Practical case painting
Ron Prouse
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Jun 13, 2007 11:11 AM
Coat your case in liquid fun.
Difficulty: Intermediate
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.
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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.
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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.
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After sanding down to the finished level, you may find that there are cavities that have been created by air bubbles that were trapped in the holes or gaps. After drying the work-piece thoroughly and wiping over with wax remover, one remedy is to repeat the previous step until the surface is uniformly smooth and even. Another answer, especially for small pinholes, is to use a product called spot putty. Spot putty in essence is a premixed body filler of thinner consistency. Again, thin layers are better than big blobs. As you can see to the right in the image below, there shouldn’t be any residual body filler above the level of the holes, or on the surface of the panel.
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Spray putty will fill in any small scratches and blemishes on the prepared surface, and applies like a thick undercoat. To get an absolutely perfect final finish, such as the mirror finish on show cars, can take as many as 30 individual coats of filler, with each coat almost completely sanded off before the next is applied. Sanding back panels should only be done with 800-grit Wet’n’Dry, plenty of water and a sanding block.
Spray putty can initially be applied in spot areas and then once all of the problem areas are looking as you want them, the whole panel can be sprayed and sanded back with 800-grit Wet’n’Dry.
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Undercoats, or etch coats, are important from several standpoints, and the word of the day here is ‘Consistency’.
Firstly, body filler and spray putty are porous, which means that they will absorb paint at a different rate to the metal or pre-painted areas of the panel. They also have a tendency to dry to a matt or semi-gloss finish. Undercoats seal these compounds and provide surface consistency.
Undercoats are also important as they lock the paint to the surface below. Imagine it like a chemical version of Velcro. Most etches especially work in this way, eroding or melting the surface underneath to create that bond as they cure (or dry). The result is a consistency in adhesion.
The third important attribute of an undercoat is to give the object a consistency of colour. The image below shows the side cover after one light dust coat of etch, and it is still easy to see the holes and spray filler – it might take several coats of a light-coloured paint to cover it up satisfactorily. An undercoat will give an even-coloured canvas to apply the final coats over.
Each application of undercoat should be allowed to dry and then gently sanded back with 800-grit Wet’n’Dry.
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When it comes to the actual process of painting there are quite a few options available, depending on the amount of cash you want to spend and the finish you’re looking for. The best results will be from using automotive finishes sprayed at high pressure in a hermetically-sealed room, and then dried under heat-lights. Not that practical for most home handypersons! Of course, it is possible to take your primped and primed case to a professional spray painter for the final squirt, and if you are not fussy as to the colour they might even offer to ‘blow some colour over it next time we are painting a (insert colour choice!) car’, usually at a very reasonable cost.
In the case of most DIY projects, the next best answer is to use automotive touch-up paints, which are widely available in a multitude of colours and relatively inexpensive in small quantities. One of our favourites is the Holts Dupli-Color range of ‘mixed for you’ aerosols, allowing you to choose colours that may not be available commercially.
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Choosing a place to paint is a very crucial point. An obvious OH&S issue is the build up of toxic fumes, however, it is also important to be aware of dust, bugs and passing traffic. The longer the painted panel can be left to dry in a pristine environment, the better. Conversely, the more chance of foreign bodies coming into contact with it quickly diminishes the chance of a great outcome. Also remember that the first thing that most people want to do with wet paint is check if it’s dry.
If you are spraying in an area where over-spray could cause damage, the use of dropsheets and backdrops might save you grief later on.
Before you start to paint your project, practice on something unimportant that has a similar finish. Every paint applies slightly differently, while ambient temperature can have a huge impact, as can humidity. Get a feel for the spray nozzle, optimum spraying distance and, well, the ‘vibe’.
The last step before applying the first layer of paint is something that you should do between each and every coat – wipe over the panel with wax and grease remover, allow it to air dry, and then blow off any residual dust, lint or fluff, as anything left on the surface is about to be stuck there for good.
The colour that we have used here is a Glasurit Indischrot (Porsche Guards Red), as it is a high quality product that is easy to use. As an aside, the Glasurit website has some fantastic fault-finding guides for home painters and covers nearly all common painting problems and their remedies.
The first colour coat is important, as it is the best opportunity to make sure that you get proper coverage in all of the nooks and crannies – in this example, inside the edges of all of the remaining ventilation holes.
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Wet sanding between coats with 1200-grit Wet’n’Dry will remove the build-up of orange peel (the insert in the below image) and unevenness of the paint, and provide the next coat with something to grip to. Just make sure to allow plenty of drying time before you start as sanding semi-wet paint will create an enormous mess! Don’t get too carried away with sanding (unless you have a major calamity to repair) in case you rub right through the paint on the edges or grooves of the panel – in fact, a fairly gentle, even rub-over should result in a smooth surface to continue on with. The main area of the picture should give some indication of what you are trying to achieve – an even amount of slight scuffing on a smooth background.
One rule that many people don’t follow is to wet sand the final colour coat if you are going to apply a layer of clear. Yes, it seems sacrilegious, but it really needs to be done regardless of how good it looks so far! Note that a clear coat is not an absolute necessity, so don’t feel bad if you decide to finish off with the colour instead. That’s what we did!
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The final coat is always the best coat. Whether it is a colour or a clear coat, this is the one that really matters, and where all of the surface preparation pays off. The aim is to get a smooth even finish, with the least amount of orange peel possible. How do you avoid orange peel? When spraying with an aerosol can it is usually caused by one or a combination of the following:
• Spray can held too far from the surface (however remember that too close will cause runs);
• Poor atomisation of paint (check and clean the spray nozzle, especially if it is spluttering blobs of paint);
• Spray pressure too low (buy another can, you cheapskate!);
• Paint being applied too thinly or thickly.
A mild amount of orange peel is relatively easy to remove by gently wet sanding with a well-used sheet of 1200-grit (so that it is more like P2000), and then polishing out the residual scratches with a cutting compound such as Glasurit Fine Polishing Paste. This takes time and elbow grease to achieve if being done by hand – as opposed to using an electric buff – however the result should be an almost piano-gloss finish with a rich depth of colour.
The final step is to finish off with a deep gloss polish, such as Meguiars Gold Class Liquid Car Wax, and a soft cloth to buff the new paint to maximum shine. Just a word of warning – as well as looking stunning, your case will now be one slippery little sucker so pick it up with care!
Spray painting
Spray across the panel in uninterrupted, even strokes that overlap the previous one, and each stroke should start and finish a few centimetres outside the perimeters of the edges. Don’t be afraid to turn the panel and spray it from different angles, as this will also help to ensure full coverage.
Paint should be applied in light, even coats, and try and keep the surface evenly ‘wet’ as you spray, especially the areas where there is overlap of your strokes. Where possible, avoid runs and orange peel, but don’t panic if this first coat is less than perfect – there is plenty of opportunity to block sand and spray again! In fact, plan on at least two repetitions of this step.