Wood Preparation

Wood preparation may be the single most important element in obtaining a professional mirror like final finish and also the phase of finishing often most casually approached. Raw wood doesn't always reveal it's secrets. In fact without careful inspection during the preparation stage many misdeeds will not be evident until the final clear coating.

Once the wood has been stripped inspect the wood to locate any problems which may become offensive. Search for such things as very deep sanding scratches, cross grain sanding or dents in the wood. Be especially diligent in searching the areas where cross grain sanding may have most likely occurred such as the area behind the bridge on an arch top or at the heel of the neck. Scratches which may be nearly invisible will become evident when dye is applied. The dye will stain the exposed end grain in the scratch and darken it. If you find a sanding scratch after the dye has been applied the dye (and the scratch) will have to be sanded out and restained.

Deep dents are most common on the back but don't overlook the peghead sides and ends and the area around the jack. If the dents are very deep they can be filled with a colored wood filler and sanded flat. A fine point graining pencil can be used to draw in grain lines if needed. Now is also the time to try and locate any low spots caused by careless (read blockless) sanding. Although barely perceptible now these swales will look like deep rounded valleys after the final polishing. Most sanding swales can be sanded flat with a sanding block. Deep swales can be cured with repeated fills of a clear nitrocellulose sand and sealer such as Parks.

One other problem should also be noted. Sometimes when chemically stripping the old finish will melt and act as a dye. Black paint is the worst followed by red. If the plan is to recolor with the same color as the color that was removed there should no problem. But if a different color or natural finish is desired and the old color still partially remains bleaching may be needed.

In my experience colors can be removed with two or three applications of chlorine laundry bleach. Some color may remain in the grain but usually not enough to affect the final finish. Water marks can be removed with oxalic acid crystals. Most hardware stores carry this type of bleach.

With the wood clean and sanded. The finish prep can be begun. The steps given may or may not be needed with a particular wood. The steps following will assume the wood being finished is a "worst case" wood, i.e.; mahogany. Rosewood, ash and walnut also fall into this category. (Note that "worst case" woods are not really that. The oily woods such as paduak are the real worst cases.)

The first step is to wipe down the wood with naphtha. This will remove any oils that may have gotten on the wood during handling. When dry the wood should be filled with a grain filler. My personal choice is an oil based grain filler. I am sure that water based fillers can work equally well. Grain fillers are available at all good wood working stores and some hardware stores. When working with a colored filler it is best to seal the wood with one or two coats of lacquer to prevent the stain in the filler from staining the "field" area of the wood. It is best to let the sealing lacquer dry overnight so that it dries into the grain and does not displace the filler.

The filler can be wiped on with a cloth although I favor using my fingers. When slightly dry (dry enough that wiping does not pull the filler from the grain) the excess can be wiped off with a rough cloth. If you are careful it can be gently scrapped off with a single edged razor. In either case wipe or scrape across the grain. The razor method seems to pack the excess filler into the grain and is why I prefer it. Remove as much as you can now while the filler is slightly wet and you will reduce the time needed in the later sanding step.

When dry (overnight) the wood can be sanded clean. Time can be saved before by using a rag damped with mineral spirits to remove the majority of excess grain filler. If you decide to wipe off the excess filler let the filler dry again for a few hours before sanding. Using #180 dry sand off all of the filler in the field of the wood. Be sure to get the filler that is in the neck to body joint, in the switch holes and over the edge and in the pickup and control cavities. Filler in the screw holes does not hurt and may even help in that the filler keeps water out of the holes when doing the final wet sanding. (Water in the screw holes may cause the wood to swell and result in lacquer chipping around the screw holes). When sanding always go with the grain of the wood to prevent scratches. Follow with #220 dry sanding.

After sanding clean I suggest (and religiously use) a second filler treatment to achieve an ultimately glass like finish. First the reasoning. The glass like finish of a nitrocellulose finished guitar comes from the multiple application of lacquer and removal by wet sanding. And although the desired finish can be obtained by multiple lacquer coating only, there are two problems which at their base are both time related. The first problem is that multiple coatings (something in the 20 to 30 coat range) and sanding flat after every few coats is in it's self very time consuming. And secondly nitrocellulose, while drying to touch and a practical use level very quickly, it continues to dry over months and perhaps even years. A finish that appears mirror flat when applied will continue to dry and if the grain was not filled totally flat, in a few weeks, the grain may begin to show as the lacquer continues to "dry in".

