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Scale model. Modelling masterclass. Prepering for paint

13 Dec
2011

Scale model. Modelling masterclass. Prepering for paint,b 24 model airplane

Vic Scheuerman continues his back-to-basics series using a Seafire as his example, describing the techniques he uses in preparing a model for painting.

Some flexible post tack (Photo 3) can be used with the one caveat that it can damage fragile details as it is forced into place. In the last two parts I covered most of the issues that crop up when dealing with canopies and clear parts. This month I start in that area again. After completing their masking and attaching the canopies, any finished openings (like the cockpit, gear bays, etc) must be masked for the upcoming paint finish (if you are spraying).

Masking

One of the easiest ways to do this is to start by ensuring a sharp paint division line by masking with tape. In this case Tamiya Tape has been cut into thin strips and applied along the fuselage/canopy edges (Photo 1). In the same photograph note that some mattress foam has also been used to protect the radio compartment aft of the cockpit. This step requires that a piece of foam is cut just a little larger then required and gently worked into place by using toothpicks. Once it is properly seated, its edges can be carefully trimmed (Photo 2) to help ensure that the paint fully reaches all the edges. Needless to say, there are other ways to mask. One of the oldest is to wet some tissue paper and put it into the opening. When it dries it will expand somewhat and works as a good mask. The only drawback is that it will sometimes want to stick to the interior parts and can be difficult to remove. About the only way around this problem is to re-soak the tissue with water and carefully remove it. In addition, some caution may be required if using acrylic paints, since the latter must be fully cured. In a similar fashion,

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Cleaning the model

Once the clears parts have been masked and all openings that require paint protection have been dealt with, all the parts that require painting must be secured and the model cleaned for paint application. The model’s surface should be cleaned for a couple of reasons. First, because I normally handle the model up to this stage with bare hands this usually means that its surface is contaminated with skin oils. This oil can affect paint adhesion. Tying in with this is that there may be tiny pieces of dust or plastic left from previous steps stuck to the surface. To remove these two concerns and provide a clean surface that is the first step to a good finish, iso-propyl rubbing alcohol is wiped across the surface with a lint-free disposable cloth. To ensure that skin oils do not re-contaminate the surface, disposable vinyl examination gloves are now worn whenever handling the model. Note that I use vinyl not latex gloves. The reason for this is that more people are becoming latex allergic and it’s simply safer to buy vinyl gloves if you can.

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Holding parts for painting

To secure, or hold the smaller parts for painting, two different methods are used. If the small part must be moved around during painting, then the small alligator clips sold at electronics stores work well. They just require the addition of a handle and it is hard to beat wooden toothpicks for this (Photo 4). Once the parts are attached with the clips, I find it best to use a piece of packing foam to hold the parts for painting and to provide a place to keep them from being touched while curing. Parts with flatter surfaces are attached with tape to a piece of stiff cardboard. In Photo 5 one can see all of the mentioned methods and materials used.

Priming

With clears parts and openings masked and the surface clear of contaminants, it is time to prime the model. As stated last month, the first paint application is to the clear parts and these receive the appropriate colour, usually the interior colour (Photo 6). Following this a light or medium grey is normally the best colour for priming. Another shade to consider is simply one of the base camouflage colours, if it is light and neutral. For this project the lower surface colour was light grey so this worked well as a primer, although if the model was being finished with a Sky underside that would work equally well. While vinyl gloves should be worn at all times from here to the end of assembly, one should also be wearing a protective mask whenever spray painting (Photo 7).

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Once the primer coat has been applied and fully cured, the next step is to look for any areas that require correction. To both smooth the exterior finish and help highlight any problem areas, give the fully cured surface a light rubbing with an abrasive pad. In this case the less aggressive ‘white’ pad is used (Photo 8). This is followed by a good look at all the places were major parts join. Iwo of the most common areas that require correction are the wing leading (Photo 9) and trailing edges. Most mistakes are best picked up under a strong light and do not hesitate to use one of those strong, small pen-lights that model show judges sometimes use. It is better and easier to correct problems at this stage than later when things have progressed. Another thing to check is the engraved panel lines. It is not unusual to fill some of these during building and these need to be replaced. While there are numerous methods for achieving this, one of the best for the crowned fuselage join is a fine-toothed razor saw (Photo 10). Normally, one will find areas that require filler, sanding and then paint reapplication. The trick here is to keep the correction to the smallest area possible and, if necessary, protect the surrounding areas with tape.

Sanding

As mentioned, you are likely to need to do some sanding. Again, we are blessed with a wide variety grits (fine to course) attached to either paper or plastic backings. Over the years, after using a variety of brands, the only one on my bench is K & S FLEX-I-GRIT (K & S Engineering Company, Chicago, 111., USA 60638). This comes in two different five-sheet pouches that encompass Regular and Micro assorted (Photo 11). Each package has five different grades of sandpaper and the great thing about this brand is that it uses plastic for the backing. This allows for flexibility (hence the name) and, by rinsing after use, the sheets last much longer then paper-backed alternatives. When sanding, one should keep in mind a few things. First, start with the most course grade that applies to the task at hand. This will not only speed up the sanding process, it will ensure that the different grit sheets wear out more uniformly. Having said that, for most tasks I start with the brown-orange or mid-grey sheets from the Regular assortment. When sanding, use water as it will both lubricate the action and hold the dust down. I usually cut the sheets into six smaller rectangles and this ensures less wastage and is more comfortable to work with. Two things to keep in mind when you are sanding is first to go in only one direction (Photo 12) (it reduces scratches) and second, let the grit work, versus you using more pressure. Work your way down to the finest grit. For odd shapes that require sanding, it really helps to find an object shaped appropriately to act as a pad.

