The body for my Kurt Cobain JagStang replica has been cut by Warmoth. The Alder is already finished in Warmoth’s workshop, to a good degree – probably about 320 grit. Since alder has a tight structure, and doesn’t usually require grain filling – I can skip the messy job of trowelling-in grain filler and, instead, seal the wood with a spirit-based sanding sealer. This has a similar effect to grain filing, but since the fine “filler” is suspended in thinned shellac, it’s soaked up by the wood, drawn into the structure some distance, and held there as the shellac cures. This provides a sandable “skin” where the outer pores in the surface of the wood are sealed, but the process leaves the internal mass still porous and resonant. The treatment prevents the wood from soaking up subsequent finishes, and is sandable to a fine degree. This properly prepares the surface of the wood for paint and lacquer finishes, prevents the surface from developing pin-holes and other finish flaws, and the total subsequent paint and lacquer load can usually be kept to an absolute minimum.
The guitar – the basics having been assembled for a “dry-run” test – is dis-assembled again, and the components safely stored away. There’s no real need to prepare the body for sealing – other than to clean out the recesses, and to lightly degrease the surface by rubbing over with some naptha on a clean cloth. Since the process of sealing will slightly raise the grain anyway – there’s no need to wet and sand the knap away first.
After the “dry assembly” – the only “modification” I want to do to the body, is to slightly countersink the screwholes I’ve drilled for the scratchplate, bridge and control plates. The countersinks don’t need to extend far down, and are only really there to prevent the screw threads coming into direct contact with the thin layers of finish around the openings. In some cases, the action of the threads can sometimes crack, lift and split the thin layers of paint and lacquer. Although the problem, (if it happens), usually occurs in places which are hidden from direct view, (like under the scratchplate) – any splits in the lacquer can, theoretically, eventually run, and spread onto the visible surface of the paint finish. These countersinks should prevent that ever happening, and will keep the job looking tidy.
Sanding sealer is available in “rattle-cans” – but I regularly use Mylands “brush-on” sealer, with excellent results. The “filler” solids are a natural colour, (not really an issue on a painted body – but useful under waxes), but the end result, when left to cure properly, sands finely – giving a super-smooth result. Because it’s a brush-on finish – I can check that the application is being soaked-up properly by the wood, and even gently scrub it in, if required. This helps at the heel of the guitar body, and around the cutaway “horns” – where the end grain is perpendicular, and fully exposed. Here, the wood can get quite “thirsty”, and sometimes, a spray over just doesn’t lay enough liquid sealer onto the surface before it begins to harden. (The sealer “goes off”, and becomes touch-dry, in seconds).
The sealer is well-mixed before application, to evenly distribute the fillers in the lacquer. I then pour off a little at a time – just enough for the job – into a small vessel. Normally – it’s not a great idea to mix shellac by shaking. It tends to develop small bubbles which, (notoriously when using in gilding), can get transferred by brush to the surface of the work. If these harden without popping – you have a potential pin-hole right there. However – since this sealed finish will be rubbed-back again – in this case, it’s not so much of an issue.
The sealer is smoothly and evenly applied to the wood with a soft, flat acrylic brush. I prefer this type of brush because they don’t tend to drop bristles, unlike the usual lacquer brushes, which tend to be made from fine animal hair. The shorter acrylic bristles also allow me to lightly scrub the surface as well – without deforming the shape of the brush, and gradually ruining it. The sealer flows on easily with the first application, and the brush really just helps it into the wood – spreading out the sealer, so that there aren’t any runs, sags or ripples once the shellac sinks into the wood and dries. It dries quickly – so the application needs to be quick and efficient. There’s no real point returning to an area that’s already dried, and the brush should be used to even things out and to keep the sealer from “pooling” anywhere. As the sealer is applied – the wood takes on a darker colour – so it’s relatively easy to monitor how the surface has been evenly treated. Since the lacquer goes off quickly – it’s possible to hold and manipulate the work in one hand, whilst the sealer is applied to both sides and all of the body edges, with the other. Once the back of the body has become touch-dry – I lay the piece down, and make sure that all of the cut-outs are also sealed. I only tend to do this on the first pass, and it’s really only just to ensure that the edges of the openings are coated and sealed properly too. I want the sprayed paint finish to be able to naturally “wrap over” the edges of the openings, and to adhere properly.
At the end grain – the sealer is readily soaked-up, and it’s important to ensure that there’s enough sealer applied to do the required job. I tend to apply plenty here, and lightly scrub across the end grain until the filler has been absorbed, and the colour of the wood darkens to match the flatter areas. Applying extra sealer means that you always have to be aware of any runs, and brush them in quickly. Once the body has been evenly coated – the lacquer is left to penetrate, dry and cure. Although it’s touch dry – it will always sand much easier if the lacquer has shrunk back, and is properly cured. 24 hours should be a minimum.
Once the lacquer has dried – the body is rubbed back with 400 grade grit paper. I like to use fresh paper regularly, and generally try to keep the grit from clogging. The sealer sands easily, and I rub back the finish until it’s even, and super-smooth to the touch. The idea is to remove just enough of the outer skin – so that the surface of the wood is exposed again, with the hardened lacquer remaining in the pores. The guitar body, once properly rubbed-down, will have no shiny areas of dried shellac on the surface, and should display a soft, consistent sheen, all over. It becomes a silky smooth, and very tactile surface to touch.
I tend to begin work around the cutaway “horns, and then work along the edges, and the delicate contours which lead onto the flat surfaces. The front and back of the body are flatted-back with fresh grit paper over a cork backing block. A gentle circular action cuts back the surface, which is then fine-sanded by running along with the grain.
Once the body has been evenly rubbed-back all over – I check the work, and then give the whole piece a gentle rub down with a red, (350 grit) Mirka “Mirlon” sanding pad. This helps to regularise the finish, and provides a light key for the next coat of sanding sealer. Before the next coat – the body needs to be completely cleaned and dusted down. The fine dust produced gets everywhere. Wear a respirator or, at least, a dust mask when sanding lacquer. A tack cloth is the perfect thing to get the fine dust off the surface – and I’m all for using a vacuum cleaner in the recesses, if it helps – (although the fine dust will quickly clog your filter).
A second coat of sanding sealer follows. This time – the wood doesn’t soak up as much of the lacquer – so it’s important to apply it a little more sparingly. The second application serves to seal any areas of bare wood which have been exposed, and left absorbent, by sanding – so some of the lacquer soaks in, and the rest tends to sit on the surface where it quickly goes off. This time, the emphasis is on using the brush to spread the lacquer evenly – leaving as few actual brush marks as possible. It’s important not to overwork any particular spots, since the lacquer coat will quickly “drag”, and become sticky and claggy, (and will just need sanding off again). Because more of the lacquer inevitably ends up sitting on the surface this time – the finished coating appears a little rougher, with some brush marks evident. Once a full pass has been completed, and all runs and drags are evened out – the body is left to dry and cure throughly again. Since any glossy, raised areas of lacquer will take longer to cure – I leave the body for a few days this time. This will make the task of sanding it level again, much, much easier.
Once the lacquer is fully hard – a second sanding with clean 400 grit paper, removes all of the surface texture, and rubs back to a smooth finish. Having had two applications of sealer – all of the open pores should now be filled and level at the surface, and any fine grain detail in the surface texture should also be levelled. After sanding carefully – the body is given a final check over for any surface defects, (low spots and scratches remain shiny – flat spots will catch the light). Once the surface looks good to go – a final, light rub over with a red, 350 grade Mirlon pad evens out the surface, and keys the body, ready for primer.