After the wood has been filled spray with one or two coats of lacquer to lock in the filler and color. To achieve a mirror finish relatively quickly (and one that will remain stable as the final lacquer coats dry) next apply a high solid content sand and sealer product. Parks Corporation makes a nitrocellulose product which fills this requirement nicely. The application is simple as the sealer can be brushed on. Brush on the first coat and allow to dry for a few minutes. When the surface is flat (non reflective) a second coat can be brushed on. Allow this double coat to dry at least an hour (I usually wait overnight). When dry the coats can be block sanded flat. I suggest that this sanding be done in an area where dust is not a concern. You will see why when you begin sanding. I also suggest that you wear a mask. When this two coat application has been sanded flat (no shiny spots) wipe down with a dry cloth, inspect again for shiny spots and repeat. That is; apply two more coats. Paint them on as before with time allowed between coats for the coats to dry flat. When dry (again at least an hour) sand the coats flat. During sanding wipe off the dust to aid in locating pits which will appear shiny. The base you are creating will be the foundation for the lacquer finishing coats. Unless corrected, any pits, runs or unfilled areas will show in the final lacquer coats. Because of the high solid content of the filler, corrections can be made much easier at this stage.

The base should appear flat with no pits showing. If you find pits they can be drop filled with the sand and sealer and sanded flat. You will find that pits and swales that are too deep to be safely sanded out can be made invisible with repeated fills. Color coats and clear coating can now be applied.

Mixing, Spraying and the "Rule of Threes"

Once the solubility has been chosen the dye needs to be mixed. Mix to the suggested formula or "to the eye". After mixing, allow the dye time to dissolve into the chosen solution. It is recommended that the dye be allowed to dissolve for about three hours after mixing. You may find that with water soluble and alcohol soluble dyes the dye will not completely dissolve. These two solubilitys seem to have a lower saturation point than does lacquer reducer and dyes dissolved into these solubilitys may leave specks of undissolved dye in the mixing container. After the dye has been dissolved it is suggested that the solution be strained to remove any particulates. An old T shirt can make a good strainer. Coffee strainers can also be used.

One cautionary note is that dyes containing blends of black should not be finely strained. Even when "completely" dissolved the black component particles are larger than the other typical color particles. Straining can remove the black component thereby lighting the color. With black dyes allow the dye to dissolve, stir the solution, let it sit for about a minute then decant the solution. Three decants should remove the heavier particles without changing the intended final color. Another note is that you should be aware that a dye mixed in alcohol will appear to be a slightly different hue when mixed in lacquer reducer. This is due to the different solubilitys of the two reducers.

In refinishing the dyes can be either bulk mixed or batch mixed. Batch mixing typically will use a ratio of 1/4 tsp.dye to 8oz. of reducer. Unless stated otherwise, the applications discussed will use lacquer/alcohol dyes batch mixed into lacquer reducer for spraying and batch mixed water based dyes for wiping.

The solution now requires one more step. If the dye is to be used to lightly color the wood or tint another base color the dye solution can be added to a 2 or 3 part reducer to 1 part lacquer solution and sprayed. An example would be the spraying of the amber of a sunburst or the tinting of a previously applied color coat.

If the dye is to be used as a medium dark to dark solid color or a dark shading color then the dye solution should be thinned with reducer, a small amount of lacquer and then sprayed. An example of this application would be the spraying of the dark edge color of a sunburst. The goal is to apply enough color to achieve the darkness required while not over applying lacquer. A typical solution would be 1 part mixed dye solution to 6 parts reducer with a cap of lacquer added to 8oz. of the mixture. The lacquer not only gives body but it will also cause the black component of the dye to "lie down". Also while wet, the lacquer will allow you a quick look at how the coloring process is progressing.

Spraying should be done in an area with adequate ventilation but also in as clean of an area as possible. Keeping the finish dust free during the spraying process will make final finishing easier. Most spraying can be done with the instrument in a hanging position. If it is difficult to spray certain areas such as the bottom or in the areas inside the cutaways the instrument can be laid flat. Suspend the body a couple of inches above the work surface with blocks positioned in the control or pick up cavities. This will make spraying the sides easier and prevent the lacquer from gluing the body to the work surface. Before spraying wipe the body with a tack cloth to pick up any stray dust particles.

