GUITAR FINISHING WITH TRU-OIL®
Of all of the finishes used on musical instruments, a wipe-on oil finish is by far the easiest to apply. Even relatively inexperienced craftsman/finishers are able to achieve an attractive, protective finish on the instrument with minimal time, skill, and effort. Although this finish lacks the depth and gloss of lacquers or French polished shellac, the thin rubbed oil finish provides an appealing low luster sheen that enhances the natural beauty of the woods.
Most oils available as wood finishes are either linseed oil or Tung oil in some form, with or without any additives. Among all of the oil varnishes available for use as a simple wipe-on finish for musical instruments we offer and support the use of the Tru-Oil® product line. Tru-Oil® is a polymerized linseed oil with other natural oils added. This formulation will actually build-up as a finish unlike the raw or boiled linseed oils. The Tru-Oil® wipe-on varnish (our part FTO) and its matching Sealer-Filler (FTOS) have been used for years to finish hardwood gun stocks so its properties and application process are well known. Even though it is not as protective and durable as a lacquer finish it produces a hard, thin and flexible finish that has no detrimental effect on the tone of the instrument.
The real strength of this oil finish is that it is extraordinarily easy and safe to use - very user-friendly. No equipment or ventilation or mask is required during finishing. Only a clean cloth is needed for application with very minimal sanding between coats. This finish is also much easier to repair and maintain than either lacquers or shellac.
Multiple thin coats can be applied directly to the raw wood for a very natural, open pore finish, or the pores in the hardwoods can be filled first so that the finish can be made nearly as smooth and flat as a factory lacquer finish. Both approaches have been successfully used on acoustic and electric guitars, so we will offer the finishing process both ways. While describing the finishing process we will refer to these two oil finish types as either the “open-pore finish” or “pore-filled finish”. Rather that list two lengthy separate processes we will interject the process variation for one or the other at the appropriate places in the wood preparation portion of the complete process. The actual oil application and final polishing is the same for both.
The application of the oil itself is incredibly simple. Just wipe the oil over the surface with a cloth, then wipe off any excess material with a fresh cloth or paper towel leaving a very thin coating. This thin coat will harden enough in several hours to apply the next coat. Four or more coats are applied over several days to achieve the desired depth or thickness.
While the application of this oil is much easier and quicker than it is for the other finishes, the sanding of the wood surfaces before application must be much more thorough - actually as near to perfection as possible. The sanding and scraping must be carried to a much finer degree of smoothness because this rubbed oil does not build a deep finish over the wood like the other finishes. The final oil finish can only be as smooth as the wood surface itself.
We will start here with a list of the materials needed, some are available through LMI while others are more commonly available.
SUGGESTED FINISHING MATERIALS:
Tru-Oil finish, 3 oz. FTO
Tru-Oil sealer, 3 oz. FTOS
LMI Micro-Bead Paste Filler FMBF8 (choose the appropriate color) - used to fill the open pores of rosewood, mahogany, etc.
TRI-M-ITE No-load Sandpapers FMTMT - 120/220/320/400 grits to sand wood surfaces before finishing.
WET-OR-DRY polishing sandpaper, 600 grit FWOD9 - for final wood sanding
Steel wool, 0000-grit FSW
Micro mesh abrasive FMIC
3M Scotchbright finishing pad, Ultra Fine (Grey) - ALTERNATIVE for 0000 steel wool
3M Scotchbright finishing pad, Finest (White) - ALTERNATIVE for final polishing
Lemon oil, finish treatment/cleaner - final finish treatment
TRU-OIL® FINISHING PROCESS - STEP BY STEP
PREPARATION OF WOOD SURFACES BEFORE FINISHING
This section describes the initial wood sanding, the pore filling process (OPTIONAL for a pore-filled finish), and the final ultra fine sanding (for BOTH open-pore and pore-filled finish).
All surfaces must be sanded smooth and scratch-free. Sand with the TRI-M-ITE no-load papers, using progressively finer grit papers from 120 to 220 grit - sanding with the direction of the grain. To maintain flat surfaces always use sanding blocks or rubber sanding pads to support the paper. Use progressively finer grit sandpapers to remove the scratches from the previous sanding.
Check for course sanding scratches that may have been missed by the final fine sanding. Closely and carefully examine the surface for any scratches or flaws. This close examination of the surface (and your sanding progress) can be enhanced by wiping the surface with Naphtha or lighter fluid and closely examining the surface while it is wet with fluid. While wet the sanded surface will appear as it will under finish and even small scratches will be apparent.
Re-sand with the finer grit sandpapers to remove any scratches or flaws found by this close examination.
