This week is a bit of a grind – trying to push stuff through before the weekend. Body preparation involves a lot of sanding. At the moment the days seem to be following the same sort of script… add a layer of some kind of filler, and then rub it all back. If it’s not that, it’s spray some paint, and then rub it down and key it back again. Repeat…
But time well spent this week will enable me to quickly move on with other things, once I’m through the lay-off. Hopefully, I’ll get to see detail with a bit more clarity then. At the moment – I’m mostly relying on process, technique, touch, and a pair of strong magnifying spectacles. (Although technically, I’m only operating with one functional eye). When it’s fine weather – it’s spray painting. When it’s not – it’s filling, sealing, and rubbing down again. Today is dull and damp – so it’s a day for the latter. At least it’s warm now in the workshop. If only I could get my radio reception to be something other than BBC Radio 2!!
The ash has already been grain filled. After burnishing, it’s had plenty of time to dry out again – so in theory, the majority of the wood’s surface porosity should have already been dealt with. However – the ash has a lot of fine grain which runs almost parallel with the face of the body. This potentially leaves a few areas where the fine grain filler may have been dragged out of the elongated pores, due to the filling and burnishing process. There also may remain a certain number of pores which were simply too fine to effectively push the grain filler into. Sanding sealer gives me the option to brush on a slightly finer filler, which is suspended in a shellac-based medium. This should fill any remaining fine detail, whilst also preparing the surface for flat-sanding. The dark grain stripes of the ash are slightly softer than the lighter areas, and this can sometimes leave the finished wood feeling like there are slight ripples in it, as you feel across the grain. Sanding sealer will help reveal any low spots – fill them, and then give me a chance to better level the surface.
I’m using Mylands “Lacacote” sanding sealer which can be easily brushed on, and is shellac based. (Meths solvent). Since it’s a first coat – the alcohol solvent, in which the shellac is disolved, helps the sealing filler penetrate into the surface of the wood, as the wood soaks it up. Once the shellac goes off, the surface hardens, and becomes finely sandable. I use a soft acrylic brush to apply the sealer, and brush on just enough to wet the surface consistently, all over. The sealer only takes a few minutes to become touch dry – especially when it’s a first coat – so it’s important to keep the brush moving evenly, and to brush out any excess quickly, before it becomes too sticky. Care is taken not to leave any runs or sags. (It’s just more work to remove them again by sanding). Applying the sealer too thickly, or overworking previously applied areas, also risks “dragging” the surface, and creating a textured surface film. This becomes more of an issue on subsequent coats – but it’s worth bearing in mind as a general rule for shellac finishes. The thinnest coats are always preferable.
The sealer application slightly darkens the wood, and begins to bring out the natural colour, which the wood will display, once finished. This isn’t as typically amber as many “natural” guitars are – so I’m already wondering whether to pursue a slightly different finish option here. (Ash might better suit a translucent white “Mary Kaye” finish). However – whichever way I go – it doesn’t really affect the sealing process at this stage, and I’ll have plenty of time to mull things over before I have to decide, one way or another.
The sealed body is given a full 24 hours to cure. Sanding back too early always risks clogging the sanding papers. I use 400 grit paper to cut back the surface – aiming to remove any shellac shine from the wood. At this stage – it’s really difficult to see much fine surface detail, and I’m relying as much on what the process is supposed to do, as I am on any particular, visible results. I’m aiming to knock the shellac back level – not to remove it entirely. Once the entire body has been rubbed over to 400 grit – I repeat with a red, 350 grade Mirka “Mirlon” sanding pad. This brings the surface together, and helps rub out any witness marks caused by clogs on the grit paper.
The body is then thoroughly cleaned down, with a little naptha on a clean cloth. All the cavities are cleaned out, and the whole piece is lightly passed over with a tack cloth.
The second coat of sealer is applied, just like the first. However, since there’s still some dried shellac on and in the surface – it’s a little harder to smooth out the new shellac without disolving the previous layer, and “dragging” the application. Spreading out the shellac sealer has to be quick and efficient. Some drag marks are inevitable – but since everything will be flat sanded again – it’s not critical. It’s just easier if they’re kept to a minimum. The second coat of sealer is allowed to dry again for at least another 24 hours. In this case – it ended up with more like 72 hours and, consequently, the dried shellac was fully cured, and much easier to sand with clean, fresh, grit paper.
Flat sanding the sealer with 400 grit paper, (over a cork block on the flat faces), begins to knock the surface back, and “low spots” are revealed as significant, persevering lines of glossy grain. The shellac surface is rubbed back to a consistent silky sheen, and special attention is then given to areas which display low spots – effectively reducing the surrounding surface until it’s sanded down to the same level, and the shiny low areas are removed. There’s a possibility that this might rub through all of the previous sealing, and down to the bare wood again – but with grain filler pushed in, and penetrating sanding sealer soaked in with shellac – the sealing effect should have developed something of a smooth, protective “skin” to the piece. If, by any chance, I have rubbed through the seal anywhere – I’ll be applying another sprayed shellac coat before I push on with my chosen finish, and it should become evident at that stage. I’ll be able to deal with any local areas individually.
Once the body is fully rubbed back – it feels super silky to the touch, and most of the “rippling” across the grain has gone. The piece feels much more regular – almost like a smooth piece of marble, (although much warmer to the touch). A final rub over – first with a 350 grade, red Mirlon pad , followed by a 1500 grade, grey pad – polishes out the surface, so that it displays a dull, but slightly polished sheen. Visually – I can’t fault it. It feels super smooth to the touch. There may be the odd open pore or line of grain still exposed – but I’ll have to deal with them individually when I come to work up the finish. For now – the body is cleaned down, left to dry thoroughly, and then stored away until I can return to it, later on in the year.