The first coats should be light. Two light spray passes followed by allowing the lacquer to dry to touch and then three more light passes will give a good base to build upon. Let the lacquer now dry at least three hours. Remember to use the tack cloth after each "hard" drying period (three hours or more). If the tack cloth is used before the lacquer is set you may transfer dust to the finish rather than removing it.

After drying check the surface for dust. If any large particles are apparent, they can be wet sanded out with #600 paper. Be careful not to get into the color coat. With larger particles you can often feel them "roll" as they become sanded out. As always when sanding thin coats, wipe the area dry often to check your progress. In this case checking every four or five sanding strokes would be prudent.

And perhaps now would be a good time to explain "coat" and "pass". A pass is just that: i.e. one spray pass. A coat is a number of passes from 1 to ?. In the technique used to develop these pages, a coat is typically three passes. Sometime two will sufficiently wet out a small area and sometimes four will be used. Five approaches foolhardiness. Six will almost always guarantee a run.

If you are using a gun that is adjustable, a typical setting would be the fan set wide enough to cover about 1/2 the area to be sprayed and air pressure at 20 to 30 psi. Liquid feed is set to allow you to wet the area by slowing down the guns movement. The setting should lean more to light. A wetter spray setting may force you to move the gun faster to prevent runs. Control the tool. Do not let it control you.

For the first wet coat (after wiping with the tack cloth) make three passes and stop. The surface will probably not appear very shiny as it dries to touch. (If it does the coats may be too heavy). Now let this first coat dry at least three hours. Tack cloth the finish and make three more passes. As you proceed, wetter passes become safer to make so you may want to slow down the guns movement as you spray. These passes will appear wetter as the finish gets deeper. Let this coat dry at least three hours. For the last coat of the day, tack cloth, spray three passes and let dry until morning.

Before spraying the next coat, wet sand the finish to remove any runs or particles that may have settled onto the finish. Start lightly with #400, #600 and end with #800. Let the surface dry and repeat yesterdays schedule. I.e., three passes, let dry three hours then repeat and then repeat. Let to the finish dry overnight and sand as you did the first day.

The third days spraying is a "re-repeat". Summing up this spray technique, spray three passes to make a coat, allow each coat to dry at least three hours and spray no more than three coats a day for at least three days. Hence, "The Rule of Threes".

Final Polishing

After allowing the instrument to dry at least three days (with nitrocellulose lacquer, the longer the better) final sanding and polishing can be done. The sanding will be done with successively finer grades of paper. The paper found at automotive color supply stores works well. The grades required are #400, #600, #800, #1000, #1200, #1500 and #2000. One sheet of each is all that is required. Allow the paper to soak overnight in water before beginning.

Use a small flat block when sanding to prevent your fingers from causing furrows in the finish. As noted a small computer battery is a personal favorite. Sanding first with the #400 grade, sand until all the shiny spots are gone. When done correctly, the finish should be uniform and matte. As you move up to the next grade check the finish in a good light. You should find that the finish is becoming more reflective and that the sanding scratches are becoming fainter. At the #1200 level the finish is now being polished and should reflect images. If you find you have missed a spot, sand backwards until the grade is reached that will blend the spot and then move back to the grade level where you were in successive grades.

Use caution when sanding to avoid sand throughs. Be especially cautious when sanding at the edges of the body. The finish may be thinner there and the difficulty of keeping the block flat when sanding over an edge can make a sanding through more likely.

After the final grade of sanding is completed, the final polishing can begin. Use a soft cotton rag either folded or shaped into a ball and held between the fingers. Either way try to prevent individual fingers from causing furrows. Polish in random circles. The polishing can be done in steps starting with a white polishing compound. If the surface was prepared as noted in the last section, red (more abrasive than white) compound should not be necessary. In fact white can probably be skipped and the finish can be polished with a swirl remover type polish. We use the 3M product, "Finesse It II" going directly from #2000 to final finish. Skipping the white and red steps may take longer to polish but on a relatively new surface the final polish seems more reflective.