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Paint tips

While paint has been used in a number of previous parts, space allows a few tips to be added here. Paint comes in glass or plastic bottles, normally with screw tops; tinlets with caps and, of course, in spray containers (Photo 13). Preserving your paint and getting the most from this ever more expensive necessity of our hobby requires a little work. Before using the paint it should be agitated to ensure it is thoroughly mixed for the best results. Do read the label as some brands would have you ‘shake’ the container, but a more common requirement is to ‘mix’ the ingredients. One of the easiest ways to do the latter is to make use of a worn-out, small square metal file (Photo 14). This tool is strong enough to move the old thick glob at the bottom and, in addition, its paddle shape ensures the contents get mixed better then using the round handle of a paint brush, for example. After use, some care is required to make sure the lid is securely on your paint container. For the normal twist-types this is down to simply wiping away the paint (Photo 15) along the thread both on the bottle and the cap. This not only ensures a good seal, but should also make removing the top easier down the road. For metal tinlets, a gentle tap with a light hammer, on a small piece of wood over the cap, should ensure a nice tight and even seal (Photo 16). When it comes to aerosol cans, then a good shake is required before they are used and wiping the nozzle off at the completion of the task should ensure it the can is ready for future use.

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Heat

An old trick borrowed from the automotive refinishing industry is to heat your paint up before application. Since paint is a combustible, this requires the application of a little common sense. The heating is accomplished using hot water. For normal paint containers I have a square dish that is half-filled with hot water and then the paint container is put into that to warm the paint. This makes the paint run more smoothly and I have to say that when I have a tough tight camouflage pattern to spray, there is no better combination then a bottle of new paint heated up, thinned appropriately and used with a freshly cleaned spray gun at about 10-15 psi. This heat application also applies to aerosol cans, but use more caution and use warm water only; avoid extremely hot water!

Applying the camouflage.

Camouflage colour boundary lines can have either hard or soft edges, and to achieve ‘good’ edges when airbrushing, preparation before applying the paint always pays off. For hard edges fine tapes are especially good (Photo 1). The narrowest tapes are available from specialist model suppliers but you can also use products available from DIY shops. Watch the level of tackiness with each tape, since high-strength glues that give the greatest adhesion tend to pull off paint when removed; for preference go for ‘low tack’ tapes. To minimise any damage to your model when removing the tape after painting, pull it back on itself (Photo 2).

Masking films

Masking films come either on rolls or in sheets and are suitable for any type of model. The majority are low tack and work really well. They allow you to draw your own designs and can be used either as a positive or a negative mask. For accurate designs, use a steel rule for straight edges and a compass cutter for circles (Photo 3). You can also now obtain pre-cut masks and designs (Photo 4) in various scales, such as those by Montex and Eduard.

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When using these types of material for masking, the objective is to apply them to the part of your model that is not to be painted in a particular colour, in such a way as to prevent paint creeping under the tape. Water-based paints are particularly prone to this when used with paper masking tape and Photo 5 shows what can happen. If you gently press down the edge of the tape, once it is in place on your model, with a small piece of plastic card this helps secure the edge of the mask and should help you overcome this potential problem.

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Where the tape ‘bridges’ over panel lines, seams and other obstructions, cut it with a sharp knife and apply a second piece over the cut (Photo 6). Straight and curved lines To mask a straight line moving into a curve on a flat surface, use as narrow a tape as you can (Photo 7). The narrower the tape, the tighter you can make a curve. It is notoriously difficult to mask a straight line over a curved surface and you need to pull the tape either ‘uphill or downhill’ to create the desired effect. The angle of the ascent or descent has to be judged by eye as the tape is applied (Photo 8). Roughly mask the remaining areas that will not ^ceive your chosen colour and spray over with light coats of paint. Make sure the paint is not too wet and build the colour up gradually. If you spot the masking tape through the paint, do not be tempted to ‘pile it on’ to cover it up, since too great a build up paint can lift the masking material, or can create an edge discernible by touch if not by eye. Once the paint is dry, carefully de-mask your model without touching the newly applied paint. Masking tapes should be pulled free of the work a soon as practical. The longer they stay on the model, the more likely they are to rip paint when finally removed.

Applying paint masks

Applying masks to flat surfaces can be easy, but going over textured surfaces is a little trickier but still achievable. Use the same techniques as described above for applying masking tape to bridged surfaces. Work, sequentially, especially when applying multiple colours. Start with lighter colours first, in this case the white of a shield insignia. Before you move from this stage to the next, make sure your work is totally dry. Use light coats of paint and build up the required insignia/marking gradually with multiple coats. (Photos 9- 14).

Liquid masks

Liquid masks are ideal for small details and uneven surfaces and are applied with a brush. They dry to a rubberised putty which can be peeled off when the painting is complete. (Photo 15). Be careful when applying them that you do not get small holes appearing before you paint.

Soft edges

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The finest quality airbrushes are unable to achieve true scale soft edges, but a representation of a soft edge can still be achieved in the larger scales. In the larger scales, you can achieve a soft edge by painting freehand (Photo 16). Adjust pressures and viscosity according to the paint you are to apply. If you are not confident of getting the right shape freehand, you can cut a template (Photo 17 & 18). Hold this just off the model and apply your colour with the airbrush held two to three inches away and you can still achieve a very acceptable effect. Another technique is to roll Silly Putty or Blue Tack (not Plasticene since this may well be too oily for the purpose) into a sausage shape and apply it around the area to be masked. Have a go and see what you can achieve – but remember practice improves each attempt.

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