Preparing the finish.
Guitar builds are typically split into two stages, the first stage is called the manufacturing phase, this is essentially the woodworking phase, timber is planed, glued, shaped and routed. The second phase is known as finishing, this involves meticulously prepping the wood with progressive sanding, and spraying lacquers or applying stains and oils to protect the wood. After finshing the manufacturing stage earlier this week I moved onto the home straight and began the finishing process.
The first step is to sand the wood, I had a few dings and scratches so I started off with a coarse grit, 60. This is pretty agressive on the wood, it takes out a big layer and creates fairly deep scratch marks, though less deep than the dings I had introduced. I used the 60 grit to create a back contour also, this is for comfort while playing, the contour lines up with the players abdomen and makes the guitar nicer to play, especially whilst playing standing up. The next step is to use the 120 grit paper. The 60 grit took care of all but the deepest marks that I had accidentally created during drilling the bridge holes, the 120 smothed off the wood and removed the rest of the holes that were amenable to sanding. At 120 the wood is still too rough to achieve a nice base coat so 240 grit is needed. Before sanding with the 240 grit I made the wood slightly wet with a damp cloth in order to raise the grain fibers of the wood, this produces a smoother finish and makes sanding easier. I also rounded off all the edges front and back to create a less sterile feel to the guitar, the straight edges weren’t looking too great. To save myself time and effort I used the orbital sander for this task, I also think the orbital sander produces a more consistent and smoother finish, for the wood stage it removes a fair amount of wood which is good. I intentionally started out with a thick guitar so any dirt that ended up on the surface during manufacturing could be removed with a bit of generous sanding.
There are many ways to finish a guitar, some people like to use brushes and rags to apply finish materials, others use products in an aerosol spray can. Most people agree that for professional looking results you need an air compressor and a spray gun. This method allows you the most flexibility in finishing materials because you can mix your own and add it to the spray gun at what ever consistency you like. I decided to invest in the spray equipment, I’m glad I did, not only has it poduced good results so far, but the air is handy to have to blow away dust that is hard to remove with a cloth.
There is no one true way to finish a guitar, the neccesary steps can be applied in different orders depending on what kind of look you are after. I have used the book “Guitar Finishing Step-By-Step” along with the accompanying video and I must say it has been esential. I knew nothing about the finishing process and by reading the book and watching the video tutorial I became much more confident and have learned enough to develop my own method for how I want to finish the guitar.
Although in an earlier post I said I was going to use polyuretane lacqeur, after more research I decided that a nitrocellulose type laqceur would be best, it’s easier to sand, buffs to a shinier gloss and can be applied thinner which affects the tone slightly. It wasn’t easy to find, in Australia you cannot simply purchase it from your local hardware store, however thanks to an internet forum search and a discussion with a local luthier I found Mirotone and purchased a 4L tin of laqceur and the reccomended thinner.
Ash is a very porous wood, this means that if you were to simply spray your finish straight over it you would end up with a pitted uneven finish somewhat like a golf ball. In order to counteract this a grainfiller is needed. Based on the internet research that I have done I decided that it would be best to start off by spraying the whole finish in a wash coat. This is a very thin coat, 3 parts thinner to 1 part lacqeur (3:1), sprayed over the whole body to seal off the wood and protect it from whatever you do afterwards. I sprayed 2 washcoats over the entire guitar, even after these two thin coats the guitar already began to look better.
The wash coats covered the pine nicely and did fill some of the pores, grainfiller was still needed though to fill the rest of the pore holes. Originally I was going to use Feast and Watson sanding sealer but after testing it on an old guitar I have decided to refinish I found I didn’t like the way it looks or the way it sands. Timbermate waterbased grain filler seemed like a popular choice in Australia and was available at Bunnings in a variety of tints, I decided to be adventurous and went with black. I thought that this would really make the pores pop being such a darker colour than the surrounding wood, not to mention I am planning on tinting a layer or two of the top coats with a stain so the dark will be even more helpful to make the pores stand out.
The grain filling is achived by basically dolloping the grain filler onto the guitar and then spreading it across the grain with a plastic applicator and wiping off the excess. It dries very quickly but does wipe off for the most part with water, I found however I was also wiping the filler out of the pores so I filled the grain a second time with a thick mixture, filling the holes with the applicator and wiping the excess down the sides to fill the pores that are on the side of the body that the applicator cannot reach, I let it dry thick and then sanded it off leaving only the wash coats below and the filled pores.
In order to seal in the grain filler and to fill the remaining depth from the pores that the grain filler was unable to fill I applied another two wash coats to the guitar. With the wash coats the guitar is looking more like the final product. The next step will be to apply more wash coats and then a layer or two of the tinted laqceur on the front and transparent black pidmented laqceur on the back. After that it’s just the clear top coats and the buffing, more on that next time…