Totally remove the sanding dust from all surfaces with compressed air and/or wiping the surface with a rag or paper towel wet with Naphtha or lighter fluid. Some finishers will wipe these surfaces with a cloth damp with water to raise the grain, then repeat the final sanding and cleaning. There are probably as many finishers that don’t do this step as there are that do. Use your own discretion.
At this stage either fill the pores, as described below for the pore-filled finish, or continue the fine sanding process as described after the pore filling directions.
FOR A PORE-FILLED FINISH FILL THE OPEN PORES IN THE HARDWOODS OF THE NECK, BACK, AND SIDES BY THE FOLLOWING METHOD
Most of the hardwoods used for guitar bodies and necks - e.g. all rosewoods, Koa, Walnut, Mahogany, and more - have very open pore structure. These open pores show as a multitude of tiny depressions throughout the smoothly sanded surface of these hardwoods. It is essential to fill these tiny depressions to achieve a flat and smooth surface. This is the most important step in the finishing process to achieving a perfect glass smooth final finish. Committing the time and keen attention toward filling the pores effectively, and thoroughly, at this stage will reduce the time and effort used to build up a smooth, pore-free finish later.
By contrast, Maple, Sycamore, and the Spruce and Cedar top woods, are non-porous and sand smoothly enough that this filling process is not required.
We recommend filling the pores with our easy-to-use, water-based pore filler - LMI Micro-Bead Acrylic Paste Filler FMBF8. This material is excellent, fast drying filler that produces a smooth flat surface on porous woods. This product is available in three shades - light Natural color, Red Mahogany, and Dark Walnut/Rosewood. Select the color that best matches your wood.
LMI Micro-Bead pore filler dries hard within a few minutes, so this water-based paste must be applied to the wood surface in an entirely different manner than the traditional oil-based filler is applied. The wet, creamy, water-based filler paste is simply squeegeed across the wood surface - and into the pores - with a flexible plastic card or palette knife. With this fast drying pore filler an instrument can be pore filled, thoroughly, then re-sealed with Tru-Oil sealer and be ready for the Tru-Oil finishing in two days.
Begin by sealing these hardwood surfaces with the Tru-Oil sealer. With a clean white cotton cloth wipe a coat of the sealer over all surfaces. Wait an hour for this to dry before proceeding.
Thin the LMI Micro-Bead Pore Filler FMBF8 about 20% (4 parts of paste to 1 part water). This will make the paste wet, creamy and easy to work with. Any time that the paste dries out it can be made more creamy or liquid by adding small amounts of water and mixing it into the paste. Always work with wet, fresh filler paste when filling the pores.
Work in small areas - maybe 3” X 3” or 4” X 4” - and closely observe the progress of the pore filling as you thoroughly work that small area.
Fill the pores with filler paste. With the flexible plastic squeegee or artist’s palette knife spread a small amount of wet filler paste over the wood surface.
Immediately scrape this wet filler off of the surface with the plastic squeegee or palette knife. This will leave wet filler in the pores and small depressions. Work the wet paste filler over the surface and into the pores and scrape it off several times in the next minute or so. Scrape as much filler off of the surface as possible and stop scraping before the filler begins to dry (within minutes).
As you finish this pore filling process in one area just continue by spreading and working fresh filler paste over new areas. You should be able to pore fill the entire back in this manner in 10 to 15 minutes - the same time for the sides and neck.
Leave the filler to dry in the pores for a minimum of one (1) hour before proceeding. With more drying time the filler is marginally harder. It is hard enough to sand after one hour of drying.
Remove any filler residue from the wood surface by sanding the entire surface lightly with 220 grit no-load paper. Some or all of the Tru-Oil sealer may also be sanded off at this point. That’s OK, just don’t sand down through the filled pores.
Seal the wood and filled pores again with Tru-Oil sealer. Wipe one good coat over the newly filled surfaces. Let this coat dry an hour or two before proceeding.
REPEAT the entire pore filling process just completed. This second pore filling will fill any tiny pores or depressions missed the first time. You may want to thin the paste even a little more for this second filling. Work the wet paste over the surface quickly, efficiently, leaving wet filler paste only in open pores and leaving very little paste residue on the wood surface. This can best be achieved by scraping the plastic squeegee or palette knife all directions across the surface. You can get very effective at this filling process with a little practice. When this second coat of paste filler has dried (about 1 hour) sand the surface smooth again with 220 grit paper. When the sandpaper clogs replace it with fresh paper. The surface now should be very smooth, pore-free, and scratch-free.