The instrument is now finished. Take more than normal care for the next month or so when playing and handling. The lacquer is still relatively soft and can scratch. The lacquer will continue to harden for literally years but should reach its practical hardness in 30 to 60 days. Enjoy your work with pride.

Trouble Shooting

Even the best planned journey will sometimes have an unplanned detour. This section will cover some of the more common "detours" that can occur with a finishing project. They are presented in no particular order along with possible causes and corrections.

There is a whitish haze in the finish..."

The haze is caused by "blushing". You will see it mainly on black but darker reds show it sometimes as well. It is caused by moisture in the color or clear coat. The moisture gets into the paint when the paint is sprayed during periods of high humidity. Spraying during a rain shower, during the cooler part of a moist day and spraying a very heavy coat on a warm humid day increases the chances of blushing.

What to do? If you see blushing, Stop. The moisture is trapped in the very top coat of the finish. Take the body into a warm and dryer area and let it dry. Lacquer allows water to move slowly through the finish and most times the blushing will disappear as the finish dries. Blushing can also be removed through sanding. It can also be removed by spraying the finish with straight lacquer thinner. (Some finishers add a small amount of retarder to the thinner). If the moisture is trapped deeply in the finish you made need to use a product called "Blush Eraser". Blush Eraser reconstitutes the lacquer to allow the moisture to escape. Behlen makes the most popular eraser and provides it in an aerosol.

After spraying the first few lacquer coats I've noticed hundreds of small pin holes in the finish...."

Pin holes can be caused by a number of factors. The most common are contamination of the wood by wax or silicon (Armor All used on the case or plastic parts can be a source of this type of contamination), temperature changes during the spraying /drying cycle and moisture in the wood. Wood contamination can be sanded out in most cases. Wiping with naphtha will also help in removing contamination. Temperature can also play a role in the formation of pinholes. If a guitar that has been in a cool environment then sprayed (as might be the case if you are spraying in an unheated garage) and after spraying moved into a warm environment to dry, air bubbles may form as the wood warms and push their way through the lacquer leaving pinholes. The last frequent cause (and probably most common) is moisture in the wood. Water can get into the wood through washing stripper from the wood, wet sanding primer or sealer coats or not allowing a water based filler or water based dye enough time to dry.

The solution? Sanding and wiping with naphtha should remove wood contamination and not subjecting the wood to major temperature changes during the spraying and drying process will prevent pin holes caused by bubbles (note that placing newly finished wood in the sun to dry is a guaranteed way to cause pin holes). Allowing the wood sufficient drying time after wetting will most likely eliminate moisture related pin holes. A sure way to prevent pin holes before spraying the lacquer coats is to seal the wood with a clear sand and sealer on translucent finishes and sand and sealer and/or a white pigmented shellac on opaque finishes. If you didn't seal the wood and now have pinholes you may be able to drop fill them with unthinned lacquer. The lacquer will over power the cause of the hole and allow subsequent sprayed coats to flow over the holes. After spraying about two coats the "bumps" from the filling can be sanded flat. Drop filling will work on sectional pinholes but if the holes are numerous and over a large area, starting over (this time either correcting the problem and/or sealing the wood before spraying the lacquer) may be the best solution.

"I accidentally sanded through the clear and color coat into the primer coat...."

Sanding through is easy to do. It will most likely occur over the edges of the body. If the sand through occurs during the color or clear building stage you can simply respray the sanded through area and respray the color or clear coat. Complete overspraying is usually not needed. If you sand through into the wood you will need to refill the wood. For such a sand through sand and sealer only can be used to seal the wood. The white primer can also be used but may not be necessary. To prevent future sand throughs use a block where you can and when beginning the wet sanding use a finer grade paper (#800 to #1000) to get a feel for the process. Once you are comfortable you can move down to #600 or #400 for faster sanding.

"There are some major belt buckle scratches on the back. How can I fill them...."

Deep scratches can be filled with a good grade wood filler. Use a solvent base filler if possible. Water based fillers sometimes swell and shrink under lacquer. Bondo will also swell under lacquer. For medium depth scratches such as buckle scratches if the scratch still is showing after the recommended four coats of sand and sealer, drop fill just the scratch with clear sand and sealer. Sand flat when dry.