to put time and effort into the initial preparation. Don’t be fooled into thinking that the final coat of paint will cover the imperfections – in fact, it will usually accentuate them.
Concentrate on one panel at a time and start off by marking any dents or damaged areas that need repair. Remove any flaking paint and ‘rough-up’ the surface with 400-grit sandpaper. This is also a good opportunity to de-burr the case, removing any rough edges and rounding off sharp corners. Major chips, deep scratches and repatriating around modifications are best filled first with a two-pack polyester resin (body filler).
To ‘sand out’ chips and scratches means removing all of the surrounding paint, down to the depth of the imperfection, and that often means abrasion right back to bare metal for the whole panel. If there are dents in the panels then they will still remain even after sanding.
Small imperfections can be removed later with a high-build spray putty, performing the same function as the body filler, but on a micro level. The spray putty will also give a good indication of the look of the final surface, as it goes on like a thick undercoat.2
After taping off the area well outside of the perimeter being filled to allow for blending or feathering of the edges of the filler, the two-pack polyester resin is mixed at a defined ratio with hardener, making sure to follow the mixing and safety directions. In a perfect mix, the resin is soft and pliable, and has the consistency of warm plasticine – avoid the use of excessive hardener as it will make the resin set too fast.
Using a sharp spatula, the resin is pushed into the holes so that all of the air is expelled; once all of the holes are filled the surface can be smoothed off with a paint scraper. In areas where the body filler has to be used fairly deeply, best results will be achieved by applying several successive layers (after allowing each layer to cure) rather than using just one thick layer. Thick layers are more likely to result in air bubbles or cracks, and therefore create more work.
Once the body filler is dry, the masking tape is removed, and the surface wet-sanded down to level using a cork sanding block (block rubbing or ‘blocking’) and 600-grit Wet’n’Dry.