Wipe or brush a more substantial coat of Tru-Oil sealer over all of the pore-filled surfaces. Allow this coat to dry at least one day. Sand this thicker coat of sealer should fill any very minor depressions still in the surface.
Carefully sand over these pore-filled and sealed surfaces with 220 grit paper again. Sand down to the wood surface only - do not sand into or through the filled pores.
These filled hardwood surfaces are now ready to complete the final ultra fine sanding.
Complete the ultra fine sanding on all surfaces -
Beginning this stage of sanding all surfaces should have been sanded, scratch-free, to 220 grit. We continue now to sand all surfaces to ultra fine smoothness.
Sand all surfaces thoroughly - first with 320 grit TRI-M-ITE sandpaper and then with 400 grit TRI-M-ITE sandpaper. Sand with flat sanding pads with moderate pressure. With the 400 grit sandpaper finish with long strokes in one direction - no back and forth action. This should make a very clean, flat surface.
Finally, sand over all surfaces with 600 grit WET-OR-DRY sandpaper. Sand dry as before but change the paper often for the cleanest, most effective polishing.
The surface preparation is complete.
APPLY TRU-OIL® FINISH
>From this point through the rest of the finishing process do not touch the instrument with bare hands. The raw wood surface and the oiled surfaces can be affected by the oils in your fingers. Handle the guitar with a white cotton glove or cloth until the finishing is completed. You can manipulate the instrument during most of the finishing by holding the neck arm (with the glove) and finish the neck arm last.
The instrument will now be coated with the Tru-Oil several times in the following manner.
Apply an oil coat-
Use a white cotton or linen pad or cloth to apply the oil. Use a fresh cloth for each application session.
Work small areas - ¼ of the top, back or sides at a time while applying the oil.
Start by applying the oil to the top surface with each application while the cloth is clean and uncolored.
Wipe a thin, wet coat over the small working area and immediately wipe off the excess oil with a white cotton rag or cheesecloth. It is important to wipe this excess oil off the surface quickly, do not let it soak into the wood. This is especially critical for finishing the hardwoods to achieve the open-pore look. For this look you want no oil to build in the pores.
Continue applying the oil to the rest of the surface and then to the other areas of the guitar in the same manner. It will only take 10 to 15 minutes to coat the entire instrument.
Make sure to wipe all wet oil from the sharp corners at the neck and fingerboard edges. This build up will not dry as well as the thin layer left after sufficient wiping.
Hang the instrument to dry. Let this thin coating dry for several hours.
Smooth the dried oil surface -
After each oil coating has dried, it is smoothed - “sanded” is too aggressive a term - with 0000 steel wool, LMI product FSW, or a 3M Scotchbright Grey sanding pad. The steel wool or sanding pad is rubbed over the surface very lightly to remove any minor roughness. This is not a leveling process like with other harder, thicker finishes. With all of the wood preparation before applying the oil the surface should already be very flat and smooth.
Building the Tru-Oil finish -
This oil application process is very simple and the surfaces will not need many coatings to achieve an adequate final coat. Only three or four coatings should result in very beautiful sheen over the entire instrument. Different woods, conditions, and varying techniques, though, may require additional coatings to reach this level.
Use your judgment of the look of the finish surface to determine when the finish is right. Do not put more finish on than is necessary to achieve a warm sheen over all surfaces.
The instrument with the final coating achieved should be left to hang and dry for at least one to two weeks. This very cured surface is then “polished” as described next.
FINAL POLISHING OF THE CURED FINISH
This final polishing treatment is actually some very light sanding with either the 0000 steel wool or Micromesh abrasive sheets. This polishing/sanding will create the final, perfect sheen on the instrument.
Rub (or lightly sand) the entire surface with the 0000 steel wool. Be cautious and avoid the surface edges, it is easiest to go through the finish at the binding edges and the edges of the neck head.
Or, alternatively -
Use the Micromesh ultra fine sanding sheets FMIC for this final polishing. Start with the 6000 sheet, then the 8000 sheet, and finally the 12000 sheet. Sand using fairly light pressure and wipe the surface clean between grits. This method/product may leave a more attractive sheen than the 0000 steel wool..
Coat this finely sanded finish with a lemon oil treatment - many are available at local woodworking stores or hardware store finishing sections. This lemon oil treatment will prevent fingerprinting of this oil finish.
Finally, polish over the instrument with a rough, natural cloth like burlap.
The finishing is complete and the instrument can be freely handled and played.
FURTHER COMMENTS
This finish is easy to repair just using these same simple materials and techniques.
WARNING - This oil product, like others, may not cure over Cocobolo. Avoid oil finishing over this oily wood.
